Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

14 files changed, 19482 insertions, 0 deletions

diff --git a/compiler/rustc_resolve/Cargo.toml b/compiler/rustc_resolve/Cargo.toml
new file mode 100644
index 000000000..5d2b606b4
--- /dev/null
+++ b/compiler/rustc_resolve/Cargo.toml
@@ -0,0 +1,27 @@
+[package]
+name = "rustc_resolve"
+version = "0.0.0"
+edition = "2021"
+
+[lib]
+doctest = false
+
+[dependencies]
+bitflags = "1.2.1"
+tracing = "0.1"
+rustc_ast = { path = "../rustc_ast" }
+rustc_arena = { path = "../rustc_arena" }
+rustc_middle = { path = "../rustc_middle" }
+rustc_ast_pretty = { path = "../rustc_ast_pretty" }
+rustc_attr = { path = "../rustc_attr" }
+rustc_data_structures = { path = "../rustc_data_structures" }
+rustc_errors = { path = "../rustc_errors" }
+rustc_expand = { path = "../rustc_expand" }
+rustc_feature = { path = "../rustc_feature" }
+rustc_hir = { path = "../rustc_hir" }
+rustc_index = { path = "../rustc_index" }
+rustc_metadata = { path = "../rustc_metadata" }
+rustc_query_system = { path = "../rustc_query_system" }
+rustc_session = { path = "../rustc_session" }
+rustc_span = { path = "../rustc_span" }
+smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
diff --git a/compiler/rustc_resolve/src/access_levels.rs b/compiler/rustc_resolve/src/access_levels.rs
new file mode 100644
index 000000000..3fba923d9
--- /dev/null
+++ b/compiler/rustc_resolve/src/access_levels.rs
@@ -0,0 +1,237 @@
+use rustc_ast::ast;
+use rustc_ast::visit;
+use rustc_ast::visit::Visitor;
+use rustc_ast::Crate;
+use rustc_ast::EnumDef;
+use rustc_ast::ForeignMod;
+use rustc_ast::NodeId;
+use rustc_hir::def_id::LocalDefId;
+use rustc_hir::def_id::CRATE_DEF_ID;
+use rustc_middle::middle::privacy::AccessLevel;
+use rustc_middle::ty::Visibility;
+use rustc_span::sym;
+
+use crate::imports::ImportKind;
+use crate::BindingKey;
+use crate::NameBinding;
+use crate::NameBindingKind;
+use crate::Resolver;
+
+pub struct AccessLevelsVisitor<'r, 'a> {
+    r: &'r mut Resolver<'a>,
+    prev_level: Option<AccessLevel>,
+    changed: bool,
+}
+
+impl<'r, 'a> AccessLevelsVisitor<'r, 'a> {
+    /// Fills the `Resolver::access_levels` table with public & exported items
+    /// For now, this doesn't resolve macros (FIXME) and cannot resolve Impl, as we
+    /// need access to a TyCtxt for that.
+    pub fn compute_access_levels<'c>(r: &'r mut Resolver<'a>, krate: &'c Crate) {
+        let mut visitor =
+            AccessLevelsVisitor { r, changed: false, prev_level: Some(AccessLevel::Public) };
+
+        visitor.set_access_level_def_id(CRATE_DEF_ID, Some(AccessLevel::Public));
+        visitor.set_exports_access_level(CRATE_DEF_ID);
+
+        while visitor.changed {
+            visitor.reset();
+            visit::walk_crate(&mut visitor, krate);
+        }
+
+        tracing::info!("resolve::access_levels: {:#?}", r.access_levels);
+    }
+
+    fn reset(&mut self) {
+        self.changed = false;
+        self.prev_level = Some(AccessLevel::Public);
+    }
+
+    /// Update the access level of the exports of the given module accordingly. The module access
+    /// level has to be Exported or Public.
+    /// This will also follow `use` chains (see PrivacyVisitor::set_import_binding_access_level).
+    fn set_exports_access_level(&mut self, module_id: LocalDefId) {
+        assert!(self.r.module_map.contains_key(&&module_id.to_def_id()));
+
+        // Set the given binding access level to `AccessLevel::Public` and
+        // sets the rest of the `use` chain to `AccessLevel::Exported` until
+        // we hit the actual exported item.
+        let set_import_binding_access_level =
+            |this: &mut Self, mut binding: &NameBinding<'a>, mut access_level| {
+                while let NameBindingKind::Import { binding: nested_binding, import, .. } =
+                    binding.kind
+                {
+                    this.set_access_level(import.id, access_level);
+                    if let ImportKind::Single { additional_ids, .. } = import.kind {
+                        this.set_access_level(additional_ids.0, access_level);
+                        this.set_access_level(additional_ids.1, access_level);
+                    }
+
+                    access_level = Some(AccessLevel::Exported);
+                    binding = nested_binding;
+                }
+            };
+
+        let module_level = self.r.access_levels.map.get(&module_id).copied();
+        assert!(module_level >= Some(AccessLevel::Exported));
+
+        if let Some(exports) = self.r.reexport_map.get(&module_id) {
+            let pub_exports = exports
+                .iter()
+                .filter(|ex| ex.vis == Visibility::Public)
+                .cloned()
+                .collect::<Vec<_>>();
+
+            let module = self.r.get_module(module_id.to_def_id()).unwrap();
+            for export in pub_exports.into_iter() {
+                if let Some(export_def_id) = export.res.opt_def_id().and_then(|id| id.as_local()) {
+                    self.set_access_level_def_id(export_def_id, Some(AccessLevel::Exported));
+                }
+
+                if let Some(ns) = export.res.ns() {
+                    let key = BindingKey { ident: export.ident, ns, disambiguator: 0 };
+                    let name_res = self.r.resolution(module, key);
+                    if let Some(binding) = name_res.borrow().binding() {
+                        set_import_binding_access_level(self, binding, module_level)
+                    }
+                }
+            }
+        }
+    }
+
+    /// Sets the access level of the `LocalDefId` corresponding to the given `NodeId`.
+    /// This function will panic if the `NodeId` does not have a `LocalDefId`
+    fn set_access_level(
+        &mut self,
+        node_id: NodeId,
+        access_level: Option<AccessLevel>,
+    ) -> Option<AccessLevel> {
+        self.set_access_level_def_id(self.r.local_def_id(node_id), access_level)
+    }
+
+    fn set_access_level_def_id(
+        &mut self,
+        def_id: LocalDefId,
+        access_level: Option<AccessLevel>,
+    ) -> Option<AccessLevel> {
+        let old_level = self.r.access_levels.map.get(&def_id).copied();
+        if old_level < access_level {
+            self.r.access_levels.map.insert(def_id, access_level.unwrap());
+            self.changed = true;
+            access_level
+        } else {
+            old_level
+        }
+    }
+}
+
+impl<'r, 'ast> Visitor<'ast> for AccessLevelsVisitor<'ast, 'r> {
+    fn visit_item(&mut self, item: &'ast ast::Item) {
+        let inherited_item_level = match item.kind {
+            // Resolved in rustc_privacy when types are available
+            ast::ItemKind::Impl(..) => return,
+
+            // Only exported `macro_rules!` items are public, but they always are
+            ast::ItemKind::MacroDef(ref macro_def) if macro_def.macro_rules => {
+                let is_macro_export =
+                    item.attrs.iter().any(|attr| attr.has_name(sym::macro_export));
+                if is_macro_export { Some(AccessLevel::Public) } else { None }
+            }
+
+            // Foreign modules inherit level from parents.
+            ast::ItemKind::ForeignMod(..) => self.prev_level,
+
+            // Other `pub` items inherit levels from parents.
+            ast::ItemKind::ExternCrate(..)
+            | ast::ItemKind::Use(..)
+            | ast::ItemKind::Static(..)
+            | ast::ItemKind::Const(..)
+            | ast::ItemKind::Fn(..)
+            | ast::ItemKind::Mod(..)
+            | ast::ItemKind::GlobalAsm(..)
+            | ast::ItemKind::TyAlias(..)
+            | ast::ItemKind::Enum(..)
+            | ast::ItemKind::Struct(..)
+            | ast::ItemKind::Union(..)
+            | ast::ItemKind::Trait(..)
+            | ast::ItemKind::TraitAlias(..)
+            | ast::ItemKind::MacroDef(..) => {
+                if item.vis.kind.is_pub() {
+                    self.prev_level
+                } else {
+                    None
+                }
+            }
+
+            // Should be unreachable at this stage
+            ast::ItemKind::MacCall(..) => panic!(
+                "ast::ItemKind::MacCall encountered, this should not anymore appear at this stage"
+            ),
+        };
+
+        let access_level = self.set_access_level(item.id, inherited_item_level);
+
+        // Set access level of nested items.
+        // If it's a mod, also make the visitor walk all of its items
+        match item.kind {
+            ast::ItemKind::Mod(..) => {
+                if access_level.is_some() {
+                    self.set_exports_access_level(self.r.local_def_id(item.id));
+                }
+
+                let orig_level = std::mem::replace(&mut self.prev_level, access_level);
+                visit::walk_item(self, item);
+                self.prev_level = orig_level;
+            }
+
+            ast::ItemKind::ForeignMod(ForeignMod { ref items, .. }) => {
+                for nested in items {
+                    if nested.vis.kind.is_pub() {
+                        self.set_access_level(nested.id, access_level);
+                    }
+                }
+            }
+            ast::ItemKind::Enum(EnumDef { ref variants }, _) => {
+                for variant in variants {
+                    let variant_level = self.set_access_level(variant.id, access_level);
+                    if let Some(ctor_id) = variant.data.ctor_id() {
+                        self.set_access_level(ctor_id, access_level);
+                    }
+
+                    for field in variant.data.fields() {
+                        self.set_access_level(field.id, variant_level);
+                    }
+                }
+            }
+            ast::ItemKind::Struct(ref def, _) | ast::ItemKind::Union(ref def, _) => {
+                if let Some(ctor_id) = def.ctor_id() {
+                    self.set_access_level(ctor_id, access_level);
+                }
+
+                for field in def.fields() {
+                    if field.vis.kind.is_pub() {
+                        self.set_access_level(field.id, access_level);
+                    }
+                }
+            }
+            ast::ItemKind::Trait(ref trait_kind) => {
+                for nested in trait_kind.items.iter() {
+                    self.set_access_level(nested.id, access_level);
+                }
+            }
+
+            ast::ItemKind::ExternCrate(..)
+            | ast::ItemKind::Use(..)
+            | ast::ItemKind::Static(..)
+            | ast::ItemKind::Const(..)
+            | ast::ItemKind::GlobalAsm(..)
+            | ast::ItemKind::TyAlias(..)
+            | ast::ItemKind::TraitAlias(..)
+            | ast::ItemKind::MacroDef(..)
+            | ast::ItemKind::Fn(..) => return,
+
+            // Unreachable kinds
+            ast::ItemKind::Impl(..) | ast::ItemKind::MacCall(..) => unreachable!(),
+        }
+    }
+}
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
new file mode 100644
index 000000000..e955a1798
--- /dev/null
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@@ -0,0 +1,1546 @@
+//! After we obtain a fresh AST fragment from a macro, code in this module helps to integrate
+//! that fragment into the module structures that are already partially built.
+//!
+//! Items from the fragment are placed into modules,
+//! unexpanded macros in the fragment are visited and registered.
+//! Imports are also considered items and placed into modules here, but not resolved yet.
+
+use crate::def_collector::collect_definitions;
+use crate::imports::{Import, ImportKind};
+use crate::macros::{MacroRulesBinding, MacroRulesScope, MacroRulesScopeRef};
+use crate::Namespace::{self, MacroNS, TypeNS, ValueNS};
+use crate::{Determinacy, ExternPreludeEntry, Finalize, Module, ModuleKind, ModuleOrUniformRoot};
+use crate::{
+    MacroData, NameBinding, NameBindingKind, ParentScope, PathResult, PerNS, ResolutionError,
+};
+use crate::{Resolver, ResolverArenas, Segment, ToNameBinding, VisResolutionError};
+
+use rustc_ast::visit::{self, AssocCtxt, Visitor};
+use rustc_ast::{self as ast, AssocItem, AssocItemKind, MetaItemKind, StmtKind};
+use rustc_ast::{Block, Fn, ForeignItem, ForeignItemKind, Impl, Item, ItemKind, NodeId};
+use rustc_attr as attr;
+use rustc_data_structures::sync::Lrc;
+use rustc_errors::{struct_span_err, Applicability};
+use rustc_expand::expand::AstFragment;
+use rustc_hir::def::{self, *};
+use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID};
+use rustc_metadata::creader::LoadedMacro;
+use rustc_middle::bug;
+use rustc_middle::metadata::ModChild;
+use rustc_middle::ty::{self, DefIdTree};
+use rustc_session::cstore::CrateStore;
+use rustc_span::hygiene::{ExpnId, LocalExpnId, MacroKind};
+use rustc_span::source_map::{respan, Spanned};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::Span;
+
+use std::cell::Cell;
+use std::ptr;
+use tracing::debug;
+
+type Res = def::Res<NodeId>;
+
+impl<'a> ToNameBinding<'a> for (Module<'a>, ty::Visibility, Span, LocalExpnId) {
+    fn to_name_binding(self, arenas: &'a ResolverArenas<'a>) -> &'a NameBinding<'a> {
+        arenas.alloc_name_binding(NameBinding {
+            kind: NameBindingKind::Module(self.0),
+            ambiguity: None,
+            vis: self.1,
+            span: self.2,
+            expansion: self.3,
+        })
+    }
+}
+
+impl<'a> ToNameBinding<'a> for (Res, ty::Visibility, Span, LocalExpnId) {
+    fn to_name_binding(self, arenas: &'a ResolverArenas<'a>) -> &'a NameBinding<'a> {
+        arenas.alloc_name_binding(NameBinding {
+            kind: NameBindingKind::Res(self.0, false),
+            ambiguity: None,
+            vis: self.1,
+            span: self.2,
+            expansion: self.3,
+        })
+    }
+}
+
+struct IsMacroExport;
+
+impl<'a> ToNameBinding<'a> for (Res, ty::Visibility, Span, LocalExpnId, IsMacroExport) {
+    fn to_name_binding(self, arenas: &'a ResolverArenas<'a>) -> &'a NameBinding<'a> {
+        arenas.alloc_name_binding(NameBinding {
+            kind: NameBindingKind::Res(self.0, true),
+            ambiguity: None,
+            vis: self.1,
+            span: self.2,
+            expansion: self.3,
+        })
+    }
+}
+
+impl<'a> Resolver<'a> {
+    /// Defines `name` in namespace `ns` of module `parent` to be `def` if it is not yet defined;
+    /// otherwise, reports an error.
+    pub(crate) fn define<T>(&mut self, parent: Module<'a>, ident: Ident, ns: Namespace, def: T)
+    where
+        T: ToNameBinding<'a>,
+    {
+        let binding = def.to_name_binding(self.arenas);
+        let key = self.new_key(ident, ns);
+        if let Err(old_binding) = self.try_define(parent, key, binding) {
+            self.report_conflict(parent, ident, ns, old_binding, &binding);
+        }
+    }
+
+    /// Walks up the tree of definitions starting at `def_id`,
+    /// stopping at the first encountered module.
+    /// Parent block modules for arbitrary def-ids are not recorded for the local crate,
+    /// and are not preserved in metadata for foreign crates, so block modules are never
+    /// returned by this function.
+    ///
+    /// For the local crate ignoring block modules may be incorrect, so use this method with care.
+    ///
+    /// For foreign crates block modules can be ignored without introducing observable differences,
+    /// moreover they has to be ignored right now because they are not kept in metadata.
+    /// Foreign parent modules are used for resolving names used by foreign macros with def-site
+    /// hygiene, therefore block module ignorability relies on macros with def-site hygiene and
+    /// block module parents being unreachable from other crates.
+    /// Reachable macros with block module parents exist due to `#[macro_export] macro_rules!`,
+    /// but they cannot use def-site hygiene, so the assumption holds
+    /// (<https://github.com/rust-lang/rust/pull/77984#issuecomment-712445508>).
+    pub fn get_nearest_non_block_module(&mut self, mut def_id: DefId) -> Module<'a> {
+        loop {
+            match self.get_module(def_id) {
+                Some(module) => return module,
+                None => def_id = self.parent(def_id),
+            }
+        }
+    }
+
+    pub fn expect_module(&mut self, def_id: DefId) -> Module<'a> {
+        self.get_module(def_id).expect("argument `DefId` is not a module")
+    }
+
+    /// If `def_id` refers to a module (in resolver's sense, i.e. a module item, crate root, enum,
+    /// or trait), then this function returns that module's resolver representation, otherwise it
+    /// returns `None`.
+    pub(crate) fn get_module(&mut self, def_id: DefId) -> Option<Module<'a>> {
+        if let module @ Some(..) = self.module_map.get(&def_id) {
+            return module.copied();
+        }
+
+        if !def_id.is_local() {
+            let def_kind = self.cstore().def_kind(def_id);
+            match def_kind {
+                DefKind::Mod | DefKind::Enum | DefKind::Trait => {
+                    let def_key = self.cstore().def_key(def_id);
+                    let parent = def_key.parent.map(|index| {
+                        self.get_nearest_non_block_module(DefId { index, krate: def_id.krate })
+                    });
+                    let name = if let Some(cnum) = def_id.as_crate_root() {
+                        self.cstore().crate_name(cnum)
+                    } else {
+                        def_key.disambiguated_data.data.get_opt_name().expect("module without name")
+                    };
+
+                    Some(self.new_module(
+                        parent,
+                        ModuleKind::Def(def_kind, def_id, name),
+                        self.cstore().module_expansion_untracked(def_id, &self.session),
+                        self.cstore().get_span_untracked(def_id, &self.session),
+                        // FIXME: Account for `#[no_implicit_prelude]` attributes.
+                        parent.map_or(false, |module| module.no_implicit_prelude),
+                    ))
+                }
+                _ => None,
+            }
+        } else {
+            None
+        }
+    }
+
+    pub(crate) fn expn_def_scope(&mut self, expn_id: ExpnId) -> Module<'a> {
+        match expn_id.expn_data().macro_def_id {
+            Some(def_id) => self.macro_def_scope(def_id),
+            None => expn_id
+                .as_local()
+                .and_then(|expn_id| self.ast_transform_scopes.get(&expn_id))
+                .unwrap_or(&self.graph_root),
+        }
+    }
+
+    pub(crate) fn macro_def_scope(&mut self, def_id: DefId) -> Module<'a> {
+        if let Some(id) = def_id.as_local() {
+            self.local_macro_def_scopes[&id]
+        } else {
+            self.get_nearest_non_block_module(def_id)
+        }
+    }
+
+    pub(crate) fn get_macro(&mut self, res: Res) -> Option<MacroData> {
+        match res {
+            Res::Def(DefKind::Macro(..), def_id) => Some(self.get_macro_by_def_id(def_id)),
+            Res::NonMacroAttr(_) => {
+                Some(MacroData { ext: self.non_macro_attr.clone(), macro_rules: false })
+            }
+            _ => None,
+        }
+    }
+
+    pub(crate) fn get_macro_by_def_id(&mut self, def_id: DefId) -> MacroData {
+        if let Some(macro_data) = self.macro_map.get(&def_id) {
+            return macro_data.clone();
+        }
+
+        let (ext, macro_rules) = match self.cstore().load_macro_untracked(def_id, &self.session) {
+            LoadedMacro::MacroDef(item, edition) => (
+                Lrc::new(self.compile_macro(&item, edition).0),
+                matches!(item.kind, ItemKind::MacroDef(def) if def.macro_rules),
+            ),
+            LoadedMacro::ProcMacro(extz) => (Lrc::new(extz), false),
+        };
+
+        let macro_data = MacroData { ext, macro_rules };
+        self.macro_map.insert(def_id, macro_data.clone());
+        macro_data
+    }
+
+    pub(crate) fn build_reduced_graph(
+        &mut self,
+        fragment: &AstFragment,
+        parent_scope: ParentScope<'a>,
+    ) -> MacroRulesScopeRef<'a> {
+        collect_definitions(self, fragment, parent_scope.expansion);
+        let mut visitor = BuildReducedGraphVisitor { r: self, parent_scope };
+        fragment.visit_with(&mut visitor);
+        visitor.parent_scope.macro_rules
+    }
+
+    pub(crate) fn build_reduced_graph_external(&mut self, module: Module<'a>) {
+        for child in self.cstore().module_children_untracked(module.def_id(), self.session) {
+            let parent_scope = ParentScope::module(module, self);
+            BuildReducedGraphVisitor { r: self, parent_scope }
+                .build_reduced_graph_for_external_crate_res(child);
+        }
+    }
+}
+
+struct BuildReducedGraphVisitor<'a, 'b> {
+    r: &'b mut Resolver<'a>,
+    parent_scope: ParentScope<'a>,
+}
+
+impl<'a> AsMut<Resolver<'a>> for BuildReducedGraphVisitor<'a, '_> {
+    fn as_mut(&mut self) -> &mut Resolver<'a> {
+        self.r
+    }
+}
+
+impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
+    fn resolve_visibility(&mut self, vis: &ast::Visibility) -> ty::Visibility {
+        self.try_resolve_visibility(vis, true).unwrap_or_else(|err| {
+            self.r.report_vis_error(err);
+            ty::Visibility::Public
+        })
+    }
+
+    fn try_resolve_visibility<'ast>(
+        &mut self,
+        vis: &'ast ast::Visibility,
+        finalize: bool,
+    ) -> Result<ty::Visibility, VisResolutionError<'ast>> {
+        let parent_scope = &self.parent_scope;
+        match vis.kind {
+            ast::VisibilityKind::Public => Ok(ty::Visibility::Public),
+            ast::VisibilityKind::Inherited => {
+                Ok(match self.parent_scope.module.kind {
+                    // Any inherited visibility resolved directly inside an enum or trait
+                    // (i.e. variants, fields, and trait items) inherits from the visibility
+                    // of the enum or trait.
+                    ModuleKind::Def(DefKind::Enum | DefKind::Trait, def_id, _) => {
+                        self.r.visibilities[&def_id.expect_local()]
+                    }
+                    // Otherwise, the visibility is restricted to the nearest parent `mod` item.
+                    _ => ty::Visibility::Restricted(self.parent_scope.module.nearest_parent_mod()),
+                })
+            }
+            ast::VisibilityKind::Restricted { ref path, id, .. } => {
+                // Make `PRIVATE_IN_PUBLIC` lint a hard error.
+                self.r.has_pub_restricted = true;
+                // For visibilities we are not ready to provide correct implementation of "uniform
+                // paths" right now, so on 2018 edition we only allow module-relative paths for now.
+                // On 2015 edition visibilities are resolved as crate-relative by default,
+                // so we are prepending a root segment if necessary.
+                let ident = path.segments.get(0).expect("empty path in visibility").ident;
+                let crate_root = if ident.is_path_segment_keyword() {
+                    None
+                } else if ident.span.rust_2015() {
+                    Some(Segment::from_ident(Ident::new(
+                        kw::PathRoot,
+                        path.span.shrink_to_lo().with_ctxt(ident.span.ctxt()),
+                    )))
+                } else {
+                    return Err(VisResolutionError::Relative2018(ident.span, path));
+                };
+
+                let segments = crate_root
+                    .into_iter()
+                    .chain(path.segments.iter().map(|seg| seg.into()))
+                    .collect::<Vec<_>>();
+                let expected_found_error = |res| {
+                    Err(VisResolutionError::ExpectedFound(
+                        path.span,
+                        Segment::names_to_string(&segments),
+                        res,
+                    ))
+                };
+                match self.r.resolve_path(
+                    &segments,
+                    Some(TypeNS),
+                    parent_scope,
+                    finalize.then(|| Finalize::new(id, path.span)),
+                    None,
+                ) {
+                    PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
+                        let res = module.res().expect("visibility resolved to unnamed block");
+                        if finalize {
+                            self.r.record_partial_res(id, PartialRes::new(res));
+                        }
+                        if module.is_normal() {
+                            if res == Res::Err {
+                                Ok(ty::Visibility::Public)
+                            } else {
+                                let vis = ty::Visibility::Restricted(res.def_id());
+                                if self.r.is_accessible_from(vis, parent_scope.module) {
+                                    Ok(vis)
+                                } else {
+                                    Err(VisResolutionError::AncestorOnly(path.span))
+                                }
+                            }
+                        } else {
+                            expected_found_error(res)
+                        }
+                    }
+                    PathResult::Module(..) => Err(VisResolutionError::ModuleOnly(path.span)),
+                    PathResult::NonModule(partial_res) => {
+                        expected_found_error(partial_res.base_res())
+                    }
+                    PathResult::Failed { span, label, suggestion, .. } => {
+                        Err(VisResolutionError::FailedToResolve(span, label, suggestion))
+                    }
+                    PathResult::Indeterminate => Err(VisResolutionError::Indeterminate(path.span)),
+                }
+            }
+        }
+    }
+
+    fn insert_field_names_local(&mut self, def_id: DefId, vdata: &ast::VariantData) {
+        let field_names = vdata
+            .fields()
+            .iter()
+            .map(|field| respan(field.span, field.ident.map_or(kw::Empty, |ident| ident.name)))
+            .collect();
+        self.insert_field_names(def_id, field_names);
+    }
+
+    fn insert_field_names(&mut self, def_id: DefId, field_names: Vec<Spanned<Symbol>>) {
+        self.r.field_names.insert(def_id, field_names);
+    }
+
+    fn block_needs_anonymous_module(&mut self, block: &Block) -> bool {
+        // If any statements are items, we need to create an anonymous module
+        block
+            .stmts
+            .iter()
+            .any(|statement| matches!(statement.kind, StmtKind::Item(_) | StmtKind::MacCall(_)))
+    }
+
+    // Add an import to the current module.
+    fn add_import(
+        &mut self,
+        module_path: Vec<Segment>,
+        kind: ImportKind<'a>,
+        span: Span,
+        id: NodeId,
+        item: &ast::Item,
+        root_span: Span,
+        root_id: NodeId,
+        vis: ty::Visibility,
+    ) {
+        let current_module = self.parent_scope.module;
+        let import = self.r.arenas.alloc_import(Import {
+            kind,
+            parent_scope: self.parent_scope,
+            module_path,
+            imported_module: Cell::new(None),
+            span,
+            id,
+            use_span: item.span,
+            use_span_with_attributes: item.span_with_attributes(),
+            has_attributes: !item.attrs.is_empty(),
+            root_span,
+            root_id,
+            vis: Cell::new(vis),
+            used: Cell::new(false),
+        });
+
+        self.r.indeterminate_imports.push(import);
+        match import.kind {
+            // Don't add unresolved underscore imports to modules
+            ImportKind::Single { target: Ident { name: kw::Underscore, .. }, .. } => {}
+            ImportKind::Single { target, type_ns_only, .. } => {
+                self.r.per_ns(|this, ns| {
+                    if !type_ns_only || ns == TypeNS {
+                        let key = this.new_key(target, ns);
+                        let mut resolution = this.resolution(current_module, key).borrow_mut();
+                        resolution.add_single_import(import);
+                    }
+                });
+            }
+            // We don't add prelude imports to the globs since they only affect lexical scopes,
+            // which are not relevant to import resolution.
+            ImportKind::Glob { is_prelude: true, .. } => {}
+            ImportKind::Glob { .. } => current_module.globs.borrow_mut().push(import),
+            _ => unreachable!(),
+        }
+    }
+
+    fn build_reduced_graph_for_use_tree(
+        &mut self,
+        // This particular use tree
+        use_tree: &ast::UseTree,
+        id: NodeId,
+        parent_prefix: &[Segment],
+        nested: bool,
+        // The whole `use` item
+        item: &Item,
+        vis: ty::Visibility,
+        root_span: Span,
+    ) {
+        debug!(
+            "build_reduced_graph_for_use_tree(parent_prefix={:?}, use_tree={:?}, nested={})",
+            parent_prefix, use_tree, nested
+        );
+
+        let mut prefix_iter = parent_prefix
+            .iter()
+            .cloned()
+            .chain(use_tree.prefix.segments.iter().map(|seg| seg.into()))
+            .peekable();
+
+        // On 2015 edition imports are resolved as crate-relative by default,
+        // so prefixes are prepended with crate root segment if necessary.
+        // The root is prepended lazily, when the first non-empty prefix or terminating glob
+        // appears, so imports in braced groups can have roots prepended independently.
+        let is_glob = matches!(use_tree.kind, ast::UseTreeKind::Glob);
+        let crate_root = match prefix_iter.peek() {
+            Some(seg) if !seg.ident.is_path_segment_keyword() && seg.ident.span.rust_2015() => {
+                Some(seg.ident.span.ctxt())
+            }
+            None if is_glob && use_tree.span.rust_2015() => Some(use_tree.span.ctxt()),
+            _ => None,
+        }
+        .map(|ctxt| {
+            Segment::from_ident(Ident::new(
+                kw::PathRoot,
+                use_tree.prefix.span.shrink_to_lo().with_ctxt(ctxt),
+            ))
+        });
+
+        let prefix = crate_root.into_iter().chain(prefix_iter).collect::<Vec<_>>();
+        debug!("build_reduced_graph_for_use_tree: prefix={:?}", prefix);
+
+        let empty_for_self = |prefix: &[Segment]| {
+            prefix.is_empty() || prefix.len() == 1 && prefix[0].ident.name == kw::PathRoot
+        };
+        match use_tree.kind {
+            ast::UseTreeKind::Simple(rename, id1, id2) => {
+                let mut ident = use_tree.ident();
+                let mut module_path = prefix;
+                let mut source = module_path.pop().unwrap();
+                let mut type_ns_only = false;
+
+                self.r.visibilities.insert(self.r.local_def_id(id), vis);
+                if id1 != ast::DUMMY_NODE_ID {
+                    self.r.visibilities.insert(self.r.local_def_id(id1), vis);
+                }
+                if id2 != ast::DUMMY_NODE_ID {
+                    self.r.visibilities.insert(self.r.local_def_id(id2), vis);
+                }
+
+                if nested {
+                    // Correctly handle `self`
+                    if source.ident.name == kw::SelfLower {
+                        type_ns_only = true;
+
+                        if empty_for_self(&module_path) {
+                            self.r.report_error(
+                                use_tree.span,
+                                ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix,
+                            );
+                            return;
+                        }
+
+                        // Replace `use foo::{ self };` with `use foo;`
+                        source = module_path.pop().unwrap();
+                        if rename.is_none() {
+                            ident = source.ident;
+                        }
+                    }
+                } else {
+                    // Disallow `self`
+                    if source.ident.name == kw::SelfLower {
+                        let parent = module_path.last();
+
+                        let span = match parent {
+                            // only `::self` from `use foo::self as bar`
+                            Some(seg) => seg.ident.span.shrink_to_hi().to(source.ident.span),
+                            None => source.ident.span,
+                        };
+                        let span_with_rename = match rename {
+                            // only `self as bar` from `use foo::self as bar`
+                            Some(rename) => source.ident.span.to(rename.span),
+                            None => source.ident.span,
+                        };
+                        self.r.report_error(
+                            span,
+                            ResolutionError::SelfImportsOnlyAllowedWithin {
+                                root: parent.is_none(),
+                                span_with_rename,
+                            },
+                        );
+
+                        // Error recovery: replace `use foo::self;` with `use foo;`
+                        if let Some(parent) = module_path.pop() {
+                            source = parent;
+                            if rename.is_none() {
+                                ident = source.ident;
+                            }
+                        }
+                    }
+
+                    // Disallow `use $crate;`
+                    if source.ident.name == kw::DollarCrate && module_path.is_empty() {
+                        let crate_root = self.r.resolve_crate_root(source.ident);
+                        let crate_name = match crate_root.kind {
+                            ModuleKind::Def(.., name) => name,
+                            ModuleKind::Block => unreachable!(),
+                        };
+                        // HACK(eddyb) unclear how good this is, but keeping `$crate`
+                        // in `source` breaks `src/test/ui/imports/import-crate-var.rs`,
+                        // while the current crate doesn't have a valid `crate_name`.
+                        if crate_name != kw::Empty {
+                            // `crate_name` should not be interpreted as relative.
+                            module_path.push(Segment::from_ident_and_id(
+                                Ident { name: kw::PathRoot, span: source.ident.span },
+                                self.r.next_node_id(),
+                            ));
+                            source.ident.name = crate_name;
+                        }
+                        if rename.is_none() {
+                            ident.name = crate_name;
+                        }
+
+                        self.r
+                            .session
+                            .struct_span_err(item.span, "`$crate` may not be imported")
+                            .emit();
+                    }
+                }
+
+                if ident.name == kw::Crate {
+                    self.r.session.span_err(
+                        ident.span,
+                        "crate root imports need to be explicitly named: \
+                         `use crate as name;`",
+                    );
+                }
+
+                let kind = ImportKind::Single {
+                    source: source.ident,
+                    target: ident,
+                    source_bindings: PerNS {
+                        type_ns: Cell::new(Err(Determinacy::Undetermined)),
+                        value_ns: Cell::new(Err(Determinacy::Undetermined)),
+                        macro_ns: Cell::new(Err(Determinacy::Undetermined)),
+                    },
+                    target_bindings: PerNS {
+                        type_ns: Cell::new(None),
+                        value_ns: Cell::new(None),
+                        macro_ns: Cell::new(None),
+                    },
+                    type_ns_only,
+                    nested,
+                    additional_ids: (id1, id2),
+                };
+
+                self.add_import(
+                    module_path,
+                    kind,
+                    use_tree.span,
+                    id,
+                    item,
+                    root_span,
+                    item.id,
+                    vis,
+                );
+            }
+            ast::UseTreeKind::Glob => {
+                let kind = ImportKind::Glob {
+                    is_prelude: self.r.session.contains_name(&item.attrs, sym::prelude_import),
+                    max_vis: Cell::new(ty::Visibility::Invisible),
+                };
+                self.r.visibilities.insert(self.r.local_def_id(id), vis);
+                self.add_import(prefix, kind, use_tree.span, id, item, root_span, item.id, vis);
+            }
+            ast::UseTreeKind::Nested(ref items) => {
+                // Ensure there is at most one `self` in the list
+                let self_spans = items
+                    .iter()
+                    .filter_map(|&(ref use_tree, _)| {
+                        if let ast::UseTreeKind::Simple(..) = use_tree.kind {
+                            if use_tree.ident().name == kw::SelfLower {
+                                return Some(use_tree.span);
+                            }
+                        }
+
+                        None
+                    })
+                    .collect::<Vec<_>>();
+                if self_spans.len() > 1 {
+                    let mut e = self.r.into_struct_error(
+                        self_spans[0],
+                        ResolutionError::SelfImportCanOnlyAppearOnceInTheList,
+                    );
+
+                    for other_span in self_spans.iter().skip(1) {
+                        e.span_label(*other_span, "another `self` import appears here");
+                    }
+
+                    e.emit();
+                }
+
+                for &(ref tree, id) in items {
+                    self.build_reduced_graph_for_use_tree(
+                        // This particular use tree
+                        tree, id, &prefix, true, // The whole `use` item
+                        item, vis, root_span,
+                    );
+                }
+
+                // Empty groups `a::b::{}` are turned into synthetic `self` imports
+                // `a::b::c::{self as _}`, so that their prefixes are correctly
+                // resolved and checked for privacy/stability/etc.
+                if items.is_empty() && !empty_for_self(&prefix) {
+                    let new_span = prefix[prefix.len() - 1].ident.span;
+                    let tree = ast::UseTree {
+                        prefix: ast::Path::from_ident(Ident::new(kw::SelfLower, new_span)),
+                        kind: ast::UseTreeKind::Simple(
+                            Some(Ident::new(kw::Underscore, new_span)),
+                            ast::DUMMY_NODE_ID,
+                            ast::DUMMY_NODE_ID,
+                        ),
+                        span: use_tree.span,
+                    };
+                    self.build_reduced_graph_for_use_tree(
+                        // This particular use tree
+                        &tree,
+                        id,
+                        &prefix,
+                        true,
+                        // The whole `use` item
+                        item,
+                        ty::Visibility::Invisible,
+                        root_span,
+                    );
+                }
+            }
+        }
+    }
+
+    /// Constructs the reduced graph for one item.
+    fn build_reduced_graph_for_item(&mut self, item: &'b Item) {
+        let parent_scope = &self.parent_scope;
+        let parent = parent_scope.module;
+        let expansion = parent_scope.expansion;
+        let ident = item.ident;
+        let sp = item.span;
+        let vis = self.resolve_visibility(&item.vis);
+        let local_def_id = self.r.local_def_id(item.id);
+        let def_id = local_def_id.to_def_id();
+
+        self.r.visibilities.insert(local_def_id, vis);
+
+        match item.kind {
+            ItemKind::Use(ref use_tree) => {
+                self.build_reduced_graph_for_use_tree(
+                    // This particular use tree
+                    use_tree,
+                    item.id,
+                    &[],
+                    false,
+                    // The whole `use` item
+                    item,
+                    vis,
+                    use_tree.span,
+                );
+            }
+
+            ItemKind::ExternCrate(orig_name) => {
+                self.build_reduced_graph_for_extern_crate(
+                    orig_name,
+                    item,
+                    local_def_id,
+                    vis,
+                    parent,
+                );
+            }
+
+            ItemKind::Mod(..) => {
+                let module = self.r.new_module(
+                    Some(parent),
+                    ModuleKind::Def(DefKind::Mod, def_id, ident.name),
+                    expansion.to_expn_id(),
+                    item.span,
+                    parent.no_implicit_prelude
+                        || self.r.session.contains_name(&item.attrs, sym::no_implicit_prelude),
+                );
+                self.r.define(parent, ident, TypeNS, (module, vis, sp, expansion));
+
+                // Descend into the module.
+                self.parent_scope.module = module;
+            }
+
+            // These items live in the value namespace.
+            ItemKind::Static(_, mt, _) => {
+                let res = Res::Def(DefKind::Static(mt), def_id);
+                self.r.define(parent, ident, ValueNS, (res, vis, sp, expansion));
+            }
+            ItemKind::Const(..) => {
+                let res = Res::Def(DefKind::Const, def_id);
+                self.r.define(parent, ident, ValueNS, (res, vis, sp, expansion));
+            }
+            ItemKind::Fn(..) => {
+                let res = Res::Def(DefKind::Fn, def_id);
+                self.r.define(parent, ident, ValueNS, (res, vis, sp, expansion));
+
+                // Functions introducing procedural macros reserve a slot
+                // in the macro namespace as well (see #52225).
+                self.define_macro(item);
+            }
+
+            // These items live in the type namespace.
+            ItemKind::TyAlias(..) => {
+                let res = Res::Def(DefKind::TyAlias, def_id);
+                self.r.define(parent, ident, TypeNS, (res, vis, sp, expansion));
+            }
+
+            ItemKind::Enum(_, _) => {
+                let module = self.r.new_module(
+                    Some(parent),
+                    ModuleKind::Def(DefKind::Enum, def_id, ident.name),
+                    expansion.to_expn_id(),
+                    item.span,
+                    parent.no_implicit_prelude,
+                );
+                self.r.define(parent, ident, TypeNS, (module, vis, sp, expansion));
+                self.parent_scope.module = module;
+            }
+
+            ItemKind::TraitAlias(..) => {
+                let res = Res::Def(DefKind::TraitAlias, def_id);
+                self.r.define(parent, ident, TypeNS, (res, vis, sp, expansion));
+            }
+
+            // These items live in both the type and value namespaces.
+            ItemKind::Struct(ref vdata, _) => {
+                // Define a name in the type namespace.
+                let res = Res::Def(DefKind::Struct, def_id);
+                self.r.define(parent, ident, TypeNS, (res, vis, sp, expansion));
+
+                // Record field names for error reporting.
+                self.insert_field_names_local(def_id, vdata);
+
+                // If this is a tuple or unit struct, define a name
+                // in the value namespace as well.
+                if let Some(ctor_node_id) = vdata.ctor_id() {
+                    // If the structure is marked as non_exhaustive then lower the visibility
+                    // to within the crate.
+                    let mut ctor_vis = if vis == ty::Visibility::Public
+                        && self.r.session.contains_name(&item.attrs, sym::non_exhaustive)
+                    {
+                        ty::Visibility::Restricted(CRATE_DEF_ID.to_def_id())
+                    } else {
+                        vis
+                    };
+
+                    let mut ret_fields = Vec::with_capacity(vdata.fields().len());
+
+                    for field in vdata.fields() {
+                        // NOTE: The field may be an expansion placeholder, but expansion sets
+                        // correct visibilities for unnamed field placeholders specifically, so the
+                        // constructor visibility should still be determined correctly.
+                        let field_vis = self
+                            .try_resolve_visibility(&field.vis, false)
+                            .unwrap_or(ty::Visibility::Public);
+                        if ctor_vis.is_at_least(field_vis, &*self.r) {
+                            ctor_vis = field_vis;
+                        }
+                        ret_fields.push(field_vis);
+                    }
+                    let ctor_def_id = self.r.local_def_id(ctor_node_id);
+                    let ctor_res = Res::Def(
+                        DefKind::Ctor(CtorOf::Struct, CtorKind::from_ast(vdata)),
+                        ctor_def_id.to_def_id(),
+                    );
+                    self.r.define(parent, ident, ValueNS, (ctor_res, ctor_vis, sp, expansion));
+                    self.r.visibilities.insert(ctor_def_id, ctor_vis);
+
+                    self.r.struct_constructors.insert(def_id, (ctor_res, ctor_vis, ret_fields));
+                }
+            }
+
+            ItemKind::Union(ref vdata, _) => {
+                let res = Res::Def(DefKind::Union, def_id);
+                self.r.define(parent, ident, TypeNS, (res, vis, sp, expansion));
+
+                // Record field names for error reporting.
+                self.insert_field_names_local(def_id, vdata);
+            }
+
+            ItemKind::Trait(..) => {
+                // Add all the items within to a new module.
+                let module = self.r.new_module(
+                    Some(parent),
+                    ModuleKind::Def(DefKind::Trait, def_id, ident.name),
+                    expansion.to_expn_id(),
+                    item.span,
+                    parent.no_implicit_prelude,
+                );
+                self.r.define(parent, ident, TypeNS, (module, vis, sp, expansion));
+                self.parent_scope.module = module;
+            }
+
+            // These items do not add names to modules.
+            ItemKind::Impl(box Impl { of_trait: Some(..), .. }) => {
+                self.r.trait_impl_items.insert(local_def_id);
+            }
+            ItemKind::Impl { .. } | ItemKind::ForeignMod(..) | ItemKind::GlobalAsm(..) => {}
+
+            ItemKind::MacroDef(..) | ItemKind::MacCall(_) => unreachable!(),
+        }
+    }
+
+    fn build_reduced_graph_for_extern_crate(
+        &mut self,
+        orig_name: Option<Symbol>,
+        item: &Item,
+        local_def_id: LocalDefId,
+        vis: ty::Visibility,
+        parent: Module<'a>,
+    ) {
+        let ident = item.ident;
+        let sp = item.span;
+        let parent_scope = self.parent_scope;
+        let expansion = parent_scope.expansion;
+
+        let (used, module, binding) = if orig_name.is_none() && ident.name == kw::SelfLower {
+            self.r
+                .session
+                .struct_span_err(item.span, "`extern crate self;` requires renaming")
+                .span_suggestion(
+                    item.span,
+                    "rename the `self` crate to be able to import it",
+                    "extern crate self as name;",
+                    Applicability::HasPlaceholders,
+                )
+                .emit();
+            return;
+        } else if orig_name == Some(kw::SelfLower) {
+            Some(self.r.graph_root)
+        } else {
+            self.r.crate_loader.process_extern_crate(item, &self.r.definitions, local_def_id).map(
+                |crate_id| {
+                    self.r.extern_crate_map.insert(local_def_id, crate_id);
+                    self.r.expect_module(crate_id.as_def_id())
+                },
+            )
+        }
+        .map(|module| {
+            let used = self.process_macro_use_imports(item, module);
+            let binding =
+                (module, ty::Visibility::Public, sp, expansion).to_name_binding(self.r.arenas);
+            (used, Some(ModuleOrUniformRoot::Module(module)), binding)
+        })
+        .unwrap_or((true, None, self.r.dummy_binding));
+        let import = self.r.arenas.alloc_import(Import {
+            kind: ImportKind::ExternCrate { source: orig_name, target: ident },
+            root_id: item.id,
+            id: item.id,
+            parent_scope: self.parent_scope,
+            imported_module: Cell::new(module),
+            has_attributes: !item.attrs.is_empty(),
+            use_span_with_attributes: item.span_with_attributes(),
+            use_span: item.span,
+            root_span: item.span,
+            span: item.span,
+            module_path: Vec::new(),
+            vis: Cell::new(vis),
+            used: Cell::new(used),
+        });
+        self.r.potentially_unused_imports.push(import);
+        let imported_binding = self.r.import(binding, import);
+        if ptr::eq(parent, self.r.graph_root) {
+            if let Some(entry) = self.r.extern_prelude.get(&ident.normalize_to_macros_2_0()) {
+                if expansion != LocalExpnId::ROOT
+                    && orig_name.is_some()
+                    && entry.extern_crate_item.is_none()
+                {
+                    let msg = "macro-expanded `extern crate` items cannot \
+                                       shadow names passed with `--extern`";
+                    self.r.session.span_err(item.span, msg);
+                }
+            }
+            let entry = self.r.extern_prelude.entry(ident.normalize_to_macros_2_0()).or_insert(
+                ExternPreludeEntry { extern_crate_item: None, introduced_by_item: true },
+            );
+            entry.extern_crate_item = Some(imported_binding);
+            if orig_name.is_some() {
+                entry.introduced_by_item = true;
+            }
+        }
+        self.r.define(parent, ident, TypeNS, imported_binding);
+    }
+
+    /// Constructs the reduced graph for one foreign item.
+    fn build_reduced_graph_for_foreign_item(&mut self, item: &ForeignItem) {
+        let local_def_id = self.r.local_def_id(item.id);
+        let def_id = local_def_id.to_def_id();
+        let (def_kind, ns) = match item.kind {
+            ForeignItemKind::Fn(..) => (DefKind::Fn, ValueNS),
+            ForeignItemKind::Static(_, mt, _) => (DefKind::Static(mt), ValueNS),
+            ForeignItemKind::TyAlias(..) => (DefKind::ForeignTy, TypeNS),
+            ForeignItemKind::MacCall(_) => unreachable!(),
+        };
+        let parent = self.parent_scope.module;
+        let expansion = self.parent_scope.expansion;
+        let vis = self.resolve_visibility(&item.vis);
+        let res = Res::Def(def_kind, def_id);
+        self.r.define(parent, item.ident, ns, (res, vis, item.span, expansion));
+        self.r.visibilities.insert(local_def_id, vis);
+    }
+
+    fn build_reduced_graph_for_block(&mut self, block: &Block) {
+        let parent = self.parent_scope.module;
+        let expansion = self.parent_scope.expansion;
+        if self.block_needs_anonymous_module(block) {
+            let module = self.r.new_module(
+                Some(parent),
+                ModuleKind::Block,
+                expansion.to_expn_id(),
+                block.span,
+                parent.no_implicit_prelude,
+            );
+            self.r.block_map.insert(block.id, module);
+            self.parent_scope.module = module; // Descend into the block.
+        }
+    }
+
+    /// Builds the reduced graph for a single item in an external crate.
+    fn build_reduced_graph_for_external_crate_res(&mut self, child: ModChild) {
+        let parent = self.parent_scope.module;
+        let ModChild { ident, res, vis, span, macro_rules } = child;
+        let res = res.expect_non_local();
+        let expansion = self.parent_scope.expansion;
+        // Record primary definitions.
+        match res {
+            Res::Def(DefKind::Mod | DefKind::Enum | DefKind::Trait, def_id) => {
+                let module = self.r.expect_module(def_id);
+                self.r.define(parent, ident, TypeNS, (module, vis, span, expansion));
+            }
+            Res::Def(
+                DefKind::Struct
+                | DefKind::Union
+                | DefKind::Variant
+                | DefKind::TyAlias
+                | DefKind::ForeignTy
+                | DefKind::OpaqueTy
+                | DefKind::TraitAlias
+                | DefKind::AssocTy,
+                _,
+            )
+            | Res::PrimTy(..)
+            | Res::ToolMod => self.r.define(parent, ident, TypeNS, (res, vis, span, expansion)),
+            Res::Def(
+                DefKind::Fn
+                | DefKind::AssocFn
+                | DefKind::Static(_)
+                | DefKind::Const
+                | DefKind::AssocConst
+                | DefKind::Ctor(..),
+                _,
+            ) => self.r.define(parent, ident, ValueNS, (res, vis, span, expansion)),
+            Res::Def(DefKind::Macro(..), _) | Res::NonMacroAttr(..) => {
+                if !macro_rules {
+                    self.r.define(parent, ident, MacroNS, (res, vis, span, expansion))
+                }
+            }
+            Res::Def(
+                DefKind::TyParam
+                | DefKind::ConstParam
+                | DefKind::ExternCrate
+                | DefKind::Use
+                | DefKind::ForeignMod
+                | DefKind::AnonConst
+                | DefKind::InlineConst
+                | DefKind::Field
+                | DefKind::LifetimeParam
+                | DefKind::GlobalAsm
+                | DefKind::Closure
+                | DefKind::Impl
+                | DefKind::Generator,
+                _,
+            )
+            | Res::Local(..)
+            | Res::SelfTy { .. }
+            | Res::SelfCtor(..)
+            | Res::Err => bug!("unexpected resolution: {:?}", res),
+        }
+        // Record some extra data for better diagnostics.
+        let cstore = self.r.cstore();
+        match res {
+            Res::Def(DefKind::Struct, def_id) => {
+                let field_names =
+                    cstore.struct_field_names_untracked(def_id, self.r.session).collect();
+                let ctor = cstore.ctor_def_id_and_kind_untracked(def_id);
+                if let Some((ctor_def_id, ctor_kind)) = ctor {
+                    let ctor_res = Res::Def(DefKind::Ctor(CtorOf::Struct, ctor_kind), ctor_def_id);
+                    let ctor_vis = cstore.visibility_untracked(ctor_def_id);
+                    let field_visibilities =
+                        cstore.struct_field_visibilities_untracked(def_id).collect();
+                    self.r
+                        .struct_constructors
+                        .insert(def_id, (ctor_res, ctor_vis, field_visibilities));
+                }
+                self.insert_field_names(def_id, field_names);
+            }
+            Res::Def(DefKind::Union, def_id) => {
+                let field_names =
+                    cstore.struct_field_names_untracked(def_id, self.r.session).collect();
+                self.insert_field_names(def_id, field_names);
+            }
+            Res::Def(DefKind::AssocFn, def_id) => {
+                if cstore.fn_has_self_parameter_untracked(def_id) {
+                    self.r.has_self.insert(def_id);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn add_macro_use_binding(
+        &mut self,
+        name: Symbol,
+        binding: &'a NameBinding<'a>,
+        span: Span,
+        allow_shadowing: bool,
+    ) {
+        if self.r.macro_use_prelude.insert(name, binding).is_some() && !allow_shadowing {
+            let msg = format!("`{}` is already in scope", name);
+            let note =
+                "macro-expanded `#[macro_use]`s may not shadow existing macros (see RFC 1560)";
+            self.r.session.struct_span_err(span, &msg).note(note).emit();
+        }
+    }
+
+    /// Returns `true` if we should consider the underlying `extern crate` to be used.
+    fn process_macro_use_imports(&mut self, item: &Item, module: Module<'a>) -> bool {
+        let mut import_all = None;
+        let mut single_imports = Vec::new();
+        for attr in &item.attrs {
+            if attr.has_name(sym::macro_use) {
+                if self.parent_scope.module.parent.is_some() {
+                    struct_span_err!(
+                        self.r.session,
+                        item.span,
+                        E0468,
+                        "an `extern crate` loading macros must be at the crate root"
+                    )
+                    .emit();
+                }
+                if let ItemKind::ExternCrate(Some(orig_name)) = item.kind {
+                    if orig_name == kw::SelfLower {
+                        self.r
+                            .session
+                            .struct_span_err(
+                                attr.span,
+                                "`#[macro_use]` is not supported on `extern crate self`",
+                            )
+                            .emit();
+                    }
+                }
+                let ill_formed = |span| {
+                    struct_span_err!(self.r.session, span, E0466, "bad macro import").emit();
+                };
+                match attr.meta() {
+                    Some(meta) => match meta.kind {
+                        MetaItemKind::Word => {
+                            import_all = Some(meta.span);
+                            break;
+                        }
+                        MetaItemKind::List(nested_metas) => {
+                            for nested_meta in nested_metas {
+                                match nested_meta.ident() {
+                                    Some(ident) if nested_meta.is_word() => {
+                                        single_imports.push(ident)
+                                    }
+                                    _ => ill_formed(nested_meta.span()),
+                                }
+                            }
+                        }
+                        MetaItemKind::NameValue(..) => ill_formed(meta.span),
+                    },
+                    None => ill_formed(attr.span),
+                }
+            }
+        }
+
+        let macro_use_import = |this: &Self, span| {
+            this.r.arenas.alloc_import(Import {
+                kind: ImportKind::MacroUse,
+                root_id: item.id,
+                id: item.id,
+                parent_scope: this.parent_scope,
+                imported_module: Cell::new(Some(ModuleOrUniformRoot::Module(module))),
+                use_span_with_attributes: item.span_with_attributes(),
+                has_attributes: !item.attrs.is_empty(),
+                use_span: item.span,
+                root_span: span,
+                span,
+                module_path: Vec::new(),
+                vis: Cell::new(ty::Visibility::Restricted(CRATE_DEF_ID.to_def_id())),
+                used: Cell::new(false),
+            })
+        };
+
+        let allow_shadowing = self.parent_scope.expansion == LocalExpnId::ROOT;
+        if let Some(span) = import_all {
+            let import = macro_use_import(self, span);
+            self.r.potentially_unused_imports.push(import);
+            module.for_each_child(self, |this, ident, ns, binding| {
+                if ns == MacroNS {
+                    let imported_binding = this.r.import(binding, import);
+                    this.add_macro_use_binding(ident.name, imported_binding, span, allow_shadowing);
+                }
+            });
+        } else {
+            for ident in single_imports.iter().cloned() {
+                let result = self.r.maybe_resolve_ident_in_module(
+                    ModuleOrUniformRoot::Module(module),
+                    ident,
+                    MacroNS,
+                    &self.parent_scope,
+                );
+                if let Ok(binding) = result {
+                    let import = macro_use_import(self, ident.span);
+                    self.r.potentially_unused_imports.push(import);
+                    let imported_binding = self.r.import(binding, import);
+                    self.add_macro_use_binding(
+                        ident.name,
+                        imported_binding,
+                        ident.span,
+                        allow_shadowing,
+                    );
+                } else {
+                    struct_span_err!(self.r.session, ident.span, E0469, "imported macro not found")
+                        .emit();
+                }
+            }
+        }
+        import_all.is_some() || !single_imports.is_empty()
+    }
+
+    /// Returns `true` if this attribute list contains `macro_use`.
+    fn contains_macro_use(&mut self, attrs: &[ast::Attribute]) -> bool {
+        for attr in attrs {
+            if attr.has_name(sym::macro_escape) {
+                let msg = "`#[macro_escape]` is a deprecated synonym for `#[macro_use]`";
+                let mut err = self.r.session.struct_span_warn(attr.span, msg);
+                if let ast::AttrStyle::Inner = attr.style {
+                    err.help("try an outer attribute: `#[macro_use]`").emit();
+                } else {
+                    err.emit();
+                }
+            } else if !attr.has_name(sym::macro_use) {
+                continue;
+            }
+
+            if !attr.is_word() {
+                self.r.session.span_err(attr.span, "arguments to `macro_use` are not allowed here");
+            }
+            return true;
+        }
+
+        false
+    }
+
+    fn visit_invoc(&mut self, id: NodeId) -> LocalExpnId {
+        let invoc_id = id.placeholder_to_expn_id();
+        let old_parent_scope = self.r.invocation_parent_scopes.insert(invoc_id, self.parent_scope);
+        assert!(old_parent_scope.is_none(), "invocation data is reset for an invocation");
+        invoc_id
+    }
+
+    /// Visit invocation in context in which it can emit a named item (possibly `macro_rules`)
+    /// directly into its parent scope's module.
+    fn visit_invoc_in_module(&mut self, id: NodeId) -> MacroRulesScopeRef<'a> {
+        let invoc_id = self.visit_invoc(id);
+        self.parent_scope.module.unexpanded_invocations.borrow_mut().insert(invoc_id);
+        self.r.arenas.alloc_macro_rules_scope(MacroRulesScope::Invocation(invoc_id))
+    }
+
+    fn proc_macro_stub(&self, item: &ast::Item) -> Option<(MacroKind, Ident, Span)> {
+        if self.r.session.contains_name(&item.attrs, sym::proc_macro) {
+            return Some((MacroKind::Bang, item.ident, item.span));
+        } else if self.r.session.contains_name(&item.attrs, sym::proc_macro_attribute) {
+            return Some((MacroKind::Attr, item.ident, item.span));
+        } else if let Some(attr) = self.r.session.find_by_name(&item.attrs, sym::proc_macro_derive)
+        {
+            if let Some(nested_meta) = attr.meta_item_list().and_then(|list| list.get(0).cloned()) {
+                if let Some(ident) = nested_meta.ident() {
+                    return Some((MacroKind::Derive, ident, ident.span));
+                }
+            }
+        }
+        None
+    }
+
+    // Mark the given macro as unused unless its name starts with `_`.
+    // Macro uses will remove items from this set, and the remaining
+    // items will be reported as `unused_macros`.
+    fn insert_unused_macro(
+        &mut self,
+        ident: Ident,
+        def_id: LocalDefId,
+        node_id: NodeId,
+        rule_spans: &[(usize, Span)],
+    ) {
+        if !ident.as_str().starts_with('_') {
+            self.r.unused_macros.insert(def_id, (node_id, ident));
+            for (rule_i, rule_span) in rule_spans.iter() {
+                self.r.unused_macro_rules.insert((def_id, *rule_i), (ident, *rule_span));
+            }
+        }
+    }
+
+    fn define_macro(&mut self, item: &ast::Item) -> MacroRulesScopeRef<'a> {
+        let parent_scope = self.parent_scope;
+        let expansion = parent_scope.expansion;
+        let def_id = self.r.local_def_id(item.id);
+        let (ext, ident, span, macro_rules, rule_spans) = match &item.kind {
+            ItemKind::MacroDef(def) => {
+                let (ext, rule_spans) = self.r.compile_macro(item, self.r.session.edition());
+                let ext = Lrc::new(ext);
+                (ext, item.ident, item.span, def.macro_rules, rule_spans)
+            }
+            ItemKind::Fn(..) => match self.proc_macro_stub(item) {
+                Some((macro_kind, ident, span)) => {
+                    self.r.proc_macro_stubs.insert(def_id);
+                    (self.r.dummy_ext(macro_kind), ident, span, false, Vec::new())
+                }
+                None => return parent_scope.macro_rules,
+            },
+            _ => unreachable!(),
+        };
+
+        let res = Res::Def(DefKind::Macro(ext.macro_kind()), def_id.to_def_id());
+        self.r.macro_map.insert(def_id.to_def_id(), MacroData { ext, macro_rules });
+        self.r.local_macro_def_scopes.insert(def_id, parent_scope.module);
+
+        if macro_rules {
+            let ident = ident.normalize_to_macros_2_0();
+            self.r.macro_names.insert(ident);
+            let is_macro_export = self.r.session.contains_name(&item.attrs, sym::macro_export);
+            let vis = if is_macro_export {
+                ty::Visibility::Public
+            } else {
+                ty::Visibility::Restricted(CRATE_DEF_ID.to_def_id())
+            };
+            let binding = (res, vis, span, expansion).to_name_binding(self.r.arenas);
+            self.r.set_binding_parent_module(binding, parent_scope.module);
+            if is_macro_export {
+                let module = self.r.graph_root;
+                self.r.define(module, ident, MacroNS, (res, vis, span, expansion, IsMacroExport));
+            } else {
+                self.r.check_reserved_macro_name(ident, res);
+                self.insert_unused_macro(ident, def_id, item.id, &rule_spans);
+            }
+            self.r.visibilities.insert(def_id, vis);
+            let scope = self.r.arenas.alloc_macro_rules_scope(MacroRulesScope::Binding(
+                self.r.arenas.alloc_macro_rules_binding(MacroRulesBinding {
+                    parent_macro_rules_scope: parent_scope.macro_rules,
+                    binding,
+                    ident,
+                }),
+            ));
+            self.r.macro_rules_scopes.insert(def_id, scope);
+            scope
+        } else {
+            let module = parent_scope.module;
+            let vis = match item.kind {
+                // Visibilities must not be resolved non-speculatively twice
+                // and we already resolved this one as a `fn` item visibility.
+                ItemKind::Fn(..) => {
+                    self.try_resolve_visibility(&item.vis, false).unwrap_or(ty::Visibility::Public)
+                }
+                _ => self.resolve_visibility(&item.vis),
+            };
+            if vis != ty::Visibility::Public {
+                self.insert_unused_macro(ident, def_id, item.id, &rule_spans);
+            }
+            self.r.define(module, ident, MacroNS, (res, vis, span, expansion));
+            self.r.visibilities.insert(def_id, vis);
+            self.parent_scope.macro_rules
+        }
+    }
+}
+
+macro_rules! method {
+    ($visit:ident: $ty:ty, $invoc:path, $walk:ident) => {
+        fn $visit(&mut self, node: &'b $ty) {
+            if let $invoc(..) = node.kind {
+                self.visit_invoc(node.id);
+            } else {
+                visit::$walk(self, node);
+            }
+        }
+    };
+}
+
+impl<'a, 'b> Visitor<'b> for BuildReducedGraphVisitor<'a, 'b> {
+    method!(visit_expr: ast::Expr, ast::ExprKind::MacCall, walk_expr);
+    method!(visit_pat: ast::Pat, ast::PatKind::MacCall, walk_pat);
+    method!(visit_ty: ast::Ty, ast::TyKind::MacCall, walk_ty);
+
+    fn visit_item(&mut self, item: &'b Item) {
+        let orig_module_scope = self.parent_scope.module;
+        self.parent_scope.macro_rules = match item.kind {
+            ItemKind::MacroDef(..) => {
+                let macro_rules_scope = self.define_macro(item);
+                visit::walk_item(self, item);
+                macro_rules_scope
+            }
+            ItemKind::MacCall(..) => {
+                let macro_rules_scope = self.visit_invoc_in_module(item.id);
+                visit::walk_item(self, item);
+                macro_rules_scope
+            }
+            _ => {
+                let orig_macro_rules_scope = self.parent_scope.macro_rules;
+                self.build_reduced_graph_for_item(item);
+                visit::walk_item(self, item);
+                match item.kind {
+                    ItemKind::Mod(..) if self.contains_macro_use(&item.attrs) => {
+                        self.parent_scope.macro_rules
+                    }
+                    _ => orig_macro_rules_scope,
+                }
+            }
+        };
+        self.parent_scope.module = orig_module_scope;
+    }
+
+    fn visit_stmt(&mut self, stmt: &'b ast::Stmt) {
+        if let ast::StmtKind::MacCall(..) = stmt.kind {
+            self.parent_scope.macro_rules = self.visit_invoc_in_module(stmt.id);
+        } else {
+            visit::walk_stmt(self, stmt);
+        }
+    }
+
+    fn visit_foreign_item(&mut self, foreign_item: &'b ForeignItem) {
+        if let ForeignItemKind::MacCall(_) = foreign_item.kind {
+            self.visit_invoc_in_module(foreign_item.id);
+            return;
+        }
+
+        self.build_reduced_graph_for_foreign_item(foreign_item);
+        visit::walk_foreign_item(self, foreign_item);
+    }
+
+    fn visit_block(&mut self, block: &'b Block) {
+        let orig_current_module = self.parent_scope.module;
+        let orig_current_macro_rules_scope = self.parent_scope.macro_rules;
+        self.build_reduced_graph_for_block(block);
+        visit::walk_block(self, block);
+        self.parent_scope.module = orig_current_module;
+        self.parent_scope.macro_rules = orig_current_macro_rules_scope;
+    }
+
+    fn visit_assoc_item(&mut self, item: &'b AssocItem, ctxt: AssocCtxt) {
+        if let AssocItemKind::MacCall(_) = item.kind {
+            match ctxt {
+                AssocCtxt::Trait => {
+                    self.visit_invoc_in_module(item.id);
+                }
+                AssocCtxt::Impl => {
+                    self.visit_invoc(item.id);
+                }
+            }
+            return;
+        }
+
+        let vis = self.resolve_visibility(&item.vis);
+        let local_def_id = self.r.local_def_id(item.id);
+        let def_id = local_def_id.to_def_id();
+
+        if !(ctxt == AssocCtxt::Impl
+            && matches!(item.vis.kind, ast::VisibilityKind::Inherited)
+            && self
+                .r
+                .trait_impl_items
+                .contains(&ty::DefIdTree::local_parent(&*self.r, local_def_id)))
+        {
+            // Trait impl item visibility is inherited from its trait when not specified
+            // explicitly. In that case we cannot determine it here in early resolve,
+            // so we leave a hole in the visibility table to be filled later.
+            self.r.visibilities.insert(local_def_id, vis);
+        }
+
+        if ctxt == AssocCtxt::Trait {
+            let (def_kind, ns) = match item.kind {
+                AssocItemKind::Const(..) => (DefKind::AssocConst, ValueNS),
+                AssocItemKind::Fn(box Fn { ref sig, .. }) => {
+                    if sig.decl.has_self() {
+                        self.r.has_self.insert(def_id);
+                    }
+                    (DefKind::AssocFn, ValueNS)
+                }
+                AssocItemKind::TyAlias(..) => (DefKind::AssocTy, TypeNS),
+                AssocItemKind::MacCall(_) => bug!(), // handled above
+            };
+
+            let parent = self.parent_scope.module;
+            let expansion = self.parent_scope.expansion;
+            let res = Res::Def(def_kind, def_id);
+            self.r.define(parent, item.ident, ns, (res, vis, item.span, expansion));
+        }
+
+        visit::walk_assoc_item(self, item, ctxt);
+    }
+
+    fn visit_attribute(&mut self, attr: &'b ast::Attribute) {
+        if !attr.is_doc_comment() && attr::is_builtin_attr(attr) {
+            self.r
+                .builtin_attrs
+                .push((attr.get_normal_item().path.segments[0].ident, self.parent_scope));
+        }
+        visit::walk_attribute(self, attr);
+    }
+
+    fn visit_arm(&mut self, arm: &'b ast::Arm) {
+        if arm.is_placeholder {
+            self.visit_invoc(arm.id);
+        } else {
+            visit::walk_arm(self, arm);
+        }
+    }
+
+    fn visit_expr_field(&mut self, f: &'b ast::ExprField) {
+        if f.is_placeholder {
+            self.visit_invoc(f.id);
+        } else {
+            visit::walk_expr_field(self, f);
+        }
+    }
+
+    fn visit_pat_field(&mut self, fp: &'b ast::PatField) {
+        if fp.is_placeholder {
+            self.visit_invoc(fp.id);
+        } else {
+            visit::walk_pat_field(self, fp);
+        }
+    }
+
+    fn visit_generic_param(&mut self, param: &'b ast::GenericParam) {
+        if param.is_placeholder {
+            self.visit_invoc(param.id);
+        } else {
+            visit::walk_generic_param(self, param);
+        }
+    }
+
+    fn visit_param(&mut self, p: &'b ast::Param) {
+        if p.is_placeholder {
+            self.visit_invoc(p.id);
+        } else {
+            visit::walk_param(self, p);
+        }
+    }
+
+    fn visit_field_def(&mut self, sf: &'b ast::FieldDef) {
+        if sf.is_placeholder {
+            self.visit_invoc(sf.id);
+        } else {
+            let vis = self.resolve_visibility(&sf.vis);
+            self.r.visibilities.insert(self.r.local_def_id(sf.id), vis);
+            visit::walk_field_def(self, sf);
+        }
+    }
+
+    // Constructs the reduced graph for one variant. Variants exist in the
+    // type and value namespaces.
+    fn visit_variant(&mut self, variant: &'b ast::Variant) {
+        if variant.is_placeholder {
+            self.visit_invoc_in_module(variant.id);
+            return;
+        }
+
+        let parent = self.parent_scope.module;
+        let expn_id = self.parent_scope.expansion;
+        let ident = variant.ident;
+
+        // Define a name in the type namespace.
+        let def_id = self.r.local_def_id(variant.id);
+        let res = Res::Def(DefKind::Variant, def_id.to_def_id());
+        let vis = self.resolve_visibility(&variant.vis);
+        self.r.define(parent, ident, TypeNS, (res, vis, variant.span, expn_id));
+        self.r.visibilities.insert(def_id, vis);
+
+        // If the variant is marked as non_exhaustive then lower the visibility to within the crate.
+        let ctor_vis = if vis == ty::Visibility::Public
+            && self.r.session.contains_name(&variant.attrs, sym::non_exhaustive)
+        {
+            ty::Visibility::Restricted(CRATE_DEF_ID.to_def_id())
+        } else {
+            vis
+        };
+
+        // Define a constructor name in the value namespace.
+        // Braced variants, unlike structs, generate unusable names in
+        // value namespace, they are reserved for possible future use.
+        // It's ok to use the variant's id as a ctor id since an
+        // error will be reported on any use of such resolution anyway.
+        let ctor_node_id = variant.data.ctor_id().unwrap_or(variant.id);
+        let ctor_def_id = self.r.local_def_id(ctor_node_id);
+        let ctor_kind = CtorKind::from_ast(&variant.data);
+        let ctor_res = Res::Def(DefKind::Ctor(CtorOf::Variant, ctor_kind), ctor_def_id.to_def_id());
+        self.r.define(parent, ident, ValueNS, (ctor_res, ctor_vis, variant.span, expn_id));
+        if ctor_def_id != def_id {
+            self.r.visibilities.insert(ctor_def_id, ctor_vis);
+        }
+        // Record field names for error reporting.
+        self.insert_field_names_local(ctor_def_id.to_def_id(), &variant.data);
+
+        visit::walk_variant(self, variant);
+    }
+
+    fn visit_crate(&mut self, krate: &'b ast::Crate) {
+        if krate.is_placeholder {
+            self.visit_invoc_in_module(krate.id);
+        } else {
+            visit::walk_crate(self, krate);
+            self.contains_macro_use(&krate.attrs);
+        }
+    }
+}
diff --git a/compiler/rustc_resolve/src/check_unused.rs b/compiler/rustc_resolve/src/check_unused.rs
new file mode 100644
index 000000000..f2f6f1d89
--- /dev/null
+++ b/compiler/rustc_resolve/src/check_unused.rs
@@ -0,0 +1,350 @@
+//
+// Unused import checking
+//
+// Although this is mostly a lint pass, it lives in here because it depends on
+// resolve data structures and because it finalises the privacy information for
+// `use` items.
+//
+// Unused trait imports can't be checked until the method resolution. We save
+// candidates here, and do the actual check in librustc_typeck/check_unused.rs.
+//
+// Checking for unused imports is split into three steps:
+//
+//  - `UnusedImportCheckVisitor` walks the AST to find all the unused imports
+//    inside of `UseTree`s, recording their `NodeId`s and grouping them by
+//    the parent `use` item
+//
+//  - `calc_unused_spans` then walks over all the `use` items marked in the
+//    previous step to collect the spans associated with the `NodeId`s and to
+//    calculate the spans that can be removed by rustfix; This is done in a
+//    separate step to be able to collapse the adjacent spans that rustfix
+//    will remove
+//
+//  - `check_crate` finally emits the diagnostics based on the data generated
+//    in the last step
+
+use crate::imports::ImportKind;
+use crate::module_to_string;
+use crate::Resolver;
+
+use rustc_ast as ast;
+use rustc_ast::node_id::NodeMap;
+use rustc_ast::visit::{self, Visitor};
+use rustc_data_structures::fx::FxHashSet;
+use rustc_errors::{pluralize, MultiSpan};
+use rustc_session::lint::builtin::{MACRO_USE_EXTERN_CRATE, UNUSED_IMPORTS};
+use rustc_session::lint::BuiltinLintDiagnostics;
+use rustc_span::{Span, DUMMY_SP};
+
+struct UnusedImport<'a> {
+    use_tree: &'a ast::UseTree,
+    use_tree_id: ast::NodeId,
+    item_span: Span,
+    unused: FxHashSet<ast::NodeId>,
+}
+
+impl<'a> UnusedImport<'a> {
+    fn add(&mut self, id: ast::NodeId) {
+        self.unused.insert(id);
+    }
+}
+
+struct UnusedImportCheckVisitor<'a, 'b> {
+    r: &'a mut Resolver<'b>,
+    /// All the (so far) unused imports, grouped path list
+    unused_imports: NodeMap<UnusedImport<'a>>,
+    base_use_tree: Option<&'a ast::UseTree>,
+    base_id: ast::NodeId,
+    item_span: Span,
+}
+
+impl<'a, 'b> UnusedImportCheckVisitor<'a, 'b> {
+    // We have information about whether `use` (import) items are actually
+    // used now. If an import is not used at all, we signal a lint error.
+    fn check_import(&mut self, id: ast::NodeId) {
+        let used = self.r.used_imports.contains(&id);
+        let def_id = self.r.local_def_id(id);
+        if !used {
+            if self.r.maybe_unused_trait_imports.contains(&def_id) {
+                // Check later.
+                return;
+            }
+            self.unused_import(self.base_id).add(id);
+        } else {
+            // This trait import is definitely used, in a way other than
+            // method resolution.
+            self.r.maybe_unused_trait_imports.remove(&def_id);
+            if let Some(i) = self.unused_imports.get_mut(&self.base_id) {
+                i.unused.remove(&id);
+            }
+        }
+    }
+
+    fn unused_import(&mut self, id: ast::NodeId) -> &mut UnusedImport<'a> {
+        let use_tree_id = self.base_id;
+        let use_tree = self.base_use_tree.unwrap();
+        let item_span = self.item_span;
+
+        self.unused_imports.entry(id).or_insert_with(|| UnusedImport {
+            use_tree,
+            use_tree_id,
+            item_span,
+            unused: FxHashSet::default(),
+        })
+    }
+}
+
+impl<'a, 'b> Visitor<'a> for UnusedImportCheckVisitor<'a, 'b> {
+    fn visit_item(&mut self, item: &'a ast::Item) {
+        self.item_span = item.span_with_attributes();
+
+        // Ignore is_public import statements because there's no way to be sure
+        // whether they're used or not. Also ignore imports with a dummy span
+        // because this means that they were generated in some fashion by the
+        // compiler and we don't need to consider them.
+        if let ast::ItemKind::Use(..) = item.kind {
+            if item.vis.kind.is_pub() || item.span.is_dummy() {
+                return;
+            }
+        }
+
+        visit::walk_item(self, item);
+    }
+
+    fn visit_use_tree(&mut self, use_tree: &'a ast::UseTree, id: ast::NodeId, nested: bool) {
+        // Use the base UseTree's NodeId as the item id
+        // This allows the grouping of all the lints in the same item
+        if !nested {
+            self.base_id = id;
+            self.base_use_tree = Some(use_tree);
+        }
+
+        if let ast::UseTreeKind::Nested(ref items) = use_tree.kind {
+            if items.is_empty() {
+                self.unused_import(self.base_id).add(id);
+            }
+        } else {
+            self.check_import(id);
+        }
+
+        visit::walk_use_tree(self, use_tree, id);
+    }
+}
+
+enum UnusedSpanResult {
+    Used,
+    FlatUnused(Span, Span),
+    NestedFullUnused(Vec<Span>, Span),
+    NestedPartialUnused(Vec<Span>, Vec<Span>),
+}
+
+fn calc_unused_spans(
+    unused_import: &UnusedImport<'_>,
+    use_tree: &ast::UseTree,
+    use_tree_id: ast::NodeId,
+) -> UnusedSpanResult {
+    // The full span is the whole item's span if this current tree is not nested inside another
+    // This tells rustfix to remove the whole item if all the imports are unused
+    let full_span = if unused_import.use_tree.span == use_tree.span {
+        unused_import.item_span
+    } else {
+        use_tree.span
+    };
+    match use_tree.kind {
+        ast::UseTreeKind::Simple(..) | ast::UseTreeKind::Glob => {
+            if unused_import.unused.contains(&use_tree_id) {
+                UnusedSpanResult::FlatUnused(use_tree.span, full_span)
+            } else {
+                UnusedSpanResult::Used
+            }
+        }
+        ast::UseTreeKind::Nested(ref nested) => {
+            if nested.is_empty() {
+                return UnusedSpanResult::FlatUnused(use_tree.span, full_span);
+            }
+
+            let mut unused_spans = Vec::new();
+            let mut to_remove = Vec::new();
+            let mut all_nested_unused = true;
+            let mut previous_unused = false;
+            for (pos, (use_tree, use_tree_id)) in nested.iter().enumerate() {
+                let remove = match calc_unused_spans(unused_import, use_tree, *use_tree_id) {
+                    UnusedSpanResult::Used => {
+                        all_nested_unused = false;
+                        None
+                    }
+                    UnusedSpanResult::FlatUnused(span, remove) => {
+                        unused_spans.push(span);
+                        Some(remove)
+                    }
+                    UnusedSpanResult::NestedFullUnused(mut spans, remove) => {
+                        unused_spans.append(&mut spans);
+                        Some(remove)
+                    }
+                    UnusedSpanResult::NestedPartialUnused(mut spans, mut to_remove_extra) => {
+                        all_nested_unused = false;
+                        unused_spans.append(&mut spans);
+                        to_remove.append(&mut to_remove_extra);
+                        None
+                    }
+                };
+                if let Some(remove) = remove {
+                    let remove_span = if nested.len() == 1 {
+                        remove
+                    } else if pos == nested.len() - 1 || !all_nested_unused {
+                        // Delete everything from the end of the last import, to delete the
+                        // previous comma
+                        nested[pos - 1].0.span.shrink_to_hi().to(use_tree.span)
+                    } else {
+                        // Delete everything until the next import, to delete the trailing commas
+                        use_tree.span.to(nested[pos + 1].0.span.shrink_to_lo())
+                    };
+
+                    // Try to collapse adjacent spans into a single one. This prevents all cases of
+                    // overlapping removals, which are not supported by rustfix
+                    if previous_unused && !to_remove.is_empty() {
+                        let previous = to_remove.pop().unwrap();
+                        to_remove.push(previous.to(remove_span));
+                    } else {
+                        to_remove.push(remove_span);
+                    }
+                }
+                previous_unused = remove.is_some();
+            }
+            if unused_spans.is_empty() {
+                UnusedSpanResult::Used
+            } else if all_nested_unused {
+                UnusedSpanResult::NestedFullUnused(unused_spans, full_span)
+            } else {
+                UnusedSpanResult::NestedPartialUnused(unused_spans, to_remove)
+            }
+        }
+    }
+}
+
+impl Resolver<'_> {
+    pub(crate) fn check_unused(&mut self, krate: &ast::Crate) {
+        for import in self.potentially_unused_imports.iter() {
+            match import.kind {
+                _ if import.used.get()
+                    || import.vis.get().is_public()
+                    || import.span.is_dummy() =>
+                {
+                    if let ImportKind::MacroUse = import.kind {
+                        if !import.span.is_dummy() {
+                            self.lint_buffer.buffer_lint(
+                                MACRO_USE_EXTERN_CRATE,
+                                import.id,
+                                import.span,
+                                "deprecated `#[macro_use]` attribute used to \
+                                import macros should be replaced at use sites \
+                                with a `use` item to import the macro \
+                                instead",
+                            );
+                        }
+                    }
+                }
+                ImportKind::ExternCrate { .. } => {
+                    let def_id = self.local_def_id(import.id);
+                    self.maybe_unused_extern_crates.push((def_id, import.span));
+                }
+                ImportKind::MacroUse => {
+                    let msg = "unused `#[macro_use]` import";
+                    self.lint_buffer.buffer_lint(UNUSED_IMPORTS, import.id, import.span, msg);
+                }
+                _ => {}
+            }
+        }
+
+        let mut visitor = UnusedImportCheckVisitor {
+            r: self,
+            unused_imports: Default::default(),
+            base_use_tree: None,
+            base_id: ast::DUMMY_NODE_ID,
+            item_span: DUMMY_SP,
+        };
+        visit::walk_crate(&mut visitor, krate);
+
+        for unused in visitor.unused_imports.values() {
+            let mut fixes = Vec::new();
+            let mut spans = match calc_unused_spans(unused, unused.use_tree, unused.use_tree_id) {
+                UnusedSpanResult::Used => continue,
+                UnusedSpanResult::FlatUnused(span, remove) => {
+                    fixes.push((remove, String::new()));
+                    vec![span]
+                }
+                UnusedSpanResult::NestedFullUnused(spans, remove) => {
+                    fixes.push((remove, String::new()));
+                    spans
+                }
+                UnusedSpanResult::NestedPartialUnused(spans, remove) => {
+                    for fix in &remove {
+                        fixes.push((*fix, String::new()));
+                    }
+                    spans
+                }
+            };
+
+            let len = spans.len();
+            spans.sort();
+            let ms = MultiSpan::from_spans(spans.clone());
+            let mut span_snippets = spans
+                .iter()
+                .filter_map(|s| match visitor.r.session.source_map().span_to_snippet(*s) {
+                    Ok(s) => Some(format!("`{}`", s)),
+                    _ => None,
+                })
+                .collect::<Vec<String>>();
+            span_snippets.sort();
+            let msg = format!(
+                "unused import{}{}",
+                pluralize!(len),
+                if !span_snippets.is_empty() {
+                    format!(": {}", span_snippets.join(", "))
+                } else {
+                    String::new()
+                }
+            );
+
+            let fix_msg = if fixes.len() == 1 && fixes[0].0 == unused.item_span {
+                "remove the whole `use` item"
+            } else if spans.len() > 1 {
+                "remove the unused imports"
+            } else {
+                "remove the unused import"
+            };
+
+            // If we are in the `--test` mode, suppress a help that adds the `#[cfg(test)]`
+            // attribute; however, if not, suggest adding the attribute. There is no way to
+            // retrieve attributes here because we do not have a `TyCtxt` yet.
+            let test_module_span = if visitor.r.session.opts.test {
+                None
+            } else {
+                let parent_module = visitor.r.get_nearest_non_block_module(
+                    visitor.r.local_def_id(unused.use_tree_id).to_def_id(),
+                );
+                match module_to_string(parent_module) {
+                    Some(module)
+                        if module == "test"
+                            || module == "tests"
+                            || module.starts_with("test_")
+                            || module.starts_with("tests_")
+                            || module.ends_with("_test")
+                            || module.ends_with("_tests") =>
+                    {
+                        Some(parent_module.span)
+                    }
+                    _ => None,
+                }
+            };
+
+            visitor.r.lint_buffer.buffer_lint_with_diagnostic(
+                UNUSED_IMPORTS,
+                unused.use_tree_id,
+                ms,
+                &msg,
+                BuiltinLintDiagnostics::UnusedImports(fix_msg.into(), fixes, test_module_span),
+            );
+        }
+    }
+}
diff --git a/compiler/rustc_resolve/src/def_collector.rs b/compiler/rustc_resolve/src/def_collector.rs
new file mode 100644
index 000000000..66641fb2c
--- /dev/null
+++ b/compiler/rustc_resolve/src/def_collector.rs
@@ -0,0 +1,354 @@
+use crate::{ImplTraitContext, Resolver};
+use rustc_ast::visit::{self, FnKind};
+use rustc_ast::walk_list;
+use rustc_ast::*;
+use rustc_expand::expand::AstFragment;
+use rustc_hir::def_id::LocalDefId;
+use rustc_hir::definitions::*;
+use rustc_span::hygiene::LocalExpnId;
+use rustc_span::symbol::sym;
+use rustc_span::Span;
+use tracing::debug;
+
+pub(crate) fn collect_definitions(
+    resolver: &mut Resolver<'_>,
+    fragment: &AstFragment,
+    expansion: LocalExpnId,
+) {
+    let (parent_def, impl_trait_context) = resolver.invocation_parents[&expansion];
+    fragment.visit_with(&mut DefCollector { resolver, parent_def, expansion, impl_trait_context });
+}
+
+/// Creates `DefId`s for nodes in the AST.
+struct DefCollector<'a, 'b> {
+    resolver: &'a mut Resolver<'b>,
+    parent_def: LocalDefId,
+    impl_trait_context: ImplTraitContext,
+    expansion: LocalExpnId,
+}
+
+impl<'a, 'b> DefCollector<'a, 'b> {
+    fn create_def(&mut self, node_id: NodeId, data: DefPathData, span: Span) -> LocalDefId {
+        let parent_def = self.parent_def;
+        debug!("create_def(node_id={:?}, data={:?}, parent_def={:?})", node_id, data, parent_def);
+        self.resolver.create_def(
+            parent_def,
+            node_id,
+            data,
+            self.expansion.to_expn_id(),
+            span.with_parent(None),
+        )
+    }
+
+    fn with_parent<F: FnOnce(&mut Self)>(&mut self, parent_def: LocalDefId, f: F) {
+        let orig_parent_def = std::mem::replace(&mut self.parent_def, parent_def);
+        f(self);
+        self.parent_def = orig_parent_def;
+    }
+
+    fn with_impl_trait<F: FnOnce(&mut Self)>(
+        &mut self,
+        impl_trait_context: ImplTraitContext,
+        f: F,
+    ) {
+        let orig_itc = std::mem::replace(&mut self.impl_trait_context, impl_trait_context);
+        f(self);
+        self.impl_trait_context = orig_itc;
+    }
+
+    fn collect_field(&mut self, field: &'a FieldDef, index: Option<usize>) {
+        let index = |this: &Self| {
+            index.unwrap_or_else(|| {
+                let node_id = NodeId::placeholder_from_expn_id(this.expansion);
+                this.resolver.placeholder_field_indices[&node_id]
+            })
+        };
+
+        if field.is_placeholder {
+            let old_index = self.resolver.placeholder_field_indices.insert(field.id, index(self));
+            assert!(old_index.is_none(), "placeholder field index is reset for a node ID");
+            self.visit_macro_invoc(field.id);
+        } else {
+            let name = field.ident.map_or_else(|| sym::integer(index(self)), |ident| ident.name);
+            let def = self.create_def(field.id, DefPathData::ValueNs(name), field.span);
+            self.with_parent(def, |this| visit::walk_field_def(this, field));
+        }
+    }
+
+    fn visit_macro_invoc(&mut self, id: NodeId) {
+        let id = id.placeholder_to_expn_id();
+        let old_parent =
+            self.resolver.invocation_parents.insert(id, (self.parent_def, self.impl_trait_context));
+        assert!(old_parent.is_none(), "parent `LocalDefId` is reset for an invocation");
+    }
+}
+
+impl<'a, 'b> visit::Visitor<'a> for DefCollector<'a, 'b> {
+    fn visit_item(&mut self, i: &'a Item) {
+        debug!("visit_item: {:?}", i);
+
+        // Pick the def data. This need not be unique, but the more
+        // information we encapsulate into, the better
+        let def_data = match &i.kind {
+            ItemKind::Impl { .. } => DefPathData::Impl,
+            ItemKind::ForeignMod(..) => DefPathData::ForeignMod,
+            ItemKind::Mod(..)
+            | ItemKind::Trait(..)
+            | ItemKind::TraitAlias(..)
+            | ItemKind::Enum(..)
+            | ItemKind::Struct(..)
+            | ItemKind::Union(..)
+            | ItemKind::ExternCrate(..)
+            | ItemKind::TyAlias(..) => DefPathData::TypeNs(i.ident.name),
+            ItemKind::Static(..) | ItemKind::Const(..) | ItemKind::Fn(..) => {
+                DefPathData::ValueNs(i.ident.name)
+            }
+            ItemKind::MacroDef(..) => DefPathData::MacroNs(i.ident.name),
+            ItemKind::MacCall(..) => {
+                visit::walk_item(self, i);
+                return self.visit_macro_invoc(i.id);
+            }
+            ItemKind::GlobalAsm(..) => DefPathData::GlobalAsm,
+            ItemKind::Use(..) => {
+                return visit::walk_item(self, i);
+            }
+        };
+        let def = self.create_def(i.id, def_data, i.span);
+
+        self.with_parent(def, |this| {
+            this.with_impl_trait(ImplTraitContext::Existential, |this| {
+                match i.kind {
+                    ItemKind::Struct(ref struct_def, _) | ItemKind::Union(ref struct_def, _) => {
+                        // If this is a unit or tuple-like struct, register the constructor.
+                        if let Some(ctor_hir_id) = struct_def.ctor_id() {
+                            this.create_def(ctor_hir_id, DefPathData::Ctor, i.span);
+                        }
+                    }
+                    _ => {}
+                }
+                visit::walk_item(this, i);
+            })
+        });
+    }
+
+    fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
+        if let FnKind::Fn(_, _, sig, _, generics, body) = fn_kind {
+            if let Async::Yes { closure_id, return_impl_trait_id, .. } = sig.header.asyncness {
+                self.visit_generics(generics);
+
+                let return_impl_trait_id =
+                    self.create_def(return_impl_trait_id, DefPathData::ImplTrait, span);
+
+                // For async functions, we need to create their inner defs inside of a
+                // closure to match their desugared representation. Besides that,
+                // we must mirror everything that `visit::walk_fn` below does.
+                self.visit_fn_header(&sig.header);
+                for param in &sig.decl.inputs {
+                    self.visit_param(param);
+                }
+                self.with_parent(return_impl_trait_id, |this| {
+                    this.visit_fn_ret_ty(&sig.decl.output)
+                });
+                let closure_def = self.create_def(closure_id, DefPathData::ClosureExpr, span);
+                self.with_parent(closure_def, |this| walk_list!(this, visit_block, body));
+                return;
+            }
+        }
+
+        visit::walk_fn(self, fn_kind, span);
+    }
+
+    fn visit_use_tree(&mut self, use_tree: &'a UseTree, id: NodeId, _nested: bool) {
+        self.create_def(id, DefPathData::Use, use_tree.span);
+        match use_tree.kind {
+            UseTreeKind::Simple(_, id1, id2) => {
+                self.create_def(id1, DefPathData::Use, use_tree.prefix.span);
+                self.create_def(id2, DefPathData::Use, use_tree.prefix.span);
+            }
+            UseTreeKind::Glob => (),
+            UseTreeKind::Nested(..) => {}
+        }
+        visit::walk_use_tree(self, use_tree, id);
+    }
+
+    fn visit_foreign_item(&mut self, foreign_item: &'a ForeignItem) {
+        if let ForeignItemKind::MacCall(_) = foreign_item.kind {
+            return self.visit_macro_invoc(foreign_item.id);
+        }
+
+        let def = self.create_def(
+            foreign_item.id,
+            DefPathData::ValueNs(foreign_item.ident.name),
+            foreign_item.span,
+        );
+
+        self.with_parent(def, |this| {
+            visit::walk_foreign_item(this, foreign_item);
+        });
+    }
+
+    fn visit_variant(&mut self, v: &'a Variant) {
+        if v.is_placeholder {
+            return self.visit_macro_invoc(v.id);
+        }
+        let def = self.create_def(v.id, DefPathData::TypeNs(v.ident.name), v.span);
+        self.with_parent(def, |this| {
+            if let Some(ctor_hir_id) = v.data.ctor_id() {
+                this.create_def(ctor_hir_id, DefPathData::Ctor, v.span);
+            }
+            visit::walk_variant(this, v)
+        });
+    }
+
+    fn visit_variant_data(&mut self, data: &'a VariantData) {
+        // The assumption here is that non-`cfg` macro expansion cannot change field indices.
+        // It currently holds because only inert attributes are accepted on fields,
+        // and every such attribute expands into a single field after it's resolved.
+        for (index, field) in data.fields().iter().enumerate() {
+            self.collect_field(field, Some(index));
+        }
+    }
+
+    fn visit_generic_param(&mut self, param: &'a GenericParam) {
+        if param.is_placeholder {
+            self.visit_macro_invoc(param.id);
+            return;
+        }
+        let name = param.ident.name;
+        let def_path_data = match param.kind {
+            GenericParamKind::Lifetime { .. } => DefPathData::LifetimeNs(name),
+            GenericParamKind::Type { .. } => DefPathData::TypeNs(name),
+            GenericParamKind::Const { .. } => DefPathData::ValueNs(name),
+        };
+        self.create_def(param.id, def_path_data, param.ident.span);
+
+        // impl-Trait can happen inside generic parameters, like
+        // ```
+        // fn foo<U: Iterator<Item = impl Clone>>() {}
+        // ```
+        //
+        // In that case, the impl-trait is lowered as an additional generic parameter.
+        self.with_impl_trait(ImplTraitContext::Universal(self.parent_def), |this| {
+            visit::walk_generic_param(this, param)
+        });
+    }
+
+    fn visit_assoc_item(&mut self, i: &'a AssocItem, ctxt: visit::AssocCtxt) {
+        let def_data = match &i.kind {
+            AssocItemKind::Fn(..) | AssocItemKind::Const(..) => DefPathData::ValueNs(i.ident.name),
+            AssocItemKind::TyAlias(..) => DefPathData::TypeNs(i.ident.name),
+            AssocItemKind::MacCall(..) => return self.visit_macro_invoc(i.id),
+        };
+
+        let def = self.create_def(i.id, def_data, i.span);
+        self.with_parent(def, |this| visit::walk_assoc_item(this, i, ctxt));
+    }
+
+    fn visit_pat(&mut self, pat: &'a Pat) {
+        match pat.kind {
+            PatKind::MacCall(..) => self.visit_macro_invoc(pat.id),
+            _ => visit::walk_pat(self, pat),
+        }
+    }
+
+    fn visit_anon_const(&mut self, constant: &'a AnonConst) {
+        let def = self.create_def(constant.id, DefPathData::AnonConst, constant.value.span);
+        self.with_parent(def, |this| visit::walk_anon_const(this, constant));
+    }
+
+    fn visit_expr(&mut self, expr: &'a Expr) {
+        let parent_def = match expr.kind {
+            ExprKind::MacCall(..) => return self.visit_macro_invoc(expr.id),
+            ExprKind::Closure(_, _, asyncness, ..) => {
+                // Async closures desugar to closures inside of closures, so
+                // we must create two defs.
+                let closure_def = self.create_def(expr.id, DefPathData::ClosureExpr, expr.span);
+                match asyncness {
+                    Async::Yes { closure_id, .. } => {
+                        self.create_def(closure_id, DefPathData::ClosureExpr, expr.span)
+                    }
+                    Async::No => closure_def,
+                }
+            }
+            ExprKind::Async(_, async_id, _) => {
+                self.create_def(async_id, DefPathData::ClosureExpr, expr.span)
+            }
+            _ => self.parent_def,
+        };
+
+        self.with_parent(parent_def, |this| visit::walk_expr(this, expr));
+    }
+
+    fn visit_ty(&mut self, ty: &'a Ty) {
+        match ty.kind {
+            TyKind::MacCall(..) => self.visit_macro_invoc(ty.id),
+            TyKind::ImplTrait(node_id, _) => {
+                let parent_def = match self.impl_trait_context {
+                    ImplTraitContext::Universal(item_def) => self.resolver.create_def(
+                        item_def,
+                        node_id,
+                        DefPathData::ImplTrait,
+                        self.expansion.to_expn_id(),
+                        ty.span,
+                    ),
+                    ImplTraitContext::Existential => {
+                        self.create_def(node_id, DefPathData::ImplTrait, ty.span)
+                    }
+                };
+                self.with_parent(parent_def, |this| visit::walk_ty(this, ty))
+            }
+            _ => visit::walk_ty(self, ty),
+        }
+    }
+
+    fn visit_stmt(&mut self, stmt: &'a Stmt) {
+        match stmt.kind {
+            StmtKind::MacCall(..) => self.visit_macro_invoc(stmt.id),
+            _ => visit::walk_stmt(self, stmt),
+        }
+    }
+
+    fn visit_arm(&mut self, arm: &'a Arm) {
+        if arm.is_placeholder { self.visit_macro_invoc(arm.id) } else { visit::walk_arm(self, arm) }
+    }
+
+    fn visit_expr_field(&mut self, f: &'a ExprField) {
+        if f.is_placeholder {
+            self.visit_macro_invoc(f.id)
+        } else {
+            visit::walk_expr_field(self, f)
+        }
+    }
+
+    fn visit_pat_field(&mut self, fp: &'a PatField) {
+        if fp.is_placeholder {
+            self.visit_macro_invoc(fp.id)
+        } else {
+            visit::walk_pat_field(self, fp)
+        }
+    }
+
+    fn visit_param(&mut self, p: &'a Param) {
+        if p.is_placeholder {
+            self.visit_macro_invoc(p.id)
+        } else {
+            self.with_impl_trait(ImplTraitContext::Universal(self.parent_def), |this| {
+                visit::walk_param(this, p)
+            })
+        }
+    }
+
+    // This method is called only when we are visiting an individual field
+    // after expanding an attribute on it.
+    fn visit_field_def(&mut self, field: &'a FieldDef) {
+        self.collect_field(field, None);
+    }
+
+    fn visit_crate(&mut self, krate: &'a Crate) {
+        if krate.is_placeholder {
+            self.visit_macro_invoc(krate.id)
+        } else {
+            visit::walk_crate(self, krate)
+        }
+    }
+}
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
new file mode 100644
index 000000000..8839fb1a1
--- /dev/null
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -0,0 +1,2714 @@
+use std::ptr;
+
+use rustc_ast::ptr::P;
+use rustc_ast::visit::{self, Visitor};
+use rustc_ast::{self as ast, Crate, ItemKind, ModKind, NodeId, Path, CRATE_NODE_ID};
+use rustc_ast_pretty::pprust;
+use rustc_data_structures::fx::FxHashSet;
+use rustc_errors::struct_span_err;
+use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan};
+use rustc_feature::BUILTIN_ATTRIBUTES;
+use rustc_hir::def::Namespace::{self, *};
+use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, NonMacroAttrKind, PerNS};
+use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
+use rustc_hir::PrimTy;
+use rustc_index::vec::IndexVec;
+use rustc_middle::bug;
+use rustc_middle::ty::DefIdTree;
+use rustc_session::lint::builtin::ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE;
+use rustc_session::lint::builtin::MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS;
+use rustc_session::lint::BuiltinLintDiagnostics;
+use rustc_session::Session;
+use rustc_span::edition::Edition;
+use rustc_span::hygiene::MacroKind;
+use rustc_span::lev_distance::find_best_match_for_name;
+use rustc_span::source_map::SourceMap;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::{BytePos, Span};
+use tracing::debug;
+
+use crate::imports::{Import, ImportKind, ImportResolver};
+use crate::late::{PatternSource, Rib};
+use crate::path_names_to_string;
+use crate::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, BindingError, Finalize};
+use crate::{HasGenericParams, MacroRulesScope, Module, ModuleKind, ModuleOrUniformRoot};
+use crate::{LexicalScopeBinding, NameBinding, NameBindingKind, PrivacyError, VisResolutionError};
+use crate::{ParentScope, PathResult, ResolutionError, Resolver, Scope, ScopeSet};
+use crate::{Segment, UseError};
+
+#[cfg(test)]
+mod tests;
+
+type Res = def::Res<ast::NodeId>;
+
+/// A vector of spans and replacements, a message and applicability.
+pub(crate) type Suggestion = (Vec<(Span, String)>, String, Applicability);
+
+/// Potential candidate for an undeclared or out-of-scope label - contains the ident of a
+/// similarly named label and whether or not it is reachable.
+pub(crate) type LabelSuggestion = (Ident, bool);
+
+pub(crate) enum SuggestionTarget {
+    /// The target has a similar name as the name used by the programmer (probably a typo)
+    SimilarlyNamed,
+    /// The target is the only valid item that can be used in the corresponding context
+    SingleItem,
+}
+
+pub(crate) struct TypoSuggestion {
+    pub candidate: Symbol,
+    pub res: Res,
+    pub target: SuggestionTarget,
+}
+
+impl TypoSuggestion {
+    pub(crate) fn typo_from_res(candidate: Symbol, res: Res) -> TypoSuggestion {
+        Self { candidate, res, target: SuggestionTarget::SimilarlyNamed }
+    }
+    pub(crate) fn single_item_from_res(candidate: Symbol, res: Res) -> TypoSuggestion {
+        Self { candidate, res, target: SuggestionTarget::SingleItem }
+    }
+}
+
+/// A free importable items suggested in case of resolution failure.
+pub(crate) struct ImportSuggestion {
+    pub did: Option<DefId>,
+    pub descr: &'static str,
+    pub path: Path,
+    pub accessible: bool,
+    /// An extra note that should be issued if this item is suggested
+    pub note: Option<String>,
+}
+
+/// Adjust the impl span so that just the `impl` keyword is taken by removing
+/// everything after `<` (`"impl<T> Iterator for A<T> {}" -> "impl"`) and
+/// everything after the first whitespace (`"impl Iterator for A" -> "impl"`).
+///
+/// *Attention*: the method used is very fragile since it essentially duplicates the work of the
+/// parser. If you need to use this function or something similar, please consider updating the
+/// `source_map` functions and this function to something more robust.
+fn reduce_impl_span_to_impl_keyword(sm: &SourceMap, impl_span: Span) -> Span {
+    let impl_span = sm.span_until_char(impl_span, '<');
+    sm.span_until_whitespace(impl_span)
+}
+
+impl<'a> Resolver<'a> {
+    pub(crate) fn report_errors(&mut self, krate: &Crate) {
+        self.report_with_use_injections(krate);
+
+        for &(span_use, span_def) in &self.macro_expanded_macro_export_errors {
+            let msg = "macro-expanded `macro_export` macros from the current crate \
+                       cannot be referred to by absolute paths";
+            self.lint_buffer.buffer_lint_with_diagnostic(
+                MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
+                CRATE_NODE_ID,
+                span_use,
+                msg,
+                BuiltinLintDiagnostics::MacroExpandedMacroExportsAccessedByAbsolutePaths(span_def),
+            );
+        }
+
+        for ambiguity_error in &self.ambiguity_errors {
+            self.report_ambiguity_error(ambiguity_error);
+        }
+
+        let mut reported_spans = FxHashSet::default();
+        for error in &self.privacy_errors {
+            if reported_spans.insert(error.dedup_span) {
+                self.report_privacy_error(error);
+            }
+        }
+    }
+
+    fn report_with_use_injections(&mut self, krate: &Crate) {
+        for UseError { mut err, candidates, def_id, instead, suggestion, path } in
+            self.use_injections.drain(..)
+        {
+            let (span, found_use) = if let Some(def_id) = def_id.as_local() {
+                UsePlacementFinder::check(krate, self.def_id_to_node_id[def_id])
+            } else {
+                (None, FoundUse::No)
+            };
+            if !candidates.is_empty() {
+                show_candidates(
+                    &self.session,
+                    &self.source_span,
+                    &mut err,
+                    span,
+                    &candidates,
+                    if instead { Instead::Yes } else { Instead::No },
+                    found_use,
+                    IsPattern::No,
+                    path,
+                );
+            } else if let Some((span, msg, sugg, appl)) = suggestion {
+                err.span_suggestion(span, msg, sugg, appl);
+            }
+            err.emit();
+        }
+    }
+
+    pub(crate) fn report_conflict<'b>(
+        &mut self,
+        parent: Module<'_>,
+        ident: Ident,
+        ns: Namespace,
+        new_binding: &NameBinding<'b>,
+        old_binding: &NameBinding<'b>,
+    ) {
+        // Error on the second of two conflicting names
+        if old_binding.span.lo() > new_binding.span.lo() {
+            return self.report_conflict(parent, ident, ns, old_binding, new_binding);
+        }
+
+        let container = match parent.kind {
+            ModuleKind::Def(kind, _, _) => kind.descr(parent.def_id()),
+            ModuleKind::Block => "block",
+        };
+
+        let old_noun = match old_binding.is_import() {
+            true => "import",
+            false => "definition",
+        };
+
+        let new_participle = match new_binding.is_import() {
+            true => "imported",
+            false => "defined",
+        };
+
+        let (name, span) =
+            (ident.name, self.session.source_map().guess_head_span(new_binding.span));
+
+        if let Some(s) = self.name_already_seen.get(&name) {
+            if s == &span {
+                return;
+            }
+        }
+
+        let old_kind = match (ns, old_binding.module()) {
+            (ValueNS, _) => "value",
+            (MacroNS, _) => "macro",
+            (TypeNS, _) if old_binding.is_extern_crate() => "extern crate",
+            (TypeNS, Some(module)) if module.is_normal() => "module",
+            (TypeNS, Some(module)) if module.is_trait() => "trait",
+            (TypeNS, _) => "type",
+        };
+
+        let msg = format!("the name `{}` is defined multiple times", name);
+
+        let mut err = match (old_binding.is_extern_crate(), new_binding.is_extern_crate()) {
+            (true, true) => struct_span_err!(self.session, span, E0259, "{}", msg),
+            (true, _) | (_, true) => match new_binding.is_import() && old_binding.is_import() {
+                true => struct_span_err!(self.session, span, E0254, "{}", msg),
+                false => struct_span_err!(self.session, span, E0260, "{}", msg),
+            },
+            _ => match (old_binding.is_import(), new_binding.is_import()) {
+                (false, false) => struct_span_err!(self.session, span, E0428, "{}", msg),
+                (true, true) => struct_span_err!(self.session, span, E0252, "{}", msg),
+                _ => struct_span_err!(self.session, span, E0255, "{}", msg),
+            },
+        };
+
+        err.note(&format!(
+            "`{}` must be defined only once in the {} namespace of this {}",
+            name,
+            ns.descr(),
+            container
+        ));
+
+        err.span_label(span, format!("`{}` re{} here", name, new_participle));
+        err.span_label(
+            self.session.source_map().guess_head_span(old_binding.span),
+            format!("previous {} of the {} `{}` here", old_noun, old_kind, name),
+        );
+
+        // See https://github.com/rust-lang/rust/issues/32354
+        use NameBindingKind::Import;
+        let import = match (&new_binding.kind, &old_binding.kind) {
+            // If there are two imports where one or both have attributes then prefer removing the
+            // import without attributes.
+            (Import { import: new, .. }, Import { import: old, .. })
+                if {
+                    !new_binding.span.is_dummy()
+                        && !old_binding.span.is_dummy()
+                        && (new.has_attributes || old.has_attributes)
+                } =>
+            {
+                if old.has_attributes {
+                    Some((new, new_binding.span, true))
+                } else {
+                    Some((old, old_binding.span, true))
+                }
+            }
+            // Otherwise prioritize the new binding.
+            (Import { import, .. }, other) if !new_binding.span.is_dummy() => {
+                Some((import, new_binding.span, other.is_import()))
+            }
+            (other, Import { import, .. }) if !old_binding.span.is_dummy() => {
+                Some((import, old_binding.span, other.is_import()))
+            }
+            _ => None,
+        };
+
+        // Check if the target of the use for both bindings is the same.
+        let duplicate = new_binding.res().opt_def_id() == old_binding.res().opt_def_id();
+        let has_dummy_span = new_binding.span.is_dummy() || old_binding.span.is_dummy();
+        let from_item =
+            self.extern_prelude.get(&ident).map_or(true, |entry| entry.introduced_by_item);
+        // Only suggest removing an import if both bindings are to the same def, if both spans
+        // aren't dummy spans. Further, if both bindings are imports, then the ident must have
+        // been introduced by an item.
+        let should_remove_import = duplicate
+            && !has_dummy_span
+            && ((new_binding.is_extern_crate() || old_binding.is_extern_crate()) || from_item);
+
+        match import {
+            Some((import, span, true)) if should_remove_import && import.is_nested() => {
+                self.add_suggestion_for_duplicate_nested_use(&mut err, import, span)
+            }
+            Some((import, _, true)) if should_remove_import && !import.is_glob() => {
+                // Simple case - remove the entire import. Due to the above match arm, this can
+                // only be a single use so just remove it entirely.
+                err.tool_only_span_suggestion(
+                    import.use_span_with_attributes,
+                    "remove unnecessary import",
+                    "",
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            Some((import, span, _)) => {
+                self.add_suggestion_for_rename_of_use(&mut err, name, import, span)
+            }
+            _ => {}
+        }
+
+        err.emit();
+        self.name_already_seen.insert(name, span);
+    }
+
+    /// This function adds a suggestion to change the binding name of a new import that conflicts
+    /// with an existing import.
+    ///
+    /// ```text,ignore (diagnostic)
+    /// help: you can use `as` to change the binding name of the import
+    ///    |
+    /// LL | use foo::bar as other_bar;
+    ///    |     ^^^^^^^^^^^^^^^^^^^^^
+    /// ```
+    fn add_suggestion_for_rename_of_use(
+        &self,
+        err: &mut Diagnostic,
+        name: Symbol,
+        import: &Import<'_>,
+        binding_span: Span,
+    ) {
+        let suggested_name = if name.as_str().chars().next().unwrap().is_uppercase() {
+            format!("Other{}", name)
+        } else {
+            format!("other_{}", name)
+        };
+
+        let mut suggestion = None;
+        match import.kind {
+            ImportKind::Single { type_ns_only: true, .. } => {
+                suggestion = Some(format!("self as {}", suggested_name))
+            }
+            ImportKind::Single { source, .. } => {
+                if let Some(pos) =
+                    source.span.hi().0.checked_sub(binding_span.lo().0).map(|pos| pos as usize)
+                {
+                    if let Ok(snippet) = self.session.source_map().span_to_snippet(binding_span) {
+                        if pos <= snippet.len() {
+                            suggestion = Some(format!(
+                                "{} as {}{}",
+                                &snippet[..pos],
+                                suggested_name,
+                                if snippet.ends_with(';') { ";" } else { "" }
+                            ))
+                        }
+                    }
+                }
+            }
+            ImportKind::ExternCrate { source, target } => {
+                suggestion = Some(format!(
+                    "extern crate {} as {};",
+                    source.unwrap_or(target.name),
+                    suggested_name,
+                ))
+            }
+            _ => unreachable!(),
+        }
+
+        let rename_msg = "you can use `as` to change the binding name of the import";
+        if let Some(suggestion) = suggestion {
+            err.span_suggestion(
+                binding_span,
+                rename_msg,
+                suggestion,
+                Applicability::MaybeIncorrect,
+            );
+        } else {
+            err.span_label(binding_span, rename_msg);
+        }
+    }
+
+    /// This function adds a suggestion to remove an unnecessary binding from an import that is
+    /// nested. In the following example, this function will be invoked to remove the `a` binding
+    /// in the second use statement:
+    ///
+    /// ```ignore (diagnostic)
+    /// use issue_52891::a;
+    /// use issue_52891::{d, a, e};
+    /// ```
+    ///
+    /// The following suggestion will be added:
+    ///
+    /// ```ignore (diagnostic)
+    /// use issue_52891::{d, a, e};
+    ///                      ^-- help: remove unnecessary import
+    /// ```
+    ///
+    /// If the nested use contains only one import then the suggestion will remove the entire
+    /// line.
+    ///
+    /// It is expected that the provided import is nested - this isn't checked by the
+    /// function. If this invariant is not upheld, this function's behaviour will be unexpected
+    /// as characters expected by span manipulations won't be present.
+    fn add_suggestion_for_duplicate_nested_use(
+        &self,
+        err: &mut Diagnostic,
+        import: &Import<'_>,
+        binding_span: Span,
+    ) {
+        assert!(import.is_nested());
+        let message = "remove unnecessary import";
+
+        // Two examples will be used to illustrate the span manipulations we're doing:
+        //
+        // - Given `use issue_52891::{d, a, e};` where `a` is a duplicate then `binding_span` is
+        //   `a` and `import.use_span` is `issue_52891::{d, a, e};`.
+        // - Given `use issue_52891::{d, e, a};` where `a` is a duplicate then `binding_span` is
+        //   `a` and `import.use_span` is `issue_52891::{d, e, a};`.
+
+        let (found_closing_brace, span) =
+            find_span_of_binding_until_next_binding(self.session, binding_span, import.use_span);
+
+        // If there was a closing brace then identify the span to remove any trailing commas from
+        // previous imports.
+        if found_closing_brace {
+            if let Some(span) = extend_span_to_previous_binding(self.session, span) {
+                err.tool_only_span_suggestion(span, message, "", Applicability::MaybeIncorrect);
+            } else {
+                // Remove the entire line if we cannot extend the span back, this indicates an
+                // `issue_52891::{self}` case.
+                err.span_suggestion(
+                    import.use_span_with_attributes,
+                    message,
+                    "",
+                    Applicability::MaybeIncorrect,
+                );
+            }
+
+            return;
+        }
+
+        err.span_suggestion(span, message, "", Applicability::MachineApplicable);
+    }
+
+    pub(crate) fn lint_if_path_starts_with_module(
+        &mut self,
+        finalize: Option<Finalize>,
+        path: &[Segment],
+        second_binding: Option<&NameBinding<'_>>,
+    ) {
+        let Some(Finalize { node_id, root_span, .. }) = finalize else {
+            return;
+        };
+
+        let first_name = match path.get(0) {
+            // In the 2018 edition this lint is a hard error, so nothing to do
+            Some(seg) if seg.ident.span.rust_2015() && self.session.rust_2015() => seg.ident.name,
+            _ => return,
+        };
+
+        // We're only interested in `use` paths which should start with
+        // `{{root}}` currently.
+        if first_name != kw::PathRoot {
+            return;
+        }
+
+        match path.get(1) {
+            // If this import looks like `crate::...` it's already good
+            Some(Segment { ident, .. }) if ident.name == kw::Crate => return,
+            // Otherwise go below to see if it's an extern crate
+            Some(_) => {}
+            // If the path has length one (and it's `PathRoot` most likely)
+            // then we don't know whether we're gonna be importing a crate or an
+            // item in our crate. Defer this lint to elsewhere
+            None => return,
+        }
+
+        // If the first element of our path was actually resolved to an
+        // `ExternCrate` (also used for `crate::...`) then no need to issue a
+        // warning, this looks all good!
+        if let Some(binding) = second_binding {
+            if let NameBindingKind::Import { import, .. } = binding.kind {
+                // Careful: we still want to rewrite paths from renamed extern crates.
+                if let ImportKind::ExternCrate { source: None, .. } = import.kind {
+                    return;
+                }
+            }
+        }
+
+        let diag = BuiltinLintDiagnostics::AbsPathWithModule(root_span);
+        self.lint_buffer.buffer_lint_with_diagnostic(
+            ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
+            node_id,
+            root_span,
+            "absolute paths must start with `self`, `super`, \
+             `crate`, or an external crate name in the 2018 edition",
+            diag,
+        );
+    }
+
+    pub(crate) fn add_module_candidates(
+        &mut self,
+        module: Module<'a>,
+        names: &mut Vec<TypoSuggestion>,
+        filter_fn: &impl Fn(Res) -> bool,
+    ) {
+        for (key, resolution) in self.resolutions(module).borrow().iter() {
+            if let Some(binding) = resolution.borrow().binding {
+                let res = binding.res();
+                if filter_fn(res) {
+                    names.push(TypoSuggestion::typo_from_res(key.ident.name, res));
+                }
+            }
+        }
+    }
+
+    /// Combines an error with provided span and emits it.
+    ///
+    /// This takes the error provided, combines it with the span and any additional spans inside the
+    /// error and emits it.
+    pub(crate) fn report_error(&mut self, span: Span, resolution_error: ResolutionError<'a>) {
+        self.into_struct_error(span, resolution_error).emit();
+    }
+
+    pub(crate) fn into_struct_error(
+        &mut self,
+        span: Span,
+        resolution_error: ResolutionError<'a>,
+    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+        match resolution_error {
+            ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0401,
+                    "can't use generic parameters from outer function",
+                );
+                err.span_label(span, "use of generic parameter from outer function");
+
+                let sm = self.session.source_map();
+                match outer_res {
+                    Res::SelfTy { trait_: maybe_trait_defid, alias_to: maybe_impl_defid } => {
+                        if let Some(impl_span) =
+                            maybe_impl_defid.and_then(|(def_id, _)| self.opt_span(def_id))
+                        {
+                            err.span_label(
+                                reduce_impl_span_to_impl_keyword(sm, impl_span),
+                                "`Self` type implicitly declared here, by this `impl`",
+                            );
+                        }
+                        match (maybe_trait_defid, maybe_impl_defid) {
+                            (Some(_), None) => {
+                                err.span_label(span, "can't use `Self` here");
+                            }
+                            (_, Some(_)) => {
+                                err.span_label(span, "use a type here instead");
+                            }
+                            (None, None) => bug!("`impl` without trait nor type?"),
+                        }
+                        return err;
+                    }
+                    Res::Def(DefKind::TyParam, def_id) => {
+                        if let Some(span) = self.opt_span(def_id) {
+                            err.span_label(span, "type parameter from outer function");
+                        }
+                    }
+                    Res::Def(DefKind::ConstParam, def_id) => {
+                        if let Some(span) = self.opt_span(def_id) {
+                            err.span_label(span, "const parameter from outer function");
+                        }
+                    }
+                    _ => {
+                        bug!(
+                            "GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
+                            DefKind::TyParam or DefKind::ConstParam"
+                        );
+                    }
+                }
+
+                if has_generic_params == HasGenericParams::Yes {
+                    // Try to retrieve the span of the function signature and generate a new
+                    // message with a local type or const parameter.
+                    let sugg_msg = "try using a local generic parameter instead";
+                    if let Some((sugg_span, snippet)) = sm.generate_local_type_param_snippet(span) {
+                        // Suggest the modification to the user
+                        err.span_suggestion(
+                            sugg_span,
+                            sugg_msg,
+                            snippet,
+                            Applicability::MachineApplicable,
+                        );
+                    } else if let Some(sp) = sm.generate_fn_name_span(span) {
+                        err.span_label(
+                            sp,
+                            "try adding a local generic parameter in this method instead",
+                        );
+                    } else {
+                        err.help("try using a local generic parameter instead");
+                    }
+                }
+
+                err
+            }
+            ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0403,
+                    "the name `{}` is already used for a generic \
+                     parameter in this item's generic parameters",
+                    name,
+                );
+                err.span_label(span, "already used");
+                err.span_label(first_use_span, format!("first use of `{}`", name));
+                err
+            }
+            ResolutionError::MethodNotMemberOfTrait(method, trait_, candidate) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0407,
+                    "method `{}` is not a member of trait `{}`",
+                    method,
+                    trait_
+                );
+                err.span_label(span, format!("not a member of trait `{}`", trait_));
+                if let Some(candidate) = candidate {
+                    err.span_suggestion(
+                        method.span,
+                        "there is an associated function with a similar name",
+                        candidate.to_ident_string(),
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+                err
+            }
+            ResolutionError::TypeNotMemberOfTrait(type_, trait_, candidate) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0437,
+                    "type `{}` is not a member of trait `{}`",
+                    type_,
+                    trait_
+                );
+                err.span_label(span, format!("not a member of trait `{}`", trait_));
+                if let Some(candidate) = candidate {
+                    err.span_suggestion(
+                        type_.span,
+                        "there is an associated type with a similar name",
+                        candidate.to_ident_string(),
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+                err
+            }
+            ResolutionError::ConstNotMemberOfTrait(const_, trait_, candidate) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0438,
+                    "const `{}` is not a member of trait `{}`",
+                    const_,
+                    trait_
+                );
+                err.span_label(span, format!("not a member of trait `{}`", trait_));
+                if let Some(candidate) = candidate {
+                    err.span_suggestion(
+                        const_.span,
+                        "there is an associated constant with a similar name",
+                        candidate.to_ident_string(),
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+                err
+            }
+            ResolutionError::VariableNotBoundInPattern(binding_error, parent_scope) => {
+                let BindingError { name, target, origin, could_be_path } = binding_error;
+
+                let target_sp = target.iter().copied().collect::<Vec<_>>();
+                let origin_sp = origin.iter().copied().collect::<Vec<_>>();
+
+                let msp = MultiSpan::from_spans(target_sp.clone());
+                let mut err = struct_span_err!(
+                    self.session,
+                    msp,
+                    E0408,
+                    "variable `{}` is not bound in all patterns",
+                    name,
+                );
+                for sp in target_sp {
+                    err.span_label(sp, format!("pattern doesn't bind `{}`", name));
+                }
+                for sp in origin_sp {
+                    err.span_label(sp, "variable not in all patterns");
+                }
+                if could_be_path {
+                    let import_suggestions = self.lookup_import_candidates(
+                        Ident::with_dummy_span(name),
+                        Namespace::ValueNS,
+                        &parent_scope,
+                        &|res: Res| match res {
+                            Res::Def(
+                                DefKind::Ctor(CtorOf::Variant, CtorKind::Const)
+                                | DefKind::Ctor(CtorOf::Struct, CtorKind::Const)
+                                | DefKind::Const
+                                | DefKind::AssocConst,
+                                _,
+                            ) => true,
+                            _ => false,
+                        },
+                    );
+
+                    if import_suggestions.is_empty() {
+                        let help_msg = format!(
+                            "if you meant to match on a variant or a `const` item, consider \
+                             making the path in the pattern qualified: `path::to::ModOrType::{}`",
+                            name,
+                        );
+                        err.span_help(span, &help_msg);
+                    }
+                    show_candidates(
+                        &self.session,
+                        &self.source_span,
+                        &mut err,
+                        Some(span),
+                        &import_suggestions,
+                        Instead::No,
+                        FoundUse::Yes,
+                        IsPattern::Yes,
+                        vec![],
+                    );
+                }
+                err
+            }
+            ResolutionError::VariableBoundWithDifferentMode(variable_name, first_binding_span) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0409,
+                    "variable `{}` is bound inconsistently across alternatives separated by `|`",
+                    variable_name
+                );
+                err.span_label(span, "bound in different ways");
+                err.span_label(first_binding_span, "first binding");
+                err
+            }
+            ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0415,
+                    "identifier `{}` is bound more than once in this parameter list",
+                    identifier
+                );
+                err.span_label(span, "used as parameter more than once");
+                err
+            }
+            ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0416,
+                    "identifier `{}` is bound more than once in the same pattern",
+                    identifier
+                );
+                err.span_label(span, "used in a pattern more than once");
+                err
+            }
+            ResolutionError::UndeclaredLabel { name, suggestion } => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0426,
+                    "use of undeclared label `{}`",
+                    name
+                );
+
+                err.span_label(span, format!("undeclared label `{}`", name));
+
+                match suggestion {
+                    // A reachable label with a similar name exists.
+                    Some((ident, true)) => {
+                        err.span_label(ident.span, "a label with a similar name is reachable");
+                        err.span_suggestion(
+                            span,
+                            "try using similarly named label",
+                            ident.name,
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                    // An unreachable label with a similar name exists.
+                    Some((ident, false)) => {
+                        err.span_label(
+                            ident.span,
+                            "a label with a similar name exists but is unreachable",
+                        );
+                    }
+                    // No similarly-named labels exist.
+                    None => (),
+                }
+
+                err
+            }
+            ResolutionError::SelfImportsOnlyAllowedWithin { root, span_with_rename } => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0429,
+                    "{}",
+                    "`self` imports are only allowed within a { } list"
+                );
+
+                // None of the suggestions below would help with a case like `use self`.
+                if !root {
+                    // use foo::bar::self        -> foo::bar
+                    // use foo::bar::self as abc -> foo::bar as abc
+                    err.span_suggestion(
+                        span,
+                        "consider importing the module directly",
+                        "",
+                        Applicability::MachineApplicable,
+                    );
+
+                    // use foo::bar::self        -> foo::bar::{self}
+                    // use foo::bar::self as abc -> foo::bar::{self as abc}
+                    let braces = vec![
+                        (span_with_rename.shrink_to_lo(), "{".to_string()),
+                        (span_with_rename.shrink_to_hi(), "}".to_string()),
+                    ];
+                    err.multipart_suggestion(
+                        "alternatively, use the multi-path `use` syntax to import `self`",
+                        braces,
+                        Applicability::MachineApplicable,
+                    );
+                }
+                err
+            }
+            ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0430,
+                    "`self` import can only appear once in an import list"
+                );
+                err.span_label(span, "can only appear once in an import list");
+                err
+            }
+            ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0431,
+                    "`self` import can only appear in an import list with \
+                                                a non-empty prefix"
+                );
+                err.span_label(span, "can only appear in an import list with a non-empty prefix");
+                err
+            }
+            ResolutionError::FailedToResolve { label, suggestion } => {
+                let mut err =
+                    struct_span_err!(self.session, span, E0433, "failed to resolve: {}", &label);
+                err.span_label(span, label);
+
+                if let Some((suggestions, msg, applicability)) = suggestion {
+                    if suggestions.is_empty() {
+                        err.help(&msg);
+                        return err;
+                    }
+                    err.multipart_suggestion(&msg, suggestions, applicability);
+                }
+
+                err
+            }
+            ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0434,
+                    "{}",
+                    "can't capture dynamic environment in a fn item"
+                );
+                err.help("use the `|| { ... }` closure form instead");
+                err
+            }
+            ResolutionError::AttemptToUseNonConstantValueInConstant(ident, sugg, current) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0435,
+                    "attempt to use a non-constant value in a constant"
+                );
+                // let foo =...
+                //     ^^^ given this Span
+                // ------- get this Span to have an applicable suggestion
+
+                // edit:
+                // only do this if the const and usage of the non-constant value are on the same line
+                // the further the two are apart, the higher the chance of the suggestion being wrong
+
+                let sp = self
+                    .session
+                    .source_map()
+                    .span_extend_to_prev_str(ident.span, current, true, false);
+
+                match sp {
+                    Some(sp) if !self.session.source_map().is_multiline(sp) => {
+                        let sp = sp.with_lo(BytePos(sp.lo().0 - (current.len() as u32)));
+                        err.span_suggestion(
+                            sp,
+                            &format!("consider using `{}` instead of `{}`", sugg, current),
+                            format!("{} {}", sugg, ident),
+                            Applicability::MaybeIncorrect,
+                        );
+                        err.span_label(span, "non-constant value");
+                    }
+                    _ => {
+                        err.span_label(ident.span, &format!("this would need to be a `{}`", sugg));
+                    }
+                }
+
+                err
+            }
+            ResolutionError::BindingShadowsSomethingUnacceptable {
+                shadowing_binding,
+                name,
+                participle,
+                article,
+                shadowed_binding,
+                shadowed_binding_span,
+            } => {
+                let shadowed_binding_descr = shadowed_binding.descr();
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0530,
+                    "{}s cannot shadow {}s",
+                    shadowing_binding.descr(),
+                    shadowed_binding_descr,
+                );
+                err.span_label(
+                    span,
+                    format!("cannot be named the same as {} {}", article, shadowed_binding_descr),
+                );
+                match (shadowing_binding, shadowed_binding) {
+                    (
+                        PatternSource::Match,
+                        Res::Def(DefKind::Ctor(CtorOf::Variant | CtorOf::Struct, CtorKind::Fn), _),
+                    ) => {
+                        err.span_suggestion(
+                            span,
+                            "try specify the pattern arguments",
+                            format!("{}(..)", name),
+                            Applicability::Unspecified,
+                        );
+                    }
+                    _ => (),
+                }
+                let msg =
+                    format!("the {} `{}` is {} here", shadowed_binding_descr, name, participle);
+                err.span_label(shadowed_binding_span, msg);
+                err
+            }
+            ResolutionError::ForwardDeclaredGenericParam => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0128,
+                    "generic parameters with a default cannot use \
+                                                forward declared identifiers"
+                );
+                err.span_label(span, "defaulted generic parameters cannot be forward declared");
+                err
+            }
+            ResolutionError::ParamInTyOfConstParam(name) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0770,
+                    "the type of const parameters must not depend on other generic parameters"
+                );
+                err.span_label(
+                    span,
+                    format!("the type must not depend on the parameter `{}`", name),
+                );
+                err
+            }
+            ResolutionError::ParamInNonTrivialAnonConst { name, is_type } => {
+                let mut err = self.session.struct_span_err(
+                    span,
+                    "generic parameters may not be used in const operations",
+                );
+                err.span_label(span, &format!("cannot perform const operation using `{}`", name));
+
+                if is_type {
+                    err.note("type parameters may not be used in const expressions");
+                } else {
+                    err.help(&format!(
+                        "const parameters may only be used as standalone arguments, i.e. `{}`",
+                        name
+                    ));
+                }
+
+                if self.session.is_nightly_build() {
+                    err.help(
+                        "use `#![feature(generic_const_exprs)]` to allow generic const expressions",
+                    );
+                }
+
+                err
+            }
+            ResolutionError::SelfInGenericParamDefault => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0735,
+                    "generic parameters cannot use `Self` in their defaults"
+                );
+                err.span_label(span, "`Self` in generic parameter default");
+                err
+            }
+            ResolutionError::UnreachableLabel { name, definition_span, suggestion } => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0767,
+                    "use of unreachable label `{}`",
+                    name,
+                );
+
+                err.span_label(definition_span, "unreachable label defined here");
+                err.span_label(span, format!("unreachable label `{}`", name));
+                err.note(
+                    "labels are unreachable through functions, closures, async blocks and modules",
+                );
+
+                match suggestion {
+                    // A reachable label with a similar name exists.
+                    Some((ident, true)) => {
+                        err.span_label(ident.span, "a label with a similar name is reachable");
+                        err.span_suggestion(
+                            span,
+                            "try using similarly named label",
+                            ident.name,
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                    // An unreachable label with a similar name exists.
+                    Some((ident, false)) => {
+                        err.span_label(
+                            ident.span,
+                            "a label with a similar name exists but is also unreachable",
+                        );
+                    }
+                    // No similarly-named labels exist.
+                    None => (),
+                }
+
+                err
+            }
+            ResolutionError::TraitImplMismatch {
+                name,
+                kind,
+                code,
+                trait_item_span,
+                trait_path,
+            } => {
+                let mut err = self.session.struct_span_err_with_code(
+                    span,
+                    &format!(
+                        "item `{}` is an associated {}, which doesn't match its trait `{}`",
+                        name, kind, trait_path,
+                    ),
+                    code,
+                );
+                err.span_label(span, "does not match trait");
+                err.span_label(trait_item_span, "item in trait");
+                err
+            }
+            ResolutionError::InvalidAsmSym => {
+                let mut err = self.session.struct_span_err(span, "invalid `sym` operand");
+                err.span_label(span, "is a local variable");
+                err.help("`sym` operands must refer to either a function or a static");
+                err
+            }
+        }
+    }
+
+    pub(crate) fn report_vis_error(
+        &mut self,
+        vis_resolution_error: VisResolutionError<'_>,
+    ) -> ErrorGuaranteed {
+        match vis_resolution_error {
+            VisResolutionError::Relative2018(span, path) => {
+                let mut err = self.session.struct_span_err(
+                    span,
+                    "relative paths are not supported in visibilities in 2018 edition or later",
+                );
+                err.span_suggestion(
+                    path.span,
+                    "try",
+                    format!("crate::{}", pprust::path_to_string(&path)),
+                    Applicability::MaybeIncorrect,
+                );
+                err
+            }
+            VisResolutionError::AncestorOnly(span) => struct_span_err!(
+                self.session,
+                span,
+                E0742,
+                "visibilities can only be restricted to ancestor modules"
+            ),
+            VisResolutionError::FailedToResolve(span, label, suggestion) => {
+                self.into_struct_error(span, ResolutionError::FailedToResolve { label, suggestion })
+            }
+            VisResolutionError::ExpectedFound(span, path_str, res) => {
+                let mut err = struct_span_err!(
+                    self.session,
+                    span,
+                    E0577,
+                    "expected module, found {} `{}`",
+                    res.descr(),
+                    path_str
+                );
+                err.span_label(span, "not a module");
+                err
+            }
+            VisResolutionError::Indeterminate(span) => struct_span_err!(
+                self.session,
+                span,
+                E0578,
+                "cannot determine resolution for the visibility"
+            ),
+            VisResolutionError::ModuleOnly(span) => {
+                self.session.struct_span_err(span, "visibility must resolve to a module")
+            }
+        }
+        .emit()
+    }
+
+    /// Lookup typo candidate in scope for a macro or import.
+    fn early_lookup_typo_candidate(
+        &mut self,
+        scope_set: ScopeSet<'a>,
+        parent_scope: &ParentScope<'a>,
+        ident: Ident,
+        filter_fn: &impl Fn(Res) -> bool,
+    ) -> Option<TypoSuggestion> {
+        let mut suggestions = Vec::new();
+        let ctxt = ident.span.ctxt();
+        self.visit_scopes(scope_set, parent_scope, ctxt, |this, scope, use_prelude, _| {
+            match scope {
+                Scope::DeriveHelpers(expn_id) => {
+                    let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
+                    if filter_fn(res) {
+                        suggestions.extend(
+                            this.helper_attrs
+                                .get(&expn_id)
+                                .into_iter()
+                                .flatten()
+                                .map(|ident| TypoSuggestion::typo_from_res(ident.name, res)),
+                        );
+                    }
+                }
+                Scope::DeriveHelpersCompat => {
+                    let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat);
+                    if filter_fn(res) {
+                        for derive in parent_scope.derives {
+                            let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
+                            if let Ok((Some(ext), _)) = this.resolve_macro_path(
+                                derive,
+                                Some(MacroKind::Derive),
+                                parent_scope,
+                                false,
+                                false,
+                            ) {
+                                suggestions.extend(
+                                    ext.helper_attrs
+                                        .iter()
+                                        .map(|name| TypoSuggestion::typo_from_res(*name, res)),
+                                );
+                            }
+                        }
+                    }
+                }
+                Scope::MacroRules(macro_rules_scope) => {
+                    if let MacroRulesScope::Binding(macro_rules_binding) = macro_rules_scope.get() {
+                        let res = macro_rules_binding.binding.res();
+                        if filter_fn(res) {
+                            suggestions.push(TypoSuggestion::typo_from_res(
+                                macro_rules_binding.ident.name,
+                                res,
+                            ))
+                        }
+                    }
+                }
+                Scope::CrateRoot => {
+                    let root_ident = Ident::new(kw::PathRoot, ident.span);
+                    let root_module = this.resolve_crate_root(root_ident);
+                    this.add_module_candidates(root_module, &mut suggestions, filter_fn);
+                }
+                Scope::Module(module, _) => {
+                    this.add_module_candidates(module, &mut suggestions, filter_fn);
+                }
+                Scope::RegisteredAttrs => {
+                    let res = Res::NonMacroAttr(NonMacroAttrKind::Registered);
+                    if filter_fn(res) {
+                        suggestions.extend(
+                            this.registered_attrs
+                                .iter()
+                                .map(|ident| TypoSuggestion::typo_from_res(ident.name, res)),
+                        );
+                    }
+                }
+                Scope::MacroUsePrelude => {
+                    suggestions.extend(this.macro_use_prelude.iter().filter_map(
+                        |(name, binding)| {
+                            let res = binding.res();
+                            filter_fn(res).then_some(TypoSuggestion::typo_from_res(*name, res))
+                        },
+                    ));
+                }
+                Scope::BuiltinAttrs => {
+                    let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin(kw::Empty));
+                    if filter_fn(res) {
+                        suggestions.extend(
+                            BUILTIN_ATTRIBUTES
+                                .iter()
+                                .map(|attr| TypoSuggestion::typo_from_res(attr.name, res)),
+                        );
+                    }
+                }
+                Scope::ExternPrelude => {
+                    suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
+                        let res = Res::Def(DefKind::Mod, CRATE_DEF_ID.to_def_id());
+                        filter_fn(res).then_some(TypoSuggestion::typo_from_res(ident.name, res))
+                    }));
+                }
+                Scope::ToolPrelude => {
+                    let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
+                    suggestions.extend(
+                        this.registered_tools
+                            .iter()
+                            .map(|ident| TypoSuggestion::typo_from_res(ident.name, res)),
+                    );
+                }
+                Scope::StdLibPrelude => {
+                    if let Some(prelude) = this.prelude {
+                        let mut tmp_suggestions = Vec::new();
+                        this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn);
+                        suggestions.extend(
+                            tmp_suggestions
+                                .into_iter()
+                                .filter(|s| use_prelude || this.is_builtin_macro(s.res)),
+                        );
+                    }
+                }
+                Scope::BuiltinTypes => {
+                    suggestions.extend(PrimTy::ALL.iter().filter_map(|prim_ty| {
+                        let res = Res::PrimTy(*prim_ty);
+                        filter_fn(res).then_some(TypoSuggestion::typo_from_res(prim_ty.name(), res))
+                    }))
+                }
+            }
+
+            None::<()>
+        });
+
+        // Make sure error reporting is deterministic.
+        suggestions.sort_by(|a, b| a.candidate.as_str().partial_cmp(b.candidate.as_str()).unwrap());
+
+        match find_best_match_for_name(
+            &suggestions.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
+            ident.name,
+            None,
+        ) {
+            Some(found) if found != ident.name => {
+                suggestions.into_iter().find(|suggestion| suggestion.candidate == found)
+            }
+            _ => None,
+        }
+    }
+
+    fn lookup_import_candidates_from_module<FilterFn>(
+        &mut self,
+        lookup_ident: Ident,
+        namespace: Namespace,
+        parent_scope: &ParentScope<'a>,
+        start_module: Module<'a>,
+        crate_name: Ident,
+        filter_fn: FilterFn,
+    ) -> Vec<ImportSuggestion>
+    where
+        FilterFn: Fn(Res) -> bool,
+    {
+        let mut candidates = Vec::new();
+        let mut seen_modules = FxHashSet::default();
+        let mut worklist = vec![(start_module, Vec::<ast::PathSegment>::new(), true)];
+        let mut worklist_via_import = vec![];
+
+        while let Some((in_module, path_segments, accessible)) = match worklist.pop() {
+            None => worklist_via_import.pop(),
+            Some(x) => Some(x),
+        } {
+            let in_module_is_extern = !in_module.def_id().is_local();
+            // We have to visit module children in deterministic order to avoid
+            // instabilities in reported imports (#43552).
+            in_module.for_each_child(self, |this, ident, ns, name_binding| {
+                // avoid non-importable candidates
+                if !name_binding.is_importable() {
+                    return;
+                }
+
+                let child_accessible =
+                    accessible && this.is_accessible_from(name_binding.vis, parent_scope.module);
+
+                // do not venture inside inaccessible items of other crates
+                if in_module_is_extern && !child_accessible {
+                    return;
+                }
+
+                let via_import = name_binding.is_import() && !name_binding.is_extern_crate();
+
+                // There is an assumption elsewhere that paths of variants are in the enum's
+                // declaration and not imported. With this assumption, the variant component is
+                // chopped and the rest of the path is assumed to be the enum's own path. For
+                // errors where a variant is used as the type instead of the enum, this causes
+                // funny looking invalid suggestions, i.e `foo` instead of `foo::MyEnum`.
+                if via_import && name_binding.is_possibly_imported_variant() {
+                    return;
+                }
+
+                // #90113: Do not count an inaccessible reexported item as a candidate.
+                if let NameBindingKind::Import { binding, .. } = name_binding.kind {
+                    if this.is_accessible_from(binding.vis, parent_scope.module)
+                        && !this.is_accessible_from(name_binding.vis, parent_scope.module)
+                    {
+                        return;
+                    }
+                }
+
+                // collect results based on the filter function
+                // avoid suggesting anything from the same module in which we are resolving
+                // avoid suggesting anything with a hygienic name
+                if ident.name == lookup_ident.name
+                    && ns == namespace
+                    && !ptr::eq(in_module, parent_scope.module)
+                    && !ident.span.normalize_to_macros_2_0().from_expansion()
+                {
+                    let res = name_binding.res();
+                    if filter_fn(res) {
+                        // create the path
+                        let mut segms = path_segments.clone();
+                        if lookup_ident.span.rust_2018() {
+                            // crate-local absolute paths start with `crate::` in edition 2018
+                            // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
+                            segms.insert(0, ast::PathSegment::from_ident(crate_name));
+                        }
+
+                        segms.push(ast::PathSegment::from_ident(ident));
+                        let path = Path { span: name_binding.span, segments: segms, tokens: None };
+                        let did = match res {
+                            Res::Def(DefKind::Ctor(..), did) => this.opt_parent(did),
+                            _ => res.opt_def_id(),
+                        };
+
+                        if child_accessible {
+                            // Remove invisible match if exists
+                            if let Some(idx) = candidates
+                                .iter()
+                                .position(|v: &ImportSuggestion| v.did == did && !v.accessible)
+                            {
+                                candidates.remove(idx);
+                            }
+                        }
+
+                        if candidates.iter().all(|v: &ImportSuggestion| v.did != did) {
+                            // See if we're recommending TryFrom, TryInto, or FromIterator and add
+                            // a note about editions
+                            let note = if let Some(did) = did {
+                                let requires_note = !did.is_local()
+                                    && this.cstore().item_attrs_untracked(did, this.session).any(
+                                        |attr| {
+                                            if attr.has_name(sym::rustc_diagnostic_item) {
+                                                [sym::TryInto, sym::TryFrom, sym::FromIterator]
+                                                    .map(|x| Some(x))
+                                                    .contains(&attr.value_str())
+                                            } else {
+                                                false
+                                            }
+                                        },
+                                    );
+
+                                requires_note.then(|| {
+                                    format!(
+                                        "'{}' is included in the prelude starting in Edition 2021",
+                                        path_names_to_string(&path)
+                                    )
+                                })
+                            } else {
+                                None
+                            };
+
+                            candidates.push(ImportSuggestion {
+                                did,
+                                descr: res.descr(),
+                                path,
+                                accessible: child_accessible,
+                                note,
+                            });
+                        }
+                    }
+                }
+
+                // collect submodules to explore
+                if let Some(module) = name_binding.module() {
+                    // form the path
+                    let mut path_segments = path_segments.clone();
+                    path_segments.push(ast::PathSegment::from_ident(ident));
+
+                    let is_extern_crate_that_also_appears_in_prelude =
+                        name_binding.is_extern_crate() && lookup_ident.span.rust_2018();
+
+                    if !is_extern_crate_that_also_appears_in_prelude {
+                        // add the module to the lookup
+                        if seen_modules.insert(module.def_id()) {
+                            if via_import { &mut worklist_via_import } else { &mut worklist }
+                                .push((module, path_segments, child_accessible));
+                        }
+                    }
+                }
+            })
+        }
+
+        // If only some candidates are accessible, take just them
+        if !candidates.iter().all(|v: &ImportSuggestion| !v.accessible) {
+            candidates = candidates.into_iter().filter(|x| x.accessible).collect();
+        }
+
+        candidates
+    }
+
+    /// When name resolution fails, this method can be used to look up candidate
+    /// entities with the expected name. It allows filtering them using the
+    /// supplied predicate (which should be used to only accept the types of
+    /// definitions expected, e.g., traits). The lookup spans across all crates.
+    ///
+    /// N.B., the method does not look into imports, but this is not a problem,
+    /// since we report the definitions (thus, the de-aliased imports).
+    pub(crate) fn lookup_import_candidates<FilterFn>(
+        &mut self,
+        lookup_ident: Ident,
+        namespace: Namespace,
+        parent_scope: &ParentScope<'a>,
+        filter_fn: FilterFn,
+    ) -> Vec<ImportSuggestion>
+    where
+        FilterFn: Fn(Res) -> bool,
+    {
+        let mut suggestions = self.lookup_import_candidates_from_module(
+            lookup_ident,
+            namespace,
+            parent_scope,
+            self.graph_root,
+            Ident::with_dummy_span(kw::Crate),
+            &filter_fn,
+        );
+
+        if lookup_ident.span.rust_2018() {
+            let extern_prelude_names = self.extern_prelude.clone();
+            for (ident, _) in extern_prelude_names.into_iter() {
+                if ident.span.from_expansion() {
+                    // Idents are adjusted to the root context before being
+                    // resolved in the extern prelude, so reporting this to the
+                    // user is no help. This skips the injected
+                    // `extern crate std` in the 2018 edition, which would
+                    // otherwise cause duplicate suggestions.
+                    continue;
+                }
+                if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(ident.name) {
+                    let crate_root = self.expect_module(crate_id.as_def_id());
+                    suggestions.extend(self.lookup_import_candidates_from_module(
+                        lookup_ident,
+                        namespace,
+                        parent_scope,
+                        crate_root,
+                        ident,
+                        &filter_fn,
+                    ));
+                }
+            }
+        }
+
+        suggestions
+    }
+
+    pub(crate) fn unresolved_macro_suggestions(
+        &mut self,
+        err: &mut Diagnostic,
+        macro_kind: MacroKind,
+        parent_scope: &ParentScope<'a>,
+        ident: Ident,
+    ) {
+        let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
+        let suggestion = self.early_lookup_typo_candidate(
+            ScopeSet::Macro(macro_kind),
+            parent_scope,
+            ident,
+            is_expected,
+        );
+        self.add_typo_suggestion(err, suggestion, ident.span);
+
+        let import_suggestions =
+            self.lookup_import_candidates(ident, Namespace::MacroNS, parent_scope, is_expected);
+        show_candidates(
+            &self.session,
+            &self.source_span,
+            err,
+            None,
+            &import_suggestions,
+            Instead::No,
+            FoundUse::Yes,
+            IsPattern::No,
+            vec![],
+        );
+
+        if macro_kind == MacroKind::Derive && (ident.name == sym::Send || ident.name == sym::Sync) {
+            let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
+            err.span_note(ident.span, &msg);
+            return;
+        }
+        if self.macro_names.contains(&ident.normalize_to_macros_2_0()) {
+            err.help("have you added the `#[macro_use]` on the module/import?");
+            return;
+        }
+        if ident.name == kw::Default
+            && let ModuleKind::Def(DefKind::Enum, def_id, _) = parent_scope.module.kind
+            && let Some(span) = self.opt_span(def_id)
+        {
+            let source_map = self.session.source_map();
+            let head_span = source_map.guess_head_span(span);
+            if let Ok(head) = source_map.span_to_snippet(head_span) {
+                err.span_suggestion(head_span, "consider adding a derive", format!("#[derive(Default)]\n{head}"), Applicability::MaybeIncorrect);
+            } else {
+                err.span_help(
+                    head_span,
+                    "consider adding `#[derive(Default)]` to this enum",
+                );
+            }
+        }
+        for ns in [Namespace::MacroNS, Namespace::TypeNS, Namespace::ValueNS] {
+            if let Ok(binding) = self.early_resolve_ident_in_lexical_scope(
+                ident,
+                ScopeSet::All(ns, false),
+                &parent_scope,
+                None,
+                false,
+                None,
+            ) {
+                let desc = match binding.res() {
+                    Res::Def(DefKind::Macro(MacroKind::Bang), _) => {
+                        "a function-like macro".to_string()
+                    }
+                    Res::Def(DefKind::Macro(MacroKind::Attr), _) | Res::NonMacroAttr(..) => {
+                        format!("an attribute: `#[{}]`", ident)
+                    }
+                    Res::Def(DefKind::Macro(MacroKind::Derive), _) => {
+                        format!("a derive macro: `#[derive({})]`", ident)
+                    }
+                    Res::ToolMod => {
+                        // Don't confuse the user with tool modules.
+                        continue;
+                    }
+                    Res::Def(DefKind::Trait, _) if macro_kind == MacroKind::Derive => {
+                        "only a trait, without a derive macro".to_string()
+                    }
+                    res => format!(
+                        "{} {}, not {} {}",
+                        res.article(),
+                        res.descr(),
+                        macro_kind.article(),
+                        macro_kind.descr_expected(),
+                    ),
+                };
+                if let crate::NameBindingKind::Import { import, .. } = binding.kind {
+                    if !import.span.is_dummy() {
+                        err.span_note(
+                            import.span,
+                            &format!("`{}` is imported here, but it is {}", ident, desc),
+                        );
+                        // Silence the 'unused import' warning we might get,
+                        // since this diagnostic already covers that import.
+                        self.record_use(ident, binding, false);
+                        return;
+                    }
+                }
+                err.note(&format!("`{}` is in scope, but it is {}", ident, desc));
+                return;
+            }
+        }
+    }
+
+    pub(crate) fn add_typo_suggestion(
+        &self,
+        err: &mut Diagnostic,
+        suggestion: Option<TypoSuggestion>,
+        span: Span,
+    ) -> bool {
+        let suggestion = match suggestion {
+            None => return false,
+            // We shouldn't suggest underscore.
+            Some(suggestion) if suggestion.candidate == kw::Underscore => return false,
+            Some(suggestion) => suggestion,
+        };
+        let def_span = suggestion.res.opt_def_id().and_then(|def_id| match def_id.krate {
+            LOCAL_CRATE => self.opt_span(def_id),
+            _ => Some(self.cstore().get_span_untracked(def_id, self.session)),
+        });
+        if let Some(def_span) = def_span {
+            if span.overlaps(def_span) {
+                // Don't suggest typo suggestion for itself like in the following:
+                // error[E0423]: expected function, tuple struct or tuple variant, found struct `X`
+                //   --> $DIR/issue-64792-bad-unicode-ctor.rs:3:14
+                //    |
+                // LL | struct X {}
+                //    | ----------- `X` defined here
+                // LL |
+                // LL | const Y: X = X("ö");
+                //    | -------------^^^^^^- similarly named constant `Y` defined here
+                //    |
+                // help: use struct literal syntax instead
+                //    |
+                // LL | const Y: X = X {};
+                //    |              ^^^^
+                // help: a constant with a similar name exists
+                //    |
+                // LL | const Y: X = Y("ö");
+                //    |              ^
+                return false;
+            }
+            let prefix = match suggestion.target {
+                SuggestionTarget::SimilarlyNamed => "similarly named ",
+                SuggestionTarget::SingleItem => "",
+            };
+
+            err.span_label(
+                self.session.source_map().guess_head_span(def_span),
+                &format!(
+                    "{}{} `{}` defined here",
+                    prefix,
+                    suggestion.res.descr(),
+                    suggestion.candidate,
+                ),
+            );
+        }
+        let msg = match suggestion.target {
+            SuggestionTarget::SimilarlyNamed => format!(
+                "{} {} with a similar name exists",
+                suggestion.res.article(),
+                suggestion.res.descr()
+            ),
+            SuggestionTarget::SingleItem => {
+                format!("maybe you meant this {}", suggestion.res.descr())
+            }
+        };
+        err.span_suggestion(span, &msg, suggestion.candidate, Applicability::MaybeIncorrect);
+        true
+    }
+
+    fn binding_description(&self, b: &NameBinding<'_>, ident: Ident, from_prelude: bool) -> String {
+        let res = b.res();
+        if b.span.is_dummy() || !self.session.source_map().is_span_accessible(b.span) {
+            // These already contain the "built-in" prefix or look bad with it.
+            let add_built_in =
+                !matches!(b.res(), Res::NonMacroAttr(..) | Res::PrimTy(..) | Res::ToolMod);
+            let (built_in, from) = if from_prelude {
+                ("", " from prelude")
+            } else if b.is_extern_crate()
+                && !b.is_import()
+                && self.session.opts.externs.get(ident.as_str()).is_some()
+            {
+                ("", " passed with `--extern`")
+            } else if add_built_in {
+                (" built-in", "")
+            } else {
+                ("", "")
+            };
+
+            let a = if built_in.is_empty() { res.article() } else { "a" };
+            format!("{a}{built_in} {thing}{from}", thing = res.descr())
+        } else {
+            let introduced = if b.is_import() { "imported" } else { "defined" };
+            format!("the {thing} {introduced} here", thing = res.descr())
+        }
+    }
+
+    fn report_ambiguity_error(&self, ambiguity_error: &AmbiguityError<'_>) {
+        let AmbiguityError { kind, ident, b1, b2, misc1, misc2 } = *ambiguity_error;
+        let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
+            // We have to print the span-less alternative first, otherwise formatting looks bad.
+            (b2, b1, misc2, misc1, true)
+        } else {
+            (b1, b2, misc1, misc2, false)
+        };
+
+        let mut err = struct_span_err!(self.session, ident.span, E0659, "`{ident}` is ambiguous");
+        err.span_label(ident.span, "ambiguous name");
+        err.note(&format!("ambiguous because of {}", kind.descr()));
+
+        let mut could_refer_to = |b: &NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
+            let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
+            let note_msg = format!("`{ident}` could{also} refer to {what}");
+
+            let thing = b.res().descr();
+            let mut help_msgs = Vec::new();
+            if b.is_glob_import()
+                && (kind == AmbiguityKind::GlobVsGlob
+                    || kind == AmbiguityKind::GlobVsExpanded
+                    || kind == AmbiguityKind::GlobVsOuter && swapped != also.is_empty())
+            {
+                help_msgs.push(format!(
+                    "consider adding an explicit import of `{ident}` to disambiguate"
+                ))
+            }
+            if b.is_extern_crate() && ident.span.rust_2018() {
+                help_msgs.push(format!("use `::{ident}` to refer to this {thing} unambiguously"))
+            }
+            if misc == AmbiguityErrorMisc::SuggestCrate {
+                help_msgs
+                    .push(format!("use `crate::{ident}` to refer to this {thing} unambiguously"))
+            } else if misc == AmbiguityErrorMisc::SuggestSelf {
+                help_msgs
+                    .push(format!("use `self::{ident}` to refer to this {thing} unambiguously"))
+            }
+
+            err.span_note(b.span, &note_msg);
+            for (i, help_msg) in help_msgs.iter().enumerate() {
+                let or = if i == 0 { "" } else { "or " };
+                err.help(&format!("{}{}", or, help_msg));
+            }
+        };
+
+        could_refer_to(b1, misc1, "");
+        could_refer_to(b2, misc2, " also");
+        err.emit();
+    }
+
+    /// If the binding refers to a tuple struct constructor with fields,
+    /// returns the span of its fields.
+    fn ctor_fields_span(&self, binding: &NameBinding<'_>) -> Option<Span> {
+        if let NameBindingKind::Res(
+            Res::Def(DefKind::Ctor(CtorOf::Struct, CtorKind::Fn), ctor_def_id),
+            _,
+        ) = binding.kind
+        {
+            let def_id = self.parent(ctor_def_id);
+            let fields = self.field_names.get(&def_id)?;
+            return fields.iter().map(|name| name.span).reduce(Span::to); // None for `struct Foo()`
+        }
+        None
+    }
+
+    fn report_privacy_error(&self, privacy_error: &PrivacyError<'_>) {
+        let PrivacyError { ident, binding, .. } = *privacy_error;
+
+        let res = binding.res();
+        let ctor_fields_span = self.ctor_fields_span(binding);
+        let plain_descr = res.descr().to_string();
+        let nonimport_descr =
+            if ctor_fields_span.is_some() { plain_descr + " constructor" } else { plain_descr };
+        let import_descr = nonimport_descr.clone() + " import";
+        let get_descr =
+            |b: &NameBinding<'_>| if b.is_import() { &import_descr } else { &nonimport_descr };
+
+        // Print the primary message.
+        let descr = get_descr(binding);
+        let mut err =
+            struct_span_err!(self.session, ident.span, E0603, "{} `{}` is private", descr, ident);
+        err.span_label(ident.span, &format!("private {}", descr));
+        if let Some(span) = ctor_fields_span {
+            err.span_label(span, "a constructor is private if any of the fields is private");
+        }
+
+        // Print the whole import chain to make it easier to see what happens.
+        let first_binding = binding;
+        let mut next_binding = Some(binding);
+        let mut next_ident = ident;
+        while let Some(binding) = next_binding {
+            let name = next_ident;
+            next_binding = match binding.kind {
+                _ if res == Res::Err => None,
+                NameBindingKind::Import { binding, import, .. } => match import.kind {
+                    _ if binding.span.is_dummy() => None,
+                    ImportKind::Single { source, .. } => {
+                        next_ident = source;
+                        Some(binding)
+                    }
+                    ImportKind::Glob { .. } | ImportKind::MacroUse => Some(binding),
+                    ImportKind::ExternCrate { .. } => None,
+                },
+                _ => None,
+            };
+
+            let first = ptr::eq(binding, first_binding);
+            let msg = format!(
+                "{and_refers_to}the {item} `{name}`{which} is defined here{dots}",
+                and_refers_to = if first { "" } else { "...and refers to " },
+                item = get_descr(binding),
+                which = if first { "" } else { " which" },
+                dots = if next_binding.is_some() { "..." } else { "" },
+            );
+            let def_span = self.session.source_map().guess_head_span(binding.span);
+            let mut note_span = MultiSpan::from_span(def_span);
+            if !first && binding.vis.is_public() {
+                note_span.push_span_label(def_span, "consider importing it directly");
+            }
+            err.span_note(note_span, &msg);
+        }
+
+        err.emit();
+    }
+
+    pub(crate) fn find_similarly_named_module_or_crate(
+        &mut self,
+        ident: Symbol,
+        current_module: &Module<'a>,
+    ) -> Option<Symbol> {
+        let mut candidates = self
+            .extern_prelude
+            .iter()
+            .map(|(ident, _)| ident.name)
+            .chain(
+                self.module_map
+                    .iter()
+                    .filter(|(_, module)| {
+                        current_module.is_ancestor_of(module) && !ptr::eq(current_module, *module)
+                    })
+                    .flat_map(|(_, module)| module.kind.name()),
+            )
+            .filter(|c| !c.to_string().is_empty())
+            .collect::<Vec<_>>();
+        candidates.sort();
+        candidates.dedup();
+        match find_best_match_for_name(&candidates, ident, None) {
+            Some(sugg) if sugg == ident => None,
+            sugg => sugg,
+        }
+    }
+
+    pub(crate) fn report_path_resolution_error(
+        &mut self,
+        path: &[Segment],
+        opt_ns: Option<Namespace>, // `None` indicates a module path in import
+        parent_scope: &ParentScope<'a>,
+        ribs: Option<&PerNS<Vec<Rib<'a>>>>,
+        ignore_binding: Option<&'a NameBinding<'a>>,
+        module: Option<ModuleOrUniformRoot<'a>>,
+        i: usize,
+        ident: Ident,
+    ) -> (String, Option<Suggestion>) {
+        let is_last = i == path.len() - 1;
+        let ns = if is_last { opt_ns.unwrap_or(TypeNS) } else { TypeNS };
+        let module_res = match module {
+            Some(ModuleOrUniformRoot::Module(module)) => module.res(),
+            _ => None,
+        };
+        if module_res == self.graph_root.res() {
+            let is_mod = |res| matches!(res, Res::Def(DefKind::Mod, _));
+            let mut candidates = self.lookup_import_candidates(ident, TypeNS, parent_scope, is_mod);
+            candidates
+                .sort_by_cached_key(|c| (c.path.segments.len(), pprust::path_to_string(&c.path)));
+            if let Some(candidate) = candidates.get(0) {
+                (
+                    String::from("unresolved import"),
+                    Some((
+                        vec![(ident.span, pprust::path_to_string(&candidate.path))],
+                        String::from("a similar path exists"),
+                        Applicability::MaybeIncorrect,
+                    )),
+                )
+            } else if self.session.edition() == Edition::Edition2015 {
+                (
+                    format!("maybe a missing crate `{ident}`?"),
+                    Some((
+                        vec![],
+                        format!(
+                            "consider adding `extern crate {ident}` to use the `{ident}` crate"
+                        ),
+                        Applicability::MaybeIncorrect,
+                    )),
+                )
+            } else {
+                (format!("could not find `{ident}` in the crate root"), None)
+            }
+        } else if i > 0 {
+            let parent = path[i - 1].ident.name;
+            let parent = match parent {
+                // ::foo is mounted at the crate root for 2015, and is the extern
+                // prelude for 2018+
+                kw::PathRoot if self.session.edition() > Edition::Edition2015 => {
+                    "the list of imported crates".to_owned()
+                }
+                kw::PathRoot | kw::Crate => "the crate root".to_owned(),
+                _ => format!("`{parent}`"),
+            };
+
+            let mut msg = format!("could not find `{}` in {}", ident, parent);
+            if ns == TypeNS || ns == ValueNS {
+                let ns_to_try = if ns == TypeNS { ValueNS } else { TypeNS };
+                let binding = if let Some(module) = module {
+                    self.resolve_ident_in_module(
+                        module,
+                        ident,
+                        ns_to_try,
+                        parent_scope,
+                        None,
+                        ignore_binding,
+                    ).ok()
+                } else if let Some(ribs) = ribs
+                    && let Some(TypeNS | ValueNS) = opt_ns
+                {
+                    match self.resolve_ident_in_lexical_scope(
+                        ident,
+                        ns_to_try,
+                        parent_scope,
+                        None,
+                        &ribs[ns_to_try],
+                        ignore_binding,
+                    ) {
+                        // we found a locally-imported or available item/module
+                        Some(LexicalScopeBinding::Item(binding)) => Some(binding),
+                        _ => None,
+                    }
+                } else {
+                    let scopes = ScopeSet::All(ns_to_try, opt_ns.is_none());
+                    self.early_resolve_ident_in_lexical_scope(
+                        ident,
+                        scopes,
+                        parent_scope,
+                        None,
+                        false,
+                        ignore_binding,
+                    ).ok()
+                };
+                if let Some(binding) = binding {
+                    let mut found = |what| {
+                        msg = format!(
+                            "expected {}, found {} `{}` in {}",
+                            ns.descr(),
+                            what,
+                            ident,
+                            parent
+                        )
+                    };
+                    if binding.module().is_some() {
+                        found("module")
+                    } else {
+                        match binding.res() {
+                            Res::Def(kind, id) => found(kind.descr(id)),
+                            _ => found(ns_to_try.descr()),
+                        }
+                    }
+                };
+            }
+            (msg, None)
+        } else if ident.name == kw::SelfUpper {
+            ("`Self` is only available in impls, traits, and type definitions".to_string(), None)
+        } else if ident.name.as_str().chars().next().map_or(false, |c| c.is_ascii_uppercase()) {
+            // Check whether the name refers to an item in the value namespace.
+            let binding = if let Some(ribs) = ribs {
+                self.resolve_ident_in_lexical_scope(
+                    ident,
+                    ValueNS,
+                    parent_scope,
+                    None,
+                    &ribs[ValueNS],
+                    ignore_binding,
+                )
+            } else {
+                None
+            };
+            let match_span = match binding {
+                // Name matches a local variable. For example:
+                // ```
+                // fn f() {
+                //     let Foo: &str = "";
+                //     println!("{}", Foo::Bar); // Name refers to local
+                //                               // variable `Foo`.
+                // }
+                // ```
+                Some(LexicalScopeBinding::Res(Res::Local(id))) => {
+                    Some(*self.pat_span_map.get(&id).unwrap())
+                }
+                // Name matches item from a local name binding
+                // created by `use` declaration. For example:
+                // ```
+                // pub Foo: &str = "";
+                //
+                // mod submod {
+                //     use super::Foo;
+                //     println!("{}", Foo::Bar); // Name refers to local
+                //                               // binding `Foo`.
+                // }
+                // ```
+                Some(LexicalScopeBinding::Item(name_binding)) => Some(name_binding.span),
+                _ => None,
+            };
+            let suggestion = if let Some(span) = match_span {
+                Some((
+                    vec![(span, String::from(""))],
+                    format!("`{}` is defined here, but is not a type", ident),
+                    Applicability::MaybeIncorrect,
+                ))
+            } else {
+                None
+            };
+
+            (format!("use of undeclared type `{}`", ident), suggestion)
+        } else {
+            let suggestion = if ident.name == sym::alloc {
+                Some((
+                    vec![],
+                    String::from("add `extern crate alloc` to use the `alloc` crate"),
+                    Applicability::MaybeIncorrect,
+                ))
+            } else {
+                self.find_similarly_named_module_or_crate(ident.name, &parent_scope.module).map(
+                    |sugg| {
+                        (
+                            vec![(ident.span, sugg.to_string())],
+                            String::from("there is a crate or module with a similar name"),
+                            Applicability::MaybeIncorrect,
+                        )
+                    },
+                )
+            };
+            (format!("use of undeclared crate or module `{}`", ident), suggestion)
+        }
+    }
+}
+
+impl<'a, 'b> ImportResolver<'a, 'b> {
+    /// Adds suggestions for a path that cannot be resolved.
+    pub(crate) fn make_path_suggestion(
+        &mut self,
+        span: Span,
+        mut path: Vec<Segment>,
+        parent_scope: &ParentScope<'b>,
+    ) -> Option<(Vec<Segment>, Option<String>)> {
+        debug!("make_path_suggestion: span={:?} path={:?}", span, path);
+
+        match (path.get(0), path.get(1)) {
+            // `{{root}}::ident::...` on both editions.
+            // On 2015 `{{root}}` is usually added implicitly.
+            (Some(fst), Some(snd))
+                if fst.ident.name == kw::PathRoot && !snd.ident.is_path_segment_keyword() => {}
+            // `ident::...` on 2018.
+            (Some(fst), _)
+                if fst.ident.span.rust_2018() && !fst.ident.is_path_segment_keyword() =>
+            {
+                // Insert a placeholder that's later replaced by `self`/`super`/etc.
+                path.insert(0, Segment::from_ident(Ident::empty()));
+            }
+            _ => return None,
+        }
+
+        self.make_missing_self_suggestion(path.clone(), parent_scope)
+            .or_else(|| self.make_missing_crate_suggestion(path.clone(), parent_scope))
+            .or_else(|| self.make_missing_super_suggestion(path.clone(), parent_scope))
+            .or_else(|| self.make_external_crate_suggestion(path, parent_scope))
+    }
+
+    /// Suggest a missing `self::` if that resolves to an correct module.
+    ///
+    /// ```text
+    ///    |
+    /// LL | use foo::Bar;
+    ///    |     ^^^ did you mean `self::foo`?
+    /// ```
+    fn make_missing_self_suggestion(
+        &mut self,
+        mut path: Vec<Segment>,
+        parent_scope: &ParentScope<'b>,
+    ) -> Option<(Vec<Segment>, Option<String>)> {
+        // Replace first ident with `self` and check if that is valid.
+        path[0].ident.name = kw::SelfLower;
+        let result = self.r.maybe_resolve_path(&path, None, parent_scope);
+        debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
+        if let PathResult::Module(..) = result { Some((path, None)) } else { None }
+    }
+
+    /// Suggests a missing `crate::` if that resolves to an correct module.
+    ///
+    /// ```text
+    ///    |
+    /// LL | use foo::Bar;
+    ///    |     ^^^ did you mean `crate::foo`?
+    /// ```
+    fn make_missing_crate_suggestion(
+        &mut self,
+        mut path: Vec<Segment>,
+        parent_scope: &ParentScope<'b>,
+    ) -> Option<(Vec<Segment>, Option<String>)> {
+        // Replace first ident with `crate` and check if that is valid.
+        path[0].ident.name = kw::Crate;
+        let result = self.r.maybe_resolve_path(&path, None, parent_scope);
+        debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
+        if let PathResult::Module(..) = result {
+            Some((
+                path,
+                Some(
+                    "`use` statements changed in Rust 2018; read more at \
+                     <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
+                     clarity.html>"
+                        .to_string(),
+                ),
+            ))
+        } else {
+            None
+        }
+    }
+
+    /// Suggests a missing `super::` if that resolves to an correct module.
+    ///
+    /// ```text
+    ///    |
+    /// LL | use foo::Bar;
+    ///    |     ^^^ did you mean `super::foo`?
+    /// ```
+    fn make_missing_super_suggestion(
+        &mut self,
+        mut path: Vec<Segment>,
+        parent_scope: &ParentScope<'b>,
+    ) -> Option<(Vec<Segment>, Option<String>)> {
+        // Replace first ident with `crate` and check if that is valid.
+        path[0].ident.name = kw::Super;
+        let result = self.r.maybe_resolve_path(&path, None, parent_scope);
+        debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
+        if let PathResult::Module(..) = result { Some((path, None)) } else { None }
+    }
+
+    /// Suggests a missing external crate name if that resolves to an correct module.
+    ///
+    /// ```text
+    ///    |
+    /// LL | use foobar::Baz;
+    ///    |     ^^^^^^ did you mean `baz::foobar`?
+    /// ```
+    ///
+    /// Used when importing a submodule of an external crate but missing that crate's
+    /// name as the first part of path.
+    fn make_external_crate_suggestion(
+        &mut self,
+        mut path: Vec<Segment>,
+        parent_scope: &ParentScope<'b>,
+    ) -> Option<(Vec<Segment>, Option<String>)> {
+        if path[1].ident.span.rust_2015() {
+            return None;
+        }
+
+        // Sort extern crate names in *reverse* order to get
+        // 1) some consistent ordering for emitted diagnostics, and
+        // 2) `std` suggestions before `core` suggestions.
+        let mut extern_crate_names =
+            self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
+        extern_crate_names.sort_by(|a, b| b.as_str().partial_cmp(a.as_str()).unwrap());
+
+        for name in extern_crate_names.into_iter() {
+            // Replace first ident with a crate name and check if that is valid.
+            path[0].ident.name = name;
+            let result = self.r.maybe_resolve_path(&path, None, parent_scope);
+            debug!(
+                "make_external_crate_suggestion: name={:?} path={:?} result={:?}",
+                name, path, result
+            );
+            if let PathResult::Module(..) = result {
+                return Some((path, None));
+            }
+        }
+
+        None
+    }
+
+    /// Suggests importing a macro from the root of the crate rather than a module within
+    /// the crate.
+    ///
+    /// ```text
+    /// help: a macro with this name exists at the root of the crate
+    ///    |
+    /// LL | use issue_59764::makro;
+    ///    |     ^^^^^^^^^^^^^^^^^^
+    ///    |
+    ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
+    ///            at the root of the crate instead of the module where it is defined
+    /// ```
+    pub(crate) fn check_for_module_export_macro(
+        &mut self,
+        import: &'b Import<'b>,
+        module: ModuleOrUniformRoot<'b>,
+        ident: Ident,
+    ) -> Option<(Option<Suggestion>, Option<String>)> {
+        let ModuleOrUniformRoot::Module(mut crate_module) = module else {
+            return None;
+        };
+
+        while let Some(parent) = crate_module.parent {
+            crate_module = parent;
+        }
+
+        if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
+            // Don't make a suggestion if the import was already from the root of the
+            // crate.
+            return None;
+        }
+
+        let resolutions = self.r.resolutions(crate_module).borrow();
+        let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
+        let binding = resolution.borrow().binding()?;
+        if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
+            let module_name = crate_module.kind.name().unwrap();
+            let import_snippet = match import.kind {
+                ImportKind::Single { source, target, .. } if source != target => {
+                    format!("{} as {}", source, target)
+                }
+                _ => format!("{}", ident),
+            };
+
+            let mut corrections: Vec<(Span, String)> = Vec::new();
+            if !import.is_nested() {
+                // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
+                // intermediate segments.
+                corrections.push((import.span, format!("{}::{}", module_name, import_snippet)));
+            } else {
+                // Find the binding span (and any trailing commas and spaces).
+                //   ie. `use a::b::{c, d, e};`
+                //                      ^^^
+                let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
+                    self.r.session,
+                    import.span,
+                    import.use_span,
+                );
+                debug!(
+                    "check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
+                    found_closing_brace, binding_span
+                );
+
+                let mut removal_span = binding_span;
+                if found_closing_brace {
+                    // If the binding span ended with a closing brace, as in the below example:
+                    //   ie. `use a::b::{c, d};`
+                    //                      ^
+                    // Then expand the span of characters to remove to include the previous
+                    // binding's trailing comma.
+                    //   ie. `use a::b::{c, d};`
+                    //                    ^^^
+                    if let Some(previous_span) =
+                        extend_span_to_previous_binding(self.r.session, binding_span)
+                    {
+                        debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
+                        removal_span = removal_span.with_lo(previous_span.lo());
+                    }
+                }
+                debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
+
+                // Remove the `removal_span`.
+                corrections.push((removal_span, "".to_string()));
+
+                // Find the span after the crate name and if it has nested imports immediately
+                // after the crate name already.
+                //   ie. `use a::b::{c, d};`
+                //               ^^^^^^^^^
+                //   or  `use a::{b, c, d}};`
+                //               ^^^^^^^^^^^
+                let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
+                    self.r.session,
+                    module_name,
+                    import.use_span,
+                );
+                debug!(
+                    "check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
+                    has_nested, after_crate_name
+                );
+
+                let source_map = self.r.session.source_map();
+
+                // Add the import to the start, with a `{` if required.
+                let start_point = source_map.start_point(after_crate_name);
+                if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
+                    corrections.push((
+                        start_point,
+                        if has_nested {
+                            // In this case, `start_snippet` must equal '{'.
+                            format!("{}{}, ", start_snippet, import_snippet)
+                        } else {
+                            // In this case, add a `{`, then the moved import, then whatever
+                            // was there before.
+                            format!("{{{}, {}", import_snippet, start_snippet)
+                        },
+                    ));
+                }
+
+                // Add a `};` to the end if nested, matching the `{` added at the start.
+                if !has_nested {
+                    corrections.push((source_map.end_point(after_crate_name), "};".to_string()));
+                }
+            }
+
+            let suggestion = Some((
+                corrections,
+                String::from("a macro with this name exists at the root of the crate"),
+                Applicability::MaybeIncorrect,
+            ));
+            Some((suggestion, Some("this could be because a macro annotated with `#[macro_export]` will be exported \
+            at the root of the crate instead of the module where it is defined"
+               .to_string())))
+        } else {
+            None
+        }
+    }
+}
+
+/// Given a `binding_span` of a binding within a use statement:
+///
+/// ```ignore (illustrative)
+/// use foo::{a, b, c};
+/// //           ^
+/// ```
+///
+/// then return the span until the next binding or the end of the statement:
+///
+/// ```ignore (illustrative)
+/// use foo::{a, b, c};
+/// //           ^^^
+/// ```
+fn find_span_of_binding_until_next_binding(
+    sess: &Session,
+    binding_span: Span,
+    use_span: Span,
+) -> (bool, Span) {
+    let source_map = sess.source_map();
+
+    // Find the span of everything after the binding.
+    //   ie. `a, e};` or `a};`
+    let binding_until_end = binding_span.with_hi(use_span.hi());
+
+    // Find everything after the binding but not including the binding.
+    //   ie. `, e};` or `};`
+    let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
+
+    // Keep characters in the span until we encounter something that isn't a comma or
+    // whitespace.
+    //   ie. `, ` or ``.
+    //
+    // Also note whether a closing brace character was encountered. If there
+    // was, then later go backwards to remove any trailing commas that are left.
+    let mut found_closing_brace = false;
+    let after_binding_until_next_binding =
+        source_map.span_take_while(after_binding_until_end, |&ch| {
+            if ch == '}' {
+                found_closing_brace = true;
+            }
+            ch == ' ' || ch == ','
+        });
+
+    // Combine the two spans.
+    //   ie. `a, ` or `a`.
+    //
+    // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
+    let span = binding_span.with_hi(after_binding_until_next_binding.hi());
+
+    (found_closing_brace, span)
+}
+
+/// Given a `binding_span`, return the span through to the comma or opening brace of the previous
+/// binding.
+///
+/// ```ignore (illustrative)
+/// use foo::a::{a, b, c};
+/// //            ^^--- binding span
+/// //            |
+/// //            returned span
+///
+/// use foo::{a, b, c};
+/// //        --- binding span
+/// ```
+fn extend_span_to_previous_binding(sess: &Session, binding_span: Span) -> Option<Span> {
+    let source_map = sess.source_map();
+
+    // `prev_source` will contain all of the source that came before the span.
+    // Then split based on a command and take the first (ie. closest to our span)
+    // snippet. In the example, this is a space.
+    let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
+
+    let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
+    let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
+    if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
+        return None;
+    }
+
+    let prev_comma = prev_comma.first().unwrap();
+    let prev_starting_brace = prev_starting_brace.first().unwrap();
+
+    // If the amount of source code before the comma is greater than
+    // the amount of source code before the starting brace then we've only
+    // got one item in the nested item (eg. `issue_52891::{self}`).
+    if prev_comma.len() > prev_starting_brace.len() {
+        return None;
+    }
+
+    Some(binding_span.with_lo(BytePos(
+        // Take away the number of bytes for the characters we've found and an
+        // extra for the comma.
+        binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1,
+    )))
+}
+
+/// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
+/// it is a nested use tree.
+///
+/// ```ignore (illustrative)
+/// use foo::a::{b, c};
+/// //       ^^^^^^^^^^ -- false
+///
+/// use foo::{a, b, c};
+/// //       ^^^^^^^^^^ -- true
+///
+/// use foo::{a, b::{c, d}};
+/// //       ^^^^^^^^^^^^^^^ -- true
+/// ```
+fn find_span_immediately_after_crate_name(
+    sess: &Session,
+    module_name: Symbol,
+    use_span: Span,
+) -> (bool, Span) {
+    debug!(
+        "find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
+        module_name, use_span
+    );
+    let source_map = sess.source_map();
+
+    // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
+    let mut num_colons = 0;
+    // Find second colon.. `use issue_59764:`
+    let until_second_colon = source_map.span_take_while(use_span, |c| {
+        if *c == ':' {
+            num_colons += 1;
+        }
+        !matches!(c, ':' if num_colons == 2)
+    });
+    // Find everything after the second colon.. `foo::{baz, makro};`
+    let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
+
+    let mut found_a_non_whitespace_character = false;
+    // Find the first non-whitespace character in `from_second_colon`.. `f`
+    let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
+        if found_a_non_whitespace_character {
+            return false;
+        }
+        if !c.is_whitespace() {
+            found_a_non_whitespace_character = true;
+        }
+        true
+    });
+
+    // Find the first `{` in from_second_colon.. `foo::{`
+    let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
+
+    (next_left_bracket == after_second_colon, from_second_colon)
+}
+
+/// A suggestion has already been emitted, change the wording slightly to clarify that both are
+/// independent options.
+enum Instead {
+    Yes,
+    No,
+}
+
+/// Whether an existing place with an `use` item was found.
+enum FoundUse {
+    Yes,
+    No,
+}
+
+/// Whether a binding is part of a pattern or an expression. Used for diagnostics.
+enum IsPattern {
+    /// The binding is part of a pattern
+    Yes,
+    /// The binding is part of an expression
+    No,
+}
+
+/// When an entity with a given name is not available in scope, we search for
+/// entities with that name in all crates. This method allows outputting the
+/// results of this search in a programmer-friendly way
+fn show_candidates(
+    session: &Session,
+    source_span: &IndexVec<LocalDefId, Span>,
+    err: &mut Diagnostic,
+    // This is `None` if all placement locations are inside expansions
+    use_placement_span: Option<Span>,
+    candidates: &[ImportSuggestion],
+    instead: Instead,
+    found_use: FoundUse,
+    is_pattern: IsPattern,
+    path: Vec<Segment>,
+) {
+    if candidates.is_empty() {
+        return;
+    }
+
+    let mut accessible_path_strings: Vec<(String, &str, Option<DefId>, &Option<String>)> =
+        Vec::new();
+    let mut inaccessible_path_strings: Vec<(String, &str, Option<DefId>, &Option<String>)> =
+        Vec::new();
+
+    candidates.iter().for_each(|c| {
+        (if c.accessible { &mut accessible_path_strings } else { &mut inaccessible_path_strings })
+            .push((path_names_to_string(&c.path), c.descr, c.did, &c.note))
+    });
+
+    // we want consistent results across executions, but candidates are produced
+    // by iterating through a hash map, so make sure they are ordered:
+    for path_strings in [&mut accessible_path_strings, &mut inaccessible_path_strings] {
+        path_strings.sort_by(|a, b| a.0.cmp(&b.0));
+        let core_path_strings =
+            path_strings.drain_filter(|p| p.0.starts_with("core::")).collect::<Vec<_>>();
+        path_strings.extend(core_path_strings);
+        path_strings.dedup_by(|a, b| a.0 == b.0);
+    }
+
+    if !accessible_path_strings.is_empty() {
+        let (determiner, kind, name) = if accessible_path_strings.len() == 1 {
+            ("this", accessible_path_strings[0].1, format!(" `{}`", accessible_path_strings[0].0))
+        } else {
+            ("one of these", "items", String::new())
+        };
+
+        let instead = if let Instead::Yes = instead { " instead" } else { "" };
+        let mut msg = if let IsPattern::Yes = is_pattern {
+            format!(
+                "if you meant to match on {}{}{}, use the full path in the pattern",
+                kind, instead, name
+            )
+        } else {
+            format!("consider importing {} {}{}", determiner, kind, instead)
+        };
+
+        for note in accessible_path_strings.iter().flat_map(|cand| cand.3.as_ref()) {
+            err.note(note);
+        }
+
+        if let (IsPattern::Yes, Some(span)) = (is_pattern, use_placement_span) {
+            err.span_suggestions(
+                span,
+                &msg,
+                accessible_path_strings.into_iter().map(|a| a.0),
+                Applicability::MaybeIncorrect,
+            );
+        } else if let Some(span) = use_placement_span {
+            for candidate in &mut accessible_path_strings {
+                // produce an additional newline to separate the new use statement
+                // from the directly following item.
+                let additional_newline = if let FoundUse::Yes = found_use { "" } else { "\n" };
+                candidate.0 = format!("use {};\n{}", &candidate.0, additional_newline);
+            }
+
+            err.span_suggestions(
+                span,
+                &msg,
+                accessible_path_strings.into_iter().map(|a| a.0),
+                Applicability::MaybeIncorrect,
+            );
+            if let [first, .., last] = &path[..] {
+                err.span_suggestion_verbose(
+                    first.ident.span.until(last.ident.span),
+                    &format!("if you import `{}`, refer to it directly", last.ident),
+                    "",
+                    Applicability::Unspecified,
+                );
+            }
+        } else {
+            msg.push(':');
+
+            for candidate in accessible_path_strings {
+                msg.push('\n');
+                msg.push_str(&candidate.0);
+            }
+
+            err.note(&msg);
+        }
+    } else {
+        assert!(!inaccessible_path_strings.is_empty());
+
+        let prefix =
+            if let IsPattern::Yes = is_pattern { "you might have meant to match on " } else { "" };
+        if inaccessible_path_strings.len() == 1 {
+            let (name, descr, def_id, note) = &inaccessible_path_strings[0];
+            let msg = format!(
+                "{}{} `{}`{} exists but is inaccessible",
+                prefix,
+                descr,
+                name,
+                if let IsPattern::Yes = is_pattern { ", which" } else { "" }
+            );
+
+            if let Some(local_def_id) = def_id.and_then(|did| did.as_local()) {
+                let span = source_span[local_def_id];
+                let span = session.source_map().guess_head_span(span);
+                let mut multi_span = MultiSpan::from_span(span);
+                multi_span.push_span_label(span, "not accessible");
+                err.span_note(multi_span, &msg);
+            } else {
+                err.note(&msg);
+            }
+            if let Some(note) = (*note).as_deref() {
+                err.note(note);
+            }
+        } else {
+            let (_, descr_first, _, _) = &inaccessible_path_strings[0];
+            let descr = if inaccessible_path_strings
+                .iter()
+                .skip(1)
+                .all(|(_, descr, _, _)| descr == descr_first)
+            {
+                descr_first
+            } else {
+                "item"
+            };
+            let plural_descr =
+                if descr.ends_with('s') { format!("{}es", descr) } else { format!("{}s", descr) };
+
+            let mut msg = format!("{}these {} exist but are inaccessible", prefix, plural_descr);
+            let mut has_colon = false;
+
+            let mut spans = Vec::new();
+            for (name, _, def_id, _) in &inaccessible_path_strings {
+                if let Some(local_def_id) = def_id.and_then(|did| did.as_local()) {
+                    let span = source_span[local_def_id];
+                    let span = session.source_map().guess_head_span(span);
+                    spans.push((name, span));
+                } else {
+                    if !has_colon {
+                        msg.push(':');
+                        has_colon = true;
+                    }
+                    msg.push('\n');
+                    msg.push_str(name);
+                }
+            }
+
+            let mut multi_span = MultiSpan::from_spans(spans.iter().map(|(_, sp)| *sp).collect());
+            for (name, span) in spans {
+                multi_span.push_span_label(span, format!("`{}`: not accessible", name));
+            }
+
+            for note in inaccessible_path_strings.iter().flat_map(|cand| cand.3.as_ref()) {
+                err.note(note);
+            }
+
+            err.span_note(multi_span, &msg);
+        }
+    }
+}
+
+#[derive(Debug)]
+struct UsePlacementFinder {
+    target_module: NodeId,
+    first_legal_span: Option<Span>,
+    first_use_span: Option<Span>,
+}
+
+impl UsePlacementFinder {
+    fn check(krate: &Crate, target_module: NodeId) -> (Option<Span>, FoundUse) {
+        let mut finder =
+            UsePlacementFinder { target_module, first_legal_span: None, first_use_span: None };
+        finder.visit_crate(krate);
+        if let Some(use_span) = finder.first_use_span {
+            (Some(use_span), FoundUse::Yes)
+        } else {
+            (finder.first_legal_span, FoundUse::No)
+        }
+    }
+}
+
+impl<'tcx> visit::Visitor<'tcx> for UsePlacementFinder {
+    fn visit_crate(&mut self, c: &Crate) {
+        if self.target_module == CRATE_NODE_ID {
+            let inject = c.spans.inject_use_span;
+            if is_span_suitable_for_use_injection(inject) {
+                self.first_legal_span = Some(inject);
+            }
+            self.first_use_span = search_for_any_use_in_items(&c.items);
+            return;
+        } else {
+            visit::walk_crate(self, c);
+        }
+    }
+
+    fn visit_item(&mut self, item: &'tcx ast::Item) {
+        if self.target_module == item.id {
+            if let ItemKind::Mod(_, ModKind::Loaded(items, _inline, mod_spans)) = &item.kind {
+                let inject = mod_spans.inject_use_span;
+                if is_span_suitable_for_use_injection(inject) {
+                    self.first_legal_span = Some(inject);
+                }
+                self.first_use_span = search_for_any_use_in_items(items);
+                return;
+            }
+        } else {
+            visit::walk_item(self, item);
+        }
+    }
+}
+
+fn search_for_any_use_in_items(items: &[P<ast::Item>]) -> Option<Span> {
+    for item in items {
+        if let ItemKind::Use(..) = item.kind {
+            if is_span_suitable_for_use_injection(item.span) {
+                return Some(item.span.shrink_to_lo());
+            }
+        }
+    }
+    return None;
+}
+
+fn is_span_suitable_for_use_injection(s: Span) -> bool {
+    // don't suggest placing a use before the prelude
+    // import or other generated ones
+    !s.from_expansion()
+}
+
+/// Convert the given number into the corresponding ordinal
+pub(crate) fn ordinalize(v: usize) -> String {
+    let suffix = match ((11..=13).contains(&(v % 100)), v % 10) {
+        (false, 1) => "st",
+        (false, 2) => "nd",
+        (false, 3) => "rd",
+        _ => "th",
+    };
+    format!("{v}{suffix}")
+}
diff --git a/compiler/rustc_resolve/src/diagnostics/tests.rs b/compiler/rustc_resolve/src/diagnostics/tests.rs
new file mode 100644
index 000000000..2aa6cc61e
--- /dev/null
+++ b/compiler/rustc_resolve/src/diagnostics/tests.rs
@@ -0,0 +1,40 @@
+use super::ordinalize;
+
+#[test]
+fn test_ordinalize() {
+    assert_eq!(ordinalize(1), "1st");
+    assert_eq!(ordinalize(2), "2nd");
+    assert_eq!(ordinalize(3), "3rd");
+    assert_eq!(ordinalize(4), "4th");
+    assert_eq!(ordinalize(5), "5th");
+    // ...
+    assert_eq!(ordinalize(10), "10th");
+    assert_eq!(ordinalize(11), "11th");
+    assert_eq!(ordinalize(12), "12th");
+    assert_eq!(ordinalize(13), "13th");
+    assert_eq!(ordinalize(14), "14th");
+    // ...
+    assert_eq!(ordinalize(20), "20th");
+    assert_eq!(ordinalize(21), "21st");
+    assert_eq!(ordinalize(22), "22nd");
+    assert_eq!(ordinalize(23), "23rd");
+    assert_eq!(ordinalize(24), "24th");
+    // ...
+    assert_eq!(ordinalize(30), "30th");
+    assert_eq!(ordinalize(31), "31st");
+    assert_eq!(ordinalize(32), "32nd");
+    assert_eq!(ordinalize(33), "33rd");
+    assert_eq!(ordinalize(34), "34th");
+    // ...
+    assert_eq!(ordinalize(7010), "7010th");
+    assert_eq!(ordinalize(7011), "7011th");
+    assert_eq!(ordinalize(7012), "7012th");
+    assert_eq!(ordinalize(7013), "7013th");
+    assert_eq!(ordinalize(7014), "7014th");
+    // ...
+    assert_eq!(ordinalize(7020), "7020th");
+    assert_eq!(ordinalize(7021), "7021st");
+    assert_eq!(ordinalize(7022), "7022nd");
+    assert_eq!(ordinalize(7023), "7023rd");
+    assert_eq!(ordinalize(7024), "7024th");
+}
diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
new file mode 100644
index 000000000..6e6782881
--- /dev/null
+++ b/compiler/rustc_resolve/src/ident.rs
@@ -0,0 +1,1556 @@
+use rustc_ast::{self as ast, NodeId};
+use rustc_feature::is_builtin_attr_name;
+use rustc_hir::def::{DefKind, Namespace, NonMacroAttrKind, PartialRes, PerNS};
+use rustc_hir::PrimTy;
+use rustc_middle::bug;
+use rustc_middle::ty;
+use rustc_session::lint::builtin::PROC_MACRO_DERIVE_RESOLUTION_FALLBACK;
+use rustc_session::lint::BuiltinLintDiagnostics;
+use rustc_span::edition::Edition;
+use rustc_span::hygiene::{ExpnId, ExpnKind, LocalExpnId, MacroKind, SyntaxContext};
+use rustc_span::symbol::{kw, Ident};
+use rustc_span::{Span, DUMMY_SP};
+
+use std::ptr;
+
+use crate::late::{ConstantItemKind, HasGenericParams, PathSource, Rib, RibKind};
+use crate::macros::{sub_namespace_match, MacroRulesScope};
+use crate::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, Determinacy, Finalize};
+use crate::{ImportKind, LexicalScopeBinding, Module, ModuleKind, ModuleOrUniformRoot};
+use crate::{NameBinding, NameBindingKind, ParentScope, PathResult, PrivacyError, Res};
+use crate::{ResolutionError, Resolver, Scope, ScopeSet, Segment, ToNameBinding, Weak};
+
+use Determinacy::*;
+use Namespace::*;
+use RibKind::*;
+
+impl<'a> Resolver<'a> {
+    /// A generic scope visitor.
+    /// Visits scopes in order to resolve some identifier in them or perform other actions.
+    /// If the callback returns `Some` result, we stop visiting scopes and return it.
+    pub(crate) fn visit_scopes<T>(
+        &mut self,
+        scope_set: ScopeSet<'a>,
+        parent_scope: &ParentScope<'a>,
+        ctxt: SyntaxContext,
+        mut visitor: impl FnMut(
+            &mut Self,
+            Scope<'a>,
+            /*use_prelude*/ bool,
+            SyntaxContext,
+        ) -> Option<T>,
+    ) -> Option<T> {
+        // General principles:
+        // 1. Not controlled (user-defined) names should have higher priority than controlled names
+        //    built into the language or standard library. This way we can add new names into the
+        //    language or standard library without breaking user code.
+        // 2. "Closed set" below means new names cannot appear after the current resolution attempt.
+        // Places to search (in order of decreasing priority):
+        // (Type NS)
+        // 1. FIXME: Ribs (type parameters), there's no necessary infrastructure yet
+        //    (open set, not controlled).
+        // 2. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
+        //    (open, not controlled).
+        // 3. Extern prelude (open, the open part is from macro expansions, not controlled).
+        // 4. Tool modules (closed, controlled right now, but not in the future).
+        // 5. Standard library prelude (de-facto closed, controlled).
+        // 6. Language prelude (closed, controlled).
+        // (Value NS)
+        // 1. FIXME: Ribs (local variables), there's no necessary infrastructure yet
+        //    (open set, not controlled).
+        // 2. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
+        //    (open, not controlled).
+        // 3. Standard library prelude (de-facto closed, controlled).
+        // (Macro NS)
+        // 1-3. Derive helpers (open, not controlled). All ambiguities with other names
+        //    are currently reported as errors. They should be higher in priority than preludes
+        //    and probably even names in modules according to the "general principles" above. They
+        //    also should be subject to restricted shadowing because are effectively produced by
+        //    derives (you need to resolve the derive first to add helpers into scope), but they
+        //    should be available before the derive is expanded for compatibility.
+        //    It's mess in general, so we are being conservative for now.
+        // 1-3. `macro_rules` (open, not controlled), loop through `macro_rules` scopes. Have higher
+        //    priority than prelude macros, but create ambiguities with macros in modules.
+        // 1-3. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
+        //    (open, not controlled). Have higher priority than prelude macros, but create
+        //    ambiguities with `macro_rules`.
+        // 4. `macro_use` prelude (open, the open part is from macro expansions, not controlled).
+        // 4a. User-defined prelude from macro-use
+        //    (open, the open part is from macro expansions, not controlled).
+        // 4b. "Standard library prelude" part implemented through `macro-use` (closed, controlled).
+        // 4c. Standard library prelude (de-facto closed, controlled).
+        // 6. Language prelude: builtin attributes (closed, controlled).
+
+        let rust_2015 = ctxt.edition() == Edition::Edition2015;
+        let (ns, macro_kind, is_absolute_path) = match scope_set {
+            ScopeSet::All(ns, _) => (ns, None, false),
+            ScopeSet::AbsolutePath(ns) => (ns, None, true),
+            ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind), false),
+            ScopeSet::Late(ns, ..) => (ns, None, false),
+        };
+        let module = match scope_set {
+            // Start with the specified module.
+            ScopeSet::Late(_, module, _) => module,
+            // Jump out of trait or enum modules, they do not act as scopes.
+            _ => parent_scope.module.nearest_item_scope(),
+        };
+        let mut scope = match ns {
+            _ if is_absolute_path => Scope::CrateRoot,
+            TypeNS | ValueNS => Scope::Module(module, None),
+            MacroNS => Scope::DeriveHelpers(parent_scope.expansion),
+        };
+        let mut ctxt = ctxt.normalize_to_macros_2_0();
+        let mut use_prelude = !module.no_implicit_prelude;
+
+        loop {
+            let visit = match scope {
+                // Derive helpers are not in scope when resolving derives in the same container.
+                Scope::DeriveHelpers(expn_id) => {
+                    !(expn_id == parent_scope.expansion && macro_kind == Some(MacroKind::Derive))
+                }
+                Scope::DeriveHelpersCompat => true,
+                Scope::MacroRules(macro_rules_scope) => {
+                    // Use "path compression" on `macro_rules` scope chains. This is an optimization
+                    // used to avoid long scope chains, see the comments on `MacroRulesScopeRef`.
+                    // As another consequence of this optimization visitors never observe invocation
+                    // scopes for macros that were already expanded.
+                    while let MacroRulesScope::Invocation(invoc_id) = macro_rules_scope.get() {
+                        if let Some(next_scope) = self.output_macro_rules_scopes.get(&invoc_id) {
+                            macro_rules_scope.set(next_scope.get());
+                        } else {
+                            break;
+                        }
+                    }
+                    true
+                }
+                Scope::CrateRoot => true,
+                Scope::Module(..) => true,
+                Scope::RegisteredAttrs => use_prelude,
+                Scope::MacroUsePrelude => use_prelude || rust_2015,
+                Scope::BuiltinAttrs => true,
+                Scope::ExternPrelude => use_prelude || is_absolute_path,
+                Scope::ToolPrelude => use_prelude,
+                Scope::StdLibPrelude => use_prelude || ns == MacroNS,
+                Scope::BuiltinTypes => true,
+            };
+
+            if visit {
+                if let break_result @ Some(..) = visitor(self, scope, use_prelude, ctxt) {
+                    return break_result;
+                }
+            }
+
+            scope = match scope {
+                Scope::DeriveHelpers(LocalExpnId::ROOT) => Scope::DeriveHelpersCompat,
+                Scope::DeriveHelpers(expn_id) => {
+                    // Derive helpers are not visible to code generated by bang or derive macros.
+                    let expn_data = expn_id.expn_data();
+                    match expn_data.kind {
+                        ExpnKind::Root
+                        | ExpnKind::Macro(MacroKind::Bang | MacroKind::Derive, _) => {
+                            Scope::DeriveHelpersCompat
+                        }
+                        _ => Scope::DeriveHelpers(expn_data.parent.expect_local()),
+                    }
+                }
+                Scope::DeriveHelpersCompat => Scope::MacroRules(parent_scope.macro_rules),
+                Scope::MacroRules(macro_rules_scope) => match macro_rules_scope.get() {
+                    MacroRulesScope::Binding(binding) => {
+                        Scope::MacroRules(binding.parent_macro_rules_scope)
+                    }
+                    MacroRulesScope::Invocation(invoc_id) => {
+                        Scope::MacroRules(self.invocation_parent_scopes[&invoc_id].macro_rules)
+                    }
+                    MacroRulesScope::Empty => Scope::Module(module, None),
+                },
+                Scope::CrateRoot => match ns {
+                    TypeNS => {
+                        ctxt.adjust(ExpnId::root());
+                        Scope::ExternPrelude
+                    }
+                    ValueNS | MacroNS => break,
+                },
+                Scope::Module(module, prev_lint_id) => {
+                    use_prelude = !module.no_implicit_prelude;
+                    let derive_fallback_lint_id = match scope_set {
+                        ScopeSet::Late(.., lint_id) => lint_id,
+                        _ => None,
+                    };
+                    match self.hygienic_lexical_parent(module, &mut ctxt, derive_fallback_lint_id) {
+                        Some((parent_module, lint_id)) => {
+                            Scope::Module(parent_module, lint_id.or(prev_lint_id))
+                        }
+                        None => {
+                            ctxt.adjust(ExpnId::root());
+                            match ns {
+                                TypeNS => Scope::ExternPrelude,
+                                ValueNS => Scope::StdLibPrelude,
+                                MacroNS => Scope::RegisteredAttrs,
+                            }
+                        }
+                    }
+                }
+                Scope::RegisteredAttrs => Scope::MacroUsePrelude,
+                Scope::MacroUsePrelude => Scope::StdLibPrelude,
+                Scope::BuiltinAttrs => break, // nowhere else to search
+                Scope::ExternPrelude if is_absolute_path => break,
+                Scope::ExternPrelude => Scope::ToolPrelude,
+                Scope::ToolPrelude => Scope::StdLibPrelude,
+                Scope::StdLibPrelude => match ns {
+                    TypeNS => Scope::BuiltinTypes,
+                    ValueNS => break, // nowhere else to search
+                    MacroNS => Scope::BuiltinAttrs,
+                },
+                Scope::BuiltinTypes => break, // nowhere else to search
+            };
+        }
+
+        None
+    }
+
+    fn hygienic_lexical_parent(
+        &mut self,
+        module: Module<'a>,
+        ctxt: &mut SyntaxContext,
+        derive_fallback_lint_id: Option<NodeId>,
+    ) -> Option<(Module<'a>, Option<NodeId>)> {
+        if !module.expansion.outer_expn_is_descendant_of(*ctxt) {
+            return Some((self.expn_def_scope(ctxt.remove_mark()), None));
+        }
+
+        if let ModuleKind::Block = module.kind {
+            return Some((module.parent.unwrap().nearest_item_scope(), None));
+        }
+
+        // We need to support the next case under a deprecation warning
+        // ```
+        // struct MyStruct;
+        // ---- begin: this comes from a proc macro derive
+        // mod implementation_details {
+        //     // Note that `MyStruct` is not in scope here.
+        //     impl SomeTrait for MyStruct { ... }
+        // }
+        // ---- end
+        // ```
+        // So we have to fall back to the module's parent during lexical resolution in this case.
+        if derive_fallback_lint_id.is_some() {
+            if let Some(parent) = module.parent {
+                // Inner module is inside the macro, parent module is outside of the macro.
+                if module.expansion != parent.expansion
+                    && module.expansion.is_descendant_of(parent.expansion)
+                {
+                    // The macro is a proc macro derive
+                    if let Some(def_id) = module.expansion.expn_data().macro_def_id {
+                        let ext = self.get_macro_by_def_id(def_id).ext;
+                        if ext.builtin_name.is_none()
+                            && ext.macro_kind() == MacroKind::Derive
+                            && parent.expansion.outer_expn_is_descendant_of(*ctxt)
+                        {
+                            return Some((parent, derive_fallback_lint_id));
+                        }
+                    }
+                }
+            }
+        }
+
+        None
+    }
+
+    /// This resolves the identifier `ident` in the namespace `ns` in the current lexical scope.
+    /// More specifically, we proceed up the hierarchy of scopes and return the binding for
+    /// `ident` in the first scope that defines it (or None if no scopes define it).
+    ///
+    /// A block's items are above its local variables in the scope hierarchy, regardless of where
+    /// the items are defined in the block. For example,
+    /// ```rust
+    /// fn f() {
+    ///    g(); // Since there are no local variables in scope yet, this resolves to the item.
+    ///    let g = || {};
+    ///    fn g() {}
+    ///    g(); // This resolves to the local variable `g` since it shadows the item.
+    /// }
+    /// ```
+    ///
+    /// Invariant: This must only be called during main resolution, not during
+    /// import resolution.
+    #[tracing::instrument(level = "debug", skip(self, ribs))]
+    pub(crate) fn resolve_ident_in_lexical_scope(
+        &mut self,
+        mut ident: Ident,
+        ns: Namespace,
+        parent_scope: &ParentScope<'a>,
+        finalize: Option<Finalize>,
+        ribs: &[Rib<'a>],
+        ignore_binding: Option<&'a NameBinding<'a>>,
+    ) -> Option<LexicalScopeBinding<'a>> {
+        assert!(ns == TypeNS || ns == ValueNS);
+        let orig_ident = ident;
+        if ident.name == kw::Empty {
+            return Some(LexicalScopeBinding::Res(Res::Err));
+        }
+        let (general_span, normalized_span) = if ident.name == kw::SelfUpper {
+            // FIXME(jseyfried) improve `Self` hygiene
+            let empty_span = ident.span.with_ctxt(SyntaxContext::root());
+            (empty_span, empty_span)
+        } else if ns == TypeNS {
+            let normalized_span = ident.span.normalize_to_macros_2_0();
+            (normalized_span, normalized_span)
+        } else {
+            (ident.span.normalize_to_macro_rules(), ident.span.normalize_to_macros_2_0())
+        };
+        ident.span = general_span;
+        let normalized_ident = Ident { span: normalized_span, ..ident };
+
+        // Walk backwards up the ribs in scope.
+        let mut module = self.graph_root;
+        for i in (0..ribs.len()).rev() {
+            debug!("walk rib\n{:?}", ribs[i].bindings);
+            // Use the rib kind to determine whether we are resolving parameters
+            // (macro 2.0 hygiene) or local variables (`macro_rules` hygiene).
+            let rib_ident = if ribs[i].kind.contains_params() { normalized_ident } else { ident };
+            if let Some((original_rib_ident_def, res)) = ribs[i].bindings.get_key_value(&rib_ident)
+            {
+                // The ident resolves to a type parameter or local variable.
+                return Some(LexicalScopeBinding::Res(self.validate_res_from_ribs(
+                    i,
+                    rib_ident,
+                    *res,
+                    finalize.map(|finalize| finalize.path_span),
+                    *original_rib_ident_def,
+                    ribs,
+                )));
+            }
+
+            module = match ribs[i].kind {
+                ModuleRibKind(module) => module,
+                MacroDefinition(def) if def == self.macro_def(ident.span.ctxt()) => {
+                    // If an invocation of this macro created `ident`, give up on `ident`
+                    // and switch to `ident`'s source from the macro definition.
+                    ident.span.remove_mark();
+                    continue;
+                }
+                _ => continue,
+            };
+
+            match module.kind {
+                ModuleKind::Block => {} // We can see through blocks
+                _ => break,
+            }
+
+            let item = self.resolve_ident_in_module_unadjusted(
+                ModuleOrUniformRoot::Module(module),
+                ident,
+                ns,
+                parent_scope,
+                finalize,
+                ignore_binding,
+            );
+            if let Ok(binding) = item {
+                // The ident resolves to an item.
+                return Some(LexicalScopeBinding::Item(binding));
+            }
+        }
+        self.early_resolve_ident_in_lexical_scope(
+            orig_ident,
+            ScopeSet::Late(ns, module, finalize.map(|finalize| finalize.node_id)),
+            parent_scope,
+            finalize,
+            finalize.is_some(),
+            ignore_binding,
+        )
+        .ok()
+        .map(LexicalScopeBinding::Item)
+    }
+
+    /// Resolve an identifier in lexical scope.
+    /// This is a variation of `fn resolve_ident_in_lexical_scope` that can be run during
+    /// expansion and import resolution (perhaps they can be merged in the future).
+    /// The function is used for resolving initial segments of macro paths (e.g., `foo` in
+    /// `foo::bar!(); or `foo!();`) and also for import paths on 2018 edition.
+    #[tracing::instrument(level = "debug", skip(self, scope_set))]
+    pub(crate) fn early_resolve_ident_in_lexical_scope(
+        &mut self,
+        orig_ident: Ident,
+        scope_set: ScopeSet<'a>,
+        parent_scope: &ParentScope<'a>,
+        finalize: Option<Finalize>,
+        force: bool,
+        ignore_binding: Option<&'a NameBinding<'a>>,
+    ) -> Result<&'a NameBinding<'a>, Determinacy> {
+        bitflags::bitflags! {
+            struct Flags: u8 {
+                const MACRO_RULES          = 1 << 0;
+                const MODULE               = 1 << 1;
+                const MISC_SUGGEST_CRATE   = 1 << 2;
+                const MISC_SUGGEST_SELF    = 1 << 3;
+                const MISC_FROM_PRELUDE    = 1 << 4;
+            }
+        }
+
+        assert!(force || !finalize.is_some()); // `finalize` implies `force`
+
+        // Make sure `self`, `super` etc produce an error when passed to here.
+        if orig_ident.is_path_segment_keyword() {
+            return Err(Determinacy::Determined);
+        }
+
+        let (ns, macro_kind, is_import) = match scope_set {
+            ScopeSet::All(ns, is_import) => (ns, None, is_import),
+            ScopeSet::AbsolutePath(ns) => (ns, None, false),
+            ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind), false),
+            ScopeSet::Late(ns, ..) => (ns, None, false),
+        };
+
+        // This is *the* result, resolution from the scope closest to the resolved identifier.
+        // However, sometimes this result is "weak" because it comes from a glob import or
+        // a macro expansion, and in this case it cannot shadow names from outer scopes, e.g.
+        // mod m { ... } // solution in outer scope
+        // {
+        //     use prefix::*; // imports another `m` - innermost solution
+        //                    // weak, cannot shadow the outer `m`, need to report ambiguity error
+        //     m::mac!();
+        // }
+        // So we have to save the innermost solution and continue searching in outer scopes
+        // to detect potential ambiguities.
+        let mut innermost_result: Option<(&NameBinding<'_>, Flags)> = None;
+        let mut determinacy = Determinacy::Determined;
+
+        // Go through all the scopes and try to resolve the name.
+        let break_result = self.visit_scopes(
+            scope_set,
+            parent_scope,
+            orig_ident.span.ctxt(),
+            |this, scope, use_prelude, ctxt| {
+                let ident = Ident::new(orig_ident.name, orig_ident.span.with_ctxt(ctxt));
+                let ok = |res, span, arenas| {
+                    Ok((
+                        (res, ty::Visibility::Public, span, LocalExpnId::ROOT)
+                            .to_name_binding(arenas),
+                        Flags::empty(),
+                    ))
+                };
+                let result = match scope {
+                    Scope::DeriveHelpers(expn_id) => {
+                        if let Some(attr) = this
+                            .helper_attrs
+                            .get(&expn_id)
+                            .and_then(|attrs| attrs.iter().rfind(|i| ident == **i))
+                        {
+                            let binding = (
+                                Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
+                                ty::Visibility::Public,
+                                attr.span,
+                                expn_id,
+                            )
+                                .to_name_binding(this.arenas);
+                            Ok((binding, Flags::empty()))
+                        } else {
+                            Err(Determinacy::Determined)
+                        }
+                    }
+                    Scope::DeriveHelpersCompat => {
+                        let mut result = Err(Determinacy::Determined);
+                        for derive in parent_scope.derives {
+                            let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
+                            match this.resolve_macro_path(
+                                derive,
+                                Some(MacroKind::Derive),
+                                parent_scope,
+                                true,
+                                force,
+                            ) {
+                                Ok((Some(ext), _)) => {
+                                    if ext.helper_attrs.contains(&ident.name) {
+                                        result = ok(
+                                            Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat),
+                                            derive.span,
+                                            this.arenas,
+                                        );
+                                        break;
+                                    }
+                                }
+                                Ok(_) | Err(Determinacy::Determined) => {}
+                                Err(Determinacy::Undetermined) => {
+                                    result = Err(Determinacy::Undetermined)
+                                }
+                            }
+                        }
+                        result
+                    }
+                    Scope::MacroRules(macro_rules_scope) => match macro_rules_scope.get() {
+                        MacroRulesScope::Binding(macro_rules_binding)
+                            if ident == macro_rules_binding.ident =>
+                        {
+                            Ok((macro_rules_binding.binding, Flags::MACRO_RULES))
+                        }
+                        MacroRulesScope::Invocation(_) => Err(Determinacy::Undetermined),
+                        _ => Err(Determinacy::Determined),
+                    },
+                    Scope::CrateRoot => {
+                        let root_ident = Ident::new(kw::PathRoot, ident.span);
+                        let root_module = this.resolve_crate_root(root_ident);
+                        let binding = this.resolve_ident_in_module_ext(
+                            ModuleOrUniformRoot::Module(root_module),
+                            ident,
+                            ns,
+                            parent_scope,
+                            finalize,
+                            ignore_binding,
+                        );
+                        match binding {
+                            Ok(binding) => Ok((binding, Flags::MODULE | Flags::MISC_SUGGEST_CRATE)),
+                            Err((Determinacy::Undetermined, Weak::No)) => {
+                                return Some(Err(Determinacy::determined(force)));
+                            }
+                            Err((Determinacy::Undetermined, Weak::Yes)) => {
+                                Err(Determinacy::Undetermined)
+                            }
+                            Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
+                        }
+                    }
+                    Scope::Module(module, derive_fallback_lint_id) => {
+                        let adjusted_parent_scope = &ParentScope { module, ..*parent_scope };
+                        let binding = this.resolve_ident_in_module_unadjusted_ext(
+                            ModuleOrUniformRoot::Module(module),
+                            ident,
+                            ns,
+                            adjusted_parent_scope,
+                            !matches!(scope_set, ScopeSet::Late(..)),
+                            finalize,
+                            ignore_binding,
+                        );
+                        match binding {
+                            Ok(binding) => {
+                                if let Some(lint_id) = derive_fallback_lint_id {
+                                    this.lint_buffer.buffer_lint_with_diagnostic(
+                                        PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
+                                        lint_id,
+                                        orig_ident.span,
+                                        &format!(
+                                            "cannot find {} `{}` in this scope",
+                                            ns.descr(),
+                                            ident
+                                        ),
+                                        BuiltinLintDiagnostics::ProcMacroDeriveResolutionFallback(
+                                            orig_ident.span,
+                                        ),
+                                    );
+                                }
+                                let misc_flags = if ptr::eq(module, this.graph_root) {
+                                    Flags::MISC_SUGGEST_CRATE
+                                } else if module.is_normal() {
+                                    Flags::MISC_SUGGEST_SELF
+                                } else {
+                                    Flags::empty()
+                                };
+                                Ok((binding, Flags::MODULE | misc_flags))
+                            }
+                            Err((Determinacy::Undetermined, Weak::No)) => {
+                                return Some(Err(Determinacy::determined(force)));
+                            }
+                            Err((Determinacy::Undetermined, Weak::Yes)) => {
+                                Err(Determinacy::Undetermined)
+                            }
+                            Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
+                        }
+                    }
+                    Scope::RegisteredAttrs => match this.registered_attrs.get(&ident).cloned() {
+                        Some(ident) => ok(
+                            Res::NonMacroAttr(NonMacroAttrKind::Registered),
+                            ident.span,
+                            this.arenas,
+                        ),
+                        None => Err(Determinacy::Determined),
+                    },
+                    Scope::MacroUsePrelude => {
+                        match this.macro_use_prelude.get(&ident.name).cloned() {
+                            Some(binding) => Ok((binding, Flags::MISC_FROM_PRELUDE)),
+                            None => Err(Determinacy::determined(
+                                this.graph_root.unexpanded_invocations.borrow().is_empty(),
+                            )),
+                        }
+                    }
+                    Scope::BuiltinAttrs => {
+                        if is_builtin_attr_name(ident.name) {
+                            ok(
+                                Res::NonMacroAttr(NonMacroAttrKind::Builtin(ident.name)),
+                                DUMMY_SP,
+                                this.arenas,
+                            )
+                        } else {
+                            Err(Determinacy::Determined)
+                        }
+                    }
+                    Scope::ExternPrelude => {
+                        match this.extern_prelude_get(ident, finalize.is_some()) {
+                            Some(binding) => Ok((binding, Flags::empty())),
+                            None => Err(Determinacy::determined(
+                                this.graph_root.unexpanded_invocations.borrow().is_empty(),
+                            )),
+                        }
+                    }
+                    Scope::ToolPrelude => match this.registered_tools.get(&ident).cloned() {
+                        Some(ident) => ok(Res::ToolMod, ident.span, this.arenas),
+                        None => Err(Determinacy::Determined),
+                    },
+                    Scope::StdLibPrelude => {
+                        let mut result = Err(Determinacy::Determined);
+                        if let Some(prelude) = this.prelude {
+                            if let Ok(binding) = this.resolve_ident_in_module_unadjusted(
+                                ModuleOrUniformRoot::Module(prelude),
+                                ident,
+                                ns,
+                                parent_scope,
+                                None,
+                                ignore_binding,
+                            ) {
+                                if use_prelude || this.is_builtin_macro(binding.res()) {
+                                    result = Ok((binding, Flags::MISC_FROM_PRELUDE));
+                                }
+                            }
+                        }
+                        result
+                    }
+                    Scope::BuiltinTypes => match PrimTy::from_name(ident.name) {
+                        Some(prim_ty) => ok(Res::PrimTy(prim_ty), DUMMY_SP, this.arenas),
+                        None => Err(Determinacy::Determined),
+                    },
+                };
+
+                match result {
+                    Ok((binding, flags))
+                        if sub_namespace_match(binding.macro_kind(), macro_kind) =>
+                    {
+                        if finalize.is_none() || matches!(scope_set, ScopeSet::Late(..)) {
+                            return Some(Ok(binding));
+                        }
+
+                        if let Some((innermost_binding, innermost_flags)) = innermost_result {
+                            // Found another solution, if the first one was "weak", report an error.
+                            let (res, innermost_res) = (binding.res(), innermost_binding.res());
+                            if res != innermost_res {
+                                let is_builtin = |res| {
+                                    matches!(res, Res::NonMacroAttr(NonMacroAttrKind::Builtin(..)))
+                                };
+                                let derive_helper =
+                                    Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
+                                let derive_helper_compat =
+                                    Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat);
+
+                                let ambiguity_error_kind = if is_import {
+                                    Some(AmbiguityKind::Import)
+                                } else if is_builtin(innermost_res) || is_builtin(res) {
+                                    Some(AmbiguityKind::BuiltinAttr)
+                                } else if innermost_res == derive_helper_compat
+                                    || res == derive_helper_compat && innermost_res != derive_helper
+                                {
+                                    Some(AmbiguityKind::DeriveHelper)
+                                } else if innermost_flags.contains(Flags::MACRO_RULES)
+                                    && flags.contains(Flags::MODULE)
+                                    && !this.disambiguate_macro_rules_vs_modularized(
+                                        innermost_binding,
+                                        binding,
+                                    )
+                                    || flags.contains(Flags::MACRO_RULES)
+                                        && innermost_flags.contains(Flags::MODULE)
+                                        && !this.disambiguate_macro_rules_vs_modularized(
+                                            binding,
+                                            innermost_binding,
+                                        )
+                                {
+                                    Some(AmbiguityKind::MacroRulesVsModularized)
+                                } else if innermost_binding.is_glob_import() {
+                                    Some(AmbiguityKind::GlobVsOuter)
+                                } else if innermost_binding
+                                    .may_appear_after(parent_scope.expansion, binding)
+                                {
+                                    Some(AmbiguityKind::MoreExpandedVsOuter)
+                                } else {
+                                    None
+                                };
+                                if let Some(kind) = ambiguity_error_kind {
+                                    let misc = |f: Flags| {
+                                        if f.contains(Flags::MISC_SUGGEST_CRATE) {
+                                            AmbiguityErrorMisc::SuggestCrate
+                                        } else if f.contains(Flags::MISC_SUGGEST_SELF) {
+                                            AmbiguityErrorMisc::SuggestSelf
+                                        } else if f.contains(Flags::MISC_FROM_PRELUDE) {
+                                            AmbiguityErrorMisc::FromPrelude
+                                        } else {
+                                            AmbiguityErrorMisc::None
+                                        }
+                                    };
+                                    this.ambiguity_errors.push(AmbiguityError {
+                                        kind,
+                                        ident: orig_ident,
+                                        b1: innermost_binding,
+                                        b2: binding,
+                                        misc1: misc(innermost_flags),
+                                        misc2: misc(flags),
+                                    });
+                                    return Some(Ok(innermost_binding));
+                                }
+                            }
+                        } else {
+                            // Found the first solution.
+                            innermost_result = Some((binding, flags));
+                        }
+                    }
+                    Ok(..) | Err(Determinacy::Determined) => {}
+                    Err(Determinacy::Undetermined) => determinacy = Determinacy::Undetermined,
+                }
+
+                None
+            },
+        );
+
+        if let Some(break_result) = break_result {
+            return break_result;
+        }
+
+        // The first found solution was the only one, return it.
+        if let Some((binding, _)) = innermost_result {
+            return Ok(binding);
+        }
+
+        Err(Determinacy::determined(determinacy == Determinacy::Determined || force))
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    pub(crate) fn maybe_resolve_ident_in_module(
+        &mut self,
+        module: ModuleOrUniformRoot<'a>,
+        ident: Ident,
+        ns: Namespace,
+        parent_scope: &ParentScope<'a>,
+    ) -> Result<&'a NameBinding<'a>, Determinacy> {
+        self.resolve_ident_in_module_ext(module, ident, ns, parent_scope, None, None)
+            .map_err(|(determinacy, _)| determinacy)
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    pub(crate) fn resolve_ident_in_module(
+        &mut self,
+        module: ModuleOrUniformRoot<'a>,
+        ident: Ident,
+        ns: Namespace,
+        parent_scope: &ParentScope<'a>,
+        finalize: Option<Finalize>,
+        ignore_binding: Option<&'a NameBinding<'a>>,
+    ) -> Result<&'a NameBinding<'a>, Determinacy> {
+        self.resolve_ident_in_module_ext(module, ident, ns, parent_scope, finalize, ignore_binding)
+            .map_err(|(determinacy, _)| determinacy)
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn resolve_ident_in_module_ext(
+        &mut self,
+        module: ModuleOrUniformRoot<'a>,
+        mut ident: Ident,
+        ns: Namespace,
+        parent_scope: &ParentScope<'a>,
+        finalize: Option<Finalize>,
+        ignore_binding: Option<&'a NameBinding<'a>>,
+    ) -> Result<&'a NameBinding<'a>, (Determinacy, Weak)> {
+        let tmp_parent_scope;
+        let mut adjusted_parent_scope = parent_scope;
+        match module {
+            ModuleOrUniformRoot::Module(m) => {
+                if let Some(def) = ident.span.normalize_to_macros_2_0_and_adjust(m.expansion) {
+                    tmp_parent_scope =
+                        ParentScope { module: self.expn_def_scope(def), ..*parent_scope };
+                    adjusted_parent_scope = &tmp_parent_scope;
+                }
+            }
+            ModuleOrUniformRoot::ExternPrelude => {
+                ident.span.normalize_to_macros_2_0_and_adjust(ExpnId::root());
+            }
+            ModuleOrUniformRoot::CrateRootAndExternPrelude | ModuleOrUniformRoot::CurrentScope => {
+                // No adjustments
+            }
+        }
+        self.resolve_ident_in_module_unadjusted_ext(
+            module,
+            ident,
+            ns,
+            adjusted_parent_scope,
+            false,
+            finalize,
+            ignore_binding,
+        )
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn resolve_ident_in_module_unadjusted(
+        &mut self,
+        module: ModuleOrUniformRoot<'a>,
+        ident: Ident,
+        ns: Namespace,
+        parent_scope: &ParentScope<'a>,
+        finalize: Option<Finalize>,
+        ignore_binding: Option<&'a NameBinding<'a>>,
+    ) -> Result<&'a NameBinding<'a>, Determinacy> {
+        self.resolve_ident_in_module_unadjusted_ext(
+            module,
+            ident,
+            ns,
+            parent_scope,
+            false,
+            finalize,
+            ignore_binding,
+        )
+        .map_err(|(determinacy, _)| determinacy)
+    }
+
+    /// Attempts to resolve `ident` in namespaces `ns` of `module`.
+    /// Invariant: if `finalize` is `Some`, expansion and import resolution must be complete.
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn resolve_ident_in_module_unadjusted_ext(
+        &mut self,
+        module: ModuleOrUniformRoot<'a>,
+        ident: Ident,
+        ns: Namespace,
+        parent_scope: &ParentScope<'a>,
+        restricted_shadowing: bool,
+        finalize: Option<Finalize>,
+        // This binding should be ignored during in-module resolution, so that we don't get
+        // "self-confirming" import resolutions during import validation and checking.
+        ignore_binding: Option<&'a NameBinding<'a>>,
+    ) -> Result<&'a NameBinding<'a>, (Determinacy, Weak)> {
+        let module = match module {
+            ModuleOrUniformRoot::Module(module) => module,
+            ModuleOrUniformRoot::CrateRootAndExternPrelude => {
+                assert!(!restricted_shadowing);
+                let binding = self.early_resolve_ident_in_lexical_scope(
+                    ident,
+                    ScopeSet::AbsolutePath(ns),
+                    parent_scope,
+                    finalize,
+                    finalize.is_some(),
+                    ignore_binding,
+                );
+                return binding.map_err(|determinacy| (determinacy, Weak::No));
+            }
+            ModuleOrUniformRoot::ExternPrelude => {
+                assert!(!restricted_shadowing);
+                return if ns != TypeNS {
+                    Err((Determined, Weak::No))
+                } else if let Some(binding) = self.extern_prelude_get(ident, finalize.is_some()) {
+                    Ok(binding)
+                } else if !self.graph_root.unexpanded_invocations.borrow().is_empty() {
+                    // Macro-expanded `extern crate` items can add names to extern prelude.
+                    Err((Undetermined, Weak::No))
+                } else {
+                    Err((Determined, Weak::No))
+                };
+            }
+            ModuleOrUniformRoot::CurrentScope => {
+                assert!(!restricted_shadowing);
+                if ns == TypeNS {
+                    if ident.name == kw::Crate || ident.name == kw::DollarCrate {
+                        let module = self.resolve_crate_root(ident);
+                        let binding =
+                            (module, ty::Visibility::Public, module.span, LocalExpnId::ROOT)
+                                .to_name_binding(self.arenas);
+                        return Ok(binding);
+                    } else if ident.name == kw::Super || ident.name == kw::SelfLower {
+                        // FIXME: Implement these with renaming requirements so that e.g.
+                        // `use super;` doesn't work, but `use super as name;` does.
+                        // Fall through here to get an error from `early_resolve_...`.
+                    }
+                }
+
+                let scopes = ScopeSet::All(ns, true);
+                let binding = self.early_resolve_ident_in_lexical_scope(
+                    ident,
+                    scopes,
+                    parent_scope,
+                    finalize,
+                    finalize.is_some(),
+                    ignore_binding,
+                );
+                return binding.map_err(|determinacy| (determinacy, Weak::No));
+            }
+        };
+
+        let key = self.new_key(ident, ns);
+        let resolution =
+            self.resolution(module, key).try_borrow_mut().map_err(|_| (Determined, Weak::No))?; // This happens when there is a cycle of imports.
+
+        if let Some(Finalize { path_span, report_private, .. }) = finalize {
+            // If the primary binding is unusable, search further and return the shadowed glob
+            // binding if it exists. What we really want here is having two separate scopes in
+            // a module - one for non-globs and one for globs, but until that's done use this
+            // hack to avoid inconsistent resolution ICEs during import validation.
+            let binding = [resolution.binding, resolution.shadowed_glob]
+                .into_iter()
+                .filter_map(|binding| match (binding, ignore_binding) {
+                    (Some(binding), Some(ignored)) if ptr::eq(binding, ignored) => None,
+                    _ => binding,
+                })
+                .next();
+            let Some(binding) = binding else {
+                return Err((Determined, Weak::No));
+            };
+
+            if !self.is_accessible_from(binding.vis, parent_scope.module) {
+                if report_private {
+                    self.privacy_errors.push(PrivacyError {
+                        ident,
+                        binding,
+                        dedup_span: path_span,
+                    });
+                } else {
+                    return Err((Determined, Weak::No));
+                }
+            }
+
+            // Forbid expanded shadowing to avoid time travel.
+            if let Some(shadowed_glob) = resolution.shadowed_glob
+                && restricted_shadowing
+                && binding.expansion != LocalExpnId::ROOT
+                && binding.res() != shadowed_glob.res()
+            {
+                self.ambiguity_errors.push(AmbiguityError {
+                    kind: AmbiguityKind::GlobVsExpanded,
+                    ident,
+                    b1: binding,
+                    b2: shadowed_glob,
+                    misc1: AmbiguityErrorMisc::None,
+                    misc2: AmbiguityErrorMisc::None,
+                });
+            }
+
+            if !restricted_shadowing && binding.expansion != LocalExpnId::ROOT {
+                if let NameBindingKind::Res(_, true) = binding.kind {
+                    self.macro_expanded_macro_export_errors.insert((path_span, binding.span));
+                }
+            }
+
+            self.record_use(ident, binding, restricted_shadowing);
+            return Ok(binding);
+        }
+
+        let check_usable = |this: &mut Self, binding: &'a NameBinding<'a>| {
+            if let Some(ignored) = ignore_binding && ptr::eq(binding, ignored) {
+                return Err((Determined, Weak::No));
+            }
+            let usable = this.is_accessible_from(binding.vis, parent_scope.module);
+            if usable { Ok(binding) } else { Err((Determined, Weak::No)) }
+        };
+
+        // Items and single imports are not shadowable, if we have one, then it's determined.
+        if let Some(binding) = resolution.binding {
+            if !binding.is_glob_import() {
+                return check_usable(self, binding);
+            }
+        }
+
+        // --- From now on we either have a glob resolution or no resolution. ---
+
+        // Check if one of single imports can still define the name,
+        // if it can then our result is not determined and can be invalidated.
+        for single_import in &resolution.single_imports {
+            if !self.is_accessible_from(single_import.vis.get(), parent_scope.module) {
+                continue;
+            }
+            let Some(module) = single_import.imported_module.get() else {
+                return Err((Undetermined, Weak::No));
+            };
+            let ImportKind::Single { source: ident, .. } = single_import.kind else {
+                unreachable!();
+            };
+            match self.resolve_ident_in_module(
+                module,
+                ident,
+                ns,
+                &single_import.parent_scope,
+                None,
+                ignore_binding,
+            ) {
+                Err(Determined) => continue,
+                Ok(binding)
+                    if !self.is_accessible_from(binding.vis, single_import.parent_scope.module) =>
+                {
+                    continue;
+                }
+                Ok(_) | Err(Undetermined) => return Err((Undetermined, Weak::No)),
+            }
+        }
+
+        // So we have a resolution that's from a glob import. This resolution is determined
+        // if it cannot be shadowed by some new item/import expanded from a macro.
+        // This happens either if there are no unexpanded macros, or expanded names cannot
+        // shadow globs (that happens in macro namespace or with restricted shadowing).
+        //
+        // Additionally, any macro in any module can plant names in the root module if it creates
+        // `macro_export` macros, so the root module effectively has unresolved invocations if any
+        // module has unresolved invocations.
+        // However, it causes resolution/expansion to stuck too often (#53144), so, to make
+        // progress, we have to ignore those potential unresolved invocations from other modules
+        // and prohibit access to macro-expanded `macro_export` macros instead (unless restricted
+        // shadowing is enabled, see `macro_expanded_macro_export_errors`).
+        let unexpanded_macros = !module.unexpanded_invocations.borrow().is_empty();
+        if let Some(binding) = resolution.binding {
+            if !unexpanded_macros || ns == MacroNS || restricted_shadowing {
+                return check_usable(self, binding);
+            } else {
+                return Err((Undetermined, Weak::No));
+            }
+        }
+
+        // --- From now on we have no resolution. ---
+
+        // Now we are in situation when new item/import can appear only from a glob or a macro
+        // expansion. With restricted shadowing names from globs and macro expansions cannot
+        // shadow names from outer scopes, so we can freely fallback from module search to search
+        // in outer scopes. For `early_resolve_ident_in_lexical_scope` to continue search in outer
+        // scopes we return `Undetermined` with `Weak::Yes`.
+
+        // Check if one of unexpanded macros can still define the name,
+        // if it can then our "no resolution" result is not determined and can be invalidated.
+        if unexpanded_macros {
+            return Err((Undetermined, Weak::Yes));
+        }
+
+        // Check if one of glob imports can still define the name,
+        // if it can then our "no resolution" result is not determined and can be invalidated.
+        for glob_import in module.globs.borrow().iter() {
+            if !self.is_accessible_from(glob_import.vis.get(), parent_scope.module) {
+                continue;
+            }
+            let module = match glob_import.imported_module.get() {
+                Some(ModuleOrUniformRoot::Module(module)) => module,
+                Some(_) => continue,
+                None => return Err((Undetermined, Weak::Yes)),
+            };
+            let tmp_parent_scope;
+            let (mut adjusted_parent_scope, mut ident) =
+                (parent_scope, ident.normalize_to_macros_2_0());
+            match ident.span.glob_adjust(module.expansion, glob_import.span) {
+                Some(Some(def)) => {
+                    tmp_parent_scope =
+                        ParentScope { module: self.expn_def_scope(def), ..*parent_scope };
+                    adjusted_parent_scope = &tmp_parent_scope;
+                }
+                Some(None) => {}
+                None => continue,
+            };
+            let result = self.resolve_ident_in_module_unadjusted(
+                ModuleOrUniformRoot::Module(module),
+                ident,
+                ns,
+                adjusted_parent_scope,
+                None,
+                ignore_binding,
+            );
+
+            match result {
+                Err(Determined) => continue,
+                Ok(binding)
+                    if !self.is_accessible_from(binding.vis, glob_import.parent_scope.module) =>
+                {
+                    continue;
+                }
+                Ok(_) | Err(Undetermined) => return Err((Undetermined, Weak::Yes)),
+            }
+        }
+
+        // No resolution and no one else can define the name - determinate error.
+        Err((Determined, Weak::No))
+    }
+
+    /// Validate a local resolution (from ribs).
+    #[tracing::instrument(level = "debug", skip(self, all_ribs))]
+    fn validate_res_from_ribs(
+        &mut self,
+        rib_index: usize,
+        rib_ident: Ident,
+        mut res: Res,
+        finalize: Option<Span>,
+        original_rib_ident_def: Ident,
+        all_ribs: &[Rib<'a>],
+    ) -> Res {
+        const CG_BUG_STR: &str = "min_const_generics resolve check didn't stop compilation";
+        debug!("validate_res_from_ribs({:?})", res);
+        let ribs = &all_ribs[rib_index + 1..];
+
+        // An invalid forward use of a generic parameter from a previous default.
+        if let ForwardGenericParamBanRibKind = all_ribs[rib_index].kind {
+            if let Some(span) = finalize {
+                let res_error = if rib_ident.name == kw::SelfUpper {
+                    ResolutionError::SelfInGenericParamDefault
+                } else {
+                    ResolutionError::ForwardDeclaredGenericParam
+                };
+                self.report_error(span, res_error);
+            }
+            assert_eq!(res, Res::Err);
+            return Res::Err;
+        }
+
+        match res {
+            Res::Local(_) => {
+                use ResolutionError::*;
+                let mut res_err = None;
+
+                for rib in ribs {
+                    match rib.kind {
+                        NormalRibKind
+                        | ClosureOrAsyncRibKind
+                        | ModuleRibKind(..)
+                        | MacroDefinition(..)
+                        | ForwardGenericParamBanRibKind => {
+                            // Nothing to do. Continue.
+                        }
+                        ItemRibKind(_) | FnItemRibKind | AssocItemRibKind => {
+                            // This was an attempt to access an upvar inside a
+                            // named function item. This is not allowed, so we
+                            // report an error.
+                            if let Some(span) = finalize {
+                                // We don't immediately trigger a resolve error, because
+                                // we want certain other resolution errors (namely those
+                                // emitted for `ConstantItemRibKind` below) to take
+                                // precedence.
+                                res_err = Some((span, CannotCaptureDynamicEnvironmentInFnItem));
+                            }
+                        }
+                        ConstantItemRibKind(_, item) => {
+                            // Still doesn't deal with upvars
+                            if let Some(span) = finalize {
+                                let (span, resolution_error) =
+                                    if let Some((ident, constant_item_kind)) = item {
+                                        let kind_str = match constant_item_kind {
+                                            ConstantItemKind::Const => "const",
+                                            ConstantItemKind::Static => "static",
+                                        };
+                                        (
+                                            span,
+                                            AttemptToUseNonConstantValueInConstant(
+                                                ident, "let", kind_str,
+                                            ),
+                                        )
+                                    } else {
+                                        (
+                                            rib_ident.span,
+                                            AttemptToUseNonConstantValueInConstant(
+                                                original_rib_ident_def,
+                                                "const",
+                                                "let",
+                                            ),
+                                        )
+                                    };
+                                self.report_error(span, resolution_error);
+                            }
+                            return Res::Err;
+                        }
+                        ConstParamTyRibKind => {
+                            if let Some(span) = finalize {
+                                self.report_error(span, ParamInTyOfConstParam(rib_ident.name));
+                            }
+                            return Res::Err;
+                        }
+                        InlineAsmSymRibKind => {
+                            if let Some(span) = finalize {
+                                self.report_error(span, InvalidAsmSym);
+                            }
+                            return Res::Err;
+                        }
+                    }
+                }
+                if let Some((span, res_err)) = res_err {
+                    self.report_error(span, res_err);
+                    return Res::Err;
+                }
+            }
+            Res::Def(DefKind::TyParam, _) | Res::SelfTy { .. } => {
+                for rib in ribs {
+                    let has_generic_params: HasGenericParams = match rib.kind {
+                        NormalRibKind
+                        | ClosureOrAsyncRibKind
+                        | AssocItemRibKind
+                        | ModuleRibKind(..)
+                        | MacroDefinition(..)
+                        | InlineAsmSymRibKind
+                        | ForwardGenericParamBanRibKind => {
+                            // Nothing to do. Continue.
+                            continue;
+                        }
+
+                        ConstantItemRibKind(trivial, _) => {
+                            let features = self.session.features_untracked();
+                            // HACK(min_const_generics): We currently only allow `N` or `{ N }`.
+                            if !(trivial == HasGenericParams::Yes || features.generic_const_exprs) {
+                                // HACK(min_const_generics): If we encounter `Self` in an anonymous constant
+                                // we can't easily tell if it's generic at this stage, so we instead remember
+                                // this and then enforce the self type to be concrete later on.
+                                if let Res::SelfTy { trait_, alias_to: Some((def, _)) } = res {
+                                    res = Res::SelfTy { trait_, alias_to: Some((def, true)) }
+                                } else {
+                                    if let Some(span) = finalize {
+                                        self.report_error(
+                                            span,
+                                            ResolutionError::ParamInNonTrivialAnonConst {
+                                                name: rib_ident.name,
+                                                is_type: true,
+                                            },
+                                        );
+                                        self.session.delay_span_bug(span, CG_BUG_STR);
+                                    }
+
+                                    return Res::Err;
+                                }
+                            }
+
+                            continue;
+                        }
+
+                        // This was an attempt to use a type parameter outside its scope.
+                        ItemRibKind(has_generic_params) => has_generic_params,
+                        FnItemRibKind => HasGenericParams::Yes,
+                        ConstParamTyRibKind => {
+                            if let Some(span) = finalize {
+                                self.report_error(
+                                    span,
+                                    ResolutionError::ParamInTyOfConstParam(rib_ident.name),
+                                );
+                            }
+                            return Res::Err;
+                        }
+                    };
+
+                    if let Some(span) = finalize {
+                        self.report_error(
+                            span,
+                            ResolutionError::GenericParamsFromOuterFunction(
+                                res,
+                                has_generic_params,
+                            ),
+                        );
+                    }
+                    return Res::Err;
+                }
+            }
+            Res::Def(DefKind::ConstParam, _) => {
+                let mut ribs = ribs.iter().peekable();
+                if let Some(Rib { kind: FnItemRibKind, .. }) = ribs.peek() {
+                    // When declaring const parameters inside function signatures, the first rib
+                    // is always a `FnItemRibKind`. In this case, we can skip it, to avoid it
+                    // (spuriously) conflicting with the const param.
+                    ribs.next();
+                }
+
+                for rib in ribs {
+                    let has_generic_params = match rib.kind {
+                        NormalRibKind
+                        | ClosureOrAsyncRibKind
+                        | AssocItemRibKind
+                        | ModuleRibKind(..)
+                        | MacroDefinition(..)
+                        | InlineAsmSymRibKind
+                        | ForwardGenericParamBanRibKind => continue,
+
+                        ConstantItemRibKind(trivial, _) => {
+                            let features = self.session.features_untracked();
+                            // HACK(min_const_generics): We currently only allow `N` or `{ N }`.
+                            if !(trivial == HasGenericParams::Yes || features.generic_const_exprs) {
+                                if let Some(span) = finalize {
+                                    self.report_error(
+                                        span,
+                                        ResolutionError::ParamInNonTrivialAnonConst {
+                                            name: rib_ident.name,
+                                            is_type: false,
+                                        },
+                                    );
+                                    self.session.delay_span_bug(span, CG_BUG_STR);
+                                }
+
+                                return Res::Err;
+                            }
+
+                            continue;
+                        }
+
+                        ItemRibKind(has_generic_params) => has_generic_params,
+                        FnItemRibKind => HasGenericParams::Yes,
+                        ConstParamTyRibKind => {
+                            if let Some(span) = finalize {
+                                self.report_error(
+                                    span,
+                                    ResolutionError::ParamInTyOfConstParam(rib_ident.name),
+                                );
+                            }
+                            return Res::Err;
+                        }
+                    };
+
+                    // This was an attempt to use a const parameter outside its scope.
+                    if let Some(span) = finalize {
+                        self.report_error(
+                            span,
+                            ResolutionError::GenericParamsFromOuterFunction(
+                                res,
+                                has_generic_params,
+                            ),
+                        );
+                    }
+                    return Res::Err;
+                }
+            }
+            _ => {}
+        }
+        res
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    pub(crate) fn maybe_resolve_path(
+        &mut self,
+        path: &[Segment],
+        opt_ns: Option<Namespace>, // `None` indicates a module path in import
+        parent_scope: &ParentScope<'a>,
+    ) -> PathResult<'a> {
+        self.resolve_path_with_ribs(path, opt_ns, parent_scope, None, None, None)
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    pub(crate) fn resolve_path(
+        &mut self,
+        path: &[Segment],
+        opt_ns: Option<Namespace>, // `None` indicates a module path in import
+        parent_scope: &ParentScope<'a>,
+        finalize: Option<Finalize>,
+        ignore_binding: Option<&'a NameBinding<'a>>,
+    ) -> PathResult<'a> {
+        self.resolve_path_with_ribs(path, opt_ns, parent_scope, finalize, None, ignore_binding)
+    }
+
+    pub(crate) fn resolve_path_with_ribs(
+        &mut self,
+        path: &[Segment],
+        opt_ns: Option<Namespace>, // `None` indicates a module path in import
+        parent_scope: &ParentScope<'a>,
+        finalize: Option<Finalize>,
+        ribs: Option<&PerNS<Vec<Rib<'a>>>>,
+        ignore_binding: Option<&'a NameBinding<'a>>,
+    ) -> PathResult<'a> {
+        debug!("resolve_path(path={:?}, opt_ns={:?}, finalize={:?})", path, opt_ns, finalize);
+
+        let mut module = None;
+        let mut allow_super = true;
+        let mut second_binding = None;
+
+        for (i, &Segment { ident, id, .. }) in path.iter().enumerate() {
+            debug!("resolve_path ident {} {:?} {:?}", i, ident, id);
+            let record_segment_res = |this: &mut Self, res| {
+                if finalize.is_some() {
+                    if let Some(id) = id {
+                        if !this.partial_res_map.contains_key(&id) {
+                            assert!(id != ast::DUMMY_NODE_ID, "Trying to resolve dummy id");
+                            this.record_partial_res(id, PartialRes::new(res));
+                        }
+                    }
+                }
+            };
+
+            let is_last = i == path.len() - 1;
+            let ns = if is_last { opt_ns.unwrap_or(TypeNS) } else { TypeNS };
+            let name = ident.name;
+
+            allow_super &= ns == TypeNS && (name == kw::SelfLower || name == kw::Super);
+
+            if ns == TypeNS {
+                if allow_super && name == kw::Super {
+                    let mut ctxt = ident.span.ctxt().normalize_to_macros_2_0();
+                    let self_module = match i {
+                        0 => Some(self.resolve_self(&mut ctxt, parent_scope.module)),
+                        _ => match module {
+                            Some(ModuleOrUniformRoot::Module(module)) => Some(module),
+                            _ => None,
+                        },
+                    };
+                    if let Some(self_module) = self_module {
+                        if let Some(parent) = self_module.parent {
+                            module = Some(ModuleOrUniformRoot::Module(
+                                self.resolve_self(&mut ctxt, parent),
+                            ));
+                            continue;
+                        }
+                    }
+                    return PathResult::failed(ident.span, false, finalize.is_some(), || {
+                        ("there are too many leading `super` keywords".to_string(), None)
+                    });
+                }
+                if i == 0 {
+                    if name == kw::SelfLower {
+                        let mut ctxt = ident.span.ctxt().normalize_to_macros_2_0();
+                        module = Some(ModuleOrUniformRoot::Module(
+                            self.resolve_self(&mut ctxt, parent_scope.module),
+                        ));
+                        continue;
+                    }
+                    if name == kw::PathRoot && ident.span.rust_2018() {
+                        module = Some(ModuleOrUniformRoot::ExternPrelude);
+                        continue;
+                    }
+                    if name == kw::PathRoot && ident.span.rust_2015() && self.session.rust_2018() {
+                        // `::a::b` from 2015 macro on 2018 global edition
+                        module = Some(ModuleOrUniformRoot::CrateRootAndExternPrelude);
+                        continue;
+                    }
+                    if name == kw::PathRoot || name == kw::Crate || name == kw::DollarCrate {
+                        // `::a::b`, `crate::a::b` or `$crate::a::b`
+                        module = Some(ModuleOrUniformRoot::Module(self.resolve_crate_root(ident)));
+                        continue;
+                    }
+                }
+            }
+
+            // Report special messages for path segment keywords in wrong positions.
+            if ident.is_path_segment_keyword() && i != 0 {
+                return PathResult::failed(ident.span, false, finalize.is_some(), || {
+                    let name_str = if name == kw::PathRoot {
+                        "crate root".to_string()
+                    } else {
+                        format!("`{}`", name)
+                    };
+                    let label = if i == 1 && path[0].ident.name == kw::PathRoot {
+                        format!("global paths cannot start with {}", name_str)
+                    } else {
+                        format!("{} in paths can only be used in start position", name_str)
+                    };
+                    (label, None)
+                });
+            }
+
+            enum FindBindingResult<'a> {
+                Binding(Result<&'a NameBinding<'a>, Determinacy>),
+                Res(Res),
+            }
+            let find_binding_in_ns = |this: &mut Self, ns| {
+                let binding = if let Some(module) = module {
+                    this.resolve_ident_in_module(
+                        module,
+                        ident,
+                        ns,
+                        parent_scope,
+                        finalize,
+                        ignore_binding,
+                    )
+                } else if let Some(ribs) = ribs
+                    && let Some(TypeNS | ValueNS) = opt_ns
+                {
+                    match this.resolve_ident_in_lexical_scope(
+                        ident,
+                        ns,
+                        parent_scope,
+                        finalize,
+                        &ribs[ns],
+                        ignore_binding,
+                    ) {
+                        // we found a locally-imported or available item/module
+                        Some(LexicalScopeBinding::Item(binding)) => Ok(binding),
+                        // we found a local variable or type param
+                        Some(LexicalScopeBinding::Res(res)) => return FindBindingResult::Res(res),
+                        _ => Err(Determinacy::determined(finalize.is_some())),
+                    }
+                } else {
+                    let scopes = ScopeSet::All(ns, opt_ns.is_none());
+                    this.early_resolve_ident_in_lexical_scope(
+                        ident,
+                        scopes,
+                        parent_scope,
+                        finalize,
+                        finalize.is_some(),
+                        ignore_binding,
+                    )
+                };
+                FindBindingResult::Binding(binding)
+            };
+            let binding = match find_binding_in_ns(self, ns) {
+                FindBindingResult::Res(res) => {
+                    record_segment_res(self, res);
+                    return PathResult::NonModule(PartialRes::with_unresolved_segments(
+                        res,
+                        path.len() - 1,
+                    ));
+                }
+                FindBindingResult::Binding(binding) => binding,
+            };
+            match binding {
+                Ok(binding) => {
+                    if i == 1 {
+                        second_binding = Some(binding);
+                    }
+                    let res = binding.res();
+                    let maybe_assoc = opt_ns != Some(MacroNS) && PathSource::Type.is_expected(res);
+                    if let Some(next_module) = binding.module() {
+                        module = Some(ModuleOrUniformRoot::Module(next_module));
+                        record_segment_res(self, res);
+                    } else if res == Res::ToolMod && i + 1 != path.len() {
+                        if binding.is_import() {
+                            self.session
+                                .struct_span_err(
+                                    ident.span,
+                                    "cannot use a tool module through an import",
+                                )
+                                .span_note(binding.span, "the tool module imported here")
+                                .emit();
+                        }
+                        let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
+                        return PathResult::NonModule(PartialRes::new(res));
+                    } else if res == Res::Err {
+                        return PathResult::NonModule(PartialRes::new(Res::Err));
+                    } else if opt_ns.is_some() && (is_last || maybe_assoc) {
+                        self.lint_if_path_starts_with_module(finalize, path, second_binding);
+                        record_segment_res(self, res);
+                        return PathResult::NonModule(PartialRes::with_unresolved_segments(
+                            res,
+                            path.len() - i - 1,
+                        ));
+                    } else {
+                        return PathResult::failed(ident.span, is_last, finalize.is_some(), || {
+                            let label = format!(
+                                "`{ident}` is {} {}, not a module",
+                                res.article(),
+                                res.descr()
+                            );
+                            (label, None)
+                        });
+                    }
+                }
+                Err(Undetermined) => return PathResult::Indeterminate,
+                Err(Determined) => {
+                    if let Some(ModuleOrUniformRoot::Module(module)) = module {
+                        if opt_ns.is_some() && !module.is_normal() {
+                            return PathResult::NonModule(PartialRes::with_unresolved_segments(
+                                module.res().unwrap(),
+                                path.len() - i,
+                            ));
+                        }
+                    }
+
+                    return PathResult::failed(ident.span, is_last, finalize.is_some(), || {
+                        self.report_path_resolution_error(
+                            path,
+                            opt_ns,
+                            parent_scope,
+                            ribs,
+                            ignore_binding,
+                            module,
+                            i,
+                            ident,
+                        )
+                    });
+                }
+            }
+        }
+
+        self.lint_if_path_starts_with_module(finalize, path, second_binding);
+
+        PathResult::Module(match module {
+            Some(module) => module,
+            None if path.is_empty() => ModuleOrUniformRoot::CurrentScope,
+            _ => bug!("resolve_path: non-empty path `{:?}` has no module", path),
+        })
+    }
+}
diff --git a/compiler/rustc_resolve/src/imports.rs b/compiler/rustc_resolve/src/imports.rs
new file mode 100644
index 000000000..b89273990
--- /dev/null
+++ b/compiler/rustc_resolve/src/imports.rs
@@ -0,0 +1,1151 @@
+//! A bunch of methods and structures more or less related to resolving imports.
+
+use crate::diagnostics::Suggestion;
+use crate::Determinacy::{self, *};
+use crate::Namespace::{MacroNS, TypeNS};
+use crate::{module_to_string, names_to_string};
+use crate::{AmbiguityKind, BindingKey, ModuleKind, ResolutionError, Resolver, Segment};
+use crate::{Finalize, Module, ModuleOrUniformRoot, ParentScope, PerNS, ScopeSet};
+use crate::{NameBinding, NameBindingKind, PathResult};
+
+use rustc_ast::NodeId;
+use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::intern::Interned;
+use rustc_errors::{pluralize, struct_span_err, Applicability, MultiSpan};
+use rustc_hir::def::{self, DefKind, PartialRes};
+use rustc_middle::metadata::ModChild;
+use rustc_middle::span_bug;
+use rustc_middle::ty;
+use rustc_session::lint::builtin::{PUB_USE_OF_PRIVATE_EXTERN_CRATE, UNUSED_IMPORTS};
+use rustc_session::lint::BuiltinLintDiagnostics;
+use rustc_span::hygiene::LocalExpnId;
+use rustc_span::lev_distance::find_best_match_for_name;
+use rustc_span::symbol::{kw, Ident, Symbol};
+use rustc_span::Span;
+
+use tracing::*;
+
+use std::cell::Cell;
+use std::{mem, ptr};
+
+type Res = def::Res<NodeId>;
+
+/// Contains data for specific kinds of imports.
+#[derive(Clone, Debug)]
+pub enum ImportKind<'a> {
+    Single {
+        /// `source` in `use prefix::source as target`.
+        source: Ident,
+        /// `target` in `use prefix::source as target`.
+        target: Ident,
+        /// Bindings to which `source` refers to.
+        source_bindings: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
+        /// Bindings introduced by `target`.
+        target_bindings: PerNS<Cell<Option<&'a NameBinding<'a>>>>,
+        /// `true` for `...::{self [as target]}` imports, `false` otherwise.
+        type_ns_only: bool,
+        /// Did this import result from a nested import? ie. `use foo::{bar, baz};`
+        nested: bool,
+        /// Additional `NodeId`s allocated to a `ast::UseTree` for automatically generated `use` statement
+        /// (eg. implicit struct constructors)
+        additional_ids: (NodeId, NodeId),
+    },
+    Glob {
+        is_prelude: bool,
+        max_vis: Cell<ty::Visibility>, // The visibility of the greatest re-export.
+                                       // n.b. `max_vis` is only used in `finalize_import` to check for re-export errors.
+    },
+    ExternCrate {
+        source: Option<Symbol>,
+        target: Ident,
+    },
+    MacroUse,
+}
+
+/// One import.
+#[derive(Debug, Clone)]
+pub(crate) struct Import<'a> {
+    pub kind: ImportKind<'a>,
+
+    /// The ID of the `extern crate`, `UseTree` etc that imported this `Import`.
+    ///
+    /// In the case where the `Import` was expanded from a "nested" use tree,
+    /// this id is the ID of the leaf tree. For example:
+    ///
+    /// ```ignore (pacify the merciless tidy)
+    /// use foo::bar::{a, b}
+    /// ```
+    ///
+    /// If this is the import for `foo::bar::a`, we would have the ID of the `UseTree`
+    /// for `a` in this field.
+    pub id: NodeId,
+
+    /// The `id` of the "root" use-kind -- this is always the same as
+    /// `id` except in the case of "nested" use trees, in which case
+    /// it will be the `id` of the root use tree. e.g., in the example
+    /// from `id`, this would be the ID of the `use foo::bar`
+    /// `UseTree` node.
+    pub root_id: NodeId,
+
+    /// Span of the entire use statement.
+    pub use_span: Span,
+
+    /// Span of the entire use statement with attributes.
+    pub use_span_with_attributes: Span,
+
+    /// Did the use statement have any attributes?
+    pub has_attributes: bool,
+
+    /// Span of this use tree.
+    pub span: Span,
+
+    /// Span of the *root* use tree (see `root_id`).
+    pub root_span: Span,
+
+    pub parent_scope: ParentScope<'a>,
+    pub module_path: Vec<Segment>,
+    /// The resolution of `module_path`.
+    pub imported_module: Cell<Option<ModuleOrUniformRoot<'a>>>,
+    pub vis: Cell<ty::Visibility>,
+    pub used: Cell<bool>,
+}
+
+impl<'a> Import<'a> {
+    pub fn is_glob(&self) -> bool {
+        matches!(self.kind, ImportKind::Glob { .. })
+    }
+
+    pub fn is_nested(&self) -> bool {
+        match self.kind {
+            ImportKind::Single { nested, .. } => nested,
+            _ => false,
+        }
+    }
+}
+
+/// Records information about the resolution of a name in a namespace of a module.
+#[derive(Clone, Default, Debug)]
+pub(crate) struct NameResolution<'a> {
+    /// Single imports that may define the name in the namespace.
+    /// Imports are arena-allocated, so it's ok to use pointers as keys.
+    pub single_imports: FxHashSet<Interned<'a, Import<'a>>>,
+    /// The least shadowable known binding for this name, or None if there are no known bindings.
+    pub binding: Option<&'a NameBinding<'a>>,
+    pub shadowed_glob: Option<&'a NameBinding<'a>>,
+}
+
+impl<'a> NameResolution<'a> {
+    // Returns the binding for the name if it is known or None if it not known.
+    pub(crate) fn binding(&self) -> Option<&'a NameBinding<'a>> {
+        self.binding.and_then(|binding| {
+            if !binding.is_glob_import() || self.single_imports.is_empty() {
+                Some(binding)
+            } else {
+                None
+            }
+        })
+    }
+
+    pub(crate) fn add_single_import(&mut self, import: &'a Import<'a>) {
+        self.single_imports.insert(Interned::new_unchecked(import));
+    }
+}
+
+// Reexports of the form `pub use foo as bar;` where `foo` is `extern crate foo;`
+// are permitted for backward-compatibility under a deprecation lint.
+fn pub_use_of_private_extern_crate_hack(import: &Import<'_>, binding: &NameBinding<'_>) -> bool {
+    match (&import.kind, &binding.kind) {
+        (
+            ImportKind::Single { .. },
+            NameBindingKind::Import {
+                import: Import { kind: ImportKind::ExternCrate { .. }, .. },
+                ..
+            },
+        ) => import.vis.get().is_public(),
+        _ => false,
+    }
+}
+
+impl<'a> Resolver<'a> {
+    // Given a binding and an import that resolves to it,
+    // return the corresponding binding defined by the import.
+    pub(crate) fn import(
+        &self,
+        binding: &'a NameBinding<'a>,
+        import: &'a Import<'a>,
+    ) -> &'a NameBinding<'a> {
+        let vis = if binding.vis.is_at_least(import.vis.get(), self)
+            || pub_use_of_private_extern_crate_hack(import, binding)
+        {
+            import.vis.get()
+        } else {
+            binding.vis
+        };
+
+        if let ImportKind::Glob { ref max_vis, .. } = import.kind {
+            if vis == import.vis.get() || vis.is_at_least(max_vis.get(), self) {
+                max_vis.set(vis)
+            }
+        }
+
+        self.arenas.alloc_name_binding(NameBinding {
+            kind: NameBindingKind::Import { binding, import, used: Cell::new(false) },
+            ambiguity: None,
+            span: import.span,
+            vis,
+            expansion: import.parent_scope.expansion,
+        })
+    }
+
+    // Define the name or return the existing binding if there is a collision.
+    pub(crate) fn try_define(
+        &mut self,
+        module: Module<'a>,
+        key: BindingKey,
+        binding: &'a NameBinding<'a>,
+    ) -> Result<(), &'a NameBinding<'a>> {
+        let res = binding.res();
+        self.check_reserved_macro_name(key.ident, res);
+        self.set_binding_parent_module(binding, module);
+        self.update_resolution(module, key, |this, resolution| {
+            if let Some(old_binding) = resolution.binding {
+                if res == Res::Err {
+                    // Do not override real bindings with `Res::Err`s from error recovery.
+                    return Ok(());
+                }
+                match (old_binding.is_glob_import(), binding.is_glob_import()) {
+                    (true, true) => {
+                        if res != old_binding.res() {
+                            resolution.binding = Some(this.ambiguity(
+                                AmbiguityKind::GlobVsGlob,
+                                old_binding,
+                                binding,
+                            ));
+                        } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
+                            // We are glob-importing the same item but with greater visibility.
+                            resolution.binding = Some(binding);
+                        }
+                    }
+                    (old_glob @ true, false) | (old_glob @ false, true) => {
+                        let (glob_binding, nonglob_binding) =
+                            if old_glob { (old_binding, binding) } else { (binding, old_binding) };
+                        if glob_binding.res() != nonglob_binding.res()
+                            && key.ns == MacroNS
+                            && nonglob_binding.expansion != LocalExpnId::ROOT
+                        {
+                            resolution.binding = Some(this.ambiguity(
+                                AmbiguityKind::GlobVsExpanded,
+                                nonglob_binding,
+                                glob_binding,
+                            ));
+                        } else {
+                            resolution.binding = Some(nonglob_binding);
+                        }
+                        resolution.shadowed_glob = Some(glob_binding);
+                    }
+                    (false, false) => {
+                        return Err(old_binding);
+                    }
+                }
+            } else {
+                resolution.binding = Some(binding);
+            }
+
+            Ok(())
+        })
+    }
+
+    fn ambiguity(
+        &self,
+        kind: AmbiguityKind,
+        primary_binding: &'a NameBinding<'a>,
+        secondary_binding: &'a NameBinding<'a>,
+    ) -> &'a NameBinding<'a> {
+        self.arenas.alloc_name_binding(NameBinding {
+            ambiguity: Some((secondary_binding, kind)),
+            ..primary_binding.clone()
+        })
+    }
+
+    // Use `f` to mutate the resolution of the name in the module.
+    // If the resolution becomes a success, define it in the module's glob importers.
+    fn update_resolution<T, F>(&mut self, module: Module<'a>, key: BindingKey, f: F) -> T
+    where
+        F: FnOnce(&mut Resolver<'a>, &mut NameResolution<'a>) -> T,
+    {
+        // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
+        // during which the resolution might end up getting re-defined via a glob cycle.
+        let (binding, t) = {
+            let resolution = &mut *self.resolution(module, key).borrow_mut();
+            let old_binding = resolution.binding();
+
+            let t = f(self, resolution);
+
+            match resolution.binding() {
+                _ if old_binding.is_some() => return t,
+                None => return t,
+                Some(binding) => match old_binding {
+                    Some(old_binding) if ptr::eq(old_binding, binding) => return t,
+                    _ => (binding, t),
+                },
+            }
+        };
+
+        // Define `binding` in `module`s glob importers.
+        for import in module.glob_importers.borrow_mut().iter() {
+            let mut ident = key.ident;
+            let scope = match ident.span.reverse_glob_adjust(module.expansion, import.span) {
+                Some(Some(def)) => self.expn_def_scope(def),
+                Some(None) => import.parent_scope.module,
+                None => continue,
+            };
+            if self.is_accessible_from(binding.vis, scope) {
+                let imported_binding = self.import(binding, import);
+                let key = BindingKey { ident, ..key };
+                let _ = self.try_define(import.parent_scope.module, key, imported_binding);
+            }
+        }
+
+        t
+    }
+
+    // Define a dummy resolution containing a `Res::Err` as a placeholder for a failed resolution,
+    // also mark such failed imports as used to avoid duplicate diagnostics.
+    fn import_dummy_binding(&mut self, import: &'a Import<'a>) {
+        if let ImportKind::Single { target, ref target_bindings, .. } = import.kind {
+            if target_bindings.iter().any(|binding| binding.get().is_some()) {
+                return; // Has resolution, do not create the dummy binding
+            }
+            let dummy_binding = self.dummy_binding;
+            let dummy_binding = self.import(dummy_binding, import);
+            self.per_ns(|this, ns| {
+                let key = this.new_key(target, ns);
+                let _ = this.try_define(import.parent_scope.module, key, dummy_binding);
+            });
+            self.record_use(target, dummy_binding, false);
+        } else if import.imported_module.get().is_none() {
+            import.used.set(true);
+            self.used_imports.insert(import.id);
+        }
+    }
+}
+
+/// An error that may be transformed into a diagnostic later. Used to combine multiple unresolved
+/// import errors within the same use tree into a single diagnostic.
+#[derive(Debug, Clone)]
+struct UnresolvedImportError {
+    span: Span,
+    label: Option<String>,
+    note: Option<String>,
+    suggestion: Option<Suggestion>,
+}
+
+pub struct ImportResolver<'a, 'b> {
+    pub r: &'a mut Resolver<'b>,
+}
+
+impl<'a, 'b> ImportResolver<'a, 'b> {
+    // Import resolution
+    //
+    // This is a fixed-point algorithm. We resolve imports until our efforts
+    // are stymied by an unresolved import; then we bail out of the current
+    // module and continue. We terminate successfully once no more imports
+    // remain or unsuccessfully when no forward progress in resolving imports
+    // is made.
+
+    /// Resolves all imports for the crate. This method performs the fixed-
+    /// point iteration.
+    pub fn resolve_imports(&mut self) {
+        let mut prev_num_indeterminates = self.r.indeterminate_imports.len() + 1;
+        while self.r.indeterminate_imports.len() < prev_num_indeterminates {
+            prev_num_indeterminates = self.r.indeterminate_imports.len();
+            for import in mem::take(&mut self.r.indeterminate_imports) {
+                match self.resolve_import(&import) {
+                    true => self.r.determined_imports.push(import),
+                    false => self.r.indeterminate_imports.push(import),
+                }
+            }
+        }
+    }
+
+    pub fn finalize_imports(&mut self) {
+        for module in self.r.arenas.local_modules().iter() {
+            self.finalize_resolutions_in(module);
+        }
+
+        let mut seen_spans = FxHashSet::default();
+        let mut errors = vec![];
+        let mut prev_root_id: NodeId = NodeId::from_u32(0);
+        let determined_imports = mem::take(&mut self.r.determined_imports);
+        let indeterminate_imports = mem::take(&mut self.r.indeterminate_imports);
+
+        for (is_indeterminate, import) in determined_imports
+            .into_iter()
+            .map(|i| (false, i))
+            .chain(indeterminate_imports.into_iter().map(|i| (true, i)))
+        {
+            let unresolved_import_error = self.finalize_import(import);
+
+            // If this import is unresolved then create a dummy import
+            // resolution for it so that later resolve stages won't complain.
+            self.r.import_dummy_binding(import);
+
+            if let Some(err) = unresolved_import_error {
+                if let ImportKind::Single { source, ref source_bindings, .. } = import.kind {
+                    if source.name == kw::SelfLower {
+                        // Silence `unresolved import` error if E0429 is already emitted
+                        if let Err(Determined) = source_bindings.value_ns.get() {
+                            continue;
+                        }
+                    }
+                }
+
+                if prev_root_id.as_u32() != 0
+                    && prev_root_id.as_u32() != import.root_id.as_u32()
+                    && !errors.is_empty()
+                {
+                    // In the case of a new import line, throw a diagnostic message
+                    // for the previous line.
+                    self.throw_unresolved_import_error(errors, None);
+                    errors = vec![];
+                }
+                if seen_spans.insert(err.span) {
+                    let path = import_path_to_string(
+                        &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
+                        &import.kind,
+                        err.span,
+                    );
+                    errors.push((path, err));
+                    prev_root_id = import.root_id;
+                }
+            } else if is_indeterminate {
+                let path = import_path_to_string(
+                    &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
+                    &import.kind,
+                    import.span,
+                );
+                let err = UnresolvedImportError {
+                    span: import.span,
+                    label: None,
+                    note: None,
+                    suggestion: None,
+                };
+                if path.contains("::") {
+                    errors.push((path, err))
+                }
+            }
+        }
+
+        if !errors.is_empty() {
+            self.throw_unresolved_import_error(errors, None);
+        }
+    }
+
+    fn throw_unresolved_import_error(
+        &self,
+        errors: Vec<(String, UnresolvedImportError)>,
+        span: Option<MultiSpan>,
+    ) {
+        /// Upper limit on the number of `span_label` messages.
+        const MAX_LABEL_COUNT: usize = 10;
+
+        let (span, msg) = if errors.is_empty() {
+            (span.unwrap(), "unresolved import".to_string())
+        } else {
+            let span = MultiSpan::from_spans(errors.iter().map(|(_, err)| err.span).collect());
+
+            let paths = errors.iter().map(|(path, _)| format!("`{}`", path)).collect::<Vec<_>>();
+
+            let msg = format!("unresolved import{} {}", pluralize!(paths.len()), paths.join(", "),);
+
+            (span, msg)
+        };
+
+        let mut diag = struct_span_err!(self.r.session, span, E0432, "{}", &msg);
+
+        if let Some((_, UnresolvedImportError { note: Some(note), .. })) = errors.iter().last() {
+            diag.note(note);
+        }
+
+        for (_, err) in errors.into_iter().take(MAX_LABEL_COUNT) {
+            if let Some(label) = err.label {
+                diag.span_label(err.span, label);
+            }
+
+            if let Some((suggestions, msg, applicability)) = err.suggestion {
+                if suggestions.is_empty() {
+                    diag.help(&msg);
+                    continue;
+                }
+                diag.multipart_suggestion(&msg, suggestions, applicability);
+            }
+        }
+
+        diag.emit();
+    }
+
+    /// Attempts to resolve the given import, returning true if its resolution is determined.
+    /// If successful, the resolved bindings are written into the module.
+    fn resolve_import(&mut self, import: &'b Import<'b>) -> bool {
+        debug!(
+            "(resolving import for module) resolving import `{}::...` in `{}`",
+            Segment::names_to_string(&import.module_path),
+            module_to_string(import.parent_scope.module).unwrap_or_else(|| "???".to_string()),
+        );
+
+        let module = if let Some(module) = import.imported_module.get() {
+            module
+        } else {
+            // For better failure detection, pretend that the import will
+            // not define any names while resolving its module path.
+            let orig_vis = import.vis.replace(ty::Visibility::Invisible);
+            let path_res =
+                self.r.maybe_resolve_path(&import.module_path, None, &import.parent_scope);
+            import.vis.set(orig_vis);
+
+            match path_res {
+                PathResult::Module(module) => module,
+                PathResult::Indeterminate => return false,
+                PathResult::NonModule(..) | PathResult::Failed { .. } => return true,
+            }
+        };
+
+        import.imported_module.set(Some(module));
+        let (source, target, source_bindings, target_bindings, type_ns_only) = match import.kind {
+            ImportKind::Single {
+                source,
+                target,
+                ref source_bindings,
+                ref target_bindings,
+                type_ns_only,
+                ..
+            } => (source, target, source_bindings, target_bindings, type_ns_only),
+            ImportKind::Glob { .. } => {
+                self.resolve_glob_import(import);
+                return true;
+            }
+            _ => unreachable!(),
+        };
+
+        let mut indeterminate = false;
+        self.r.per_ns(|this, ns| {
+            if !type_ns_only || ns == TypeNS {
+                if let Err(Undetermined) = source_bindings[ns].get() {
+                    // For better failure detection, pretend that the import will
+                    // not define any names while resolving its module path.
+                    let orig_vis = import.vis.replace(ty::Visibility::Invisible);
+                    let binding = this.resolve_ident_in_module(
+                        module,
+                        source,
+                        ns,
+                        &import.parent_scope,
+                        None,
+                        None,
+                    );
+                    import.vis.set(orig_vis);
+                    source_bindings[ns].set(binding);
+                } else {
+                    return;
+                };
+
+                let parent = import.parent_scope.module;
+                match source_bindings[ns].get() {
+                    Err(Undetermined) => indeterminate = true,
+                    // Don't update the resolution, because it was never added.
+                    Err(Determined) if target.name == kw::Underscore => {}
+                    Ok(binding) if binding.is_importable() => {
+                        let imported_binding = this.import(binding, import);
+                        target_bindings[ns].set(Some(imported_binding));
+                        this.define(parent, target, ns, imported_binding);
+                    }
+                    source_binding @ (Ok(..) | Err(Determined)) => {
+                        if source_binding.is_ok() {
+                            let msg = format!("`{}` is not directly importable", target);
+                            struct_span_err!(this.session, import.span, E0253, "{}", &msg)
+                                .span_label(import.span, "cannot be imported directly")
+                                .emit();
+                        }
+                        let key = this.new_key(target, ns);
+                        this.update_resolution(parent, key, |_, resolution| {
+                            resolution.single_imports.remove(&Interned::new_unchecked(import));
+                        });
+                    }
+                }
+            }
+        });
+
+        !indeterminate
+    }
+
+    /// Performs final import resolution, consistency checks and error reporting.
+    ///
+    /// Optionally returns an unresolved import error. This error is buffered and used to
+    /// consolidate multiple unresolved import errors into a single diagnostic.
+    fn finalize_import(&mut self, import: &'b Import<'b>) -> Option<UnresolvedImportError> {
+        let orig_vis = import.vis.replace(ty::Visibility::Invisible);
+        let ignore_binding = match &import.kind {
+            ImportKind::Single { target_bindings, .. } => target_bindings[TypeNS].get(),
+            _ => None,
+        };
+        let prev_ambiguity_errors_len = self.r.ambiguity_errors.len();
+        let finalize = Finalize::with_root_span(import.root_id, import.span, import.root_span);
+        let path_res = self.r.resolve_path(
+            &import.module_path,
+            None,
+            &import.parent_scope,
+            Some(finalize),
+            ignore_binding,
+        );
+        let no_ambiguity = self.r.ambiguity_errors.len() == prev_ambiguity_errors_len;
+        import.vis.set(orig_vis);
+        let module = match path_res {
+            PathResult::Module(module) => {
+                // Consistency checks, analogous to `finalize_macro_resolutions`.
+                if let Some(initial_module) = import.imported_module.get() {
+                    if !ModuleOrUniformRoot::same_def(module, initial_module) && no_ambiguity {
+                        span_bug!(import.span, "inconsistent resolution for an import");
+                    }
+                } else if self.r.privacy_errors.is_empty() {
+                    let msg = "cannot determine resolution for the import";
+                    let msg_note = "import resolution is stuck, try simplifying other imports";
+                    self.r.session.struct_span_err(import.span, msg).note(msg_note).emit();
+                }
+
+                module
+            }
+            PathResult::Failed { is_error_from_last_segment: false, span, label, suggestion } => {
+                if no_ambiguity {
+                    assert!(import.imported_module.get().is_none());
+                    self.r
+                        .report_error(span, ResolutionError::FailedToResolve { label, suggestion });
+                }
+                return None;
+            }
+            PathResult::Failed { is_error_from_last_segment: true, span, label, suggestion } => {
+                if no_ambiguity {
+                    assert!(import.imported_module.get().is_none());
+                    let err = match self.make_path_suggestion(
+                        span,
+                        import.module_path.clone(),
+                        &import.parent_scope,
+                    ) {
+                        Some((suggestion, note)) => UnresolvedImportError {
+                            span,
+                            label: None,
+                            note,
+                            suggestion: Some((
+                                vec![(span, Segment::names_to_string(&suggestion))],
+                                String::from("a similar path exists"),
+                                Applicability::MaybeIncorrect,
+                            )),
+                        },
+                        None => UnresolvedImportError {
+                            span,
+                            label: Some(label),
+                            note: None,
+                            suggestion,
+                        },
+                    };
+                    return Some(err);
+                }
+                return None;
+            }
+            PathResult::NonModule(_) => {
+                if no_ambiguity {
+                    assert!(import.imported_module.get().is_none());
+                }
+                // The error was already reported earlier.
+                return None;
+            }
+            PathResult::Indeterminate => unreachable!(),
+        };
+
+        let (ident, target, source_bindings, target_bindings, type_ns_only) = match import.kind {
+            ImportKind::Single {
+                source,
+                target,
+                ref source_bindings,
+                ref target_bindings,
+                type_ns_only,
+                ..
+            } => (source, target, source_bindings, target_bindings, type_ns_only),
+            ImportKind::Glob { is_prelude, ref max_vis } => {
+                if import.module_path.len() <= 1 {
+                    // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
+                    // 2 segments, so the `resolve_path` above won't trigger it.
+                    let mut full_path = import.module_path.clone();
+                    full_path.push(Segment::from_ident(Ident::empty()));
+                    self.r.lint_if_path_starts_with_module(Some(finalize), &full_path, None);
+                }
+
+                if let ModuleOrUniformRoot::Module(module) = module {
+                    if ptr::eq(module, import.parent_scope.module) {
+                        // Importing a module into itself is not allowed.
+                        return Some(UnresolvedImportError {
+                            span: import.span,
+                            label: Some(String::from("cannot glob-import a module into itself")),
+                            note: None,
+                            suggestion: None,
+                        });
+                    }
+                }
+                if !is_prelude &&
+                   max_vis.get() != ty::Visibility::Invisible && // Allow empty globs.
+                   !max_vis.get().is_at_least(import.vis.get(), &*self.r)
+                {
+                    let msg = "glob import doesn't reexport anything because no candidate is public enough";
+                    self.r.lint_buffer.buffer_lint(UNUSED_IMPORTS, import.id, import.span, msg);
+                }
+                return None;
+            }
+            _ => unreachable!(),
+        };
+
+        let mut all_ns_err = true;
+        self.r.per_ns(|this, ns| {
+            if !type_ns_only || ns == TypeNS {
+                let orig_vis = import.vis.replace(ty::Visibility::Invisible);
+                let binding = this.resolve_ident_in_module(
+                    module,
+                    ident,
+                    ns,
+                    &import.parent_scope,
+                    Some(Finalize { report_private: false, ..finalize }),
+                    target_bindings[ns].get(),
+                );
+                import.vis.set(orig_vis);
+
+                match binding {
+                    Ok(binding) => {
+                        // Consistency checks, analogous to `finalize_macro_resolutions`.
+                        let initial_res = source_bindings[ns].get().map(|initial_binding| {
+                            all_ns_err = false;
+                            if let Some(target_binding) = target_bindings[ns].get() {
+                                if target.name == kw::Underscore
+                                    && initial_binding.is_extern_crate()
+                                    && !initial_binding.is_import()
+                                {
+                                    this.record_use(
+                                        ident,
+                                        target_binding,
+                                        import.module_path.is_empty(),
+                                    );
+                                }
+                            }
+                            initial_binding.res()
+                        });
+                        let res = binding.res();
+                        if let Ok(initial_res) = initial_res {
+                            if res != initial_res && this.ambiguity_errors.is_empty() {
+                                span_bug!(import.span, "inconsistent resolution for an import");
+                            }
+                        } else if res != Res::Err
+                            && this.ambiguity_errors.is_empty()
+                            && this.privacy_errors.is_empty()
+                        {
+                            let msg = "cannot determine resolution for the import";
+                            let msg_note =
+                                "import resolution is stuck, try simplifying other imports";
+                            this.session.struct_span_err(import.span, msg).note(msg_note).emit();
+                        }
+                    }
+                    Err(..) => {
+                        // FIXME: This assert may fire if public glob is later shadowed by a private
+                        // single import (see test `issue-55884-2.rs`). In theory single imports should
+                        // always block globs, even if they are not yet resolved, so that this kind of
+                        // self-inconsistent resolution never happens.
+                        // Re-enable the assert when the issue is fixed.
+                        // assert!(result[ns].get().is_err());
+                    }
+                }
+            }
+        });
+
+        if all_ns_err {
+            let mut all_ns_failed = true;
+            self.r.per_ns(|this, ns| {
+                if !type_ns_only || ns == TypeNS {
+                    let binding = this.resolve_ident_in_module(
+                        module,
+                        ident,
+                        ns,
+                        &import.parent_scope,
+                        Some(finalize),
+                        None,
+                    );
+                    if binding.is_ok() {
+                        all_ns_failed = false;
+                    }
+                }
+            });
+
+            return if all_ns_failed {
+                let resolutions = match module {
+                    ModuleOrUniformRoot::Module(module) => {
+                        Some(self.r.resolutions(module).borrow())
+                    }
+                    _ => None,
+                };
+                let resolutions = resolutions.as_ref().into_iter().flat_map(|r| r.iter());
+                let names = resolutions
+                    .filter_map(|(BindingKey { ident: i, .. }, resolution)| {
+                        if *i == ident {
+                            return None;
+                        } // Never suggest the same name
+                        match *resolution.borrow() {
+                            NameResolution { binding: Some(name_binding), .. } => {
+                                match name_binding.kind {
+                                    NameBindingKind::Import { binding, .. } => {
+                                        match binding.kind {
+                                            // Never suggest the name that has binding error
+                                            // i.e., the name that cannot be previously resolved
+                                            NameBindingKind::Res(Res::Err, _) => None,
+                                            _ => Some(i.name),
+                                        }
+                                    }
+                                    _ => Some(i.name),
+                                }
+                            }
+                            NameResolution { ref single_imports, .. }
+                                if single_imports.is_empty() =>
+                            {
+                                None
+                            }
+                            _ => Some(i.name),
+                        }
+                    })
+                    .collect::<Vec<Symbol>>();
+
+                let lev_suggestion =
+                    find_best_match_for_name(&names, ident.name, None).map(|suggestion| {
+                        (
+                            vec![(ident.span, suggestion.to_string())],
+                            String::from("a similar name exists in the module"),
+                            Applicability::MaybeIncorrect,
+                        )
+                    });
+
+                let (suggestion, note) =
+                    match self.check_for_module_export_macro(import, module, ident) {
+                        Some((suggestion, note)) => (suggestion.or(lev_suggestion), note),
+                        _ => (lev_suggestion, None),
+                    };
+
+                let label = match module {
+                    ModuleOrUniformRoot::Module(module) => {
+                        let module_str = module_to_string(module);
+                        if let Some(module_str) = module_str {
+                            format!("no `{}` in `{}`", ident, module_str)
+                        } else {
+                            format!("no `{}` in the root", ident)
+                        }
+                    }
+                    _ => {
+                        if !ident.is_path_segment_keyword() {
+                            format!("no external crate `{}`", ident)
+                        } else {
+                            // HACK(eddyb) this shows up for `self` & `super`, which
+                            // should work instead - for now keep the same error message.
+                            format!("no `{}` in the root", ident)
+                        }
+                    }
+                };
+
+                Some(UnresolvedImportError {
+                    span: import.span,
+                    label: Some(label),
+                    note,
+                    suggestion,
+                })
+            } else {
+                // `resolve_ident_in_module` reported a privacy error.
+                None
+            };
+        }
+
+        let mut reexport_error = None;
+        let mut any_successful_reexport = false;
+        let mut crate_private_reexport = false;
+        self.r.per_ns(|this, ns| {
+            if let Ok(binding) = source_bindings[ns].get() {
+                let vis = import.vis.get();
+                if !binding.vis.is_at_least(vis, &*this) {
+                    reexport_error = Some((ns, binding));
+                    if let ty::Visibility::Restricted(binding_def_id) = binding.vis {
+                        if binding_def_id.is_top_level_module() {
+                            crate_private_reexport = true;
+                        }
+                    }
+                } else {
+                    any_successful_reexport = true;
+                }
+            }
+        });
+
+        // All namespaces must be re-exported with extra visibility for an error to occur.
+        if !any_successful_reexport {
+            let (ns, binding) = reexport_error.unwrap();
+            if pub_use_of_private_extern_crate_hack(import, binding) {
+                let msg = format!(
+                    "extern crate `{}` is private, and cannot be \
+                                   re-exported (error E0365), consider declaring with \
+                                   `pub`",
+                    ident
+                );
+                self.r.lint_buffer.buffer_lint(
+                    PUB_USE_OF_PRIVATE_EXTERN_CRATE,
+                    import.id,
+                    import.span,
+                    &msg,
+                );
+            } else {
+                let error_msg = if crate_private_reexport {
+                    format!(
+                        "`{}` is only public within the crate, and cannot be re-exported outside",
+                        ident
+                    )
+                } else {
+                    format!("`{}` is private, and cannot be re-exported", ident)
+                };
+
+                if ns == TypeNS {
+                    let label_msg = if crate_private_reexport {
+                        format!("re-export of crate public `{}`", ident)
+                    } else {
+                        format!("re-export of private `{}`", ident)
+                    };
+
+                    struct_span_err!(self.r.session, import.span, E0365, "{}", error_msg)
+                        .span_label(import.span, label_msg)
+                        .note(&format!("consider declaring type or module `{}` with `pub`", ident))
+                        .emit();
+                } else {
+                    let mut err =
+                        struct_span_err!(self.r.session, import.span, E0364, "{error_msg}");
+                    match binding.kind {
+                        NameBindingKind::Res(Res::Def(DefKind::Macro(_), def_id), _)
+                            // exclude decl_macro
+                            if self.r.get_macro_by_def_id(def_id).macro_rules =>
+                        {
+                            err.span_help(
+                                binding.span,
+                                "consider adding a `#[macro_export]` to the macro in the imported module",
+                            );
+                        }
+                        _ => {
+                            err.span_note(
+                                import.span,
+                                &format!(
+                                    "consider marking `{ident}` as `pub` in the imported module"
+                                ),
+                            );
+                        }
+                    }
+                    err.emit();
+                }
+            }
+        }
+
+        if import.module_path.len() <= 1 {
+            // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
+            // 2 segments, so the `resolve_path` above won't trigger it.
+            let mut full_path = import.module_path.clone();
+            full_path.push(Segment::from_ident(ident));
+            self.r.per_ns(|this, ns| {
+                if let Ok(binding) = source_bindings[ns].get() {
+                    this.lint_if_path_starts_with_module(Some(finalize), &full_path, Some(binding));
+                }
+            });
+        }
+
+        // Record what this import resolves to for later uses in documentation,
+        // this may resolve to either a value or a type, but for documentation
+        // purposes it's good enough to just favor one over the other.
+        self.r.per_ns(|this, ns| {
+            if let Ok(binding) = source_bindings[ns].get() {
+                this.import_res_map.entry(import.id).or_default()[ns] = Some(binding.res());
+            }
+        });
+
+        self.check_for_redundant_imports(ident, import, source_bindings, target_bindings, target);
+
+        debug!("(resolving single import) successfully resolved import");
+        None
+    }
+
+    fn check_for_redundant_imports(
+        &mut self,
+        ident: Ident,
+        import: &'b Import<'b>,
+        source_bindings: &PerNS<Cell<Result<&'b NameBinding<'b>, Determinacy>>>,
+        target_bindings: &PerNS<Cell<Option<&'b NameBinding<'b>>>>,
+        target: Ident,
+    ) {
+        // Skip if the import was produced by a macro.
+        if import.parent_scope.expansion != LocalExpnId::ROOT {
+            return;
+        }
+
+        // Skip if we are inside a named module (in contrast to an anonymous
+        // module defined by a block).
+        if let ModuleKind::Def(..) = import.parent_scope.module.kind {
+            return;
+        }
+
+        let mut is_redundant = PerNS { value_ns: None, type_ns: None, macro_ns: None };
+
+        let mut redundant_span = PerNS { value_ns: None, type_ns: None, macro_ns: None };
+
+        self.r.per_ns(|this, ns| {
+            if let Ok(binding) = source_bindings[ns].get() {
+                if binding.res() == Res::Err {
+                    return;
+                }
+
+                match this.early_resolve_ident_in_lexical_scope(
+                    target,
+                    ScopeSet::All(ns, false),
+                    &import.parent_scope,
+                    None,
+                    false,
+                    target_bindings[ns].get(),
+                ) {
+                    Ok(other_binding) => {
+                        is_redundant[ns] = Some(
+                            binding.res() == other_binding.res() && !other_binding.is_ambiguity(),
+                        );
+                        redundant_span[ns] = Some((other_binding.span, other_binding.is_import()));
+                    }
+                    Err(_) => is_redundant[ns] = Some(false),
+                }
+            }
+        });
+
+        if !is_redundant.is_empty() && is_redundant.present_items().all(|is_redundant| is_redundant)
+        {
+            let mut redundant_spans: Vec<_> = redundant_span.present_items().collect();
+            redundant_spans.sort();
+            redundant_spans.dedup();
+            self.r.lint_buffer.buffer_lint_with_diagnostic(
+                UNUSED_IMPORTS,
+                import.id,
+                import.span,
+                &format!("the item `{}` is imported redundantly", ident),
+                BuiltinLintDiagnostics::RedundantImport(redundant_spans, ident),
+            );
+        }
+    }
+
+    fn resolve_glob_import(&mut self, import: &'b Import<'b>) {
+        let ModuleOrUniformRoot::Module(module) = import.imported_module.get().unwrap() else {
+            self.r.session.span_err(import.span, "cannot glob-import all possible crates");
+            return;
+        };
+
+        if module.is_trait() {
+            self.r.session.span_err(import.span, "items in traits are not importable");
+            return;
+        } else if ptr::eq(module, import.parent_scope.module) {
+            return;
+        } else if let ImportKind::Glob { is_prelude: true, .. } = import.kind {
+            self.r.prelude = Some(module);
+            return;
+        }
+
+        // Add to module's glob_importers
+        module.glob_importers.borrow_mut().push(import);
+
+        // Ensure that `resolutions` isn't borrowed during `try_define`,
+        // since it might get updated via a glob cycle.
+        let bindings = self
+            .r
+            .resolutions(module)
+            .borrow()
+            .iter()
+            .filter_map(|(key, resolution)| {
+                resolution.borrow().binding().map(|binding| (*key, binding))
+            })
+            .collect::<Vec<_>>();
+        for (mut key, binding) in bindings {
+            let scope = match key.ident.span.reverse_glob_adjust(module.expansion, import.span) {
+                Some(Some(def)) => self.r.expn_def_scope(def),
+                Some(None) => import.parent_scope.module,
+                None => continue,
+            };
+            if self.r.is_accessible_from(binding.vis, scope) {
+                let imported_binding = self.r.import(binding, import);
+                let _ = self.r.try_define(import.parent_scope.module, key, imported_binding);
+            }
+        }
+
+        // Record the destination of this import
+        self.r.record_partial_res(import.id, PartialRes::new(module.res().unwrap()));
+    }
+
+    // Miscellaneous post-processing, including recording re-exports,
+    // reporting conflicts, and reporting unresolved imports.
+    fn finalize_resolutions_in(&mut self, module: Module<'b>) {
+        // Since import resolution is finished, globs will not define any more names.
+        *module.globs.borrow_mut() = Vec::new();
+
+        if let Some(def_id) = module.opt_def_id() {
+            let mut reexports = Vec::new();
+
+            module.for_each_child(self.r, |_, ident, _, binding| {
+                // FIXME: Consider changing the binding inserted by `#[macro_export] macro_rules`
+                // into the crate root to actual `NameBindingKind::Import`.
+                if binding.is_import()
+                    || matches!(binding.kind, NameBindingKind::Res(_, _is_macro_export @ true))
+                {
+                    let res = binding.res().expect_non_local();
+                    // Ambiguous imports are treated as errors at this point and are
+                    // not exposed to other crates (see #36837 for more details).
+                    if res != def::Res::Err && !binding.is_ambiguity() {
+                        reexports.push(ModChild {
+                            ident,
+                            res,
+                            vis: binding.vis,
+                            span: binding.span,
+                            macro_rules: false,
+                        });
+                    }
+                }
+            });
+
+            if !reexports.is_empty() {
+                // Call to `expect_local` should be fine because current
+                // code is only called for local modules.
+                self.r.reexport_map.insert(def_id.expect_local(), reexports);
+            }
+        }
+    }
+}
+
+fn import_path_to_string(names: &[Ident], import_kind: &ImportKind<'_>, span: Span) -> String {
+    let pos = names.iter().position(|p| span == p.span && p.name != kw::PathRoot);
+    let global = !names.is_empty() && names[0].name == kw::PathRoot;
+    if let Some(pos) = pos {
+        let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
+        names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>())
+    } else {
+        let names = if global { &names[1..] } else { names };
+        if names.is_empty() {
+            import_kind_to_string(import_kind)
+        } else {
+            format!(
+                "{}::{}",
+                names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>()),
+                import_kind_to_string(import_kind),
+            )
+        }
+    }
+}
+
+fn import_kind_to_string(import_kind: &ImportKind<'_>) -> String {
+    match import_kind {
+        ImportKind::Single { source, .. } => source.to_string(),
+        ImportKind::Glob { .. } => "*".to_string(),
+        ImportKind::ExternCrate { .. } => "<extern crate>".to_string(),
+        ImportKind::MacroUse => "#[macro_use]".to_string(),
+    }
+}
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
new file mode 100644
index 000000000..dea3eaecd
--- /dev/null
+++ b/compiler/rustc_resolve/src/late.rs
@@ -0,0 +1,3984 @@
+// ignore-tidy-filelength
+//! "Late resolution" is the pass that resolves most of names in a crate beside imports and macros.
+//! It runs when the crate is fully expanded and its module structure is fully built.
+//! So it just walks through the crate and resolves all the expressions, types, etc.
+//!
+//! If you wonder why there's no `early.rs`, that's because it's split into three files -
+//! `build_reduced_graph.rs`, `macros.rs` and `imports.rs`.
+
+use RibKind::*;
+
+use crate::{path_names_to_string, BindingError, Finalize, LexicalScopeBinding};
+use crate::{Module, ModuleOrUniformRoot, NameBinding, ParentScope, PathResult};
+use crate::{ResolutionError, Resolver, Segment, UseError};
+
+use rustc_ast::ptr::P;
+use rustc_ast::visit::{self, AssocCtxt, BoundKind, FnCtxt, FnKind, Visitor};
+use rustc_ast::*;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
+use rustc_errors::DiagnosticId;
+use rustc_hir::def::Namespace::{self, *};
+use rustc_hir::def::{self, CtorKind, DefKind, LifetimeRes, PartialRes, PerNS};
+use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID};
+use rustc_hir::{PrimTy, TraitCandidate};
+use rustc_middle::middle::resolve_lifetime::Set1;
+use rustc_middle::ty::DefIdTree;
+use rustc_middle::{bug, span_bug};
+use rustc_session::lint;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::{BytePos, Span};
+use smallvec::{smallvec, SmallVec};
+
+use rustc_span::source_map::{respan, Spanned};
+use std::collections::{hash_map::Entry, BTreeSet};
+use std::mem::{replace, take};
+use tracing::debug;
+
+mod diagnostics;
+pub(crate) mod lifetimes;
+
+type Res = def::Res<NodeId>;
+
+type IdentMap<T> = FxHashMap<Ident, T>;
+
+/// Map from the name in a pattern to its binding mode.
+type BindingMap = IdentMap<BindingInfo>;
+
+use diagnostics::{
+    ElisionFnParameter, LifetimeElisionCandidate, MissingLifetime, MissingLifetimeKind,
+};
+
+#[derive(Copy, Clone, Debug)]
+struct BindingInfo {
+    span: Span,
+    binding_mode: BindingMode,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum PatternSource {
+    Match,
+    Let,
+    For,
+    FnParam,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+enum IsRepeatExpr {
+    No,
+    Yes,
+}
+
+impl PatternSource {
+    pub fn descr(self) -> &'static str {
+        match self {
+            PatternSource::Match => "match binding",
+            PatternSource::Let => "let binding",
+            PatternSource::For => "for binding",
+            PatternSource::FnParam => "function parameter",
+        }
+    }
+}
+
+/// Denotes whether the context for the set of already bound bindings is a `Product`
+/// or `Or` context. This is used in e.g., `fresh_binding` and `resolve_pattern_inner`.
+/// See those functions for more information.
+#[derive(PartialEq)]
+enum PatBoundCtx {
+    /// A product pattern context, e.g., `Variant(a, b)`.
+    Product,
+    /// An or-pattern context, e.g., `p_0 | ... | p_n`.
+    Or,
+}
+
+/// Does this the item (from the item rib scope) allow generic parameters?
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub(crate) enum HasGenericParams {
+    Yes,
+    No,
+}
+
+impl HasGenericParams {
+    fn force_yes_if(self, b: bool) -> Self {
+        if b { Self::Yes } else { self }
+    }
+}
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub(crate) enum ConstantItemKind {
+    Const,
+    Static,
+}
+
+/// The rib kind restricts certain accesses,
+/// e.g. to a `Res::Local` of an outer item.
+#[derive(Copy, Clone, Debug)]
+pub(crate) enum RibKind<'a> {
+    /// No restriction needs to be applied.
+    NormalRibKind,
+
+    /// We passed through an impl or trait and are now in one of its
+    /// methods or associated types. Allow references to ty params that impl or trait
+    /// binds. Disallow any other upvars (including other ty params that are
+    /// upvars).
+    AssocItemRibKind,
+
+    /// We passed through a closure. Disallow labels.
+    ClosureOrAsyncRibKind,
+
+    /// We passed through a function definition. Disallow upvars.
+    /// Permit only those const parameters that are specified in the function's generics.
+    FnItemRibKind,
+
+    /// We passed through an item scope. Disallow upvars.
+    ItemRibKind(HasGenericParams),
+
+    /// We're in a constant item. Can't refer to dynamic stuff.
+    ///
+    /// The item may reference generic parameters in trivial constant expressions.
+    /// All other constants aren't allowed to use generic params at all.
+    ConstantItemRibKind(HasGenericParams, Option<(Ident, ConstantItemKind)>),
+
+    /// We passed through a module.
+    ModuleRibKind(Module<'a>),
+
+    /// We passed through a `macro_rules!` statement
+    MacroDefinition(DefId),
+
+    /// All bindings in this rib are generic parameters that can't be used
+    /// from the default of a generic parameter because they're not declared
+    /// before said generic parameter. Also see the `visit_generics` override.
+    ForwardGenericParamBanRibKind,
+
+    /// We are inside of the type of a const parameter. Can't refer to any
+    /// parameters.
+    ConstParamTyRibKind,
+
+    /// We are inside a `sym` inline assembly operand. Can only refer to
+    /// globals.
+    InlineAsmSymRibKind,
+}
+
+impl RibKind<'_> {
+    /// Whether this rib kind contains generic parameters, as opposed to local
+    /// variables.
+    pub(crate) fn contains_params(&self) -> bool {
+        match self {
+            NormalRibKind
+            | ClosureOrAsyncRibKind
+            | FnItemRibKind
+            | ConstantItemRibKind(..)
+            | ModuleRibKind(_)
+            | MacroDefinition(_)
+            | ConstParamTyRibKind
+            | InlineAsmSymRibKind => false,
+            AssocItemRibKind | ItemRibKind(_) | ForwardGenericParamBanRibKind => true,
+        }
+    }
+
+    /// This rib forbids referring to labels defined in upwards ribs.
+    fn is_label_barrier(self) -> bool {
+        match self {
+            NormalRibKind | MacroDefinition(..) => false,
+
+            AssocItemRibKind
+            | ClosureOrAsyncRibKind
+            | FnItemRibKind
+            | ItemRibKind(..)
+            | ConstantItemRibKind(..)
+            | ModuleRibKind(..)
+            | ForwardGenericParamBanRibKind
+            | ConstParamTyRibKind
+            | InlineAsmSymRibKind => true,
+        }
+    }
+}
+
+/// A single local scope.
+///
+/// A rib represents a scope names can live in. Note that these appear in many places, not just
+/// around braces. At any place where the list of accessible names (of the given namespace)
+/// changes or a new restrictions on the name accessibility are introduced, a new rib is put onto a
+/// stack. This may be, for example, a `let` statement (because it introduces variables), a macro,
+/// etc.
+///
+/// Different [rib kinds](enum@RibKind) are transparent for different names.
+///
+/// The resolution keeps a separate stack of ribs as it traverses the AST for each namespace. When
+/// resolving, the name is looked up from inside out.
+#[derive(Debug)]
+pub(crate) struct Rib<'a, R = Res> {
+    pub bindings: IdentMap<R>,
+    pub kind: RibKind<'a>,
+}
+
+impl<'a, R> Rib<'a, R> {
+    fn new(kind: RibKind<'a>) -> Rib<'a, R> {
+        Rib { bindings: Default::default(), kind }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+enum LifetimeUseSet {
+    One { use_span: Span, use_ctxt: visit::LifetimeCtxt },
+    Many,
+}
+
+#[derive(Copy, Clone, Debug)]
+enum LifetimeRibKind {
+    /// This rib acts as a barrier to forbid reference to lifetimes of a parent item.
+    Item,
+
+    /// This rib declares generic parameters.
+    Generics { binder: NodeId, span: Span, kind: LifetimeBinderKind },
+
+    /// FIXME(const_generics): This patches over an ICE caused by non-'static lifetimes in const
+    /// generics. We are disallowing this until we can decide on how we want to handle non-'static
+    /// lifetimes in const generics. See issue #74052 for discussion.
+    ConstGeneric,
+
+    /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
+    /// This function will emit an error if `generic_const_exprs` is not enabled, the body identified by
+    /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
+    AnonConst,
+
+    /// Create a new anonymous lifetime parameter and reference it.
+    ///
+    /// If `report_in_path`, report an error when encountering lifetime elision in a path:
+    /// ```compile_fail
+    /// struct Foo<'a> { x: &'a () }
+    /// async fn foo(x: Foo) {}
+    /// ```
+    ///
+    /// Note: the error should not trigger when the elided lifetime is in a pattern or
+    /// expression-position path:
+    /// ```
+    /// struct Foo<'a> { x: &'a () }
+    /// async fn foo(Foo { x: _ }: Foo<'_>) {}
+    /// ```
+    AnonymousCreateParameter { binder: NodeId, report_in_path: bool },
+
+    /// Give a hard error when either `&` or `'_` is written. Used to
+    /// rule out things like `where T: Foo<'_>`. Does not imply an
+    /// error on default object bounds (e.g., `Box<dyn Foo>`).
+    AnonymousReportError,
+
+    /// Replace all anonymous lifetimes by provided lifetime.
+    Elided(LifetimeRes),
+
+    /// Signal we cannot find which should be the anonymous lifetime.
+    ElisionFailure,
+}
+
+#[derive(Copy, Clone, Debug)]
+enum LifetimeBinderKind {
+    BareFnType,
+    PolyTrait,
+    WhereBound,
+    Item,
+    Function,
+    Closure,
+    ImplBlock,
+}
+
+impl LifetimeBinderKind {
+    fn descr(self) -> &'static str {
+        use LifetimeBinderKind::*;
+        match self {
+            BareFnType => "type",
+            PolyTrait => "bound",
+            WhereBound => "bound",
+            Item => "item",
+            ImplBlock => "impl block",
+            Function => "function",
+            Closure => "closure",
+        }
+    }
+}
+
+#[derive(Debug)]
+struct LifetimeRib {
+    kind: LifetimeRibKind,
+    // We need to preserve insertion order for async fns.
+    bindings: FxIndexMap<Ident, (NodeId, LifetimeRes)>,
+}
+
+impl LifetimeRib {
+    fn new(kind: LifetimeRibKind) -> LifetimeRib {
+        LifetimeRib { bindings: Default::default(), kind }
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub(crate) enum AliasPossibility {
+    No,
+    Maybe,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub(crate) enum PathSource<'a> {
+    // Type paths `Path`.
+    Type,
+    // Trait paths in bounds or impls.
+    Trait(AliasPossibility),
+    // Expression paths `path`, with optional parent context.
+    Expr(Option<&'a Expr>),
+    // Paths in path patterns `Path`.
+    Pat,
+    // Paths in struct expressions and patterns `Path { .. }`.
+    Struct,
+    // Paths in tuple struct patterns `Path(..)`.
+    TupleStruct(Span, &'a [Span]),
+    // `m::A::B` in `<T as m::A>::B::C`.
+    TraitItem(Namespace),
+}
+
+impl<'a> PathSource<'a> {
+    fn namespace(self) -> Namespace {
+        match self {
+            PathSource::Type | PathSource::Trait(_) | PathSource::Struct => TypeNS,
+            PathSource::Expr(..) | PathSource::Pat | PathSource::TupleStruct(..) => ValueNS,
+            PathSource::TraitItem(ns) => ns,
+        }
+    }
+
+    fn defer_to_typeck(self) -> bool {
+        match self {
+            PathSource::Type
+            | PathSource::Expr(..)
+            | PathSource::Pat
+            | PathSource::Struct
+            | PathSource::TupleStruct(..) => true,
+            PathSource::Trait(_) | PathSource::TraitItem(..) => false,
+        }
+    }
+
+    fn descr_expected(self) -> &'static str {
+        match &self {
+            PathSource::Type => "type",
+            PathSource::Trait(_) => "trait",
+            PathSource::Pat => "unit struct, unit variant or constant",
+            PathSource::Struct => "struct, variant or union type",
+            PathSource::TupleStruct(..) => "tuple struct or tuple variant",
+            PathSource::TraitItem(ns) => match ns {
+                TypeNS => "associated type",
+                ValueNS => "method or associated constant",
+                MacroNS => bug!("associated macro"),
+            },
+            PathSource::Expr(parent) => match parent.as_ref().map(|p| &p.kind) {
+                // "function" here means "anything callable" rather than `DefKind::Fn`,
+                // this is not precise but usually more helpful than just "value".
+                Some(ExprKind::Call(call_expr, _)) => match &call_expr.kind {
+                    // the case of `::some_crate()`
+                    ExprKind::Path(_, path)
+                        if path.segments.len() == 2
+                            && path.segments[0].ident.name == kw::PathRoot =>
+                    {
+                        "external crate"
+                    }
+                    ExprKind::Path(_, path) => {
+                        let mut msg = "function";
+                        if let Some(segment) = path.segments.iter().last() {
+                            if let Some(c) = segment.ident.to_string().chars().next() {
+                                if c.is_uppercase() {
+                                    msg = "function, tuple struct or tuple variant";
+                                }
+                            }
+                        }
+                        msg
+                    }
+                    _ => "function",
+                },
+                _ => "value",
+            },
+        }
+    }
+
+    fn is_call(self) -> bool {
+        matches!(self, PathSource::Expr(Some(&Expr { kind: ExprKind::Call(..), .. })))
+    }
+
+    pub(crate) fn is_expected(self, res: Res) -> bool {
+        match self {
+            PathSource::Type => matches!(
+                res,
+                Res::Def(
+                    DefKind::Struct
+                        | DefKind::Union
+                        | DefKind::Enum
+                        | DefKind::Trait
+                        | DefKind::TraitAlias
+                        | DefKind::TyAlias
+                        | DefKind::AssocTy
+                        | DefKind::TyParam
+                        | DefKind::OpaqueTy
+                        | DefKind::ForeignTy,
+                    _,
+                ) | Res::PrimTy(..)
+                    | Res::SelfTy { .. }
+            ),
+            PathSource::Trait(AliasPossibility::No) => matches!(res, Res::Def(DefKind::Trait, _)),
+            PathSource::Trait(AliasPossibility::Maybe) => {
+                matches!(res, Res::Def(DefKind::Trait | DefKind::TraitAlias, _))
+            }
+            PathSource::Expr(..) => matches!(
+                res,
+                Res::Def(
+                    DefKind::Ctor(_, CtorKind::Const | CtorKind::Fn)
+                        | DefKind::Const
+                        | DefKind::Static(_)
+                        | DefKind::Fn
+                        | DefKind::AssocFn
+                        | DefKind::AssocConst
+                        | DefKind::ConstParam,
+                    _,
+                ) | Res::Local(..)
+                    | Res::SelfCtor(..)
+            ),
+            PathSource::Pat => {
+                res.expected_in_unit_struct_pat()
+                    || matches!(res, Res::Def(DefKind::Const | DefKind::AssocConst, _))
+            }
+            PathSource::TupleStruct(..) => res.expected_in_tuple_struct_pat(),
+            PathSource::Struct => matches!(
+                res,
+                Res::Def(
+                    DefKind::Struct
+                        | DefKind::Union
+                        | DefKind::Variant
+                        | DefKind::TyAlias
+                        | DefKind::AssocTy,
+                    _,
+                ) | Res::SelfTy { .. }
+            ),
+            PathSource::TraitItem(ns) => match res {
+                Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) if ns == ValueNS => true,
+                Res::Def(DefKind::AssocTy, _) if ns == TypeNS => true,
+                _ => false,
+            },
+        }
+    }
+
+    fn error_code(self, has_unexpected_resolution: bool) -> DiagnosticId {
+        use rustc_errors::error_code;
+        match (self, has_unexpected_resolution) {
+            (PathSource::Trait(_), true) => error_code!(E0404),
+            (PathSource::Trait(_), false) => error_code!(E0405),
+            (PathSource::Type, true) => error_code!(E0573),
+            (PathSource::Type, false) => error_code!(E0412),
+            (PathSource::Struct, true) => error_code!(E0574),
+            (PathSource::Struct, false) => error_code!(E0422),
+            (PathSource::Expr(..), true) => error_code!(E0423),
+            (PathSource::Expr(..), false) => error_code!(E0425),
+            (PathSource::Pat | PathSource::TupleStruct(..), true) => error_code!(E0532),
+            (PathSource::Pat | PathSource::TupleStruct(..), false) => error_code!(E0531),
+            (PathSource::TraitItem(..), true) => error_code!(E0575),
+            (PathSource::TraitItem(..), false) => error_code!(E0576),
+        }
+    }
+}
+
+#[derive(Default)]
+struct DiagnosticMetadata<'ast> {
+    /// The current trait's associated items' ident, used for diagnostic suggestions.
+    current_trait_assoc_items: Option<&'ast [P<AssocItem>]>,
+
+    /// The current self type if inside an impl (used for better errors).
+    current_self_type: Option<Ty>,
+
+    /// The current self item if inside an ADT (used for better errors).
+    current_self_item: Option<NodeId>,
+
+    /// The current trait (used to suggest).
+    current_item: Option<&'ast Item>,
+
+    /// When processing generics and encountering a type not found, suggest introducing a type
+    /// param.
+    currently_processing_generics: bool,
+
+    /// The current enclosing (non-closure) function (used for better errors).
+    current_function: Option<(FnKind<'ast>, Span)>,
+
+    /// A list of labels as of yet unused. Labels will be removed from this map when
+    /// they are used (in a `break` or `continue` statement)
+    unused_labels: FxHashMap<NodeId, Span>,
+
+    /// Only used for better errors on `fn(): fn()`.
+    current_type_ascription: Vec<Span>,
+
+    /// Only used for better errors on `let x = { foo: bar };`.
+    /// In the case of a parse error with `let x = { foo: bar, };`, this isn't needed, it's only
+    /// needed for cases where this parses as a correct type ascription.
+    current_block_could_be_bare_struct_literal: Option<Span>,
+
+    /// Only used for better errors on `let <pat>: <expr, not type>;`.
+    current_let_binding: Option<(Span, Option<Span>, Option<Span>)>,
+
+    /// Used to detect possible `if let` written without `let` and to provide structured suggestion.
+    in_if_condition: Option<&'ast Expr>,
+
+    /// If we are currently in a trait object definition. Used to point at the bounds when
+    /// encountering a struct or enum.
+    current_trait_object: Option<&'ast [ast::GenericBound]>,
+
+    /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
+    current_where_predicate: Option<&'ast WherePredicate>,
+
+    current_type_path: Option<&'ast Ty>,
+
+    /// The current impl items (used to suggest).
+    current_impl_items: Option<&'ast [P<AssocItem>]>,
+
+    /// When processing impl trait
+    currently_processing_impl_trait: Option<(TraitRef, Ty)>,
+
+    /// Accumulate the errors due to missed lifetime elision,
+    /// and report them all at once for each function.
+    current_elision_failures: Vec<MissingLifetime>,
+}
+
+struct LateResolutionVisitor<'a, 'b, 'ast> {
+    r: &'b mut Resolver<'a>,
+
+    /// The module that represents the current item scope.
+    parent_scope: ParentScope<'a>,
+
+    /// The current set of local scopes for types and values.
+    /// FIXME #4948: Reuse ribs to avoid allocation.
+    ribs: PerNS<Vec<Rib<'a>>>,
+
+    /// The current set of local scopes, for labels.
+    label_ribs: Vec<Rib<'a, NodeId>>,
+
+    /// The current set of local scopes for lifetimes.
+    lifetime_ribs: Vec<LifetimeRib>,
+
+    /// We are looking for lifetimes in an elision context.
+    /// The set contains all the resolutions that we encountered so far.
+    /// They will be used to determine the correct lifetime for the fn return type.
+    /// The `LifetimeElisionCandidate` is used for diagnostics, to suggest introducing named
+    /// lifetimes.
+    lifetime_elision_candidates: Option<FxIndexMap<LifetimeRes, LifetimeElisionCandidate>>,
+
+    /// The trait that the current context can refer to.
+    current_trait_ref: Option<(Module<'a>, TraitRef)>,
+
+    /// Fields used to add information to diagnostic errors.
+    diagnostic_metadata: Box<DiagnosticMetadata<'ast>>,
+
+    /// State used to know whether to ignore resolution errors for function bodies.
+    ///
+    /// In particular, rustdoc uses this to avoid giving errors for `cfg()` items.
+    /// In most cases this will be `None`, in which case errors will always be reported.
+    /// If it is `true`, then it will be updated when entering a nested function or trait body.
+    in_func_body: bool,
+
+    /// Count the number of places a lifetime is used.
+    lifetime_uses: FxHashMap<LocalDefId, LifetimeUseSet>,
+}
+
+/// Walks the whole crate in DFS order, visiting each item, resolving names as it goes.
+impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
+    fn visit_attribute(&mut self, _: &'ast Attribute) {
+        // We do not want to resolve expressions that appear in attributes,
+        // as they do not correspond to actual code.
+    }
+    fn visit_item(&mut self, item: &'ast Item) {
+        let prev = replace(&mut self.diagnostic_metadata.current_item, Some(item));
+        // Always report errors in items we just entered.
+        let old_ignore = replace(&mut self.in_func_body, false);
+        self.with_lifetime_rib(LifetimeRibKind::Item, |this| this.resolve_item(item));
+        self.in_func_body = old_ignore;
+        self.diagnostic_metadata.current_item = prev;
+    }
+    fn visit_arm(&mut self, arm: &'ast Arm) {
+        self.resolve_arm(arm);
+    }
+    fn visit_block(&mut self, block: &'ast Block) {
+        self.resolve_block(block);
+    }
+    fn visit_anon_const(&mut self, constant: &'ast AnonConst) {
+        // We deal with repeat expressions explicitly in `resolve_expr`.
+        self.with_lifetime_rib(LifetimeRibKind::AnonConst, |this| {
+            this.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Static), |this| {
+                this.resolve_anon_const(constant, IsRepeatExpr::No);
+            })
+        })
+    }
+    fn visit_expr(&mut self, expr: &'ast Expr) {
+        self.resolve_expr(expr, None);
+    }
+    fn visit_local(&mut self, local: &'ast Local) {
+        let local_spans = match local.pat.kind {
+            // We check for this to avoid tuple struct fields.
+            PatKind::Wild => None,
+            _ => Some((
+                local.pat.span,
+                local.ty.as_ref().map(|ty| ty.span),
+                local.kind.init().map(|init| init.span),
+            )),
+        };
+        let original = replace(&mut self.diagnostic_metadata.current_let_binding, local_spans);
+        self.resolve_local(local);
+        self.diagnostic_metadata.current_let_binding = original;
+    }
+    fn visit_ty(&mut self, ty: &'ast Ty) {
+        let prev = self.diagnostic_metadata.current_trait_object;
+        let prev_ty = self.diagnostic_metadata.current_type_path;
+        match ty.kind {
+            TyKind::Rptr(None, _) => {
+                // Elided lifetime in reference: we resolve as if there was some lifetime `'_` with
+                // NodeId `ty.id`.
+                // This span will be used in case of elision failure.
+                let span = self.r.session.source_map().next_point(ty.span.shrink_to_lo());
+                self.resolve_elided_lifetime(ty.id, span);
+                visit::walk_ty(self, ty);
+            }
+            TyKind::Path(ref qself, ref path) => {
+                self.diagnostic_metadata.current_type_path = Some(ty);
+                self.smart_resolve_path(ty.id, qself.as_ref(), path, PathSource::Type);
+
+                // Check whether we should interpret this as a bare trait object.
+                if qself.is_none()
+                    && let Some(partial_res) = self.r.partial_res_map.get(&ty.id)
+                    && partial_res.unresolved_segments() == 0
+                    && let Res::Def(DefKind::Trait | DefKind::TraitAlias, _) = partial_res.base_res()
+                {
+                    // This path is actually a bare trait object.  In case of a bare `Fn`-trait
+                    // object with anonymous lifetimes, we need this rib to correctly place the
+                    // synthetic lifetimes.
+                    let span = ty.span.shrink_to_lo().to(path.span.shrink_to_lo());
+                    self.with_generic_param_rib(
+                        &[],
+                        NormalRibKind,
+                        LifetimeRibKind::Generics {
+                            binder: ty.id,
+                            kind: LifetimeBinderKind::PolyTrait,
+                            span,
+                        },
+                        |this| this.visit_path(&path, ty.id),
+                    );
+                } else {
+                    visit::walk_ty(self, ty)
+                }
+            }
+            TyKind::ImplicitSelf => {
+                let self_ty = Ident::with_dummy_span(kw::SelfUpper);
+                let res = self
+                    .resolve_ident_in_lexical_scope(
+                        self_ty,
+                        TypeNS,
+                        Some(Finalize::new(ty.id, ty.span)),
+                        None,
+                    )
+                    .map_or(Res::Err, |d| d.res());
+                self.r.record_partial_res(ty.id, PartialRes::new(res));
+                visit::walk_ty(self, ty)
+            }
+            TyKind::ImplTrait(..) => {
+                let candidates = self.lifetime_elision_candidates.take();
+                visit::walk_ty(self, ty);
+                self.lifetime_elision_candidates = candidates;
+            }
+            TyKind::TraitObject(ref bounds, ..) => {
+                self.diagnostic_metadata.current_trait_object = Some(&bounds[..]);
+                visit::walk_ty(self, ty)
+            }
+            TyKind::BareFn(ref bare_fn) => {
+                let span = ty.span.shrink_to_lo().to(bare_fn.decl_span.shrink_to_lo());
+                self.with_generic_param_rib(
+                    &bare_fn.generic_params,
+                    NormalRibKind,
+                    LifetimeRibKind::Generics {
+                        binder: ty.id,
+                        kind: LifetimeBinderKind::BareFnType,
+                        span,
+                    },
+                    |this| {
+                        this.visit_generic_params(&bare_fn.generic_params, false);
+                        this.with_lifetime_rib(
+                            LifetimeRibKind::AnonymousCreateParameter {
+                                binder: ty.id,
+                                report_in_path: false,
+                            },
+                            |this| {
+                                this.resolve_fn_signature(
+                                    ty.id,
+                                    false,
+                                    // We don't need to deal with patterns in parameters, because
+                                    // they are not possible for foreign or bodiless functions.
+                                    bare_fn
+                                        .decl
+                                        .inputs
+                                        .iter()
+                                        .map(|Param { ty, .. }| (None, &**ty)),
+                                    &bare_fn.decl.output,
+                                )
+                            },
+                        );
+                    },
+                )
+            }
+            _ => visit::walk_ty(self, ty),
+        }
+        self.diagnostic_metadata.current_trait_object = prev;
+        self.diagnostic_metadata.current_type_path = prev_ty;
+    }
+    fn visit_poly_trait_ref(&mut self, tref: &'ast PolyTraitRef, _: &'ast TraitBoundModifier) {
+        let span = tref.span.shrink_to_lo().to(tref.trait_ref.path.span.shrink_to_lo());
+        self.with_generic_param_rib(
+            &tref.bound_generic_params,
+            NormalRibKind,
+            LifetimeRibKind::Generics {
+                binder: tref.trait_ref.ref_id,
+                kind: LifetimeBinderKind::PolyTrait,
+                span,
+            },
+            |this| {
+                this.visit_generic_params(&tref.bound_generic_params, false);
+                this.smart_resolve_path(
+                    tref.trait_ref.ref_id,
+                    None,
+                    &tref.trait_ref.path,
+                    PathSource::Trait(AliasPossibility::Maybe),
+                );
+                this.visit_trait_ref(&tref.trait_ref);
+            },
+        );
+    }
+    fn visit_foreign_item(&mut self, foreign_item: &'ast ForeignItem) {
+        match foreign_item.kind {
+            ForeignItemKind::TyAlias(box TyAlias { ref generics, .. }) => {
+                self.with_lifetime_rib(LifetimeRibKind::Item, |this| {
+                    this.with_generic_param_rib(
+                        &generics.params,
+                        ItemRibKind(HasGenericParams::Yes),
+                        LifetimeRibKind::Generics {
+                            binder: foreign_item.id,
+                            kind: LifetimeBinderKind::Item,
+                            span: generics.span,
+                        },
+                        |this| visit::walk_foreign_item(this, foreign_item),
+                    )
+                });
+            }
+            ForeignItemKind::Fn(box Fn { ref generics, .. }) => {
+                self.with_lifetime_rib(LifetimeRibKind::Item, |this| {
+                    this.with_generic_param_rib(
+                        &generics.params,
+                        ItemRibKind(HasGenericParams::Yes),
+                        LifetimeRibKind::Generics {
+                            binder: foreign_item.id,
+                            kind: LifetimeBinderKind::Function,
+                            span: generics.span,
+                        },
+                        |this| visit::walk_foreign_item(this, foreign_item),
+                    )
+                });
+            }
+            ForeignItemKind::Static(..) => {
+                self.with_item_rib(|this| {
+                    visit::walk_foreign_item(this, foreign_item);
+                });
+            }
+            ForeignItemKind::MacCall(..) => {
+                panic!("unexpanded macro in resolve!")
+            }
+        }
+    }
+    fn visit_fn(&mut self, fn_kind: FnKind<'ast>, sp: Span, fn_id: NodeId) {
+        let rib_kind = match fn_kind {
+            // Bail if the function is foreign, and thus cannot validly have
+            // a body, or if there's no body for some other reason.
+            FnKind::Fn(FnCtxt::Foreign, _, sig, _, generics, _)
+            | FnKind::Fn(_, _, sig, _, generics, None) => {
+                self.visit_fn_header(&sig.header);
+                self.visit_generics(generics);
+                self.with_lifetime_rib(
+                    LifetimeRibKind::AnonymousCreateParameter {
+                        binder: fn_id,
+                        report_in_path: false,
+                    },
+                    |this| {
+                        this.resolve_fn_signature(
+                            fn_id,
+                            sig.decl.has_self(),
+                            sig.decl.inputs.iter().map(|Param { ty, .. }| (None, &**ty)),
+                            &sig.decl.output,
+                        )
+                    },
+                );
+                return;
+            }
+            FnKind::Fn(FnCtxt::Free, ..) => FnItemRibKind,
+            FnKind::Fn(FnCtxt::Assoc(_), ..) => NormalRibKind,
+            FnKind::Closure(..) => ClosureOrAsyncRibKind,
+        };
+        let previous_value = self.diagnostic_metadata.current_function;
+        if matches!(fn_kind, FnKind::Fn(..)) {
+            self.diagnostic_metadata.current_function = Some((fn_kind, sp));
+        }
+        debug!("(resolving function) entering function");
+
+        // Create a value rib for the function.
+        self.with_rib(ValueNS, rib_kind, |this| {
+            // Create a label rib for the function.
+            this.with_label_rib(FnItemRibKind, |this| {
+                match fn_kind {
+                    FnKind::Fn(_, _, sig, _, generics, body) => {
+                        this.visit_generics(generics);
+
+                        let declaration = &sig.decl;
+                        let async_node_id = sig.header.asyncness.opt_return_id();
+
+                        this.with_lifetime_rib(
+                            LifetimeRibKind::AnonymousCreateParameter {
+                                binder: fn_id,
+                                report_in_path: async_node_id.is_some(),
+                            },
+                            |this| {
+                                this.resolve_fn_signature(
+                                    fn_id,
+                                    declaration.has_self(),
+                                    declaration
+                                        .inputs
+                                        .iter()
+                                        .map(|Param { pat, ty, .. }| (Some(&**pat), &**ty)),
+                                    &declaration.output,
+                                )
+                            },
+                        );
+
+                        // Construct the list of in-scope lifetime parameters for async lowering.
+                        // We include all lifetime parameters, either named or "Fresh".
+                        // The order of those parameters does not matter, as long as it is
+                        // deterministic.
+                        if let Some(async_node_id) = async_node_id {
+                            let mut extra_lifetime_params = this
+                                .r
+                                .extra_lifetime_params_map
+                                .get(&fn_id)
+                                .cloned()
+                                .unwrap_or_default();
+                            for rib in this.lifetime_ribs.iter().rev() {
+                                extra_lifetime_params.extend(
+                                    rib.bindings
+                                        .iter()
+                                        .map(|(&ident, &(node_id, res))| (ident, node_id, res)),
+                                );
+                                match rib.kind {
+                                    LifetimeRibKind::Item => break,
+                                    LifetimeRibKind::AnonymousCreateParameter {
+                                        binder, ..
+                                    } => {
+                                        if let Some(earlier_fresh) =
+                                            this.r.extra_lifetime_params_map.get(&binder)
+                                        {
+                                            extra_lifetime_params.extend(earlier_fresh);
+                                        }
+                                    }
+                                    _ => {}
+                                }
+                            }
+                            this.r
+                                .extra_lifetime_params_map
+                                .insert(async_node_id, extra_lifetime_params);
+                        }
+
+                        if let Some(body) = body {
+                            // Ignore errors in function bodies if this is rustdoc
+                            // Be sure not to set this until the function signature has been resolved.
+                            let previous_state = replace(&mut this.in_func_body, true);
+                            // Resolve the function body, potentially inside the body of an async closure
+                            this.with_lifetime_rib(
+                                LifetimeRibKind::Elided(LifetimeRes::Infer),
+                                |this| this.visit_block(body),
+                            );
+
+                            debug!("(resolving function) leaving function");
+                            this.in_func_body = previous_state;
+                        }
+                    }
+                    FnKind::Closure(binder, declaration, body) => {
+                        this.visit_closure_binder(binder);
+
+                        this.with_lifetime_rib(
+                            match binder {
+                                // We do not have any explicit generic lifetime parameter.
+                                ClosureBinder::NotPresent => {
+                                    LifetimeRibKind::AnonymousCreateParameter {
+                                        binder: fn_id,
+                                        report_in_path: false,
+                                    }
+                                }
+                                ClosureBinder::For { .. } => LifetimeRibKind::AnonymousReportError,
+                            },
+                            // Add each argument to the rib.
+                            |this| this.resolve_params(&declaration.inputs),
+                        );
+                        this.with_lifetime_rib(
+                            match binder {
+                                ClosureBinder::NotPresent => {
+                                    LifetimeRibKind::Elided(LifetimeRes::Infer)
+                                }
+                                ClosureBinder::For { .. } => LifetimeRibKind::AnonymousReportError,
+                            },
+                            |this| visit::walk_fn_ret_ty(this, &declaration.output),
+                        );
+
+                        // Ignore errors in function bodies if this is rustdoc
+                        // Be sure not to set this until the function signature has been resolved.
+                        let previous_state = replace(&mut this.in_func_body, true);
+                        // Resolve the function body, potentially inside the body of an async closure
+                        this.with_lifetime_rib(
+                            LifetimeRibKind::Elided(LifetimeRes::Infer),
+                            |this| this.visit_expr(body),
+                        );
+
+                        debug!("(resolving function) leaving function");
+                        this.in_func_body = previous_state;
+                    }
+                }
+            })
+        });
+        self.diagnostic_metadata.current_function = previous_value;
+    }
+    fn visit_lifetime(&mut self, lifetime: &'ast Lifetime, use_ctxt: visit::LifetimeCtxt) {
+        self.resolve_lifetime(lifetime, use_ctxt)
+    }
+
+    fn visit_generics(&mut self, generics: &'ast Generics) {
+        self.visit_generic_params(
+            &generics.params,
+            self.diagnostic_metadata.current_self_item.is_some(),
+        );
+        for p in &generics.where_clause.predicates {
+            self.visit_where_predicate(p);
+        }
+    }
+
+    fn visit_closure_binder(&mut self, b: &'ast ClosureBinder) {
+        match b {
+            ClosureBinder::NotPresent => {}
+            ClosureBinder::For { generic_params, .. } => {
+                self.visit_generic_params(
+                    &generic_params,
+                    self.diagnostic_metadata.current_self_item.is_some(),
+                );
+            }
+        }
+    }
+
+    fn visit_generic_arg(&mut self, arg: &'ast GenericArg) {
+        debug!("visit_generic_arg({:?})", arg);
+        let prev = replace(&mut self.diagnostic_metadata.currently_processing_generics, true);
+        match arg {
+            GenericArg::Type(ref ty) => {
+                // We parse const arguments as path types as we cannot distinguish them during
+                // parsing. We try to resolve that ambiguity by attempting resolution the type
+                // namespace first, and if that fails we try again in the value namespace. If
+                // resolution in the value namespace succeeds, we have an generic const argument on
+                // our hands.
+                if let TyKind::Path(ref qself, ref path) = ty.kind {
+                    // We cannot disambiguate multi-segment paths right now as that requires type
+                    // checking.
+                    if path.segments.len() == 1 && path.segments[0].args.is_none() {
+                        let mut check_ns = |ns| {
+                            self.maybe_resolve_ident_in_lexical_scope(path.segments[0].ident, ns)
+                                .is_some()
+                        };
+                        if !check_ns(TypeNS) && check_ns(ValueNS) {
+                            // This must be equivalent to `visit_anon_const`, but we cannot call it
+                            // directly due to visitor lifetimes so we have to copy-paste some code.
+                            //
+                            // Note that we might not be inside of an repeat expression here,
+                            // but considering that `IsRepeatExpr` is only relevant for
+                            // non-trivial constants this is doesn't matter.
+                            self.with_constant_rib(
+                                IsRepeatExpr::No,
+                                HasGenericParams::Yes,
+                                None,
+                                |this| {
+                                    this.smart_resolve_path(
+                                        ty.id,
+                                        qself.as_ref(),
+                                        path,
+                                        PathSource::Expr(None),
+                                    );
+
+                                    if let Some(ref qself) = *qself {
+                                        this.visit_ty(&qself.ty);
+                                    }
+                                    this.visit_path(path, ty.id);
+                                },
+                            );
+
+                            self.diagnostic_metadata.currently_processing_generics = prev;
+                            return;
+                        }
+                    }
+                }
+
+                self.visit_ty(ty);
+            }
+            GenericArg::Lifetime(lt) => self.visit_lifetime(lt, visit::LifetimeCtxt::GenericArg),
+            GenericArg::Const(ct) => self.visit_anon_const(ct),
+        }
+        self.diagnostic_metadata.currently_processing_generics = prev;
+    }
+
+    fn visit_assoc_constraint(&mut self, constraint: &'ast AssocConstraint) {
+        self.visit_ident(constraint.ident);
+        if let Some(ref gen_args) = constraint.gen_args {
+            // Forbid anonymous lifetimes in GAT parameters until proper semantics are decided.
+            self.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
+                this.visit_generic_args(gen_args.span(), gen_args)
+            });
+        }
+        match constraint.kind {
+            AssocConstraintKind::Equality { ref term } => match term {
+                Term::Ty(ty) => self.visit_ty(ty),
+                Term::Const(c) => self.visit_anon_const(c),
+            },
+            AssocConstraintKind::Bound { ref bounds } => {
+                walk_list!(self, visit_param_bound, bounds, BoundKind::Bound);
+            }
+        }
+    }
+
+    fn visit_path_segment(&mut self, path_span: Span, path_segment: &'ast PathSegment) {
+        if let Some(ref args) = path_segment.args {
+            match &**args {
+                GenericArgs::AngleBracketed(..) => visit::walk_generic_args(self, path_span, args),
+                GenericArgs::Parenthesized(p_args) => {
+                    // Probe the lifetime ribs to know how to behave.
+                    for rib in self.lifetime_ribs.iter().rev() {
+                        match rib.kind {
+                            // We are inside a `PolyTraitRef`.  The lifetimes are
+                            // to be intoduced in that (maybe implicit) `for<>` binder.
+                            LifetimeRibKind::Generics {
+                                binder,
+                                kind: LifetimeBinderKind::PolyTrait,
+                                ..
+                            } => {
+                                self.with_lifetime_rib(
+                                    LifetimeRibKind::AnonymousCreateParameter {
+                                        binder,
+                                        report_in_path: false,
+                                    },
+                                    |this| {
+                                        this.resolve_fn_signature(
+                                            binder,
+                                            false,
+                                            p_args.inputs.iter().map(|ty| (None, &**ty)),
+                                            &p_args.output,
+                                        )
+                                    },
+                                );
+                                break;
+                            }
+                            // We have nowhere to introduce generics.  Code is malformed,
+                            // so use regular lifetime resolution to avoid spurious errors.
+                            LifetimeRibKind::Item | LifetimeRibKind::Generics { .. } => {
+                                visit::walk_generic_args(self, path_span, args);
+                                break;
+                            }
+                            LifetimeRibKind::AnonymousCreateParameter { .. }
+                            | LifetimeRibKind::AnonymousReportError
+                            | LifetimeRibKind::Elided(_)
+                            | LifetimeRibKind::ElisionFailure
+                            | LifetimeRibKind::AnonConst
+                            | LifetimeRibKind::ConstGeneric => {}
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fn visit_where_predicate(&mut self, p: &'ast WherePredicate) {
+        debug!("visit_where_predicate {:?}", p);
+        let previous_value =
+            replace(&mut self.diagnostic_metadata.current_where_predicate, Some(p));
+        self.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
+            if let WherePredicate::BoundPredicate(WhereBoundPredicate {
+                ref bounded_ty,
+                ref bounds,
+                ref bound_generic_params,
+                span: predicate_span,
+                ..
+            }) = p
+            {
+                let span = predicate_span.shrink_to_lo().to(bounded_ty.span.shrink_to_lo());
+                this.with_generic_param_rib(
+                    &bound_generic_params,
+                    NormalRibKind,
+                    LifetimeRibKind::Generics {
+                        binder: bounded_ty.id,
+                        kind: LifetimeBinderKind::WhereBound,
+                        span,
+                    },
+                    |this| {
+                        this.visit_generic_params(&bound_generic_params, false);
+                        this.visit_ty(bounded_ty);
+                        for bound in bounds {
+                            this.visit_param_bound(bound, BoundKind::Bound)
+                        }
+                    },
+                );
+            } else {
+                visit::walk_where_predicate(this, p);
+            }
+        });
+        self.diagnostic_metadata.current_where_predicate = previous_value;
+    }
+
+    fn visit_inline_asm(&mut self, asm: &'ast InlineAsm) {
+        for (op, _) in &asm.operands {
+            match op {
+                InlineAsmOperand::In { expr, .. }
+                | InlineAsmOperand::Out { expr: Some(expr), .. }
+                | InlineAsmOperand::InOut { expr, .. } => self.visit_expr(expr),
+                InlineAsmOperand::Out { expr: None, .. } => {}
+                InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
+                    self.visit_expr(in_expr);
+                    if let Some(out_expr) = out_expr {
+                        self.visit_expr(out_expr);
+                    }
+                }
+                InlineAsmOperand::Const { anon_const, .. } => {
+                    // Although this is `DefKind::AnonConst`, it is allowed to reference outer
+                    // generic parameters like an inline const.
+                    self.resolve_inline_const(anon_const);
+                }
+                InlineAsmOperand::Sym { sym } => self.visit_inline_asm_sym(sym),
+            }
+        }
+    }
+
+    fn visit_inline_asm_sym(&mut self, sym: &'ast InlineAsmSym) {
+        // This is similar to the code for AnonConst.
+        self.with_rib(ValueNS, InlineAsmSymRibKind, |this| {
+            this.with_rib(TypeNS, InlineAsmSymRibKind, |this| {
+                this.with_label_rib(InlineAsmSymRibKind, |this| {
+                    this.smart_resolve_path(
+                        sym.id,
+                        sym.qself.as_ref(),
+                        &sym.path,
+                        PathSource::Expr(None),
+                    );
+                    visit::walk_inline_asm_sym(this, sym);
+                });
+            })
+        });
+    }
+}
+
+impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
+    fn new(resolver: &'b mut Resolver<'a>) -> LateResolutionVisitor<'a, 'b, 'ast> {
+        // During late resolution we only track the module component of the parent scope,
+        // although it may be useful to track other components as well for diagnostics.
+        let graph_root = resolver.graph_root;
+        let parent_scope = ParentScope::module(graph_root, resolver);
+        let start_rib_kind = ModuleRibKind(graph_root);
+        LateResolutionVisitor {
+            r: resolver,
+            parent_scope,
+            ribs: PerNS {
+                value_ns: vec![Rib::new(start_rib_kind)],
+                type_ns: vec![Rib::new(start_rib_kind)],
+                macro_ns: vec![Rib::new(start_rib_kind)],
+            },
+            label_ribs: Vec::new(),
+            lifetime_ribs: Vec::new(),
+            lifetime_elision_candidates: None,
+            current_trait_ref: None,
+            diagnostic_metadata: Box::new(DiagnosticMetadata::default()),
+            // errors at module scope should always be reported
+            in_func_body: false,
+            lifetime_uses: Default::default(),
+        }
+    }
+
+    fn maybe_resolve_ident_in_lexical_scope(
+        &mut self,
+        ident: Ident,
+        ns: Namespace,
+    ) -> Option<LexicalScopeBinding<'a>> {
+        self.r.resolve_ident_in_lexical_scope(
+            ident,
+            ns,
+            &self.parent_scope,
+            None,
+            &self.ribs[ns],
+            None,
+        )
+    }
+
+    fn resolve_ident_in_lexical_scope(
+        &mut self,
+        ident: Ident,
+        ns: Namespace,
+        finalize: Option<Finalize>,
+        ignore_binding: Option<&'a NameBinding<'a>>,
+    ) -> Option<LexicalScopeBinding<'a>> {
+        self.r.resolve_ident_in_lexical_scope(
+            ident,
+            ns,
+            &self.parent_scope,
+            finalize,
+            &self.ribs[ns],
+            ignore_binding,
+        )
+    }
+
+    fn resolve_path(
+        &mut self,
+        path: &[Segment],
+        opt_ns: Option<Namespace>, // `None` indicates a module path in import
+        finalize: Option<Finalize>,
+    ) -> PathResult<'a> {
+        self.r.resolve_path_with_ribs(
+            path,
+            opt_ns,
+            &self.parent_scope,
+            finalize,
+            Some(&self.ribs),
+            None,
+        )
+    }
+
+    // AST resolution
+    //
+    // We maintain a list of value ribs and type ribs.
+    //
+    // Simultaneously, we keep track of the current position in the module
+    // graph in the `parent_scope.module` pointer. When we go to resolve a name in
+    // the value or type namespaces, we first look through all the ribs and
+    // then query the module graph. When we resolve a name in the module
+    // namespace, we can skip all the ribs (since nested modules are not
+    // allowed within blocks in Rust) and jump straight to the current module
+    // graph node.
+    //
+    // Named implementations are handled separately. When we find a method
+    // call, we consult the module node to find all of the implementations in
+    // scope. This information is lazily cached in the module node. We then
+    // generate a fake "implementation scope" containing all the
+    // implementations thus found, for compatibility with old resolve pass.
+
+    /// Do some `work` within a new innermost rib of the given `kind` in the given namespace (`ns`).
+    fn with_rib<T>(
+        &mut self,
+        ns: Namespace,
+        kind: RibKind<'a>,
+        work: impl FnOnce(&mut Self) -> T,
+    ) -> T {
+        self.ribs[ns].push(Rib::new(kind));
+        let ret = work(self);
+        self.ribs[ns].pop();
+        ret
+    }
+
+    fn with_scope<T>(&mut self, id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
+        if let Some(module) = self.r.get_module(self.r.local_def_id(id).to_def_id()) {
+            // Move down in the graph.
+            let orig_module = replace(&mut self.parent_scope.module, module);
+            self.with_rib(ValueNS, ModuleRibKind(module), |this| {
+                this.with_rib(TypeNS, ModuleRibKind(module), |this| {
+                    let ret = f(this);
+                    this.parent_scope.module = orig_module;
+                    ret
+                })
+            })
+        } else {
+            f(self)
+        }
+    }
+
+    fn visit_generic_params(&mut self, params: &'ast [GenericParam], add_self_upper: bool) {
+        // For type parameter defaults, we have to ban access
+        // to following type parameters, as the InternalSubsts can only
+        // provide previous type parameters as they're built. We
+        // put all the parameters on the ban list and then remove
+        // them one by one as they are processed and become available.
+        let mut forward_ty_ban_rib = Rib::new(ForwardGenericParamBanRibKind);
+        let mut forward_const_ban_rib = Rib::new(ForwardGenericParamBanRibKind);
+        for param in params.iter() {
+            match param.kind {
+                GenericParamKind::Type { .. } => {
+                    forward_ty_ban_rib
+                        .bindings
+                        .insert(Ident::with_dummy_span(param.ident.name), Res::Err);
+                }
+                GenericParamKind::Const { .. } => {
+                    forward_const_ban_rib
+                        .bindings
+                        .insert(Ident::with_dummy_span(param.ident.name), Res::Err);
+                }
+                GenericParamKind::Lifetime => {}
+            }
+        }
+
+        // rust-lang/rust#61631: The type `Self` is essentially
+        // another type parameter. For ADTs, we consider it
+        // well-defined only after all of the ADT type parameters have
+        // been provided. Therefore, we do not allow use of `Self`
+        // anywhere in ADT type parameter defaults.
+        //
+        // (We however cannot ban `Self` for defaults on *all* generic
+        // lists; e.g. trait generics can usefully refer to `Self`,
+        // such as in the case of `trait Add<Rhs = Self>`.)
+        if add_self_upper {
+            // (`Some` if + only if we are in ADT's generics.)
+            forward_ty_ban_rib.bindings.insert(Ident::with_dummy_span(kw::SelfUpper), Res::Err);
+        }
+
+        self.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
+            for param in params {
+                match param.kind {
+                    GenericParamKind::Lifetime => {
+                        for bound in &param.bounds {
+                            this.visit_param_bound(bound, BoundKind::Bound);
+                        }
+                    }
+                    GenericParamKind::Type { ref default } => {
+                        for bound in &param.bounds {
+                            this.visit_param_bound(bound, BoundKind::Bound);
+                        }
+
+                        if let Some(ref ty) = default {
+                            this.ribs[TypeNS].push(forward_ty_ban_rib);
+                            this.ribs[ValueNS].push(forward_const_ban_rib);
+                            this.visit_ty(ty);
+                            forward_const_ban_rib = this.ribs[ValueNS].pop().unwrap();
+                            forward_ty_ban_rib = this.ribs[TypeNS].pop().unwrap();
+                        }
+
+                        // Allow all following defaults to refer to this type parameter.
+                        forward_ty_ban_rib
+                            .bindings
+                            .remove(&Ident::with_dummy_span(param.ident.name));
+                    }
+                    GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
+                        // Const parameters can't have param bounds.
+                        assert!(param.bounds.is_empty());
+
+                        this.ribs[TypeNS].push(Rib::new(ConstParamTyRibKind));
+                        this.ribs[ValueNS].push(Rib::new(ConstParamTyRibKind));
+                        this.with_lifetime_rib(LifetimeRibKind::ConstGeneric, |this| {
+                            this.visit_ty(ty)
+                        });
+                        this.ribs[TypeNS].pop().unwrap();
+                        this.ribs[ValueNS].pop().unwrap();
+
+                        if let Some(ref expr) = default {
+                            this.ribs[TypeNS].push(forward_ty_ban_rib);
+                            this.ribs[ValueNS].push(forward_const_ban_rib);
+                            this.with_lifetime_rib(LifetimeRibKind::ConstGeneric, |this| {
+                                this.resolve_anon_const(expr, IsRepeatExpr::No)
+                            });
+                            forward_const_ban_rib = this.ribs[ValueNS].pop().unwrap();
+                            forward_ty_ban_rib = this.ribs[TypeNS].pop().unwrap();
+                        }
+
+                        // Allow all following defaults to refer to this const parameter.
+                        forward_const_ban_rib
+                            .bindings
+                            .remove(&Ident::with_dummy_span(param.ident.name));
+                    }
+                }
+            }
+        })
+    }
+
+    #[tracing::instrument(level = "debug", skip(self, work))]
+    fn with_lifetime_rib<T>(
+        &mut self,
+        kind: LifetimeRibKind,
+        work: impl FnOnce(&mut Self) -> T,
+    ) -> T {
+        self.lifetime_ribs.push(LifetimeRib::new(kind));
+        let outer_elision_candidates = self.lifetime_elision_candidates.take();
+        let ret = work(self);
+        self.lifetime_elision_candidates = outer_elision_candidates;
+        self.lifetime_ribs.pop();
+        ret
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn resolve_lifetime(&mut self, lifetime: &'ast Lifetime, use_ctxt: visit::LifetimeCtxt) {
+        let ident = lifetime.ident;
+
+        if ident.name == kw::StaticLifetime {
+            self.record_lifetime_res(
+                lifetime.id,
+                LifetimeRes::Static,
+                LifetimeElisionCandidate::Named,
+            );
+            return;
+        }
+
+        if ident.name == kw::UnderscoreLifetime {
+            return self.resolve_anonymous_lifetime(lifetime, false);
+        }
+
+        let mut indices = (0..self.lifetime_ribs.len()).rev();
+        for i in &mut indices {
+            let rib = &self.lifetime_ribs[i];
+            let normalized_ident = ident.normalize_to_macros_2_0();
+            if let Some(&(_, res)) = rib.bindings.get(&normalized_ident) {
+                self.record_lifetime_res(lifetime.id, res, LifetimeElisionCandidate::Named);
+
+                if let LifetimeRes::Param { param, .. } = res {
+                    match self.lifetime_uses.entry(param) {
+                        Entry::Vacant(v) => {
+                            debug!("First use of {:?} at {:?}", res, ident.span);
+                            let use_set = self
+                                .lifetime_ribs
+                                .iter()
+                                .rev()
+                                .find_map(|rib| match rib.kind {
+                                    // Do not suggest eliding a lifetime where an anonymous
+                                    // lifetime would be illegal.
+                                    LifetimeRibKind::Item
+                                    | LifetimeRibKind::AnonymousReportError
+                                    | LifetimeRibKind::ElisionFailure => Some(LifetimeUseSet::Many),
+                                    // An anonymous lifetime is legal here, go ahead.
+                                    LifetimeRibKind::AnonymousCreateParameter { .. } => {
+                                        Some(LifetimeUseSet::One { use_span: ident.span, use_ctxt })
+                                    }
+                                    // Only report if eliding the lifetime would have the same
+                                    // semantics.
+                                    LifetimeRibKind::Elided(r) => Some(if res == r {
+                                        LifetimeUseSet::One { use_span: ident.span, use_ctxt }
+                                    } else {
+                                        LifetimeUseSet::Many
+                                    }),
+                                    LifetimeRibKind::Generics { .. }
+                                    | LifetimeRibKind::ConstGeneric
+                                    | LifetimeRibKind::AnonConst => None,
+                                })
+                                .unwrap_or(LifetimeUseSet::Many);
+                            debug!(?use_ctxt, ?use_set);
+                            v.insert(use_set);
+                        }
+                        Entry::Occupied(mut o) => {
+                            debug!("Many uses of {:?} at {:?}", res, ident.span);
+                            *o.get_mut() = LifetimeUseSet::Many;
+                        }
+                    }
+                }
+                return;
+            }
+
+            match rib.kind {
+                LifetimeRibKind::Item => break,
+                LifetimeRibKind::ConstGeneric => {
+                    self.emit_non_static_lt_in_const_generic_error(lifetime);
+                    self.record_lifetime_res(
+                        lifetime.id,
+                        LifetimeRes::Error,
+                        LifetimeElisionCandidate::Ignore,
+                    );
+                    return;
+                }
+                LifetimeRibKind::AnonConst => {
+                    self.maybe_emit_forbidden_non_static_lifetime_error(lifetime);
+                    self.record_lifetime_res(
+                        lifetime.id,
+                        LifetimeRes::Error,
+                        LifetimeElisionCandidate::Ignore,
+                    );
+                    return;
+                }
+                _ => {}
+            }
+        }
+
+        let mut outer_res = None;
+        for i in indices {
+            let rib = &self.lifetime_ribs[i];
+            let normalized_ident = ident.normalize_to_macros_2_0();
+            if let Some((&outer, _)) = rib.bindings.get_key_value(&normalized_ident) {
+                outer_res = Some(outer);
+                break;
+            }
+        }
+
+        self.emit_undeclared_lifetime_error(lifetime, outer_res);
+        self.record_lifetime_res(lifetime.id, LifetimeRes::Error, LifetimeElisionCandidate::Named);
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn resolve_anonymous_lifetime(&mut self, lifetime: &Lifetime, elided: bool) {
+        debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
+
+        let missing_lifetime = MissingLifetime {
+            id: lifetime.id,
+            span: lifetime.ident.span,
+            kind: if elided {
+                MissingLifetimeKind::Ampersand
+            } else {
+                MissingLifetimeKind::Underscore
+            },
+            count: 1,
+        };
+        let elision_candidate = LifetimeElisionCandidate::Missing(missing_lifetime);
+        for i in (0..self.lifetime_ribs.len()).rev() {
+            let rib = &mut self.lifetime_ribs[i];
+            debug!(?rib.kind);
+            match rib.kind {
+                LifetimeRibKind::AnonymousCreateParameter { binder, .. } => {
+                    let res = self.create_fresh_lifetime(lifetime.id, lifetime.ident, binder);
+                    self.record_lifetime_res(lifetime.id, res, elision_candidate);
+                    return;
+                }
+                LifetimeRibKind::AnonymousReportError => {
+                    let (msg, note) = if elided {
+                        (
+                            "`&` without an explicit lifetime name cannot be used here",
+                            "explicit lifetime name needed here",
+                        )
+                    } else {
+                        ("`'_` cannot be used here", "`'_` is a reserved lifetime name")
+                    };
+                    rustc_errors::struct_span_err!(
+                        self.r.session,
+                        lifetime.ident.span,
+                        E0637,
+                        "{}",
+                        msg,
+                    )
+                    .span_label(lifetime.ident.span, note)
+                    .emit();
+
+                    self.record_lifetime_res(lifetime.id, LifetimeRes::Error, elision_candidate);
+                    return;
+                }
+                LifetimeRibKind::Elided(res) => {
+                    self.record_lifetime_res(lifetime.id, res, elision_candidate);
+                    return;
+                }
+                LifetimeRibKind::ElisionFailure => {
+                    self.diagnostic_metadata.current_elision_failures.push(missing_lifetime);
+                    self.record_lifetime_res(lifetime.id, LifetimeRes::Error, elision_candidate);
+                    return;
+                }
+                LifetimeRibKind::Item => break,
+                LifetimeRibKind::Generics { .. }
+                | LifetimeRibKind::ConstGeneric
+                | LifetimeRibKind::AnonConst => {}
+            }
+        }
+        self.record_lifetime_res(lifetime.id, LifetimeRes::Error, elision_candidate);
+        self.report_missing_lifetime_specifiers(vec![missing_lifetime], None);
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn resolve_elided_lifetime(&mut self, anchor_id: NodeId, span: Span) {
+        let id = self.r.next_node_id();
+        let lt = Lifetime { id, ident: Ident::new(kw::UnderscoreLifetime, span) };
+
+        self.record_lifetime_res(
+            anchor_id,
+            LifetimeRes::ElidedAnchor { start: id, end: NodeId::from_u32(id.as_u32() + 1) },
+            LifetimeElisionCandidate::Ignore,
+        );
+        self.resolve_anonymous_lifetime(&lt, true);
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn create_fresh_lifetime(&mut self, id: NodeId, ident: Ident, binder: NodeId) -> LifetimeRes {
+        debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
+        debug!(?ident.span);
+
+        // Leave the responsibility to create the `LocalDefId` to lowering.
+        let param = self.r.next_node_id();
+        let res = LifetimeRes::Fresh { param, binder };
+
+        // Record the created lifetime parameter so lowering can pick it up and add it to HIR.
+        self.r
+            .extra_lifetime_params_map
+            .entry(binder)
+            .or_insert_with(Vec::new)
+            .push((ident, param, res));
+        res
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn resolve_elided_lifetimes_in_path(
+        &mut self,
+        path_id: NodeId,
+        partial_res: PartialRes,
+        path: &[Segment],
+        source: PathSource<'_>,
+        path_span: Span,
+    ) {
+        let proj_start = path.len() - partial_res.unresolved_segments();
+        for (i, segment) in path.iter().enumerate() {
+            if segment.has_lifetime_args {
+                continue;
+            }
+            let Some(segment_id) = segment.id else {
+                continue;
+            };
+
+            // Figure out if this is a type/trait segment,
+            // which may need lifetime elision performed.
+            let type_def_id = match partial_res.base_res() {
+                Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => self.r.parent(def_id),
+                Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => self.r.parent(def_id),
+                Res::Def(DefKind::Struct, def_id)
+                | Res::Def(DefKind::Union, def_id)
+                | Res::Def(DefKind::Enum, def_id)
+                | Res::Def(DefKind::TyAlias, def_id)
+                | Res::Def(DefKind::Trait, def_id)
+                    if i + 1 == proj_start =>
+                {
+                    def_id
+                }
+                _ => continue,
+            };
+
+            let expected_lifetimes = self.r.item_generics_num_lifetimes(type_def_id);
+            if expected_lifetimes == 0 {
+                continue;
+            }
+
+            let node_ids = self.r.next_node_ids(expected_lifetimes);
+            self.record_lifetime_res(
+                segment_id,
+                LifetimeRes::ElidedAnchor { start: node_ids.start, end: node_ids.end },
+                LifetimeElisionCandidate::Ignore,
+            );
+
+            let inferred = match source {
+                PathSource::Trait(..) | PathSource::TraitItem(..) | PathSource::Type => false,
+                PathSource::Expr(..)
+                | PathSource::Pat
+                | PathSource::Struct
+                | PathSource::TupleStruct(..) => true,
+            };
+            if inferred {
+                // Do not create a parameter for patterns and expressions: type checking can infer
+                // the appropriate lifetime for us.
+                for id in node_ids {
+                    self.record_lifetime_res(
+                        id,
+                        LifetimeRes::Infer,
+                        LifetimeElisionCandidate::Named,
+                    );
+                }
+                continue;
+            }
+
+            let elided_lifetime_span = if segment.has_generic_args {
+                // If there are brackets, but not generic arguments, then use the opening bracket
+                segment.args_span.with_hi(segment.args_span.lo() + BytePos(1))
+            } else {
+                // If there are no brackets, use the identifier span.
+                // HACK: we use find_ancestor_inside to properly suggest elided spans in paths
+                // originating from macros, since the segment's span might be from a macro arg.
+                segment.ident.span.find_ancestor_inside(path_span).unwrap_or(path_span)
+            };
+            let ident = Ident::new(kw::UnderscoreLifetime, elided_lifetime_span);
+
+            let missing_lifetime = MissingLifetime {
+                id: node_ids.start,
+                span: elided_lifetime_span,
+                kind: if segment.has_generic_args {
+                    MissingLifetimeKind::Comma
+                } else {
+                    MissingLifetimeKind::Brackets
+                },
+                count: expected_lifetimes,
+            };
+            let mut should_lint = true;
+            for rib in self.lifetime_ribs.iter().rev() {
+                match rib.kind {
+                    // In create-parameter mode we error here because we don't want to support
+                    // deprecated impl elision in new features like impl elision and `async fn`,
+                    // both of which work using the `CreateParameter` mode:
+                    //
+                    //     impl Foo for std::cell::Ref<u32> // note lack of '_
+                    //     async fn foo(_: std::cell::Ref<u32>) { ... }
+                    LifetimeRibKind::AnonymousCreateParameter { report_in_path: true, .. } => {
+                        let sess = self.r.session;
+                        let mut err = rustc_errors::struct_span_err!(
+                            sess,
+                            path_span,
+                            E0726,
+                            "implicit elided lifetime not allowed here"
+                        );
+                        rustc_errors::add_elided_lifetime_in_path_suggestion(
+                            sess.source_map(),
+                            &mut err,
+                            expected_lifetimes,
+                            path_span,
+                            !segment.has_generic_args,
+                            elided_lifetime_span,
+                        );
+                        err.note("assuming a `'static` lifetime...");
+                        err.emit();
+                        should_lint = false;
+
+                        for id in node_ids {
+                            self.record_lifetime_res(
+                                id,
+                                LifetimeRes::Error,
+                                LifetimeElisionCandidate::Named,
+                            );
+                        }
+                        break;
+                    }
+                    // Do not create a parameter for patterns and expressions.
+                    LifetimeRibKind::AnonymousCreateParameter { binder, .. } => {
+                        // Group all suggestions into the first record.
+                        let mut candidate = LifetimeElisionCandidate::Missing(missing_lifetime);
+                        for id in node_ids {
+                            let res = self.create_fresh_lifetime(id, ident, binder);
+                            self.record_lifetime_res(
+                                id,
+                                res,
+                                replace(&mut candidate, LifetimeElisionCandidate::Named),
+                            );
+                        }
+                        break;
+                    }
+                    LifetimeRibKind::Elided(res) => {
+                        let mut candidate = LifetimeElisionCandidate::Missing(missing_lifetime);
+                        for id in node_ids {
+                            self.record_lifetime_res(
+                                id,
+                                res,
+                                replace(&mut candidate, LifetimeElisionCandidate::Ignore),
+                            );
+                        }
+                        break;
+                    }
+                    LifetimeRibKind::ElisionFailure => {
+                        self.diagnostic_metadata.current_elision_failures.push(missing_lifetime);
+                        for id in node_ids {
+                            self.record_lifetime_res(
+                                id,
+                                LifetimeRes::Error,
+                                LifetimeElisionCandidate::Ignore,
+                            );
+                        }
+                        break;
+                    }
+                    // `LifetimeRes::Error`, which would usually be used in the case of
+                    // `ReportError`, is unsuitable here, as we don't emit an error yet.  Instead,
+                    // we simply resolve to an implicit lifetime, which will be checked later, at
+                    // which point a suitable error will be emitted.
+                    LifetimeRibKind::AnonymousReportError | LifetimeRibKind::Item => {
+                        for id in node_ids {
+                            self.record_lifetime_res(
+                                id,
+                                LifetimeRes::Error,
+                                LifetimeElisionCandidate::Ignore,
+                            );
+                        }
+                        self.report_missing_lifetime_specifiers(vec![missing_lifetime], None);
+                        break;
+                    }
+                    LifetimeRibKind::Generics { .. }
+                    | LifetimeRibKind::ConstGeneric
+                    | LifetimeRibKind::AnonConst => {}
+                }
+            }
+
+            if should_lint {
+                self.r.lint_buffer.buffer_lint_with_diagnostic(
+                    lint::builtin::ELIDED_LIFETIMES_IN_PATHS,
+                    segment_id,
+                    elided_lifetime_span,
+                    "hidden lifetime parameters in types are deprecated",
+                    lint::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
+                        expected_lifetimes,
+                        path_span,
+                        !segment.has_generic_args,
+                        elided_lifetime_span,
+                    ),
+                );
+            }
+        }
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn record_lifetime_res(
+        &mut self,
+        id: NodeId,
+        res: LifetimeRes,
+        candidate: LifetimeElisionCandidate,
+    ) {
+        if let Some(prev_res) = self.r.lifetimes_res_map.insert(id, res) {
+            panic!(
+                "lifetime {:?} resolved multiple times ({:?} before, {:?} now)",
+                id, prev_res, res
+            )
+        }
+        match res {
+            LifetimeRes::Param { .. } | LifetimeRes::Fresh { .. } | LifetimeRes::Static => {
+                if let Some(ref mut candidates) = self.lifetime_elision_candidates {
+                    candidates.insert(res, candidate);
+                }
+            }
+            LifetimeRes::Infer | LifetimeRes::Error | LifetimeRes::ElidedAnchor { .. } => {}
+        }
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn record_lifetime_param(&mut self, id: NodeId, res: LifetimeRes) {
+        if let Some(prev_res) = self.r.lifetimes_res_map.insert(id, res) {
+            panic!(
+                "lifetime parameter {:?} resolved multiple times ({:?} before, {:?} now)",
+                id, prev_res, res
+            )
+        }
+    }
+
+    /// Perform resolution of a function signature, accounting for lifetime elision.
+    #[tracing::instrument(level = "debug", skip(self, inputs))]
+    fn resolve_fn_signature(
+        &mut self,
+        fn_id: NodeId,
+        has_self: bool,
+        inputs: impl Iterator<Item = (Option<&'ast Pat>, &'ast Ty)> + Clone,
+        output_ty: &'ast FnRetTy,
+    ) {
+        // Add each argument to the rib.
+        let elision_lifetime = self.resolve_fn_params(has_self, inputs);
+        debug!(?elision_lifetime);
+
+        let outer_failures = take(&mut self.diagnostic_metadata.current_elision_failures);
+        let output_rib = if let Ok(res) = elision_lifetime.as_ref() {
+            LifetimeRibKind::Elided(*res)
+        } else {
+            LifetimeRibKind::ElisionFailure
+        };
+        self.with_lifetime_rib(output_rib, |this| visit::walk_fn_ret_ty(this, &output_ty));
+        let elision_failures =
+            replace(&mut self.diagnostic_metadata.current_elision_failures, outer_failures);
+        if !elision_failures.is_empty() {
+            let Err(failure_info) = elision_lifetime else { bug!() };
+            self.report_missing_lifetime_specifiers(elision_failures, Some(failure_info));
+        }
+    }
+
+    /// Resolve inside function parameters and parameter types.
+    /// Returns the lifetime for elision in fn return type,
+    /// or diagnostic information in case of elision failure.
+    fn resolve_fn_params(
+        &mut self,
+        has_self: bool,
+        inputs: impl Iterator<Item = (Option<&'ast Pat>, &'ast Ty)>,
+    ) -> Result<LifetimeRes, (Vec<MissingLifetime>, Vec<ElisionFnParameter>)> {
+        let outer_candidates =
+            replace(&mut self.lifetime_elision_candidates, Some(Default::default()));
+
+        let mut elision_lifetime = None;
+        let mut lifetime_count = 0;
+        let mut parameter_info = Vec::new();
+
+        let mut bindings = smallvec![(PatBoundCtx::Product, Default::default())];
+        for (index, (pat, ty)) in inputs.enumerate() {
+            debug!(?pat, ?ty);
+            if let Some(pat) = pat {
+                self.resolve_pattern(pat, PatternSource::FnParam, &mut bindings);
+            }
+            self.visit_ty(ty);
+
+            if let Some(ref candidates) = self.lifetime_elision_candidates {
+                let new_count = candidates.len();
+                let local_count = new_count - lifetime_count;
+                if local_count != 0 {
+                    parameter_info.push(ElisionFnParameter {
+                        index,
+                        ident: if let Some(pat) = pat && let PatKind::Ident(_, ident, _) = pat.kind {
+                            Some(ident)
+                        } else {
+                            None
+                        },
+                        lifetime_count: local_count,
+                        span: ty.span,
+                    });
+                }
+                lifetime_count = new_count;
+            }
+
+            // Handle `self` specially.
+            if index == 0 && has_self {
+                let self_lifetime = self.find_lifetime_for_self(ty);
+                if let Set1::One(lifetime) = self_lifetime {
+                    elision_lifetime = Some(lifetime);
+                    self.lifetime_elision_candidates = None;
+                } else {
+                    self.lifetime_elision_candidates = Some(Default::default());
+                    lifetime_count = 0;
+                }
+            }
+            debug!("(resolving function / closure) recorded parameter");
+        }
+
+        let all_candidates = replace(&mut self.lifetime_elision_candidates, outer_candidates);
+        debug!(?all_candidates);
+
+        if let Some(res) = elision_lifetime {
+            return Ok(res);
+        }
+
+        // We do not have a `self` candidate, look at the full list.
+        let all_candidates = all_candidates.unwrap();
+        if all_candidates.len() == 1 {
+            Ok(*all_candidates.first().unwrap().0)
+        } else {
+            let all_candidates = all_candidates
+                .into_iter()
+                .filter_map(|(_, candidate)| match candidate {
+                    LifetimeElisionCandidate::Ignore | LifetimeElisionCandidate::Named => None,
+                    LifetimeElisionCandidate::Missing(missing) => Some(missing),
+                })
+                .collect();
+            Err((all_candidates, parameter_info))
+        }
+    }
+
+    /// List all the lifetimes that appear in the provided type.
+    fn find_lifetime_for_self(&self, ty: &'ast Ty) -> Set1<LifetimeRes> {
+        struct SelfVisitor<'r, 'a> {
+            r: &'r Resolver<'a>,
+            impl_self: Option<Res>,
+            lifetime: Set1<LifetimeRes>,
+        }
+
+        impl SelfVisitor<'_, '_> {
+            // Look for `self: &'a Self` - also desugared from `&'a self`,
+            // and if that matches, use it for elision and return early.
+            fn is_self_ty(&self, ty: &Ty) -> bool {
+                match ty.kind {
+                    TyKind::ImplicitSelf => true,
+                    TyKind::Path(None, _) => {
+                        let path_res = self.r.partial_res_map[&ty.id].base_res();
+                        if let Res::SelfTy { .. } = path_res {
+                            return true;
+                        }
+                        Some(path_res) == self.impl_self
+                    }
+                    _ => false,
+                }
+            }
+        }
+
+        impl<'a> Visitor<'a> for SelfVisitor<'_, '_> {
+            fn visit_ty(&mut self, ty: &'a Ty) {
+                trace!("SelfVisitor considering ty={:?}", ty);
+                if let TyKind::Rptr(lt, ref mt) = ty.kind && self.is_self_ty(&mt.ty) {
+                    let lt_id = if let Some(lt) = lt {
+                        lt.id
+                    } else {
+                        let res = self.r.lifetimes_res_map[&ty.id];
+                        let LifetimeRes::ElidedAnchor { start, .. } = res else { bug!() };
+                        start
+                    };
+                    let lt_res = self.r.lifetimes_res_map[&lt_id];
+                    trace!("SelfVisitor inserting res={:?}", lt_res);
+                    self.lifetime.insert(lt_res);
+                }
+                visit::walk_ty(self, ty)
+            }
+        }
+
+        let impl_self = self
+            .diagnostic_metadata
+            .current_self_type
+            .as_ref()
+            .and_then(|ty| {
+                if let TyKind::Path(None, _) = ty.kind {
+                    self.r.partial_res_map.get(&ty.id)
+                } else {
+                    None
+                }
+            })
+            .map(|res| res.base_res())
+            .filter(|res| {
+                // Permit the types that unambiguously always
+                // result in the same type constructor being used
+                // (it can't differ between `Self` and `self`).
+                matches!(
+                    res,
+                    Res::Def(DefKind::Struct | DefKind::Union | DefKind::Enum, _,) | Res::PrimTy(_)
+                )
+            });
+        let mut visitor = SelfVisitor { r: self.r, impl_self, lifetime: Set1::Empty };
+        visitor.visit_ty(ty);
+        trace!("SelfVisitor found={:?}", visitor.lifetime);
+        visitor.lifetime
+    }
+
+    /// Searches the current set of local scopes for labels. Returns the `NodeId` of the resolved
+    /// label and reports an error if the label is not found or is unreachable.
+    fn resolve_label(&mut self, mut label: Ident) -> Result<(NodeId, Span), ResolutionError<'a>> {
+        let mut suggestion = None;
+
+        for i in (0..self.label_ribs.len()).rev() {
+            let rib = &self.label_ribs[i];
+
+            if let MacroDefinition(def) = rib.kind {
+                // If an invocation of this macro created `ident`, give up on `ident`
+                // and switch to `ident`'s source from the macro definition.
+                if def == self.r.macro_def(label.span.ctxt()) {
+                    label.span.remove_mark();
+                }
+            }
+
+            let ident = label.normalize_to_macro_rules();
+            if let Some((ident, id)) = rib.bindings.get_key_value(&ident) {
+                let definition_span = ident.span;
+                return if self.is_label_valid_from_rib(i) {
+                    Ok((*id, definition_span))
+                } else {
+                    Err(ResolutionError::UnreachableLabel {
+                        name: label.name,
+                        definition_span,
+                        suggestion,
+                    })
+                };
+            }
+
+            // Diagnostics: Check if this rib contains a label with a similar name, keep track of
+            // the first such label that is encountered.
+            suggestion = suggestion.or_else(|| self.suggestion_for_label_in_rib(i, label));
+        }
+
+        Err(ResolutionError::UndeclaredLabel { name: label.name, suggestion })
+    }
+
+    /// Determine whether or not a label from the `rib_index`th label rib is reachable.
+    fn is_label_valid_from_rib(&self, rib_index: usize) -> bool {
+        let ribs = &self.label_ribs[rib_index + 1..];
+
+        for rib in ribs {
+            if rib.kind.is_label_barrier() {
+                return false;
+            }
+        }
+
+        true
+    }
+
+    fn resolve_adt(&mut self, item: &'ast Item, generics: &'ast Generics) {
+        debug!("resolve_adt");
+        self.with_current_self_item(item, |this| {
+            this.with_generic_param_rib(
+                &generics.params,
+                ItemRibKind(HasGenericParams::Yes),
+                LifetimeRibKind::Generics {
+                    binder: item.id,
+                    kind: LifetimeBinderKind::Item,
+                    span: generics.span,
+                },
+                |this| {
+                    let item_def_id = this.r.local_def_id(item.id).to_def_id();
+                    this.with_self_rib(
+                        Res::SelfTy { trait_: None, alias_to: Some((item_def_id, false)) },
+                        |this| {
+                            visit::walk_item(this, item);
+                        },
+                    );
+                },
+            );
+        });
+    }
+
+    fn future_proof_import(&mut self, use_tree: &UseTree) {
+        let segments = &use_tree.prefix.segments;
+        if !segments.is_empty() {
+            let ident = segments[0].ident;
+            if ident.is_path_segment_keyword() || ident.span.rust_2015() {
+                return;
+            }
+
+            let nss = match use_tree.kind {
+                UseTreeKind::Simple(..) if segments.len() == 1 => &[TypeNS, ValueNS][..],
+                _ => &[TypeNS],
+            };
+            let report_error = |this: &Self, ns| {
+                let what = if ns == TypeNS { "type parameters" } else { "local variables" };
+                if this.should_report_errs() {
+                    this.r
+                        .session
+                        .span_err(ident.span, &format!("imports cannot refer to {}", what));
+                }
+            };
+
+            for &ns in nss {
+                match self.maybe_resolve_ident_in_lexical_scope(ident, ns) {
+                    Some(LexicalScopeBinding::Res(..)) => {
+                        report_error(self, ns);
+                    }
+                    Some(LexicalScopeBinding::Item(binding)) => {
+                        if let Some(LexicalScopeBinding::Res(..)) =
+                            self.resolve_ident_in_lexical_scope(ident, ns, None, Some(binding))
+                        {
+                            report_error(self, ns);
+                        }
+                    }
+                    None => {}
+                }
+            }
+        } else if let UseTreeKind::Nested(use_trees) = &use_tree.kind {
+            for (use_tree, _) in use_trees {
+                self.future_proof_import(use_tree);
+            }
+        }
+    }
+
+    fn resolve_item(&mut self, item: &'ast Item) {
+        let name = item.ident.name;
+        debug!("(resolving item) resolving {} ({:?})", name, item.kind);
+
+        match item.kind {
+            ItemKind::TyAlias(box TyAlias { ref generics, .. }) => {
+                self.with_generic_param_rib(
+                    &generics.params,
+                    ItemRibKind(HasGenericParams::Yes),
+                    LifetimeRibKind::Generics {
+                        binder: item.id,
+                        kind: LifetimeBinderKind::Item,
+                        span: generics.span,
+                    },
+                    |this| visit::walk_item(this, item),
+                );
+            }
+
+            ItemKind::Fn(box Fn { ref generics, .. }) => {
+                self.with_generic_param_rib(
+                    &generics.params,
+                    ItemRibKind(HasGenericParams::Yes),
+                    LifetimeRibKind::Generics {
+                        binder: item.id,
+                        kind: LifetimeBinderKind::Function,
+                        span: generics.span,
+                    },
+                    |this| visit::walk_item(this, item),
+                );
+            }
+
+            ItemKind::Enum(_, ref generics)
+            | ItemKind::Struct(_, ref generics)
+            | ItemKind::Union(_, ref generics) => {
+                self.resolve_adt(item, generics);
+            }
+
+            ItemKind::Impl(box Impl {
+                ref generics,
+                ref of_trait,
+                ref self_ty,
+                items: ref impl_items,
+                ..
+            }) => {
+                self.diagnostic_metadata.current_impl_items = Some(impl_items);
+                self.resolve_implementation(generics, of_trait, &self_ty, item.id, impl_items);
+                self.diagnostic_metadata.current_impl_items = None;
+            }
+
+            ItemKind::Trait(box Trait { ref generics, ref bounds, ref items, .. }) => {
+                // Create a new rib for the trait-wide type parameters.
+                self.with_generic_param_rib(
+                    &generics.params,
+                    ItemRibKind(HasGenericParams::Yes),
+                    LifetimeRibKind::Generics {
+                        binder: item.id,
+                        kind: LifetimeBinderKind::Item,
+                        span: generics.span,
+                    },
+                    |this| {
+                        let local_def_id = this.r.local_def_id(item.id).to_def_id();
+                        this.with_self_rib(
+                            Res::SelfTy { trait_: Some(local_def_id), alias_to: None },
+                            |this| {
+                                this.visit_generics(generics);
+                                walk_list!(this, visit_param_bound, bounds, BoundKind::SuperTraits);
+                                this.resolve_trait_items(items);
+                            },
+                        );
+                    },
+                );
+            }
+
+            ItemKind::TraitAlias(ref generics, ref bounds) => {
+                // Create a new rib for the trait-wide type parameters.
+                self.with_generic_param_rib(
+                    &generics.params,
+                    ItemRibKind(HasGenericParams::Yes),
+                    LifetimeRibKind::Generics {
+                        binder: item.id,
+                        kind: LifetimeBinderKind::Item,
+                        span: generics.span,
+                    },
+                    |this| {
+                        let local_def_id = this.r.local_def_id(item.id).to_def_id();
+                        this.with_self_rib(
+                            Res::SelfTy { trait_: Some(local_def_id), alias_to: None },
+                            |this| {
+                                this.visit_generics(generics);
+                                walk_list!(this, visit_param_bound, bounds, BoundKind::Bound);
+                            },
+                        );
+                    },
+                );
+            }
+
+            ItemKind::Mod(..) | ItemKind::ForeignMod(_) => {
+                self.with_scope(item.id, |this| {
+                    visit::walk_item(this, item);
+                });
+            }
+
+            ItemKind::Static(ref ty, _, ref expr) | ItemKind::Const(_, ref ty, ref expr) => {
+                self.with_item_rib(|this| {
+                    this.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Static), |this| {
+                        this.visit_ty(ty);
+                    });
+                    this.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Infer), |this| {
+                        if let Some(expr) = expr {
+                            let constant_item_kind = match item.kind {
+                                ItemKind::Const(..) => ConstantItemKind::Const,
+                                ItemKind::Static(..) => ConstantItemKind::Static,
+                                _ => unreachable!(),
+                            };
+                            // We already forbid generic params because of the above item rib,
+                            // so it doesn't matter whether this is a trivial constant.
+                            this.with_constant_rib(
+                                IsRepeatExpr::No,
+                                HasGenericParams::Yes,
+                                Some((item.ident, constant_item_kind)),
+                                |this| this.visit_expr(expr),
+                            );
+                        }
+                    });
+                });
+            }
+
+            ItemKind::Use(ref use_tree) => {
+                self.future_proof_import(use_tree);
+            }
+
+            ItemKind::ExternCrate(..) | ItemKind::MacroDef(..) => {
+                // do nothing, these are just around to be encoded
+            }
+
+            ItemKind::GlobalAsm(_) => {
+                visit::walk_item(self, item);
+            }
+
+            ItemKind::MacCall(_) => panic!("unexpanded macro in resolve!"),
+        }
+    }
+
+    fn with_generic_param_rib<'c, F>(
+        &'c mut self,
+        params: &'c [GenericParam],
+        kind: RibKind<'a>,
+        lifetime_kind: LifetimeRibKind,
+        f: F,
+    ) where
+        F: FnOnce(&mut Self),
+    {
+        debug!("with_generic_param_rib");
+        let LifetimeRibKind::Generics { binder, span: generics_span, kind: generics_kind, .. }
+            = lifetime_kind else { panic!() };
+
+        let mut function_type_rib = Rib::new(kind);
+        let mut function_value_rib = Rib::new(kind);
+        let mut function_lifetime_rib = LifetimeRib::new(lifetime_kind);
+        let mut seen_bindings = FxHashMap::default();
+        // Store all seen lifetimes names from outer scopes.
+        let mut seen_lifetimes = FxHashSet::default();
+
+        // We also can't shadow bindings from the parent item
+        if let AssocItemRibKind = kind {
+            let mut add_bindings_for_ns = |ns| {
+                let parent_rib = self.ribs[ns]
+                    .iter()
+                    .rfind(|r| matches!(r.kind, ItemRibKind(_)))
+                    .expect("associated item outside of an item");
+                seen_bindings
+                    .extend(parent_rib.bindings.iter().map(|(ident, _)| (*ident, ident.span)));
+            };
+            add_bindings_for_ns(ValueNS);
+            add_bindings_for_ns(TypeNS);
+        }
+
+        // Forbid shadowing lifetime bindings
+        for rib in self.lifetime_ribs.iter().rev() {
+            seen_lifetimes.extend(rib.bindings.iter().map(|(ident, _)| *ident));
+            if let LifetimeRibKind::Item = rib.kind {
+                break;
+            }
+        }
+
+        for param in params {
+            let ident = param.ident.normalize_to_macros_2_0();
+            debug!("with_generic_param_rib: {}", param.id);
+
+            if let GenericParamKind::Lifetime = param.kind
+                && let Some(&original) = seen_lifetimes.get(&ident)
+            {
+                diagnostics::signal_lifetime_shadowing(self.r.session, original, param.ident);
+                // Record lifetime res, so lowering knows there is something fishy.
+                self.record_lifetime_param(param.id, LifetimeRes::Error);
+                continue;
+            }
+
+            match seen_bindings.entry(ident) {
+                Entry::Occupied(entry) => {
+                    let span = *entry.get();
+                    let err = ResolutionError::NameAlreadyUsedInParameterList(ident.name, span);
+                    self.report_error(param.ident.span, err);
+                    if let GenericParamKind::Lifetime = param.kind {
+                        // Record lifetime res, so lowering knows there is something fishy.
+                        self.record_lifetime_param(param.id, LifetimeRes::Error);
+                        continue;
+                    }
+                }
+                Entry::Vacant(entry) => {
+                    entry.insert(param.ident.span);
+                }
+            }
+
+            if param.ident.name == kw::UnderscoreLifetime {
+                rustc_errors::struct_span_err!(
+                    self.r.session,
+                    param.ident.span,
+                    E0637,
+                    "`'_` cannot be used here"
+                )
+                .span_label(param.ident.span, "`'_` is a reserved lifetime name")
+                .emit();
+                // Record lifetime res, so lowering knows there is something fishy.
+                self.record_lifetime_param(param.id, LifetimeRes::Error);
+                continue;
+            }
+
+            if param.ident.name == kw::StaticLifetime {
+                rustc_errors::struct_span_err!(
+                    self.r.session,
+                    param.ident.span,
+                    E0262,
+                    "invalid lifetime parameter name: `{}`",
+                    param.ident,
+                )
+                .span_label(param.ident.span, "'static is a reserved lifetime name")
+                .emit();
+                // Record lifetime res, so lowering knows there is something fishy.
+                self.record_lifetime_param(param.id, LifetimeRes::Error);
+                continue;
+            }
+
+            let def_id = self.r.local_def_id(param.id);
+
+            // Plain insert (no renaming).
+            let (rib, def_kind) = match param.kind {
+                GenericParamKind::Type { .. } => (&mut function_type_rib, DefKind::TyParam),
+                GenericParamKind::Const { .. } => (&mut function_value_rib, DefKind::ConstParam),
+                GenericParamKind::Lifetime => {
+                    let res = LifetimeRes::Param { param: def_id, binder };
+                    self.record_lifetime_param(param.id, res);
+                    function_lifetime_rib.bindings.insert(ident, (param.id, res));
+                    continue;
+                }
+            };
+
+            let res = match kind {
+                ItemRibKind(..) | AssocItemRibKind => Res::Def(def_kind, def_id.to_def_id()),
+                NormalRibKind => Res::Err,
+                _ => span_bug!(param.ident.span, "Unexpected rib kind {:?}", kind),
+            };
+            self.r.record_partial_res(param.id, PartialRes::new(res));
+            rib.bindings.insert(ident, res);
+        }
+
+        self.lifetime_ribs.push(function_lifetime_rib);
+        self.ribs[ValueNS].push(function_value_rib);
+        self.ribs[TypeNS].push(function_type_rib);
+
+        f(self);
+
+        self.ribs[TypeNS].pop();
+        self.ribs[ValueNS].pop();
+        let function_lifetime_rib = self.lifetime_ribs.pop().unwrap();
+
+        // Do not account for the parameters we just bound for function lifetime elision.
+        if let Some(ref mut candidates) = self.lifetime_elision_candidates {
+            for (_, res) in function_lifetime_rib.bindings.values() {
+                candidates.remove(res);
+            }
+        }
+
+        if let LifetimeBinderKind::BareFnType
+        | LifetimeBinderKind::WhereBound
+        | LifetimeBinderKind::Function
+        | LifetimeBinderKind::ImplBlock = generics_kind
+        {
+            self.maybe_report_lifetime_uses(generics_span, params)
+        }
+    }
+
+    fn with_label_rib(&mut self, kind: RibKind<'a>, f: impl FnOnce(&mut Self)) {
+        self.label_ribs.push(Rib::new(kind));
+        f(self);
+        self.label_ribs.pop();
+    }
+
+    fn with_item_rib(&mut self, f: impl FnOnce(&mut Self)) {
+        let kind = ItemRibKind(HasGenericParams::No);
+        self.with_lifetime_rib(LifetimeRibKind::Item, |this| {
+            this.with_rib(ValueNS, kind, |this| this.with_rib(TypeNS, kind, f))
+        })
+    }
+
+    // HACK(min_const_generics,const_evaluatable_unchecked): We
+    // want to keep allowing `[0; std::mem::size_of::<*mut T>()]`
+    // with a future compat lint for now. We do this by adding an
+    // additional special case for repeat expressions.
+    //
+    // Note that we intentionally still forbid `[0; N + 1]` during
+    // name resolution so that we don't extend the future
+    // compat lint to new cases.
+    #[instrument(level = "debug", skip(self, f))]
+    fn with_constant_rib(
+        &mut self,
+        is_repeat: IsRepeatExpr,
+        may_use_generics: HasGenericParams,
+        item: Option<(Ident, ConstantItemKind)>,
+        f: impl FnOnce(&mut Self),
+    ) {
+        self.with_rib(ValueNS, ConstantItemRibKind(may_use_generics, item), |this| {
+            this.with_rib(
+                TypeNS,
+                ConstantItemRibKind(
+                    may_use_generics.force_yes_if(is_repeat == IsRepeatExpr::Yes),
+                    item,
+                ),
+                |this| {
+                    this.with_label_rib(ConstantItemRibKind(may_use_generics, item), f);
+                },
+            )
+        });
+    }
+
+    fn with_current_self_type<T>(&mut self, self_type: &Ty, f: impl FnOnce(&mut Self) -> T) -> T {
+        // Handle nested impls (inside fn bodies)
+        let previous_value =
+            replace(&mut self.diagnostic_metadata.current_self_type, Some(self_type.clone()));
+        let result = f(self);
+        self.diagnostic_metadata.current_self_type = previous_value;
+        result
+    }
+
+    fn with_current_self_item<T>(&mut self, self_item: &Item, f: impl FnOnce(&mut Self) -> T) -> T {
+        let previous_value =
+            replace(&mut self.diagnostic_metadata.current_self_item, Some(self_item.id));
+        let result = f(self);
+        self.diagnostic_metadata.current_self_item = previous_value;
+        result
+    }
+
+    /// When evaluating a `trait` use its associated types' idents for suggestions in E0412.
+    fn resolve_trait_items(&mut self, trait_items: &'ast [P<AssocItem>]) {
+        let trait_assoc_items =
+            replace(&mut self.diagnostic_metadata.current_trait_assoc_items, Some(&trait_items));
+
+        let walk_assoc_item =
+            |this: &mut Self, generics: &Generics, kind, item: &'ast AssocItem| {
+                this.with_generic_param_rib(
+                    &generics.params,
+                    AssocItemRibKind,
+                    LifetimeRibKind::Generics { binder: item.id, span: generics.span, kind },
+                    |this| visit::walk_assoc_item(this, item, AssocCtxt::Trait),
+                );
+            };
+
+        for item in trait_items {
+            match &item.kind {
+                AssocItemKind::Const(_, ty, default) => {
+                    self.visit_ty(ty);
+                    // Only impose the restrictions of `ConstRibKind` for an
+                    // actual constant expression in a provided default.
+                    if let Some(expr) = default {
+                        // We allow arbitrary const expressions inside of associated consts,
+                        // even if they are potentially not const evaluatable.
+                        //
+                        // Type parameters can already be used and as associated consts are
+                        // not used as part of the type system, this is far less surprising.
+                        self.with_lifetime_rib(
+                            LifetimeRibKind::Elided(LifetimeRes::Infer),
+                            |this| {
+                                this.with_constant_rib(
+                                    IsRepeatExpr::No,
+                                    HasGenericParams::Yes,
+                                    None,
+                                    |this| this.visit_expr(expr),
+                                )
+                            },
+                        );
+                    }
+                }
+                AssocItemKind::Fn(box Fn { generics, .. }) => {
+                    walk_assoc_item(self, generics, LifetimeBinderKind::Function, item);
+                }
+                AssocItemKind::TyAlias(box TyAlias { generics, .. }) => self
+                    .with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
+                        walk_assoc_item(this, generics, LifetimeBinderKind::Item, item)
+                    }),
+                AssocItemKind::MacCall(_) => {
+                    panic!("unexpanded macro in resolve!")
+                }
+            };
+        }
+
+        self.diagnostic_metadata.current_trait_assoc_items = trait_assoc_items;
+    }
+
+    /// This is called to resolve a trait reference from an `impl` (i.e., `impl Trait for Foo`).
+    fn with_optional_trait_ref<T>(
+        &mut self,
+        opt_trait_ref: Option<&TraitRef>,
+        self_type: &'ast Ty,
+        f: impl FnOnce(&mut Self, Option<DefId>) -> T,
+    ) -> T {
+        let mut new_val = None;
+        let mut new_id = None;
+        if let Some(trait_ref) = opt_trait_ref {
+            let path: Vec<_> = Segment::from_path(&trait_ref.path);
+            self.diagnostic_metadata.currently_processing_impl_trait =
+                Some((trait_ref.clone(), self_type.clone()));
+            let res = self.smart_resolve_path_fragment(
+                None,
+                &path,
+                PathSource::Trait(AliasPossibility::No),
+                Finalize::new(trait_ref.ref_id, trait_ref.path.span),
+            );
+            self.diagnostic_metadata.currently_processing_impl_trait = None;
+            if let Some(def_id) = res.base_res().opt_def_id() {
+                new_id = Some(def_id);
+                new_val = Some((self.r.expect_module(def_id), trait_ref.clone()));
+            }
+        }
+        let original_trait_ref = replace(&mut self.current_trait_ref, new_val);
+        let result = f(self, new_id);
+        self.current_trait_ref = original_trait_ref;
+        result
+    }
+
+    fn with_self_rib_ns(&mut self, ns: Namespace, self_res: Res, f: impl FnOnce(&mut Self)) {
+        let mut self_type_rib = Rib::new(NormalRibKind);
+
+        // Plain insert (no renaming, since types are not currently hygienic)
+        self_type_rib.bindings.insert(Ident::with_dummy_span(kw::SelfUpper), self_res);
+        self.ribs[ns].push(self_type_rib);
+        f(self);
+        self.ribs[ns].pop();
+    }
+
+    fn with_self_rib(&mut self, self_res: Res, f: impl FnOnce(&mut Self)) {
+        self.with_self_rib_ns(TypeNS, self_res, f)
+    }
+
+    fn resolve_implementation(
+        &mut self,
+        generics: &'ast Generics,
+        opt_trait_reference: &'ast Option<TraitRef>,
+        self_type: &'ast Ty,
+        item_id: NodeId,
+        impl_items: &'ast [P<AssocItem>],
+    ) {
+        debug!("resolve_implementation");
+        // If applicable, create a rib for the type parameters.
+        self.with_generic_param_rib(
+            &generics.params,
+            ItemRibKind(HasGenericParams::Yes),
+            LifetimeRibKind::Generics {
+                span: generics.span,
+                binder: item_id,
+                kind: LifetimeBinderKind::ImplBlock,
+            },
+            |this| {
+                // Dummy self type for better errors if `Self` is used in the trait path.
+                this.with_self_rib(Res::SelfTy { trait_: None, alias_to: None }, |this| {
+                    this.with_lifetime_rib(
+                        LifetimeRibKind::AnonymousCreateParameter {
+                            binder: item_id,
+                            report_in_path: true
+                        },
+                        |this| {
+                            // Resolve the trait reference, if necessary.
+                            this.with_optional_trait_ref(
+                                opt_trait_reference.as_ref(),
+                                self_type,
+                                |this, trait_id| {
+                                    let item_def_id = this.r.local_def_id(item_id);
+
+                                    // Register the trait definitions from here.
+                                    if let Some(trait_id) = trait_id {
+                                        this.r
+                                            .trait_impls
+                                            .entry(trait_id)
+                                            .or_default()
+                                            .push(item_def_id);
+                                    }
+
+                                    let item_def_id = item_def_id.to_def_id();
+                                    let res = Res::SelfTy {
+                                        trait_: trait_id,
+                                        alias_to: Some((item_def_id, false)),
+                                    };
+                                    this.with_self_rib(res, |this| {
+                                        if let Some(trait_ref) = opt_trait_reference.as_ref() {
+                                            // Resolve type arguments in the trait path.
+                                            visit::walk_trait_ref(this, trait_ref);
+                                        }
+                                        // Resolve the self type.
+                                        this.visit_ty(self_type);
+                                        // Resolve the generic parameters.
+                                        this.visit_generics(generics);
+
+                                        // Resolve the items within the impl.
+                                        this.with_current_self_type(self_type, |this| {
+                                            this.with_self_rib_ns(ValueNS, Res::SelfCtor(item_def_id), |this| {
+                                                debug!("resolve_implementation with_self_rib_ns(ValueNS, ...)");
+                                                for item in impl_items {
+                                                    this.resolve_impl_item(&**item);
+                                                }
+                                            });
+                                        });
+                                    });
+                                },
+                            )
+                        },
+                    );
+                });
+            },
+        );
+    }
+
+    fn resolve_impl_item(&mut self, item: &'ast AssocItem) {
+        use crate::ResolutionError::*;
+        match &item.kind {
+            AssocItemKind::Const(_, ty, default) => {
+                debug!("resolve_implementation AssocItemKind::Const");
+                // If this is a trait impl, ensure the const
+                // exists in trait
+                self.check_trait_item(
+                    item.id,
+                    item.ident,
+                    &item.kind,
+                    ValueNS,
+                    item.span,
+                    |i, s, c| ConstNotMemberOfTrait(i, s, c),
+                );
+
+                self.visit_ty(ty);
+                if let Some(expr) = default {
+                    // We allow arbitrary const expressions inside of associated consts,
+                    // even if they are potentially not const evaluatable.
+                    //
+                    // Type parameters can already be used and as associated consts are
+                    // not used as part of the type system, this is far less surprising.
+                    self.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Infer), |this| {
+                        this.with_constant_rib(
+                            IsRepeatExpr::No,
+                            HasGenericParams::Yes,
+                            None,
+                            |this| this.visit_expr(expr),
+                        )
+                    });
+                }
+            }
+            AssocItemKind::Fn(box Fn { generics, .. }) => {
+                debug!("resolve_implementation AssocItemKind::Fn");
+                // We also need a new scope for the impl item type parameters.
+                self.with_generic_param_rib(
+                    &generics.params,
+                    AssocItemRibKind,
+                    LifetimeRibKind::Generics {
+                        binder: item.id,
+                        span: generics.span,
+                        kind: LifetimeBinderKind::Function,
+                    },
+                    |this| {
+                        // If this is a trait impl, ensure the method
+                        // exists in trait
+                        this.check_trait_item(
+                            item.id,
+                            item.ident,
+                            &item.kind,
+                            ValueNS,
+                            item.span,
+                            |i, s, c| MethodNotMemberOfTrait(i, s, c),
+                        );
+
+                        visit::walk_assoc_item(this, item, AssocCtxt::Impl)
+                    },
+                );
+            }
+            AssocItemKind::TyAlias(box TyAlias { generics, .. }) => {
+                debug!("resolve_implementation AssocItemKind::TyAlias");
+                // We also need a new scope for the impl item type parameters.
+                self.with_generic_param_rib(
+                    &generics.params,
+                    AssocItemRibKind,
+                    LifetimeRibKind::Generics {
+                        binder: item.id,
+                        span: generics.span,
+                        kind: LifetimeBinderKind::Item,
+                    },
+                    |this| {
+                        this.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
+                            // If this is a trait impl, ensure the type
+                            // exists in trait
+                            this.check_trait_item(
+                                item.id,
+                                item.ident,
+                                &item.kind,
+                                TypeNS,
+                                item.span,
+                                |i, s, c| TypeNotMemberOfTrait(i, s, c),
+                            );
+
+                            visit::walk_assoc_item(this, item, AssocCtxt::Impl)
+                        });
+                    },
+                );
+            }
+            AssocItemKind::MacCall(_) => {
+                panic!("unexpanded macro in resolve!")
+            }
+        }
+    }
+
+    fn check_trait_item<F>(
+        &mut self,
+        id: NodeId,
+        mut ident: Ident,
+        kind: &AssocItemKind,
+        ns: Namespace,
+        span: Span,
+        err: F,
+    ) where
+        F: FnOnce(Ident, String, Option<Symbol>) -> ResolutionError<'a>,
+    {
+        // If there is a TraitRef in scope for an impl, then the method must be in the trait.
+        let Some((module, _)) = &self.current_trait_ref else { return; };
+        ident.span.normalize_to_macros_2_0_and_adjust(module.expansion);
+        let key = self.r.new_key(ident, ns);
+        let mut binding = self.r.resolution(module, key).try_borrow().ok().and_then(|r| r.binding);
+        debug!(?binding);
+        if binding.is_none() {
+            // We could not find the trait item in the correct namespace.
+            // Check the other namespace to report an error.
+            let ns = match ns {
+                ValueNS => TypeNS,
+                TypeNS => ValueNS,
+                _ => ns,
+            };
+            let key = self.r.new_key(ident, ns);
+            binding = self.r.resolution(module, key).try_borrow().ok().and_then(|r| r.binding);
+            debug!(?binding);
+        }
+        let Some(binding) = binding else {
+            // We could not find the method: report an error.
+            let candidate = self.find_similarly_named_assoc_item(ident.name, kind);
+            let path = &self.current_trait_ref.as_ref().unwrap().1.path;
+            let path_names = path_names_to_string(path);
+            self.report_error(span, err(ident, path_names, candidate));
+            return;
+        };
+
+        let res = binding.res();
+        let Res::Def(def_kind, _) = res else { bug!() };
+        match (def_kind, kind) {
+            (DefKind::AssocTy, AssocItemKind::TyAlias(..))
+            | (DefKind::AssocFn, AssocItemKind::Fn(..))
+            | (DefKind::AssocConst, AssocItemKind::Const(..)) => {
+                self.r.record_partial_res(id, PartialRes::new(res));
+                return;
+            }
+            _ => {}
+        }
+
+        // The method kind does not correspond to what appeared in the trait, report.
+        let path = &self.current_trait_ref.as_ref().unwrap().1.path;
+        let (code, kind) = match kind {
+            AssocItemKind::Const(..) => (rustc_errors::error_code!(E0323), "const"),
+            AssocItemKind::Fn(..) => (rustc_errors::error_code!(E0324), "method"),
+            AssocItemKind::TyAlias(..) => (rustc_errors::error_code!(E0325), "type"),
+            AssocItemKind::MacCall(..) => span_bug!(span, "unexpanded macro"),
+        };
+        let trait_path = path_names_to_string(path);
+        self.report_error(
+            span,
+            ResolutionError::TraitImplMismatch {
+                name: ident.name,
+                kind,
+                code,
+                trait_path,
+                trait_item_span: binding.span,
+            },
+        );
+    }
+
+    fn resolve_params(&mut self, params: &'ast [Param]) {
+        let mut bindings = smallvec![(PatBoundCtx::Product, Default::default())];
+        for Param { pat, ty, .. } in params {
+            self.resolve_pattern(pat, PatternSource::FnParam, &mut bindings);
+            self.visit_ty(ty);
+            debug!("(resolving function / closure) recorded parameter");
+        }
+    }
+
+    fn resolve_local(&mut self, local: &'ast Local) {
+        debug!("resolving local ({:?})", local);
+        // Resolve the type.
+        walk_list!(self, visit_ty, &local.ty);
+
+        // Resolve the initializer.
+        if let Some((init, els)) = local.kind.init_else_opt() {
+            self.visit_expr(init);
+
+            // Resolve the `else` block
+            if let Some(els) = els {
+                self.visit_block(els);
+            }
+        }
+
+        // Resolve the pattern.
+        self.resolve_pattern_top(&local.pat, PatternSource::Let);
+    }
+
+    /// build a map from pattern identifiers to binding-info's.
+    /// this is done hygienically. This could arise for a macro
+    /// that expands into an or-pattern where one 'x' was from the
+    /// user and one 'x' came from the macro.
+    fn binding_mode_map(&mut self, pat: &Pat) -> BindingMap {
+        let mut binding_map = FxHashMap::default();
+
+        pat.walk(&mut |pat| {
+            match pat.kind {
+                PatKind::Ident(binding_mode, ident, ref sub_pat)
+                    if sub_pat.is_some() || self.is_base_res_local(pat.id) =>
+                {
+                    binding_map.insert(ident, BindingInfo { span: ident.span, binding_mode });
+                }
+                PatKind::Or(ref ps) => {
+                    // Check the consistency of this or-pattern and
+                    // then add all bindings to the larger map.
+                    for bm in self.check_consistent_bindings(ps) {
+                        binding_map.extend(bm);
+                    }
+                    return false;
+                }
+                _ => {}
+            }
+
+            true
+        });
+
+        binding_map
+    }
+
+    fn is_base_res_local(&self, nid: NodeId) -> bool {
+        matches!(self.r.partial_res_map.get(&nid).map(|res| res.base_res()), Some(Res::Local(..)))
+    }
+
+    /// Checks that all of the arms in an or-pattern have exactly the
+    /// same set of bindings, with the same binding modes for each.
+    fn check_consistent_bindings(&mut self, pats: &[P<Pat>]) -> Vec<BindingMap> {
+        let mut missing_vars = FxHashMap::default();
+        let mut inconsistent_vars = FxHashMap::default();
+
+        // 1) Compute the binding maps of all arms.
+        let maps = pats.iter().map(|pat| self.binding_mode_map(pat)).collect::<Vec<_>>();
+
+        // 2) Record any missing bindings or binding mode inconsistencies.
+        for (map_outer, pat_outer) in pats.iter().enumerate().map(|(idx, pat)| (&maps[idx], pat)) {
+            // Check against all arms except for the same pattern which is always self-consistent.
+            let inners = pats
+                .iter()
+                .enumerate()
+                .filter(|(_, pat)| pat.id != pat_outer.id)
+                .flat_map(|(idx, _)| maps[idx].iter())
+                .map(|(key, binding)| (key.name, map_outer.get(&key), binding));
+
+            for (name, info, &binding_inner) in inners {
+                match info {
+                    None => {
+                        // The inner binding is missing in the outer.
+                        let binding_error =
+                            missing_vars.entry(name).or_insert_with(|| BindingError {
+                                name,
+                                origin: BTreeSet::new(),
+                                target: BTreeSet::new(),
+                                could_be_path: name.as_str().starts_with(char::is_uppercase),
+                            });
+                        binding_error.origin.insert(binding_inner.span);
+                        binding_error.target.insert(pat_outer.span);
+                    }
+                    Some(binding_outer) => {
+                        if binding_outer.binding_mode != binding_inner.binding_mode {
+                            // The binding modes in the outer and inner bindings differ.
+                            inconsistent_vars
+                                .entry(name)
+                                .or_insert((binding_inner.span, binding_outer.span));
+                        }
+                    }
+                }
+            }
+        }
+
+        // 3) Report all missing variables we found.
+        let mut missing_vars = missing_vars.into_iter().collect::<Vec<_>>();
+        missing_vars.sort_by_key(|&(sym, ref _err)| sym);
+
+        for (name, mut v) in missing_vars.into_iter() {
+            if inconsistent_vars.contains_key(&name) {
+                v.could_be_path = false;
+            }
+            self.report_error(
+                *v.origin.iter().next().unwrap(),
+                ResolutionError::VariableNotBoundInPattern(v, self.parent_scope),
+            );
+        }
+
+        // 4) Report all inconsistencies in binding modes we found.
+        let mut inconsistent_vars = inconsistent_vars.iter().collect::<Vec<_>>();
+        inconsistent_vars.sort();
+        for (name, v) in inconsistent_vars {
+            self.report_error(v.0, ResolutionError::VariableBoundWithDifferentMode(*name, v.1));
+        }
+
+        // 5) Finally bubble up all the binding maps.
+        maps
+    }
+
+    /// Check the consistency of the outermost or-patterns.
+    fn check_consistent_bindings_top(&mut self, pat: &'ast Pat) {
+        pat.walk(&mut |pat| match pat.kind {
+            PatKind::Or(ref ps) => {
+                self.check_consistent_bindings(ps);
+                false
+            }
+            _ => true,
+        })
+    }
+
+    fn resolve_arm(&mut self, arm: &'ast Arm) {
+        self.with_rib(ValueNS, NormalRibKind, |this| {
+            this.resolve_pattern_top(&arm.pat, PatternSource::Match);
+            walk_list!(this, visit_expr, &arm.guard);
+            this.visit_expr(&arm.body);
+        });
+    }
+
+    /// Arising from `source`, resolve a top level pattern.
+    fn resolve_pattern_top(&mut self, pat: &'ast Pat, pat_src: PatternSource) {
+        let mut bindings = smallvec![(PatBoundCtx::Product, Default::default())];
+        self.resolve_pattern(pat, pat_src, &mut bindings);
+    }
+
+    fn resolve_pattern(
+        &mut self,
+        pat: &'ast Pat,
+        pat_src: PatternSource,
+        bindings: &mut SmallVec<[(PatBoundCtx, FxHashSet<Ident>); 1]>,
+    ) {
+        // We walk the pattern before declaring the pattern's inner bindings,
+        // so that we avoid resolving a literal expression to a binding defined
+        // by the pattern.
+        visit::walk_pat(self, pat);
+        self.resolve_pattern_inner(pat, pat_src, bindings);
+        // This has to happen *after* we determine which pat_idents are variants:
+        self.check_consistent_bindings_top(pat);
+    }
+
+    /// Resolve bindings in a pattern. This is a helper to `resolve_pattern`.
+    ///
+    /// ### `bindings`
+    ///
+    /// A stack of sets of bindings accumulated.
+    ///
+    /// In each set, `PatBoundCtx::Product` denotes that a found binding in it should
+    /// be interpreted as re-binding an already bound binding. This results in an error.
+    /// Meanwhile, `PatBound::Or` denotes that a found binding in the set should result
+    /// in reusing this binding rather than creating a fresh one.
+    ///
+    /// When called at the top level, the stack must have a single element
+    /// with `PatBound::Product`. Otherwise, pushing to the stack happens as
+    /// or-patterns (`p_0 | ... | p_n`) are encountered and the context needs
+    /// to be switched to `PatBoundCtx::Or` and then `PatBoundCtx::Product` for each `p_i`.
+    /// When each `p_i` has been dealt with, the top set is merged with its parent.
+    /// When a whole or-pattern has been dealt with, the thing happens.
+    ///
+    /// See the implementation and `fresh_binding` for more details.
+    fn resolve_pattern_inner(
+        &mut self,
+        pat: &Pat,
+        pat_src: PatternSource,
+        bindings: &mut SmallVec<[(PatBoundCtx, FxHashSet<Ident>); 1]>,
+    ) {
+        // Visit all direct subpatterns of this pattern.
+        pat.walk(&mut |pat| {
+            debug!("resolve_pattern pat={:?} node={:?}", pat, pat.kind);
+            match pat.kind {
+                PatKind::Ident(bmode, ident, ref sub) => {
+                    // First try to resolve the identifier as some existing entity,
+                    // then fall back to a fresh binding.
+                    let has_sub = sub.is_some();
+                    let res = self
+                        .try_resolve_as_non_binding(pat_src, bmode, ident, has_sub)
+                        .unwrap_or_else(|| self.fresh_binding(ident, pat.id, pat_src, bindings));
+                    self.r.record_partial_res(pat.id, PartialRes::new(res));
+                    self.r.record_pat_span(pat.id, pat.span);
+                }
+                PatKind::TupleStruct(ref qself, ref path, ref sub_patterns) => {
+                    self.smart_resolve_path(
+                        pat.id,
+                        qself.as_ref(),
+                        path,
+                        PathSource::TupleStruct(
+                            pat.span,
+                            self.r.arenas.alloc_pattern_spans(sub_patterns.iter().map(|p| p.span)),
+                        ),
+                    );
+                }
+                PatKind::Path(ref qself, ref path) => {
+                    self.smart_resolve_path(pat.id, qself.as_ref(), path, PathSource::Pat);
+                }
+                PatKind::Struct(ref qself, ref path, ..) => {
+                    self.smart_resolve_path(pat.id, qself.as_ref(), path, PathSource::Struct);
+                }
+                PatKind::Or(ref ps) => {
+                    // Add a new set of bindings to the stack. `Or` here records that when a
+                    // binding already exists in this set, it should not result in an error because
+                    // `V1(a) | V2(a)` must be allowed and are checked for consistency later.
+                    bindings.push((PatBoundCtx::Or, Default::default()));
+                    for p in ps {
+                        // Now we need to switch back to a product context so that each
+                        // part of the or-pattern internally rejects already bound names.
+                        // For example, `V1(a) | V2(a, a)` and `V1(a, a) | V2(a)` are bad.
+                        bindings.push((PatBoundCtx::Product, Default::default()));
+                        self.resolve_pattern_inner(p, pat_src, bindings);
+                        // Move up the non-overlapping bindings to the or-pattern.
+                        // Existing bindings just get "merged".
+                        let collected = bindings.pop().unwrap().1;
+                        bindings.last_mut().unwrap().1.extend(collected);
+                    }
+                    // This or-pattern itself can itself be part of a product,
+                    // e.g. `(V1(a) | V2(a), a)` or `(a, V1(a) | V2(a))`.
+                    // Both cases bind `a` again in a product pattern and must be rejected.
+                    let collected = bindings.pop().unwrap().1;
+                    bindings.last_mut().unwrap().1.extend(collected);
+
+                    // Prevent visiting `ps` as we've already done so above.
+                    return false;
+                }
+                _ => {}
+            }
+            true
+        });
+    }
+
+    fn fresh_binding(
+        &mut self,
+        ident: Ident,
+        pat_id: NodeId,
+        pat_src: PatternSource,
+        bindings: &mut SmallVec<[(PatBoundCtx, FxHashSet<Ident>); 1]>,
+    ) -> Res {
+        // Add the binding to the local ribs, if it doesn't already exist in the bindings map.
+        // (We must not add it if it's in the bindings map because that breaks the assumptions
+        // later passes make about or-patterns.)
+        let ident = ident.normalize_to_macro_rules();
+
+        let mut bound_iter = bindings.iter().filter(|(_, set)| set.contains(&ident));
+        // Already bound in a product pattern? e.g. `(a, a)` which is not allowed.
+        let already_bound_and = bound_iter.clone().any(|(ctx, _)| *ctx == PatBoundCtx::Product);
+        // Already bound in an or-pattern? e.g. `V1(a) | V2(a)`.
+        // This is *required* for consistency which is checked later.
+        let already_bound_or = bound_iter.any(|(ctx, _)| *ctx == PatBoundCtx::Or);
+
+        if already_bound_and {
+            // Overlap in a product pattern somewhere; report an error.
+            use ResolutionError::*;
+            let error = match pat_src {
+                // `fn f(a: u8, a: u8)`:
+                PatternSource::FnParam => IdentifierBoundMoreThanOnceInParameterList,
+                // `Variant(a, a)`:
+                _ => IdentifierBoundMoreThanOnceInSamePattern,
+            };
+            self.report_error(ident.span, error(ident.name));
+        }
+
+        // Record as bound if it's valid:
+        let ident_valid = ident.name != kw::Empty;
+        if ident_valid {
+            bindings.last_mut().unwrap().1.insert(ident);
+        }
+
+        if already_bound_or {
+            // `Variant1(a) | Variant2(a)`, ok
+            // Reuse definition from the first `a`.
+            self.innermost_rib_bindings(ValueNS)[&ident]
+        } else {
+            let res = Res::Local(pat_id);
+            if ident_valid {
+                // A completely fresh binding add to the set if it's valid.
+                self.innermost_rib_bindings(ValueNS).insert(ident, res);
+            }
+            res
+        }
+    }
+
+    fn innermost_rib_bindings(&mut self, ns: Namespace) -> &mut IdentMap<Res> {
+        &mut self.ribs[ns].last_mut().unwrap().bindings
+    }
+
+    fn try_resolve_as_non_binding(
+        &mut self,
+        pat_src: PatternSource,
+        bm: BindingMode,
+        ident: Ident,
+        has_sub: bool,
+    ) -> Option<Res> {
+        // An immutable (no `mut`) by-value (no `ref`) binding pattern without
+        // a sub pattern (no `@ $pat`) is syntactically ambiguous as it could
+        // also be interpreted as a path to e.g. a constant, variant, etc.
+        let is_syntactic_ambiguity = !has_sub && bm == BindingMode::ByValue(Mutability::Not);
+
+        let ls_binding = self.maybe_resolve_ident_in_lexical_scope(ident, ValueNS)?;
+        let (res, binding) = match ls_binding {
+            LexicalScopeBinding::Item(binding)
+                if is_syntactic_ambiguity && binding.is_ambiguity() =>
+            {
+                // For ambiguous bindings we don't know all their definitions and cannot check
+                // whether they can be shadowed by fresh bindings or not, so force an error.
+                // issues/33118#issuecomment-233962221 (see below) still applies here,
+                // but we have to ignore it for backward compatibility.
+                self.r.record_use(ident, binding, false);
+                return None;
+            }
+            LexicalScopeBinding::Item(binding) => (binding.res(), Some(binding)),
+            LexicalScopeBinding::Res(res) => (res, None),
+        };
+
+        match res {
+            Res::SelfCtor(_) // See #70549.
+            | Res::Def(
+                DefKind::Ctor(_, CtorKind::Const) | DefKind::Const | DefKind::ConstParam,
+                _,
+            ) if is_syntactic_ambiguity => {
+                // Disambiguate in favor of a unit struct/variant or constant pattern.
+                if let Some(binding) = binding {
+                    self.r.record_use(ident, binding, false);
+                }
+                Some(res)
+            }
+            Res::Def(DefKind::Ctor(..) | DefKind::Const | DefKind::Static(_), _) => {
+                // This is unambiguously a fresh binding, either syntactically
+                // (e.g., `IDENT @ PAT` or `ref IDENT`) or because `IDENT` resolves
+                // to something unusable as a pattern (e.g., constructor function),
+                // but we still conservatively report an error, see
+                // issues/33118#issuecomment-233962221 for one reason why.
+                let binding = binding.expect("no binding for a ctor or static");
+                self.report_error(
+                    ident.span,
+                    ResolutionError::BindingShadowsSomethingUnacceptable {
+                        shadowing_binding: pat_src,
+                        name: ident.name,
+                        participle: if binding.is_import() { "imported" } else { "defined" },
+                        article: binding.res().article(),
+                        shadowed_binding: binding.res(),
+                        shadowed_binding_span: binding.span,
+                    },
+                );
+                None
+            }
+            Res::Def(DefKind::ConstParam, def_id) => {
+                // Same as for DefKind::Const above, but here, `binding` is `None`, so we
+                // have to construct the error differently
+                self.report_error(
+                    ident.span,
+                    ResolutionError::BindingShadowsSomethingUnacceptable {
+                        shadowing_binding: pat_src,
+                        name: ident.name,
+                        participle: "defined",
+                        article: res.article(),
+                        shadowed_binding: res,
+                        shadowed_binding_span: self.r.opt_span(def_id).expect("const parameter defined outside of local crate"),
+                    }
+                );
+                None
+            }
+            Res::Def(DefKind::Fn, _) | Res::Local(..) | Res::Err => {
+                // These entities are explicitly allowed to be shadowed by fresh bindings.
+                None
+            }
+            Res::SelfCtor(_) => {
+                // We resolve `Self` in pattern position as an ident sometimes during recovery,
+                // so delay a bug instead of ICEing.
+                self.r.session.delay_span_bug(
+                    ident.span,
+                    "unexpected `SelfCtor` in pattern, expected identifier"
+                );
+                None
+            }
+            _ => span_bug!(
+                ident.span,
+                "unexpected resolution for an identifier in pattern: {:?}",
+                res,
+            ),
+        }
+    }
+
+    // High-level and context dependent path resolution routine.
+    // Resolves the path and records the resolution into definition map.
+    // If resolution fails tries several techniques to find likely
+    // resolution candidates, suggest imports or other help, and report
+    // errors in user friendly way.
+    fn smart_resolve_path(
+        &mut self,
+        id: NodeId,
+        qself: Option<&QSelf>,
+        path: &Path,
+        source: PathSource<'ast>,
+    ) {
+        self.smart_resolve_path_fragment(
+            qself,
+            &Segment::from_path(path),
+            source,
+            Finalize::new(id, path.span),
+        );
+    }
+
+    fn smart_resolve_path_fragment(
+        &mut self,
+        qself: Option<&QSelf>,
+        path: &[Segment],
+        source: PathSource<'ast>,
+        finalize: Finalize,
+    ) -> PartialRes {
+        tracing::debug!(
+            "smart_resolve_path_fragment(qself={:?}, path={:?}, finalize={:?})",
+            qself,
+            path,
+            finalize,
+        );
+        let ns = source.namespace();
+
+        let Finalize { node_id, path_span, .. } = finalize;
+        let report_errors = |this: &mut Self, res: Option<Res>| {
+            if this.should_report_errs() {
+                let (err, candidates) =
+                    this.smart_resolve_report_errors(path, path_span, source, res);
+
+                let def_id = this.parent_scope.module.nearest_parent_mod();
+                let instead = res.is_some();
+                let suggestion =
+                    if res.is_none() { this.report_missing_type_error(path) } else { None };
+
+                this.r.use_injections.push(UseError {
+                    err,
+                    candidates,
+                    def_id,
+                    instead,
+                    suggestion,
+                    path: path.into(),
+                });
+            }
+
+            PartialRes::new(Res::Err)
+        };
+
+        // For paths originating from calls (like in `HashMap::new()`), tries
+        // to enrich the plain `failed to resolve: ...` message with hints
+        // about possible missing imports.
+        //
+        // Similar thing, for types, happens in `report_errors` above.
+        let report_errors_for_call = |this: &mut Self, parent_err: Spanned<ResolutionError<'a>>| {
+            if !source.is_call() {
+                return Some(parent_err);
+            }
+
+            // Before we start looking for candidates, we have to get our hands
+            // on the type user is trying to perform invocation on; basically:
+            // we're transforming `HashMap::new` into just `HashMap`.
+            let path = match path.split_last() {
+                Some((_, path)) if !path.is_empty() => path,
+                _ => return Some(parent_err),
+            };
+
+            let (mut err, candidates) =
+                this.smart_resolve_report_errors(path, path_span, PathSource::Type, None);
+
+            if candidates.is_empty() {
+                err.cancel();
+                return Some(parent_err);
+            }
+
+            // There are two different error messages user might receive at
+            // this point:
+            // - E0412 cannot find type `{}` in this scope
+            // - E0433 failed to resolve: use of undeclared type or module `{}`
+            //
+            // The first one is emitted for paths in type-position, and the
+            // latter one - for paths in expression-position.
+            //
+            // Thus (since we're in expression-position at this point), not to
+            // confuse the user, we want to keep the *message* from E0432 (so
+            // `parent_err`), but we want *hints* from E0412 (so `err`).
+            //
+            // And that's what happens below - we're just mixing both messages
+            // into a single one.
+            let mut parent_err = this.r.into_struct_error(parent_err.span, parent_err.node);
+
+            err.message = take(&mut parent_err.message);
+            err.code = take(&mut parent_err.code);
+            err.children = take(&mut parent_err.children);
+
+            parent_err.cancel();
+
+            let def_id = this.parent_scope.module.nearest_parent_mod();
+
+            if this.should_report_errs() {
+                this.r.use_injections.push(UseError {
+                    err,
+                    candidates,
+                    def_id,
+                    instead: false,
+                    suggestion: None,
+                    path: path.into(),
+                });
+            } else {
+                err.cancel();
+            }
+
+            // We don't return `Some(parent_err)` here, because the error will
+            // be already printed as part of the `use` injections
+            None
+        };
+
+        let partial_res = match self.resolve_qpath_anywhere(
+            qself,
+            path,
+            ns,
+            path_span,
+            source.defer_to_typeck(),
+            finalize,
+        ) {
+            Ok(Some(partial_res)) if partial_res.unresolved_segments() == 0 => {
+                if source.is_expected(partial_res.base_res()) || partial_res.base_res() == Res::Err
+                {
+                    partial_res
+                } else {
+                    report_errors(self, Some(partial_res.base_res()))
+                }
+            }
+
+            Ok(Some(partial_res)) if source.defer_to_typeck() => {
+                // Not fully resolved associated item `T::A::B` or `<T as Tr>::A::B`
+                // or `<T>::A::B`. If `B` should be resolved in value namespace then
+                // it needs to be added to the trait map.
+                if ns == ValueNS {
+                    let item_name = path.last().unwrap().ident;
+                    let traits = self.traits_in_scope(item_name, ns);
+                    self.r.trait_map.insert(node_id, traits);
+                }
+
+                if PrimTy::from_name(path[0].ident.name).is_some() {
+                    let mut std_path = Vec::with_capacity(1 + path.len());
+
+                    std_path.push(Segment::from_ident(Ident::with_dummy_span(sym::std)));
+                    std_path.extend(path);
+                    if let PathResult::Module(_) | PathResult::NonModule(_) =
+                        self.resolve_path(&std_path, Some(ns), None)
+                    {
+                        // Check if we wrote `str::from_utf8` instead of `std::str::from_utf8`
+                        let item_span =
+                            path.iter().last().map_or(path_span, |segment| segment.ident.span);
+
+                        self.r.confused_type_with_std_module.insert(item_span, path_span);
+                        self.r.confused_type_with_std_module.insert(path_span, path_span);
+                    }
+                }
+
+                partial_res
+            }
+
+            Err(err) => {
+                if let Some(err) = report_errors_for_call(self, err) {
+                    self.report_error(err.span, err.node);
+                }
+
+                PartialRes::new(Res::Err)
+            }
+
+            _ => report_errors(self, None),
+        };
+
+        if !matches!(source, PathSource::TraitItem(..)) {
+            // Avoid recording definition of `A::B` in `<T as A>::B::C`.
+            self.r.record_partial_res(node_id, partial_res);
+            self.resolve_elided_lifetimes_in_path(node_id, partial_res, path, source, path_span);
+        }
+
+        partial_res
+    }
+
+    fn self_type_is_available(&mut self) -> bool {
+        let binding = self
+            .maybe_resolve_ident_in_lexical_scope(Ident::with_dummy_span(kw::SelfUpper), TypeNS);
+        if let Some(LexicalScopeBinding::Res(res)) = binding { res != Res::Err } else { false }
+    }
+
+    fn self_value_is_available(&mut self, self_span: Span) -> bool {
+        let ident = Ident::new(kw::SelfLower, self_span);
+        let binding = self.maybe_resolve_ident_in_lexical_scope(ident, ValueNS);
+        if let Some(LexicalScopeBinding::Res(res)) = binding { res != Res::Err } else { false }
+    }
+
+    /// A wrapper around [`Resolver::report_error`].
+    ///
+    /// This doesn't emit errors for function bodies if this is rustdoc.
+    fn report_error(&mut self, span: Span, resolution_error: ResolutionError<'a>) {
+        if self.should_report_errs() {
+            self.r.report_error(span, resolution_error);
+        }
+    }
+
+    #[inline]
+    /// If we're actually rustdoc then avoid giving a name resolution error for `cfg()` items.
+    fn should_report_errs(&self) -> bool {
+        !(self.r.session.opts.actually_rustdoc && self.in_func_body)
+    }
+
+    // Resolve in alternative namespaces if resolution in the primary namespace fails.
+    fn resolve_qpath_anywhere(
+        &mut self,
+        qself: Option<&QSelf>,
+        path: &[Segment],
+        primary_ns: Namespace,
+        span: Span,
+        defer_to_typeck: bool,
+        finalize: Finalize,
+    ) -> Result<Option<PartialRes>, Spanned<ResolutionError<'a>>> {
+        let mut fin_res = None;
+
+        for (i, &ns) in [primary_ns, TypeNS, ValueNS].iter().enumerate() {
+            if i == 0 || ns != primary_ns {
+                match self.resolve_qpath(qself, path, ns, finalize)? {
+                    Some(partial_res)
+                        if partial_res.unresolved_segments() == 0 || defer_to_typeck =>
+                    {
+                        return Ok(Some(partial_res));
+                    }
+                    partial_res => {
+                        if fin_res.is_none() {
+                            fin_res = partial_res;
+                        }
+                    }
+                }
+            }
+        }
+
+        assert!(primary_ns != MacroNS);
+
+        if qself.is_none() {
+            let path_seg = |seg: &Segment| PathSegment::from_ident(seg.ident);
+            let path = Path { segments: path.iter().map(path_seg).collect(), span, tokens: None };
+            if let Ok((_, res)) =
+                self.r.resolve_macro_path(&path, None, &self.parent_scope, false, false)
+            {
+                return Ok(Some(PartialRes::new(res)));
+            }
+        }
+
+        Ok(fin_res)
+    }
+
+    /// Handles paths that may refer to associated items.
+    fn resolve_qpath(
+        &mut self,
+        qself: Option<&QSelf>,
+        path: &[Segment],
+        ns: Namespace,
+        finalize: Finalize,
+    ) -> Result<Option<PartialRes>, Spanned<ResolutionError<'a>>> {
+        debug!(
+            "resolve_qpath(qself={:?}, path={:?}, ns={:?}, finalize={:?})",
+            qself, path, ns, finalize,
+        );
+
+        if let Some(qself) = qself {
+            if qself.position == 0 {
+                // This is a case like `<T>::B`, where there is no
+                // trait to resolve.  In that case, we leave the `B`
+                // segment to be resolved by type-check.
+                return Ok(Some(PartialRes::with_unresolved_segments(
+                    Res::Def(DefKind::Mod, CRATE_DEF_ID.to_def_id()),
+                    path.len(),
+                )));
+            }
+
+            // Make sure `A::B` in `<T as A::B>::C` is a trait item.
+            //
+            // Currently, `path` names the full item (`A::B::C`, in
+            // our example).  so we extract the prefix of that that is
+            // the trait (the slice upto and including
+            // `qself.position`). And then we recursively resolve that,
+            // but with `qself` set to `None`.
+            let ns = if qself.position + 1 == path.len() { ns } else { TypeNS };
+            let partial_res = self.smart_resolve_path_fragment(
+                None,
+                &path[..=qself.position],
+                PathSource::TraitItem(ns),
+                Finalize::with_root_span(finalize.node_id, finalize.path_span, qself.path_span),
+            );
+
+            // The remaining segments (the `C` in our example) will
+            // have to be resolved by type-check, since that requires doing
+            // trait resolution.
+            return Ok(Some(PartialRes::with_unresolved_segments(
+                partial_res.base_res(),
+                partial_res.unresolved_segments() + path.len() - qself.position - 1,
+            )));
+        }
+
+        let result = match self.resolve_path(&path, Some(ns), Some(finalize)) {
+            PathResult::NonModule(path_res) => path_res,
+            PathResult::Module(ModuleOrUniformRoot::Module(module)) if !module.is_normal() => {
+                PartialRes::new(module.res().unwrap())
+            }
+            // In `a(::assoc_item)*` `a` cannot be a module. If `a` does resolve to a module we
+            // don't report an error right away, but try to fallback to a primitive type.
+            // So, we are still able to successfully resolve something like
+            //
+            // use std::u8; // bring module u8 in scope
+            // fn f() -> u8 { // OK, resolves to primitive u8, not to std::u8
+            //     u8::max_value() // OK, resolves to associated function <u8>::max_value,
+            //                     // not to non-existent std::u8::max_value
+            // }
+            //
+            // Such behavior is required for backward compatibility.
+            // The same fallback is used when `a` resolves to nothing.
+            PathResult::Module(ModuleOrUniformRoot::Module(_)) | PathResult::Failed { .. }
+                if (ns == TypeNS || path.len() > 1)
+                    && PrimTy::from_name(path[0].ident.name).is_some() =>
+            {
+                let prim = PrimTy::from_name(path[0].ident.name).unwrap();
+                PartialRes::with_unresolved_segments(Res::PrimTy(prim), path.len() - 1)
+            }
+            PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
+                PartialRes::new(module.res().unwrap())
+            }
+            PathResult::Failed { is_error_from_last_segment: false, span, label, suggestion } => {
+                return Err(respan(span, ResolutionError::FailedToResolve { label, suggestion }));
+            }
+            PathResult::Module(..) | PathResult::Failed { .. } => return Ok(None),
+            PathResult::Indeterminate => bug!("indeterminate path result in resolve_qpath"),
+        };
+
+        if path.len() > 1
+            && result.base_res() != Res::Err
+            && path[0].ident.name != kw::PathRoot
+            && path[0].ident.name != kw::DollarCrate
+        {
+            let unqualified_result = {
+                match self.resolve_path(&[*path.last().unwrap()], Some(ns), None) {
+                    PathResult::NonModule(path_res) => path_res.base_res(),
+                    PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
+                        module.res().unwrap()
+                    }
+                    _ => return Ok(Some(result)),
+                }
+            };
+            if result.base_res() == unqualified_result {
+                let lint = lint::builtin::UNUSED_QUALIFICATIONS;
+                self.r.lint_buffer.buffer_lint(
+                    lint,
+                    finalize.node_id,
+                    finalize.path_span,
+                    "unnecessary qualification",
+                )
+            }
+        }
+
+        Ok(Some(result))
+    }
+
+    fn with_resolved_label(&mut self, label: Option<Label>, id: NodeId, f: impl FnOnce(&mut Self)) {
+        if let Some(label) = label {
+            if label.ident.as_str().as_bytes()[1] != b'_' {
+                self.diagnostic_metadata.unused_labels.insert(id, label.ident.span);
+            }
+
+            if let Ok((_, orig_span)) = self.resolve_label(label.ident) {
+                diagnostics::signal_label_shadowing(self.r.session, orig_span, label.ident)
+            }
+
+            self.with_label_rib(NormalRibKind, |this| {
+                let ident = label.ident.normalize_to_macro_rules();
+                this.label_ribs.last_mut().unwrap().bindings.insert(ident, id);
+                f(this);
+            });
+        } else {
+            f(self);
+        }
+    }
+
+    fn resolve_labeled_block(&mut self, label: Option<Label>, id: NodeId, block: &'ast Block) {
+        self.with_resolved_label(label, id, |this| this.visit_block(block));
+    }
+
+    fn resolve_block(&mut self, block: &'ast Block) {
+        debug!("(resolving block) entering block");
+        // Move down in the graph, if there's an anonymous module rooted here.
+        let orig_module = self.parent_scope.module;
+        let anonymous_module = self.r.block_map.get(&block.id).cloned(); // clones a reference
+
+        let mut num_macro_definition_ribs = 0;
+        if let Some(anonymous_module) = anonymous_module {
+            debug!("(resolving block) found anonymous module, moving down");
+            self.ribs[ValueNS].push(Rib::new(ModuleRibKind(anonymous_module)));
+            self.ribs[TypeNS].push(Rib::new(ModuleRibKind(anonymous_module)));
+            self.parent_scope.module = anonymous_module;
+        } else {
+            self.ribs[ValueNS].push(Rib::new(NormalRibKind));
+        }
+
+        let prev = self.diagnostic_metadata.current_block_could_be_bare_struct_literal.take();
+        if let (true, [Stmt { kind: StmtKind::Expr(expr), .. }]) =
+            (block.could_be_bare_literal, &block.stmts[..])
+            && let ExprKind::Type(..) = expr.kind
+        {
+            self.diagnostic_metadata.current_block_could_be_bare_struct_literal =
+            Some(block.span);
+        }
+        // Descend into the block.
+        for stmt in &block.stmts {
+            if let StmtKind::Item(ref item) = stmt.kind
+                && let ItemKind::MacroDef(..) = item.kind {
+                num_macro_definition_ribs += 1;
+                let res = self.r.local_def_id(item.id).to_def_id();
+                self.ribs[ValueNS].push(Rib::new(MacroDefinition(res)));
+                self.label_ribs.push(Rib::new(MacroDefinition(res)));
+            }
+
+            self.visit_stmt(stmt);
+        }
+        self.diagnostic_metadata.current_block_could_be_bare_struct_literal = prev;
+
+        // Move back up.
+        self.parent_scope.module = orig_module;
+        for _ in 0..num_macro_definition_ribs {
+            self.ribs[ValueNS].pop();
+            self.label_ribs.pop();
+        }
+        self.ribs[ValueNS].pop();
+        if anonymous_module.is_some() {
+            self.ribs[TypeNS].pop();
+        }
+        debug!("(resolving block) leaving block");
+    }
+
+    fn resolve_anon_const(&mut self, constant: &'ast AnonConst, is_repeat: IsRepeatExpr) {
+        debug!("resolve_anon_const {:?} is_repeat: {:?}", constant, is_repeat);
+        self.with_constant_rib(
+            is_repeat,
+            if constant.value.is_potential_trivial_const_param() {
+                HasGenericParams::Yes
+            } else {
+                HasGenericParams::No
+            },
+            None,
+            |this| visit::walk_anon_const(this, constant),
+        );
+    }
+
+    fn resolve_inline_const(&mut self, constant: &'ast AnonConst) {
+        debug!("resolve_anon_const {constant:?}");
+        self.with_constant_rib(IsRepeatExpr::No, HasGenericParams::Yes, None, |this| {
+            visit::walk_anon_const(this, constant);
+        });
+    }
+
+    fn resolve_expr(&mut self, expr: &'ast Expr, parent: Option<&'ast Expr>) {
+        // First, record candidate traits for this expression if it could
+        // result in the invocation of a method call.
+
+        self.record_candidate_traits_for_expr_if_necessary(expr);
+
+        // Next, resolve the node.
+        match expr.kind {
+            ExprKind::Path(ref qself, ref path) => {
+                self.smart_resolve_path(expr.id, qself.as_ref(), path, PathSource::Expr(parent));
+                visit::walk_expr(self, expr);
+            }
+
+            ExprKind::Struct(ref se) => {
+                self.smart_resolve_path(expr.id, se.qself.as_ref(), &se.path, PathSource::Struct);
+                visit::walk_expr(self, expr);
+            }
+
+            ExprKind::Break(Some(label), _) | ExprKind::Continue(Some(label)) => {
+                match self.resolve_label(label.ident) {
+                    Ok((node_id, _)) => {
+                        // Since this res is a label, it is never read.
+                        self.r.label_res_map.insert(expr.id, node_id);
+                        self.diagnostic_metadata.unused_labels.remove(&node_id);
+                    }
+                    Err(error) => {
+                        self.report_error(label.ident.span, error);
+                    }
+                }
+
+                // visit `break` argument if any
+                visit::walk_expr(self, expr);
+            }
+
+            ExprKind::Break(None, Some(ref e)) => {
+                // We use this instead of `visit::walk_expr` to keep the parent expr around for
+                // better diagnostics.
+                self.resolve_expr(e, Some(&expr));
+            }
+
+            ExprKind::Let(ref pat, ref scrutinee, _) => {
+                self.visit_expr(scrutinee);
+                self.resolve_pattern_top(pat, PatternSource::Let);
+            }
+
+            ExprKind::If(ref cond, ref then, ref opt_else) => {
+                self.with_rib(ValueNS, NormalRibKind, |this| {
+                    let old = this.diagnostic_metadata.in_if_condition.replace(cond);
+                    this.visit_expr(cond);
+                    this.diagnostic_metadata.in_if_condition = old;
+                    this.visit_block(then);
+                });
+                if let Some(expr) = opt_else {
+                    self.visit_expr(expr);
+                }
+            }
+
+            ExprKind::Loop(ref block, label) => self.resolve_labeled_block(label, expr.id, &block),
+
+            ExprKind::While(ref cond, ref block, label) => {
+                self.with_resolved_label(label, expr.id, |this| {
+                    this.with_rib(ValueNS, NormalRibKind, |this| {
+                        let old = this.diagnostic_metadata.in_if_condition.replace(cond);
+                        this.visit_expr(cond);
+                        this.diagnostic_metadata.in_if_condition = old;
+                        this.visit_block(block);
+                    })
+                });
+            }
+
+            ExprKind::ForLoop(ref pat, ref iter_expr, ref block, label) => {
+                self.visit_expr(iter_expr);
+                self.with_rib(ValueNS, NormalRibKind, |this| {
+                    this.resolve_pattern_top(pat, PatternSource::For);
+                    this.resolve_labeled_block(label, expr.id, block);
+                });
+            }
+
+            ExprKind::Block(ref block, label) => self.resolve_labeled_block(label, block.id, block),
+
+            // Equivalent to `visit::walk_expr` + passing some context to children.
+            ExprKind::Field(ref subexpression, _) => {
+                self.resolve_expr(subexpression, Some(expr));
+            }
+            ExprKind::MethodCall(ref segment, ref arguments, _) => {
+                let mut arguments = arguments.iter();
+                self.resolve_expr(arguments.next().unwrap(), Some(expr));
+                for argument in arguments {
+                    self.resolve_expr(argument, None);
+                }
+                self.visit_path_segment(expr.span, segment);
+            }
+
+            ExprKind::Call(ref callee, ref arguments) => {
+                self.resolve_expr(callee, Some(expr));
+                let const_args = self.r.legacy_const_generic_args(callee).unwrap_or_default();
+                for (idx, argument) in arguments.iter().enumerate() {
+                    // Constant arguments need to be treated as AnonConst since
+                    // that is how they will be later lowered to HIR.
+                    if const_args.contains(&idx) {
+                        self.with_constant_rib(
+                            IsRepeatExpr::No,
+                            if argument.is_potential_trivial_const_param() {
+                                HasGenericParams::Yes
+                            } else {
+                                HasGenericParams::No
+                            },
+                            None,
+                            |this| {
+                                this.resolve_expr(argument, None);
+                            },
+                        );
+                    } else {
+                        self.resolve_expr(argument, None);
+                    }
+                }
+            }
+            ExprKind::Type(ref type_expr, ref ty) => {
+                // `ParseSess::type_ascription_path_suggestions` keeps spans of colon tokens in
+                // type ascription. Here we are trying to retrieve the span of the colon token as
+                // well, but only if it's written without spaces `expr:Ty` and therefore confusable
+                // with `expr::Ty`, only in this case it will match the span from
+                // `type_ascription_path_suggestions`.
+                self.diagnostic_metadata
+                    .current_type_ascription
+                    .push(type_expr.span.between(ty.span));
+                visit::walk_expr(self, expr);
+                self.diagnostic_metadata.current_type_ascription.pop();
+            }
+            // `async |x| ...` gets desugared to `|x| future_from_generator(|| ...)`, so we need to
+            // resolve the arguments within the proper scopes so that usages of them inside the
+            // closure are detected as upvars rather than normal closure arg usages.
+            ExprKind::Closure(_, _, Async::Yes { .. }, _, ref fn_decl, ref body, _span) => {
+                self.with_rib(ValueNS, NormalRibKind, |this| {
+                    this.with_label_rib(ClosureOrAsyncRibKind, |this| {
+                        // Resolve arguments:
+                        this.resolve_params(&fn_decl.inputs);
+                        // No need to resolve return type --
+                        // the outer closure return type is `FnRetTy::Default`.
+
+                        // Now resolve the inner closure
+                        {
+                            // No need to resolve arguments: the inner closure has none.
+                            // Resolve the return type:
+                            visit::walk_fn_ret_ty(this, &fn_decl.output);
+                            // Resolve the body
+                            this.visit_expr(body);
+                        }
+                    })
+                });
+            }
+            // For closures, ClosureOrAsyncRibKind is added in visit_fn
+            ExprKind::Closure(ClosureBinder::For { ref generic_params, span }, ..) => {
+                self.with_generic_param_rib(
+                    &generic_params,
+                    NormalRibKind,
+                    LifetimeRibKind::Generics {
+                        binder: expr.id,
+                        kind: LifetimeBinderKind::Closure,
+                        span,
+                    },
+                    |this| visit::walk_expr(this, expr),
+                );
+            }
+            ExprKind::Closure(..) => visit::walk_expr(self, expr),
+            ExprKind::Async(..) => {
+                self.with_label_rib(ClosureOrAsyncRibKind, |this| visit::walk_expr(this, expr));
+            }
+            ExprKind::Repeat(ref elem, ref ct) => {
+                self.visit_expr(elem);
+                self.with_lifetime_rib(LifetimeRibKind::AnonConst, |this| {
+                    this.with_lifetime_rib(LifetimeRibKind::Elided(LifetimeRes::Static), |this| {
+                        this.resolve_anon_const(ct, IsRepeatExpr::Yes)
+                    })
+                });
+            }
+            ExprKind::ConstBlock(ref ct) => {
+                self.resolve_inline_const(ct);
+            }
+            ExprKind::Index(ref elem, ref idx) => {
+                self.resolve_expr(elem, Some(expr));
+                self.visit_expr(idx);
+            }
+            _ => {
+                visit::walk_expr(self, expr);
+            }
+        }
+    }
+
+    fn record_candidate_traits_for_expr_if_necessary(&mut self, expr: &'ast Expr) {
+        match expr.kind {
+            ExprKind::Field(_, ident) => {
+                // FIXME(#6890): Even though you can't treat a method like a
+                // field, we need to add any trait methods we find that match
+                // the field name so that we can do some nice error reporting
+                // later on in typeck.
+                let traits = self.traits_in_scope(ident, ValueNS);
+                self.r.trait_map.insert(expr.id, traits);
+            }
+            ExprKind::MethodCall(ref segment, ..) => {
+                debug!("(recording candidate traits for expr) recording traits for {}", expr.id);
+                let traits = self.traits_in_scope(segment.ident, ValueNS);
+                self.r.trait_map.insert(expr.id, traits);
+            }
+            _ => {
+                // Nothing to do.
+            }
+        }
+    }
+
+    fn traits_in_scope(&mut self, ident: Ident, ns: Namespace) -> Vec<TraitCandidate> {
+        self.r.traits_in_scope(
+            self.current_trait_ref.as_ref().map(|(module, _)| *module),
+            &self.parent_scope,
+            ident.span.ctxt(),
+            Some((ident.name, ns)),
+        )
+    }
+}
+
+struct LifetimeCountVisitor<'a, 'b> {
+    r: &'b mut Resolver<'a>,
+}
+
+/// Walks the whole crate in DFS order, visiting each item, counting the declared number of
+/// lifetime generic parameters.
+impl<'ast> Visitor<'ast> for LifetimeCountVisitor<'_, '_> {
+    fn visit_item(&mut self, item: &'ast Item) {
+        match &item.kind {
+            ItemKind::TyAlias(box TyAlias { ref generics, .. })
+            | ItemKind::Fn(box Fn { ref generics, .. })
+            | ItemKind::Enum(_, ref generics)
+            | ItemKind::Struct(_, ref generics)
+            | ItemKind::Union(_, ref generics)
+            | ItemKind::Impl(box Impl { ref generics, .. })
+            | ItemKind::Trait(box Trait { ref generics, .. })
+            | ItemKind::TraitAlias(ref generics, _) => {
+                let def_id = self.r.local_def_id(item.id);
+                let count = generics
+                    .params
+                    .iter()
+                    .filter(|param| matches!(param.kind, ast::GenericParamKind::Lifetime { .. }))
+                    .count();
+                self.r.item_generics_num_lifetimes.insert(def_id, count);
+            }
+
+            ItemKind::Mod(..)
+            | ItemKind::ForeignMod(..)
+            | ItemKind::Static(..)
+            | ItemKind::Const(..)
+            | ItemKind::Use(..)
+            | ItemKind::ExternCrate(..)
+            | ItemKind::MacroDef(..)
+            | ItemKind::GlobalAsm(..)
+            | ItemKind::MacCall(..) => {}
+        }
+        visit::walk_item(self, item)
+    }
+}
+
+impl<'a> Resolver<'a> {
+    pub(crate) fn late_resolve_crate(&mut self, krate: &Crate) {
+        visit::walk_crate(&mut LifetimeCountVisitor { r: self }, krate);
+        let mut late_resolution_visitor = LateResolutionVisitor::new(self);
+        visit::walk_crate(&mut late_resolution_visitor, krate);
+        for (id, span) in late_resolution_visitor.diagnostic_metadata.unused_labels.iter() {
+            self.lint_buffer.buffer_lint(lint::builtin::UNUSED_LABELS, *id, *span, "unused label");
+        }
+    }
+}
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
new file mode 100644
index 000000000..2b1f2b88e
--- /dev/null
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -0,0 +1,2369 @@
+use crate::diagnostics::{ImportSuggestion, LabelSuggestion, TypoSuggestion};
+use crate::late::{AliasPossibility, LateResolutionVisitor, RibKind};
+use crate::late::{LifetimeBinderKind, LifetimeRes, LifetimeRibKind, LifetimeUseSet};
+use crate::path_names_to_string;
+use crate::{Module, ModuleKind, ModuleOrUniformRoot};
+use crate::{PathResult, PathSource, Segment};
+
+use rustc_ast::visit::{FnCtxt, FnKind, LifetimeCtxt};
+use rustc_ast::{
+    self as ast, AssocItemKind, Expr, ExprKind, GenericParam, GenericParamKind, Item, ItemKind,
+    NodeId, Path, Ty, TyKind, DUMMY_NODE_ID,
+};
+use rustc_ast_pretty::pprust::path_segment_to_string;
+use rustc_data_structures::fx::FxHashSet;
+use rustc_errors::{
+    pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
+    MultiSpan,
+};
+use rustc_hir as hir;
+use rustc_hir::def::Namespace::{self, *};
+use rustc_hir::def::{self, CtorKind, CtorOf, DefKind};
+use rustc_hir::def_id::{DefId, CRATE_DEF_ID, LOCAL_CRATE};
+use rustc_hir::PrimTy;
+use rustc_session::lint;
+use rustc_session::parse::feature_err;
+use rustc_session::Session;
+use rustc_span::edition::Edition;
+use rustc_span::hygiene::MacroKind;
+use rustc_span::lev_distance::find_best_match_for_name;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::{BytePos, Span};
+
+use std::iter;
+use std::ops::Deref;
+
+use tracing::debug;
+
+type Res = def::Res<ast::NodeId>;
+
+/// A field or associated item from self type suggested in case of resolution failure.
+enum AssocSuggestion {
+    Field,
+    MethodWithSelf,
+    AssocFn,
+    AssocType,
+    AssocConst,
+}
+
+impl AssocSuggestion {
+    fn action(&self) -> &'static str {
+        match self {
+            AssocSuggestion::Field => "use the available field",
+            AssocSuggestion::MethodWithSelf => "call the method with the fully-qualified path",
+            AssocSuggestion::AssocFn => "call the associated function",
+            AssocSuggestion::AssocConst => "use the associated `const`",
+            AssocSuggestion::AssocType => "use the associated type",
+        }
+    }
+}
+
+fn is_self_type(path: &[Segment], namespace: Namespace) -> bool {
+    namespace == TypeNS && path.len() == 1 && path[0].ident.name == kw::SelfUpper
+}
+
+fn is_self_value(path: &[Segment], namespace: Namespace) -> bool {
+    namespace == ValueNS && path.len() == 1 && path[0].ident.name == kw::SelfLower
+}
+
+/// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
+fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
+    let variant_path = &suggestion.path;
+    let variant_path_string = path_names_to_string(variant_path);
+
+    let path_len = suggestion.path.segments.len();
+    let enum_path = ast::Path {
+        span: suggestion.path.span,
+        segments: suggestion.path.segments[0..path_len - 1].to_vec(),
+        tokens: None,
+    };
+    let enum_path_string = path_names_to_string(&enum_path);
+
+    (variant_path_string, enum_path_string)
+}
+
+/// Description of an elided lifetime.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
+pub(super) struct MissingLifetime {
+    /// Used to overwrite the resolution with the suggestion, to avoid cascasing errors.
+    pub id: NodeId,
+    /// Where to suggest adding the lifetime.
+    pub span: Span,
+    /// How the lifetime was introduced, to have the correct space and comma.
+    pub kind: MissingLifetimeKind,
+    /// Number of elided lifetimes, used for elision in path.
+    pub count: usize,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
+pub(super) enum MissingLifetimeKind {
+    /// An explicit `'_`.
+    Underscore,
+    /// An elided lifetime `&' ty`.
+    Ampersand,
+    /// An elided lifetime in brackets with written brackets.
+    Comma,
+    /// An elided lifetime with elided brackets.
+    Brackets,
+}
+
+/// Description of the lifetimes appearing in a function parameter.
+/// This is used to provide a literal explanation to the elision failure.
+#[derive(Clone, Debug)]
+pub(super) struct ElisionFnParameter {
+    /// The index of the argument in the original definition.
+    pub index: usize,
+    /// The name of the argument if it's a simple ident.
+    pub ident: Option<Ident>,
+    /// The number of lifetimes in the parameter.
+    pub lifetime_count: usize,
+    /// The span of the parameter.
+    pub span: Span,
+}
+
+/// Description of lifetimes that appear as candidates for elision.
+/// This is used to suggest introducing an explicit lifetime.
+#[derive(Debug)]
+pub(super) enum LifetimeElisionCandidate {
+    /// This is not a real lifetime.
+    Ignore,
+    /// There is a named lifetime, we won't suggest anything.
+    Named,
+    Missing(MissingLifetime),
+}
+
+impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
+    fn def_span(&self, def_id: DefId) -> Option<Span> {
+        match def_id.krate {
+            LOCAL_CRATE => self.r.opt_span(def_id),
+            _ => Some(self.r.cstore().get_span_untracked(def_id, self.r.session)),
+        }
+    }
+
+    /// Handles error reporting for `smart_resolve_path_fragment` function.
+    /// Creates base error and amends it with one short label and possibly some longer helps/notes.
+    pub(crate) fn smart_resolve_report_errors(
+        &mut self,
+        path: &[Segment],
+        span: Span,
+        source: PathSource<'_>,
+        res: Option<Res>,
+    ) -> (DiagnosticBuilder<'a, ErrorGuaranteed>, Vec<ImportSuggestion>) {
+        let ident_span = path.last().map_or(span, |ident| ident.ident.span);
+        let ns = source.namespace();
+        let is_expected = &|res| source.is_expected(res);
+        let is_enum_variant = &|res| matches!(res, Res::Def(DefKind::Variant, _));
+
+        debug!(?res, ?source);
+
+        // Make the base error.
+        struct BaseError<'a> {
+            msg: String,
+            fallback_label: String,
+            span: Span,
+            could_be_expr: bool,
+            suggestion: Option<(Span, &'a str, String)>,
+        }
+        let mut expected = source.descr_expected();
+        let path_str = Segment::names_to_string(path);
+        let item_str = path.last().unwrap().ident;
+        let base_error = if let Some(res) = res {
+            BaseError {
+                msg: format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
+                fallback_label: format!("not a {expected}"),
+                span,
+                could_be_expr: match res {
+                    Res::Def(DefKind::Fn, _) => {
+                        // Verify whether this is a fn call or an Fn used as a type.
+                        self.r
+                            .session
+                            .source_map()
+                            .span_to_snippet(span)
+                            .map(|snippet| snippet.ends_with(')'))
+                            .unwrap_or(false)
+                    }
+                    Res::Def(
+                        DefKind::Ctor(..) | DefKind::AssocFn | DefKind::Const | DefKind::AssocConst,
+                        _,
+                    )
+                    | Res::SelfCtor(_)
+                    | Res::PrimTy(_)
+                    | Res::Local(_) => true,
+                    _ => false,
+                },
+                suggestion: None,
+            }
+        } else {
+            let item_span = path.last().unwrap().ident.span;
+            let (mod_prefix, mod_str, suggestion) = if path.len() == 1 {
+                debug!(?self.diagnostic_metadata.current_impl_items);
+                debug!(?self.diagnostic_metadata.current_function);
+                let suggestion = if let Some(items) = self.diagnostic_metadata.current_impl_items
+                    && let Some((fn_kind, _)) = self.diagnostic_metadata.current_function
+                    && self.current_trait_ref.is_none()
+                    && let Some(FnCtxt::Assoc(_)) = fn_kind.ctxt()
+                    && let Some(item) = items.iter().find(|i| {
+                        if let AssocItemKind::Fn(fn_) = &i.kind
+                            && !fn_.sig.decl.has_self()
+                            && i.ident.name == item_str.name
+                        {
+                            debug!(?item_str.name);
+                            debug!(?fn_.sig.decl.inputs);
+                            return true
+                        }
+                        false
+                    })
+                {
+                    Some((
+                        item_span,
+                        "consider using the associated function",
+                        format!("Self::{}", item.ident)
+                    ))
+                } else {
+                    None
+                };
+                (String::new(), "this scope".to_string(), suggestion)
+            } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
+                if self.r.session.edition() > Edition::Edition2015 {
+                    // In edition 2018 onwards, the `::foo` syntax may only pull from the extern prelude
+                    // which overrides all other expectations of item type
+                    expected = "crate";
+                    (String::new(), "the list of imported crates".to_string(), None)
+                } else {
+                    (String::new(), "the crate root".to_string(), None)
+                }
+            } else if path.len() == 2 && path[0].ident.name == kw::Crate {
+                (String::new(), "the crate root".to_string(), None)
+            } else {
+                let mod_path = &path[..path.len() - 1];
+                let mod_prefix = match self.resolve_path(mod_path, Some(TypeNS), None) {
+                    PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
+                    _ => None,
+                }
+                .map_or_else(String::new, |res| format!("{} ", res.descr()));
+                (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)), None)
+            };
+            BaseError {
+                msg: format!("cannot find {expected} `{item_str}` in {mod_prefix}{mod_str}"),
+                fallback_label: if path_str == "async" && expected.starts_with("struct") {
+                    "`async` blocks are only allowed in Rust 2018 or later".to_string()
+                } else {
+                    format!("not found in {mod_str}")
+                },
+                span: item_span,
+                could_be_expr: false,
+                suggestion,
+            }
+        };
+
+        let code = source.error_code(res.is_some());
+        let mut err =
+            self.r.session.struct_span_err_with_code(base_error.span, &base_error.msg, code);
+
+        self.suggest_swapping_misplaced_self_ty_and_trait(&mut err, source, res, base_error.span);
+
+        if let Some(sugg) = base_error.suggestion {
+            err.span_suggestion_verbose(sugg.0, sugg.1, sugg.2, Applicability::MaybeIncorrect);
+        }
+
+        if let Some(span) = self.diagnostic_metadata.current_block_could_be_bare_struct_literal {
+            err.multipart_suggestion(
+                "you might have meant to write a `struct` literal",
+                vec![
+                    (span.shrink_to_lo(), "{ SomeStruct ".to_string()),
+                    (span.shrink_to_hi(), "}".to_string()),
+                ],
+                Applicability::HasPlaceholders,
+            );
+        }
+        match (source, self.diagnostic_metadata.in_if_condition) {
+            (
+                PathSource::Expr(_),
+                Some(Expr { span: expr_span, kind: ExprKind::Assign(lhs, _, _), .. }),
+            ) => {
+                // Icky heuristic so we don't suggest:
+                // `if (i + 2) = 2` => `if let (i + 2) = 2` (approximately pattern)
+                // `if 2 = i` => `if let 2 = i` (lhs needs to contain error span)
+                if lhs.is_approximately_pattern() && lhs.span.contains(span) {
+                    err.span_suggestion_verbose(
+                        expr_span.shrink_to_lo(),
+                        "you might have meant to use pattern matching",
+                        "let ",
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+            }
+            _ => {}
+        }
+
+        let is_assoc_fn = self.self_type_is_available();
+        // Emit help message for fake-self from other languages (e.g., `this` in Javascript).
+        if ["this", "my"].contains(&item_str.as_str()) && is_assoc_fn {
+            err.span_suggestion_short(
+                span,
+                "you might have meant to use `self` here instead",
+                "self",
+                Applicability::MaybeIncorrect,
+            );
+            if !self.self_value_is_available(path[0].ident.span) {
+                if let Some((FnKind::Fn(_, _, sig, ..), fn_span)) =
+                    &self.diagnostic_metadata.current_function
+                {
+                    let (span, sugg) = if let Some(param) = sig.decl.inputs.get(0) {
+                        (param.span.shrink_to_lo(), "&self, ")
+                    } else {
+                        (
+                            self.r
+                                .session
+                                .source_map()
+                                .span_through_char(*fn_span, '(')
+                                .shrink_to_hi(),
+                            "&self",
+                        )
+                    };
+                    err.span_suggestion_verbose(
+                        span,
+                        "if you meant to use `self`, you are also missing a `self` receiver \
+                         argument",
+                        sugg,
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+            }
+        }
+
+        self.detect_assoct_type_constraint_meant_as_path(base_error.span, &mut err);
+
+        // Emit special messages for unresolved `Self` and `self`.
+        if is_self_type(path, ns) {
+            err.code(rustc_errors::error_code!(E0411));
+            err.span_label(
+                span,
+                "`Self` is only available in impls, traits, and type definitions".to_string(),
+            );
+            if let Some(item_kind) = self.diagnostic_metadata.current_item {
+                err.span_label(
+                    item_kind.ident.span,
+                    format!(
+                        "`Self` not allowed in {} {}",
+                        item_kind.kind.article(),
+                        item_kind.kind.descr()
+                    ),
+                );
+            }
+            return (err, Vec::new());
+        }
+        if is_self_value(path, ns) {
+            debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
+
+            err.code(rustc_errors::error_code!(E0424));
+            err.span_label(span, match source {
+                PathSource::Pat => "`self` value is a keyword and may not be bound to variables or shadowed",
+                _ => "`self` value is a keyword only available in methods with a `self` parameter",
+            });
+            if let Some((fn_kind, span)) = &self.diagnostic_metadata.current_function {
+                // The current function has a `self' parameter, but we were unable to resolve
+                // a reference to `self`. This can only happen if the `self` identifier we
+                // are resolving came from a different hygiene context.
+                if fn_kind.decl().inputs.get(0).map_or(false, |p| p.is_self()) {
+                    err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
+                } else {
+                    let doesnt = if is_assoc_fn {
+                        let (span, sugg) = fn_kind
+                            .decl()
+                            .inputs
+                            .get(0)
+                            .map(|p| (p.span.shrink_to_lo(), "&self, "))
+                            .unwrap_or_else(|| {
+                                // Try to look for the "(" after the function name, if possible.
+                                // This avoids placing the suggestion into the visibility specifier.
+                                let span = fn_kind
+                                    .ident()
+                                    .map_or(*span, |ident| span.with_lo(ident.span.hi()));
+                                (
+                                    self.r
+                                        .session
+                                        .source_map()
+                                        .span_through_char(span, '(')
+                                        .shrink_to_hi(),
+                                    "&self",
+                                )
+                            });
+                        err.span_suggestion_verbose(
+                            span,
+                            "add a `self` receiver parameter to make the associated `fn` a method",
+                            sugg,
+                            Applicability::MaybeIncorrect,
+                        );
+                        "doesn't"
+                    } else {
+                        "can't"
+                    };
+                    if let Some(ident) = fn_kind.ident() {
+                        err.span_label(
+                            ident.span,
+                            &format!("this function {} have a `self` parameter", doesnt),
+                        );
+                    }
+                }
+            } else if let Some(item_kind) = self.diagnostic_metadata.current_item {
+                err.span_label(
+                    item_kind.ident.span,
+                    format!(
+                        "`self` not allowed in {} {}",
+                        item_kind.kind.article(),
+                        item_kind.kind.descr()
+                    ),
+                );
+            }
+            return (err, Vec::new());
+        }
+
+        // Try to lookup name in more relaxed fashion for better error reporting.
+        let ident = path.last().unwrap().ident;
+        let mut candidates = self
+            .r
+            .lookup_import_candidates(ident, ns, &self.parent_scope, is_expected)
+            .into_iter()
+            .filter(|ImportSuggestion { did, .. }| {
+                match (did, res.and_then(|res| res.opt_def_id())) {
+                    (Some(suggestion_did), Some(actual_did)) => *suggestion_did != actual_did,
+                    _ => true,
+                }
+            })
+            .collect::<Vec<_>>();
+        let crate_def_id = CRATE_DEF_ID.to_def_id();
+        // Try to filter out intrinsics candidates, as long as we have
+        // some other candidates to suggest.
+        let intrinsic_candidates: Vec<_> = candidates
+            .drain_filter(|sugg| {
+                let path = path_names_to_string(&sugg.path);
+                path.starts_with("core::intrinsics::") || path.starts_with("std::intrinsics::")
+            })
+            .collect();
+        if candidates.is_empty() {
+            // Put them back if we have no more candidates to suggest...
+            candidates.extend(intrinsic_candidates);
+        }
+        if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
+            let mut enum_candidates: Vec<_> = self
+                .r
+                .lookup_import_candidates(ident, ns, &self.parent_scope, is_enum_variant)
+                .into_iter()
+                .map(|suggestion| import_candidate_to_enum_paths(&suggestion))
+                .filter(|(_, enum_ty_path)| !enum_ty_path.starts_with("std::prelude::"))
+                .collect();
+            if !enum_candidates.is_empty() {
+                if let (PathSource::Type, Some(span)) =
+                    (source, self.diagnostic_metadata.current_type_ascription.last())
+                {
+                    if self
+                        .r
+                        .session
+                        .parse_sess
+                        .type_ascription_path_suggestions
+                        .borrow()
+                        .contains(span)
+                    {
+                        // Already reported this issue on the lhs of the type ascription.
+                        err.delay_as_bug();
+                        return (err, candidates);
+                    }
+                }
+
+                enum_candidates.sort();
+
+                // Contextualize for E0412 "cannot find type", but don't belabor the point
+                // (that it's a variant) for E0573 "expected type, found variant".
+                let preamble = if res.is_none() {
+                    let others = match enum_candidates.len() {
+                        1 => String::new(),
+                        2 => " and 1 other".to_owned(),
+                        n => format!(" and {} others", n),
+                    };
+                    format!("there is an enum variant `{}`{}; ", enum_candidates[0].0, others)
+                } else {
+                    String::new()
+                };
+                let msg = format!("{}try using the variant's enum", preamble);
+
+                err.span_suggestions(
+                    span,
+                    &msg,
+                    enum_candidates.into_iter().map(|(_variant_path, enum_ty_path)| enum_ty_path),
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+        // Try Levenshtein algorithm.
+        let typo_sugg = self.lookup_typo_candidate(path, ns, is_expected);
+        if path.len() == 1 && self.self_type_is_available() {
+            if let Some(candidate) = self.lookup_assoc_candidate(ident, ns, is_expected) {
+                let self_is_available = self.self_value_is_available(path[0].ident.span);
+                match candidate {
+                    AssocSuggestion::Field => {
+                        if self_is_available {
+                            err.span_suggestion(
+                                span,
+                                "you might have meant to use the available field",
+                                format!("self.{path_str}"),
+                                Applicability::MachineApplicable,
+                            );
+                        } else {
+                            err.span_label(span, "a field by this name exists in `Self`");
+                        }
+                    }
+                    AssocSuggestion::MethodWithSelf if self_is_available => {
+                        err.span_suggestion(
+                            span,
+                            "you might have meant to call the method",
+                            format!("self.{path_str}"),
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                    AssocSuggestion::MethodWithSelf
+                    | AssocSuggestion::AssocFn
+                    | AssocSuggestion::AssocConst
+                    | AssocSuggestion::AssocType => {
+                        err.span_suggestion(
+                            span,
+                            &format!("you might have meant to {}", candidate.action()),
+                            format!("Self::{path_str}"),
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                }
+                self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
+                return (err, candidates);
+            }
+
+            // If the first argument in call is `self` suggest calling a method.
+            if let Some((call_span, args_span)) = self.call_has_self_arg(source) {
+                let mut args_snippet = String::new();
+                if let Some(args_span) = args_span {
+                    if let Ok(snippet) = self.r.session.source_map().span_to_snippet(args_span) {
+                        args_snippet = snippet;
+                    }
+                }
+
+                err.span_suggestion(
+                    call_span,
+                    &format!("try calling `{ident}` as a method"),
+                    format!("self.{path_str}({args_snippet})"),
+                    Applicability::MachineApplicable,
+                );
+                return (err, candidates);
+            }
+        }
+
+        // Try context-dependent help if relaxed lookup didn't work.
+        if let Some(res) = res {
+            if self.smart_resolve_context_dependent_help(
+                &mut err,
+                span,
+                source,
+                res,
+                &path_str,
+                &base_error.fallback_label,
+            ) {
+                // We do this to avoid losing a secondary span when we override the main error span.
+                self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
+                return (err, candidates);
+            }
+        }
+
+        let is_macro =
+            base_error.span.from_expansion() && base_error.span.desugaring_kind().is_none();
+        if !self.type_ascription_suggestion(&mut err, base_error.span) {
+            let mut fallback = false;
+            if let (
+                PathSource::Trait(AliasPossibility::Maybe),
+                Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)),
+                false,
+            ) = (source, res, is_macro)
+            {
+                if let Some(bounds @ [_, .., _]) = self.diagnostic_metadata.current_trait_object {
+                    fallback = true;
+                    let spans: Vec<Span> = bounds
+                        .iter()
+                        .map(|bound| bound.span())
+                        .filter(|&sp| sp != base_error.span)
+                        .collect();
+
+                    let start_span = bounds.iter().map(|bound| bound.span()).next().unwrap();
+                    // `end_span` is the end of the poly trait ref (Foo + 'baz + Bar><)
+                    let end_span = bounds.iter().map(|bound| bound.span()).last().unwrap();
+                    // `last_bound_span` is the last bound of the poly trait ref (Foo + >'baz< + Bar)
+                    let last_bound_span = spans.last().cloned().unwrap();
+                    let mut multi_span: MultiSpan = spans.clone().into();
+                    for sp in spans {
+                        let msg = if sp == last_bound_span {
+                            format!(
+                                "...because of {these} bound{s}",
+                                these = pluralize!("this", bounds.len() - 1),
+                                s = pluralize!(bounds.len() - 1),
+                            )
+                        } else {
+                            String::new()
+                        };
+                        multi_span.push_span_label(sp, msg);
+                    }
+                    multi_span
+                        .push_span_label(base_error.span, "expected this type to be a trait...");
+                    err.span_help(
+                        multi_span,
+                        "`+` is used to constrain a \"trait object\" type with lifetimes or \
+                         auto-traits; structs and enums can't be bound in that way",
+                    );
+                    if bounds.iter().all(|bound| match bound {
+                        ast::GenericBound::Outlives(_) => true,
+                        ast::GenericBound::Trait(tr, _) => tr.span == base_error.span,
+                    }) {
+                        let mut sugg = vec![];
+                        if base_error.span != start_span {
+                            sugg.push((start_span.until(base_error.span), String::new()));
+                        }
+                        if base_error.span != end_span {
+                            sugg.push((base_error.span.shrink_to_hi().to(end_span), String::new()));
+                        }
+
+                        err.multipart_suggestion(
+                            "if you meant to use a type and not a trait here, remove the bounds",
+                            sugg,
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                }
+            }
+
+            fallback |= self.restrict_assoc_type_in_where_clause(span, &mut err);
+
+            if !self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span) {
+                fallback = true;
+                match self.diagnostic_metadata.current_let_binding {
+                    Some((pat_sp, Some(ty_sp), None))
+                        if ty_sp.contains(base_error.span) && base_error.could_be_expr =>
+                    {
+                        err.span_suggestion_short(
+                            pat_sp.between(ty_sp),
+                            "use `=` if you meant to assign",
+                            " = ",
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                    _ => {}
+                }
+
+                // If the trait has a single item (which wasn't matched by Levenshtein), suggest it
+                let suggestion = self.get_single_associated_item(&path, &source, is_expected);
+                self.r.add_typo_suggestion(&mut err, suggestion, ident_span);
+            }
+            if fallback {
+                // Fallback label.
+                err.span_label(base_error.span, base_error.fallback_label);
+            }
+        }
+        if let Some(err_code) = &err.code {
+            if err_code == &rustc_errors::error_code!(E0425) {
+                for label_rib in &self.label_ribs {
+                    for (label_ident, node_id) in &label_rib.bindings {
+                        if format!("'{}", ident) == label_ident.to_string() {
+                            err.span_label(label_ident.span, "a label with a similar name exists");
+                            if let PathSource::Expr(Some(Expr {
+                                kind: ExprKind::Break(None, Some(_)),
+                                ..
+                            })) = source
+                            {
+                                err.span_suggestion(
+                                    span,
+                                    "use the similarly named label",
+                                    label_ident.name,
+                                    Applicability::MaybeIncorrect,
+                                );
+                                // Do not lint against unused label when we suggest them.
+                                self.diagnostic_metadata.unused_labels.remove(node_id);
+                            }
+                        }
+                    }
+                }
+            } else if err_code == &rustc_errors::error_code!(E0412) {
+                if let Some(correct) = Self::likely_rust_type(path) {
+                    err.span_suggestion(
+                        span,
+                        "perhaps you intended to use this type",
+                        correct,
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+            }
+        }
+
+        (err, candidates)
+    }
+
+    fn detect_assoct_type_constraint_meant_as_path(&self, base_span: Span, err: &mut Diagnostic) {
+        let Some(ty) = self.diagnostic_metadata.current_type_path else { return; };
+        let TyKind::Path(_, path) = &ty.kind else { return; };
+        for segment in &path.segments {
+            let Some(params) = &segment.args else { continue; };
+            let ast::GenericArgs::AngleBracketed(ref params) = params.deref() else { continue; };
+            for param in &params.args {
+                let ast::AngleBracketedArg::Constraint(constraint) = param else { continue; };
+                let ast::AssocConstraintKind::Bound { bounds } = &constraint.kind else {
+                    continue;
+                };
+                for bound in bounds {
+                    let ast::GenericBound::Trait(trait_ref, ast::TraitBoundModifier::None)
+                        = bound else
+                    {
+                        continue;
+                    };
+                    if base_span == trait_ref.span {
+                        err.span_suggestion_verbose(
+                            constraint.ident.span.between(trait_ref.span),
+                            "you might have meant to write a path instead of an associated type bound",
+                            "::",
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                }
+            }
+        }
+    }
+
+    fn suggest_swapping_misplaced_self_ty_and_trait(
+        &mut self,
+        err: &mut Diagnostic,
+        source: PathSource<'_>,
+        res: Option<Res>,
+        span: Span,
+    ) {
+        if let Some((trait_ref, self_ty)) =
+            self.diagnostic_metadata.currently_processing_impl_trait.clone()
+            && let TyKind::Path(_, self_ty_path) = &self_ty.kind
+            && let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
+                self.resolve_path(&Segment::from_path(self_ty_path), Some(TypeNS), None)
+            && let ModuleKind::Def(DefKind::Trait, ..) = module.kind
+            && trait_ref.path.span == span
+            && let PathSource::Trait(_) = source
+            && let Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)) = res
+            && let Ok(self_ty_str) =
+                self.r.session.source_map().span_to_snippet(self_ty.span)
+            && let Ok(trait_ref_str) =
+                self.r.session.source_map().span_to_snippet(trait_ref.path.span)
+        {
+                err.multipart_suggestion(
+                    "`impl` items mention the trait being implemented first and the type it is being implemented for second",
+                    vec![(trait_ref.path.span, self_ty_str), (self_ty.span, trait_ref_str)],
+                    Applicability::MaybeIncorrect,
+                );
+        }
+    }
+
+    fn get_single_associated_item(
+        &mut self,
+        path: &[Segment],
+        source: &PathSource<'_>,
+        filter_fn: &impl Fn(Res) -> bool,
+    ) -> Option<TypoSuggestion> {
+        if let crate::PathSource::TraitItem(_) = source {
+            let mod_path = &path[..path.len() - 1];
+            if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
+                self.resolve_path(mod_path, None, None)
+            {
+                let resolutions = self.r.resolutions(module).borrow();
+                let targets: Vec<_> =
+                    resolutions
+                        .iter()
+                        .filter_map(|(key, resolution)| {
+                            resolution.borrow().binding.map(|binding| binding.res()).and_then(
+                                |res| if filter_fn(res) { Some((key, res)) } else { None },
+                            )
+                        })
+                        .collect();
+                if targets.len() == 1 {
+                    let target = targets[0];
+                    return Some(TypoSuggestion::single_item_from_res(
+                        target.0.ident.name,
+                        target.1,
+                    ));
+                }
+            }
+        }
+        None
+    }
+
+    /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
+    fn restrict_assoc_type_in_where_clause(&mut self, span: Span, err: &mut Diagnostic) -> bool {
+        // Detect that we are actually in a `where` predicate.
+        let (bounded_ty, bounds, where_span) =
+            if let Some(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
+                bounded_ty,
+                bound_generic_params,
+                bounds,
+                span,
+            })) = self.diagnostic_metadata.current_where_predicate
+            {
+                if !bound_generic_params.is_empty() {
+                    return false;
+                }
+                (bounded_ty, bounds, span)
+            } else {
+                return false;
+            };
+
+        // Confirm that the target is an associated type.
+        let (ty, position, path) = if let ast::TyKind::Path(
+            Some(ast::QSelf { ty, position, .. }),
+            path,
+        ) = &bounded_ty.kind
+        {
+            // use this to verify that ident is a type param.
+            let Some(partial_res) = self.r.partial_res_map.get(&bounded_ty.id) else {
+                return false;
+            };
+            if !(matches!(
+                partial_res.base_res(),
+                hir::def::Res::Def(hir::def::DefKind::AssocTy, _)
+            ) && partial_res.unresolved_segments() == 0)
+            {
+                return false;
+            }
+            (ty, position, path)
+        } else {
+            return false;
+        };
+
+        let peeled_ty = ty.peel_refs();
+        if let ast::TyKind::Path(None, type_param_path) = &peeled_ty.kind {
+            // Confirm that the `SelfTy` is a type parameter.
+            let Some(partial_res) = self.r.partial_res_map.get(&peeled_ty.id) else {
+                return false;
+            };
+            if !(matches!(
+                partial_res.base_res(),
+                hir::def::Res::Def(hir::def::DefKind::TyParam, _)
+            ) && partial_res.unresolved_segments() == 0)
+            {
+                return false;
+            }
+            if let (
+                [ast::PathSegment { ident: constrain_ident, args: None, .. }],
+                [ast::GenericBound::Trait(poly_trait_ref, ast::TraitBoundModifier::None)],
+            ) = (&type_param_path.segments[..], &bounds[..])
+            {
+                if let [ast::PathSegment { ident, args: None, .. }] =
+                    &poly_trait_ref.trait_ref.path.segments[..]
+                {
+                    if ident.span == span {
+                        err.span_suggestion_verbose(
+                            *where_span,
+                            &format!("constrain the associated type to `{}`", ident),
+                            format!(
+                                "{}: {}<{} = {}>",
+                                self.r
+                                    .session
+                                    .source_map()
+                                    .span_to_snippet(ty.span) // Account for `<&'a T as Foo>::Bar`.
+                                    .unwrap_or_else(|_| constrain_ident.to_string()),
+                                path.segments[..*position]
+                                    .iter()
+                                    .map(|segment| path_segment_to_string(segment))
+                                    .collect::<Vec<_>>()
+                                    .join("::"),
+                                path.segments[*position..]
+                                    .iter()
+                                    .map(|segment| path_segment_to_string(segment))
+                                    .collect::<Vec<_>>()
+                                    .join("::"),
+                                ident,
+                            ),
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                    return true;
+                }
+            }
+        }
+        false
+    }
+
+    /// Check if the source is call expression and the first argument is `self`. If true,
+    /// return the span of whole call and the span for all arguments expect the first one (`self`).
+    fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
+        let mut has_self_arg = None;
+        if let PathSource::Expr(Some(parent)) = source {
+            match &parent.kind {
+                ExprKind::Call(_, args) if !args.is_empty() => {
+                    let mut expr_kind = &args[0].kind;
+                    loop {
+                        match expr_kind {
+                            ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
+                                if arg_name.segments[0].ident.name == kw::SelfLower {
+                                    let call_span = parent.span;
+                                    let tail_args_span = if args.len() > 1 {
+                                        Some(Span::new(
+                                            args[1].span.lo(),
+                                            args.last().unwrap().span.hi(),
+                                            call_span.ctxt(),
+                                            None,
+                                        ))
+                                    } else {
+                                        None
+                                    };
+                                    has_self_arg = Some((call_span, tail_args_span));
+                                }
+                                break;
+                            }
+                            ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
+                            _ => break,
+                        }
+                    }
+                }
+                _ => (),
+            }
+        };
+        has_self_arg
+    }
+
+    fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
+        // HACK(estebank): find a better way to figure out that this was a
+        // parser issue where a struct literal is being used on an expression
+        // where a brace being opened means a block is being started. Look
+        // ahead for the next text to see if `span` is followed by a `{`.
+        let sm = self.r.session.source_map();
+        let mut sp = span;
+        loop {
+            sp = sm.next_point(sp);
+            match sm.span_to_snippet(sp) {
+                Ok(ref snippet) => {
+                    if snippet.chars().any(|c| !c.is_whitespace()) {
+                        break;
+                    }
+                }
+                _ => break,
+            }
+        }
+        let followed_by_brace = matches!(sm.span_to_snippet(sp), Ok(ref snippet) if snippet == "{");
+        // In case this could be a struct literal that needs to be surrounded
+        // by parentheses, find the appropriate span.
+        let mut i = 0;
+        let mut closing_brace = None;
+        loop {
+            sp = sm.next_point(sp);
+            match sm.span_to_snippet(sp) {
+                Ok(ref snippet) => {
+                    if snippet == "}" {
+                        closing_brace = Some(span.to(sp));
+                        break;
+                    }
+                }
+                _ => break,
+            }
+            i += 1;
+            // The bigger the span, the more likely we're incorrect --
+            // bound it to 100 chars long.
+            if i > 100 {
+                break;
+            }
+        }
+        (followed_by_brace, closing_brace)
+    }
+
+    /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
+    /// function.
+    /// Returns `true` if able to provide context-dependent help.
+    fn smart_resolve_context_dependent_help(
+        &mut self,
+        err: &mut Diagnostic,
+        span: Span,
+        source: PathSource<'_>,
+        res: Res,
+        path_str: &str,
+        fallback_label: &str,
+    ) -> bool {
+        let ns = source.namespace();
+        let is_expected = &|res| source.is_expected(res);
+
+        let path_sep = |err: &mut Diagnostic, expr: &Expr| match expr.kind {
+            ExprKind::Field(_, ident) => {
+                err.span_suggestion(
+                    expr.span,
+                    "use the path separator to refer to an item",
+                    format!("{}::{}", path_str, ident),
+                    Applicability::MaybeIncorrect,
+                );
+                true
+            }
+            ExprKind::MethodCall(ref segment, ..) => {
+                let span = expr.span.with_hi(segment.ident.span.hi());
+                err.span_suggestion(
+                    span,
+                    "use the path separator to refer to an item",
+                    format!("{}::{}", path_str, segment.ident),
+                    Applicability::MaybeIncorrect,
+                );
+                true
+            }
+            _ => false,
+        };
+
+        let find_span = |source: &PathSource<'_>, err: &mut Diagnostic| {
+            match source {
+                PathSource::Expr(Some(Expr { span, kind: ExprKind::Call(_, _), .. }))
+                | PathSource::TupleStruct(span, _) => {
+                    // We want the main underline to cover the suggested code as well for
+                    // cleaner output.
+                    err.set_span(*span);
+                    *span
+                }
+                _ => span,
+            }
+        };
+
+        let mut bad_struct_syntax_suggestion = |def_id: DefId| {
+            let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
+
+            match source {
+                PathSource::Expr(Some(
+                    parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
+                )) if path_sep(err, &parent) => {}
+                PathSource::Expr(
+                    None
+                    | Some(Expr {
+                        kind:
+                            ExprKind::Path(..)
+                            | ExprKind::Binary(..)
+                            | ExprKind::Unary(..)
+                            | ExprKind::If(..)
+                            | ExprKind::While(..)
+                            | ExprKind::ForLoop(..)
+                            | ExprKind::Match(..),
+                        ..
+                    }),
+                ) if followed_by_brace => {
+                    if let Some(sp) = closing_brace {
+                        err.span_label(span, fallback_label);
+                        err.multipart_suggestion(
+                            "surround the struct literal with parentheses",
+                            vec![
+                                (sp.shrink_to_lo(), "(".to_string()),
+                                (sp.shrink_to_hi(), ")".to_string()),
+                            ],
+                            Applicability::MaybeIncorrect,
+                        );
+                    } else {
+                        err.span_label(
+                            span, // Note the parentheses surrounding the suggestion below
+                            format!(
+                                "you might want to surround a struct literal with parentheses: \
+                                 `({} {{ /* fields */ }})`?",
+                                path_str
+                            ),
+                        );
+                    }
+                }
+                PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
+                    let span = find_span(&source, err);
+                    if let Some(span) = self.def_span(def_id) {
+                        err.span_label(span, &format!("`{}` defined here", path_str));
+                    }
+                    let (tail, descr, applicability) = match source {
+                        PathSource::Pat | PathSource::TupleStruct(..) => {
+                            ("", "pattern", Applicability::MachineApplicable)
+                        }
+                        _ => (": val", "literal", Applicability::HasPlaceholders),
+                    };
+                    let (fields, applicability) = match self.r.field_names.get(&def_id) {
+                        Some(fields) => (
+                            fields
+                                .iter()
+                                .map(|f| format!("{}{}", f.node, tail))
+                                .collect::<Vec<String>>()
+                                .join(", "),
+                            applicability,
+                        ),
+                        None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
+                    };
+                    let pad = match self.r.field_names.get(&def_id) {
+                        Some(fields) if fields.is_empty() => "",
+                        _ => " ",
+                    };
+                    err.span_suggestion(
+                        span,
+                        &format!("use struct {} syntax instead", descr),
+                        format!("{path_str} {{{pad}{fields}{pad}}}"),
+                        applicability,
+                    );
+                }
+                _ => {
+                    err.span_label(span, fallback_label);
+                }
+            }
+        };
+
+        match (res, source) {
+            (
+                Res::Def(DefKind::Macro(MacroKind::Bang), _),
+                PathSource::Expr(Some(Expr {
+                    kind: ExprKind::Index(..) | ExprKind::Call(..), ..
+                }))
+                | PathSource::Struct,
+            ) => {
+                err.span_label(span, fallback_label);
+                err.span_suggestion_verbose(
+                    span.shrink_to_hi(),
+                    "use `!` to invoke the macro",
+                    "!",
+                    Applicability::MaybeIncorrect,
+                );
+                if path_str == "try" && span.rust_2015() {
+                    err.note("if you want the `try` keyword, you need Rust 2018 or later");
+                }
+            }
+            (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
+                err.span_label(span, fallback_label);
+            }
+            (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
+                err.span_label(span, "type aliases cannot be used as traits");
+                if self.r.session.is_nightly_build() {
+                    let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
+                               `type` alias";
+                    if let Some(span) = self.def_span(def_id) {
+                        if let Ok(snip) = self.r.session.source_map().span_to_snippet(span) {
+                            // The span contains a type alias so we should be able to
+                            // replace `type` with `trait`.
+                            let snip = snip.replacen("type", "trait", 1);
+                            err.span_suggestion(span, msg, snip, Applicability::MaybeIncorrect);
+                        } else {
+                            err.span_help(span, msg);
+                        }
+                    } else {
+                        err.help(msg);
+                    }
+                }
+            }
+            (Res::Def(DefKind::Mod, _), PathSource::Expr(Some(parent))) => {
+                if !path_sep(err, &parent) {
+                    return false;
+                }
+            }
+            (
+                Res::Def(DefKind::Enum, def_id),
+                PathSource::TupleStruct(..) | PathSource::Expr(..),
+            ) => {
+                if self
+                    .diagnostic_metadata
+                    .current_type_ascription
+                    .last()
+                    .map(|sp| {
+                        self.r
+                            .session
+                            .parse_sess
+                            .type_ascription_path_suggestions
+                            .borrow()
+                            .contains(&sp)
+                    })
+                    .unwrap_or(false)
+                {
+                    err.downgrade_to_delayed_bug();
+                    // We already suggested changing `:` into `::` during parsing.
+                    return false;
+                }
+
+                self.suggest_using_enum_variant(err, source, def_id, span);
+            }
+            (Res::Def(DefKind::Struct, def_id), source) if ns == ValueNS => {
+                let (ctor_def, ctor_vis, fields) =
+                    if let Some(struct_ctor) = self.r.struct_constructors.get(&def_id).cloned() {
+                        if let PathSource::Expr(Some(parent)) = source {
+                            if let ExprKind::Field(..) | ExprKind::MethodCall(..) = parent.kind {
+                                bad_struct_syntax_suggestion(def_id);
+                                return true;
+                            }
+                        }
+                        struct_ctor
+                    } else {
+                        bad_struct_syntax_suggestion(def_id);
+                        return true;
+                    };
+
+                let is_accessible = self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
+                if !is_expected(ctor_def) || is_accessible {
+                    return true;
+                }
+
+                let field_spans = match source {
+                    // e.g. `if let Enum::TupleVariant(field1, field2) = _`
+                    PathSource::TupleStruct(_, pattern_spans) => {
+                        err.set_primary_message(
+                            "cannot match against a tuple struct which contains private fields",
+                        );
+
+                        // Use spans of the tuple struct pattern.
+                        Some(Vec::from(pattern_spans))
+                    }
+                    // e.g. `let _ = Enum::TupleVariant(field1, field2);`
+                    _ if source.is_call() => {
+                        err.set_primary_message(
+                            "cannot initialize a tuple struct which contains private fields",
+                        );
+
+                        // Use spans of the tuple struct definition.
+                        self.r
+                            .field_names
+                            .get(&def_id)
+                            .map(|fields| fields.iter().map(|f| f.span).collect::<Vec<_>>())
+                    }
+                    _ => None,
+                };
+
+                if let Some(spans) =
+                    field_spans.filter(|spans| spans.len() > 0 && fields.len() == spans.len())
+                {
+                    let non_visible_spans: Vec<Span> = iter::zip(&fields, &spans)
+                        .filter(|(vis, _)| {
+                            !self.r.is_accessible_from(**vis, self.parent_scope.module)
+                        })
+                        .map(|(_, span)| *span)
+                        .collect();
+
+                    if non_visible_spans.len() > 0 {
+                        let mut m: MultiSpan = non_visible_spans.clone().into();
+                        non_visible_spans
+                            .into_iter()
+                            .for_each(|s| m.push_span_label(s, "private field"));
+                        err.span_note(m, "constructor is not visible here due to private fields");
+                    }
+
+                    return true;
+                }
+
+                err.span_label(span, "constructor is not visible here due to private fields");
+            }
+            (
+                Res::Def(
+                    DefKind::Union | DefKind::Variant | DefKind::Ctor(_, CtorKind::Fictive),
+                    def_id,
+                ),
+                _,
+            ) if ns == ValueNS => {
+                bad_struct_syntax_suggestion(def_id);
+            }
+            (Res::Def(DefKind::Ctor(_, CtorKind::Const), def_id), _) if ns == ValueNS => {
+                match source {
+                    PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
+                        let span = find_span(&source, err);
+                        if let Some(span) = self.def_span(def_id) {
+                            err.span_label(span, &format!("`{}` defined here", path_str));
+                        }
+                        err.span_suggestion(
+                            span,
+                            "use this syntax instead",
+                            path_str,
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                    _ => return false,
+                }
+            }
+            (Res::Def(DefKind::Ctor(_, CtorKind::Fn), def_id), _) if ns == ValueNS => {
+                if let Some(span) = self.def_span(def_id) {
+                    err.span_label(span, &format!("`{}` defined here", path_str));
+                }
+                let fields = self.r.field_names.get(&def_id).map_or_else(
+                    || "/* fields */".to_string(),
+                    |fields| vec!["_"; fields.len()].join(", "),
+                );
+                err.span_suggestion(
+                    span,
+                    "use the tuple variant pattern syntax instead",
+                    format!("{}({})", path_str, fields),
+                    Applicability::HasPlaceholders,
+                );
+            }
+            (Res::SelfTy { .. }, _) if ns == ValueNS => {
+                err.span_label(span, fallback_label);
+                err.note("can't use `Self` as a constructor, you must use the implemented struct");
+            }
+            (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
+                err.note("can't use a type alias as a constructor");
+            }
+            _ => return false,
+        }
+        true
+    }
+
+    /// Given the target `ident` and `kind`, search for the similarly named associated item
+    /// in `self.current_trait_ref`.
+    pub(crate) fn find_similarly_named_assoc_item(
+        &mut self,
+        ident: Symbol,
+        kind: &AssocItemKind,
+    ) -> Option<Symbol> {
+        let (module, _) = self.current_trait_ref.as_ref()?;
+        if ident == kw::Underscore {
+            // We do nothing for `_`.
+            return None;
+        }
+
+        let resolutions = self.r.resolutions(module);
+        let targets = resolutions
+            .borrow()
+            .iter()
+            .filter_map(|(key, res)| res.borrow().binding.map(|binding| (key, binding.res())))
+            .filter(|(_, res)| match (kind, res) {
+                (AssocItemKind::Const(..), Res::Def(DefKind::AssocConst, _)) => true,
+                (AssocItemKind::Fn(_), Res::Def(DefKind::AssocFn, _)) => true,
+                (AssocItemKind::TyAlias(..), Res::Def(DefKind::AssocTy, _)) => true,
+                _ => false,
+            })
+            .map(|(key, _)| key.ident.name)
+            .collect::<Vec<_>>();
+
+        find_best_match_for_name(&targets, ident, None)
+    }
+
+    fn lookup_assoc_candidate<FilterFn>(
+        &mut self,
+        ident: Ident,
+        ns: Namespace,
+        filter_fn: FilterFn,
+    ) -> Option<AssocSuggestion>
+    where
+        FilterFn: Fn(Res) -> bool,
+    {
+        fn extract_node_id(t: &Ty) -> Option<NodeId> {
+            match t.kind {
+                TyKind::Path(None, _) => Some(t.id),
+                TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
+                // This doesn't handle the remaining `Ty` variants as they are not
+                // that commonly the self_type, it might be interesting to provide
+                // support for those in future.
+                _ => None,
+            }
+        }
+
+        // Fields are generally expected in the same contexts as locals.
+        if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
+            if let Some(node_id) =
+                self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
+            {
+                // Look for a field with the same name in the current self_type.
+                if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
+                    match resolution.base_res() {
+                        Res::Def(DefKind::Struct | DefKind::Union, did)
+                            if resolution.unresolved_segments() == 0 =>
+                        {
+                            if let Some(field_names) = self.r.field_names.get(&did) {
+                                if field_names
+                                    .iter()
+                                    .any(|&field_name| ident.name == field_name.node)
+                                {
+                                    return Some(AssocSuggestion::Field);
+                                }
+                            }
+                        }
+                        _ => {}
+                    }
+                }
+            }
+        }
+
+        if let Some(items) = self.diagnostic_metadata.current_trait_assoc_items {
+            for assoc_item in items {
+                if assoc_item.ident == ident {
+                    return Some(match &assoc_item.kind {
+                        ast::AssocItemKind::Const(..) => AssocSuggestion::AssocConst,
+                        ast::AssocItemKind::Fn(box ast::Fn { sig, .. }) if sig.decl.has_self() => {
+                            AssocSuggestion::MethodWithSelf
+                        }
+                        ast::AssocItemKind::Fn(..) => AssocSuggestion::AssocFn,
+                        ast::AssocItemKind::TyAlias(..) => AssocSuggestion::AssocType,
+                        ast::AssocItemKind::MacCall(_) => continue,
+                    });
+                }
+            }
+        }
+
+        // Look for associated items in the current trait.
+        if let Some((module, _)) = self.current_trait_ref {
+            if let Ok(binding) = self.r.maybe_resolve_ident_in_module(
+                ModuleOrUniformRoot::Module(module),
+                ident,
+                ns,
+                &self.parent_scope,
+            ) {
+                let res = binding.res();
+                if filter_fn(res) {
+                    if self.r.has_self.contains(&res.def_id()) {
+                        return Some(AssocSuggestion::MethodWithSelf);
+                    } else {
+                        match res {
+                            Res::Def(DefKind::AssocFn, _) => return Some(AssocSuggestion::AssocFn),
+                            Res::Def(DefKind::AssocConst, _) => {
+                                return Some(AssocSuggestion::AssocConst);
+                            }
+                            Res::Def(DefKind::AssocTy, _) => {
+                                return Some(AssocSuggestion::AssocType);
+                            }
+                            _ => {}
+                        }
+                    }
+                }
+            }
+        }
+
+        None
+    }
+
+    fn lookup_typo_candidate(
+        &mut self,
+        path: &[Segment],
+        ns: Namespace,
+        filter_fn: &impl Fn(Res) -> bool,
+    ) -> Option<TypoSuggestion> {
+        let mut names = Vec::new();
+        if path.len() == 1 {
+            // Search in lexical scope.
+            // Walk backwards up the ribs in scope and collect candidates.
+            for rib in self.ribs[ns].iter().rev() {
+                // Locals and type parameters
+                for (ident, &res) in &rib.bindings {
+                    if filter_fn(res) {
+                        names.push(TypoSuggestion::typo_from_res(ident.name, res));
+                    }
+                }
+                // Items in scope
+                if let RibKind::ModuleRibKind(module) = rib.kind {
+                    // Items from this module
+                    self.r.add_module_candidates(module, &mut names, &filter_fn);
+
+                    if let ModuleKind::Block = module.kind {
+                        // We can see through blocks
+                    } else {
+                        // Items from the prelude
+                        if !module.no_implicit_prelude {
+                            let extern_prelude = self.r.extern_prelude.clone();
+                            names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
+                                self.r.crate_loader.maybe_process_path_extern(ident.name).and_then(
+                                    |crate_id| {
+                                        let crate_mod =
+                                            Res::Def(DefKind::Mod, crate_id.as_def_id());
+
+                                        if filter_fn(crate_mod) {
+                                            Some(TypoSuggestion::typo_from_res(
+                                                ident.name, crate_mod,
+                                            ))
+                                        } else {
+                                            None
+                                        }
+                                    },
+                                )
+                            }));
+
+                            if let Some(prelude) = self.r.prelude {
+                                self.r.add_module_candidates(prelude, &mut names, &filter_fn);
+                            }
+                        }
+                        break;
+                    }
+                }
+            }
+            // Add primitive types to the mix
+            if filter_fn(Res::PrimTy(PrimTy::Bool)) {
+                names.extend(PrimTy::ALL.iter().map(|prim_ty| {
+                    TypoSuggestion::typo_from_res(prim_ty.name(), Res::PrimTy(*prim_ty))
+                }))
+            }
+        } else {
+            // Search in module.
+            let mod_path = &path[..path.len() - 1];
+            if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
+                self.resolve_path(mod_path, Some(TypeNS), None)
+            {
+                self.r.add_module_candidates(module, &mut names, &filter_fn);
+            }
+        }
+
+        let name = path[path.len() - 1].ident.name;
+        // Make sure error reporting is deterministic.
+        names.sort_by(|a, b| a.candidate.as_str().partial_cmp(b.candidate.as_str()).unwrap());
+
+        match find_best_match_for_name(
+            &names.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
+            name,
+            None,
+        ) {
+            Some(found) if found != name => {
+                names.into_iter().find(|suggestion| suggestion.candidate == found)
+            }
+            _ => None,
+        }
+    }
+
+    // Returns the name of the Rust type approximately corresponding to
+    // a type name in another programming language.
+    fn likely_rust_type(path: &[Segment]) -> Option<Symbol> {
+        let name = path[path.len() - 1].ident.as_str();
+        // Common Java types
+        Some(match name {
+            "byte" => sym::u8, // In Java, bytes are signed, but in practice one almost always wants unsigned bytes.
+            "short" => sym::i16,
+            "Bool" => sym::bool,
+            "Boolean" => sym::bool,
+            "boolean" => sym::bool,
+            "int" => sym::i32,
+            "long" => sym::i64,
+            "float" => sym::f32,
+            "double" => sym::f64,
+            _ => return None,
+        })
+    }
+
+    /// Only used in a specific case of type ascription suggestions
+    fn get_colon_suggestion_span(&self, start: Span) -> Span {
+        let sm = self.r.session.source_map();
+        start.to(sm.next_point(start))
+    }
+
+    fn type_ascription_suggestion(&self, err: &mut Diagnostic, base_span: Span) -> bool {
+        let sm = self.r.session.source_map();
+        let base_snippet = sm.span_to_snippet(base_span);
+        if let Some(&sp) = self.diagnostic_metadata.current_type_ascription.last() {
+            if let Ok(snippet) = sm.span_to_snippet(sp) {
+                let len = snippet.trim_end().len() as u32;
+                if snippet.trim() == ":" {
+                    let colon_sp =
+                        sp.with_lo(sp.lo() + BytePos(len - 1)).with_hi(sp.lo() + BytePos(len));
+                    let mut show_label = true;
+                    if sm.is_multiline(sp) {
+                        err.span_suggestion_short(
+                            colon_sp,
+                            "maybe you meant to write `;` here",
+                            ";",
+                            Applicability::MaybeIncorrect,
+                        );
+                    } else {
+                        let after_colon_sp =
+                            self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
+                        if snippet.len() == 1 {
+                            // `foo:bar`
+                            err.span_suggestion(
+                                colon_sp,
+                                "maybe you meant to write a path separator here",
+                                "::",
+                                Applicability::MaybeIncorrect,
+                            );
+                            show_label = false;
+                            if !self
+                                .r
+                                .session
+                                .parse_sess
+                                .type_ascription_path_suggestions
+                                .borrow_mut()
+                                .insert(colon_sp)
+                            {
+                                err.downgrade_to_delayed_bug();
+                            }
+                        }
+                        if let Ok(base_snippet) = base_snippet {
+                            let mut sp = after_colon_sp;
+                            for _ in 0..100 {
+                                // Try to find an assignment
+                                sp = sm.next_point(sp);
+                                let snippet = sm.span_to_snippet(sp.to(sm.next_point(sp)));
+                                match snippet {
+                                    Ok(ref x) if x.as_str() == "=" => {
+                                        err.span_suggestion(
+                                            base_span,
+                                            "maybe you meant to write an assignment here",
+                                            format!("let {}", base_snippet),
+                                            Applicability::MaybeIncorrect,
+                                        );
+                                        show_label = false;
+                                        break;
+                                    }
+                                    Ok(ref x) if x.as_str() == "\n" => break,
+                                    Err(_) => break,
+                                    Ok(_) => {}
+                                }
+                            }
+                        }
+                    }
+                    if show_label {
+                        err.span_label(
+                            base_span,
+                            "expecting a type here because of type ascription",
+                        );
+                    }
+                    return show_label;
+                }
+            }
+        }
+        false
+    }
+
+    fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
+        let mut result = None;
+        let mut seen_modules = FxHashSet::default();
+        let mut worklist = vec![(self.r.graph_root, Vec::new())];
+
+        while let Some((in_module, path_segments)) = worklist.pop() {
+            // abort if the module is already found
+            if result.is_some() {
+                break;
+            }
+
+            in_module.for_each_child(self.r, |_, ident, _, name_binding| {
+                // abort if the module is already found or if name_binding is private external
+                if result.is_some() || !name_binding.vis.is_visible_locally() {
+                    return;
+                }
+                if let Some(module) = name_binding.module() {
+                    // form the path
+                    let mut path_segments = path_segments.clone();
+                    path_segments.push(ast::PathSegment::from_ident(ident));
+                    let module_def_id = module.def_id();
+                    if module_def_id == def_id {
+                        let path =
+                            Path { span: name_binding.span, segments: path_segments, tokens: None };
+                        result = Some((
+                            module,
+                            ImportSuggestion {
+                                did: Some(def_id),
+                                descr: "module",
+                                path,
+                                accessible: true,
+                                note: None,
+                            },
+                        ));
+                    } else {
+                        // add the module to the lookup
+                        if seen_modules.insert(module_def_id) {
+                            worklist.push((module, path_segments));
+                        }
+                    }
+                }
+            });
+        }
+
+        result
+    }
+
+    fn collect_enum_ctors(&mut self, def_id: DefId) -> Option<Vec<(Path, DefId, CtorKind)>> {
+        self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
+            let mut variants = Vec::new();
+            enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
+                if let Res::Def(DefKind::Ctor(CtorOf::Variant, kind), def_id) = name_binding.res() {
+                    let mut segms = enum_import_suggestion.path.segments.clone();
+                    segms.push(ast::PathSegment::from_ident(ident));
+                    let path = Path { span: name_binding.span, segments: segms, tokens: None };
+                    variants.push((path, def_id, kind));
+                }
+            });
+            variants
+        })
+    }
+
+    /// Adds a suggestion for using an enum's variant when an enum is used instead.
+    fn suggest_using_enum_variant(
+        &mut self,
+        err: &mut Diagnostic,
+        source: PathSource<'_>,
+        def_id: DefId,
+        span: Span,
+    ) {
+        let Some(variants) = self.collect_enum_ctors(def_id) else {
+            err.note("you might have meant to use one of the enum's variants");
+            return;
+        };
+
+        let suggest_only_tuple_variants =
+            matches!(source, PathSource::TupleStruct(..)) || source.is_call();
+        if suggest_only_tuple_variants {
+            // Suggest only tuple variants regardless of whether they have fields and do not
+            // suggest path with added parentheses.
+            let suggestable_variants = variants
+                .iter()
+                .filter(|(.., kind)| *kind == CtorKind::Fn)
+                .map(|(variant, ..)| path_names_to_string(variant))
+                .collect::<Vec<_>>();
+
+            let non_suggestable_variant_count = variants.len() - suggestable_variants.len();
+
+            let source_msg = if source.is_call() {
+                "to construct"
+            } else if matches!(source, PathSource::TupleStruct(..)) {
+                "to match against"
+            } else {
+                unreachable!()
+            };
+
+            if !suggestable_variants.is_empty() {
+                let msg = if non_suggestable_variant_count == 0 && suggestable_variants.len() == 1 {
+                    format!("try {} the enum's variant", source_msg)
+                } else {
+                    format!("try {} one of the enum's variants", source_msg)
+                };
+
+                err.span_suggestions(
+                    span,
+                    &msg,
+                    suggestable_variants.into_iter(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+
+            // If the enum has no tuple variants..
+            if non_suggestable_variant_count == variants.len() {
+                err.help(&format!("the enum has no tuple variants {}", source_msg));
+            }
+
+            // If there are also non-tuple variants..
+            if non_suggestable_variant_count == 1 {
+                err.help(&format!(
+                    "you might have meant {} the enum's non-tuple variant",
+                    source_msg
+                ));
+            } else if non_suggestable_variant_count >= 1 {
+                err.help(&format!(
+                    "you might have meant {} one of the enum's non-tuple variants",
+                    source_msg
+                ));
+            }
+        } else {
+            let needs_placeholder = |def_id: DefId, kind: CtorKind| {
+                let has_no_fields = self.r.field_names.get(&def_id).map_or(false, |f| f.is_empty());
+                match kind {
+                    CtorKind::Const => false,
+                    CtorKind::Fn | CtorKind::Fictive if has_no_fields => false,
+                    _ => true,
+                }
+            };
+
+            let mut suggestable_variants = variants
+                .iter()
+                .filter(|(_, def_id, kind)| !needs_placeholder(*def_id, *kind))
+                .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
+                .map(|(variant, kind)| match kind {
+                    CtorKind::Const => variant,
+                    CtorKind::Fn => format!("({}())", variant),
+                    CtorKind::Fictive => format!("({} {{}})", variant),
+                })
+                .collect::<Vec<_>>();
+
+            if !suggestable_variants.is_empty() {
+                let msg = if suggestable_variants.len() == 1 {
+                    "you might have meant to use the following enum variant"
+                } else {
+                    "you might have meant to use one of the following enum variants"
+                };
+
+                err.span_suggestions(
+                    span,
+                    msg,
+                    suggestable_variants.drain(..),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+
+            let suggestable_variants_with_placeholders = variants
+                .iter()
+                .filter(|(_, def_id, kind)| needs_placeholder(*def_id, *kind))
+                .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
+                .filter_map(|(variant, kind)| match kind {
+                    CtorKind::Fn => Some(format!("({}(/* fields */))", variant)),
+                    CtorKind::Fictive => Some(format!("({} {{ /* fields */ }})", variant)),
+                    _ => None,
+                })
+                .collect::<Vec<_>>();
+
+            if !suggestable_variants_with_placeholders.is_empty() {
+                let msg = match (
+                    suggestable_variants.is_empty(),
+                    suggestable_variants_with_placeholders.len(),
+                ) {
+                    (true, 1) => "the following enum variant is available",
+                    (true, _) => "the following enum variants are available",
+                    (false, 1) => "alternatively, the following enum variant is available",
+                    (false, _) => "alternatively, the following enum variants are also available",
+                };
+
+                err.span_suggestions(
+                    span,
+                    msg,
+                    suggestable_variants_with_placeholders.into_iter(),
+                    Applicability::HasPlaceholders,
+                );
+            }
+        };
+
+        if def_id.is_local() {
+            if let Some(span) = self.def_span(def_id) {
+                err.span_note(span, "the enum is defined here");
+            }
+        }
+    }
+
+    pub(crate) fn report_missing_type_error(
+        &self,
+        path: &[Segment],
+    ) -> Option<(Span, &'static str, String, Applicability)> {
+        let (ident, span) = match path {
+            [segment] if !segment.has_generic_args && segment.ident.name != kw::SelfUpper => {
+                (segment.ident.to_string(), segment.ident.span)
+            }
+            _ => return None,
+        };
+        let mut iter = ident.chars().map(|c| c.is_uppercase());
+        let single_uppercase_char =
+            matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
+        if !self.diagnostic_metadata.currently_processing_generics && !single_uppercase_char {
+            return None;
+        }
+        match (self.diagnostic_metadata.current_item, single_uppercase_char, self.diagnostic_metadata.currently_processing_generics) {
+            (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _, _) if ident.name == sym::main => {
+                // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
+            }
+            (
+                Some(Item {
+                    kind:
+                        kind @ ItemKind::Fn(..)
+                        | kind @ ItemKind::Enum(..)
+                        | kind @ ItemKind::Struct(..)
+                        | kind @ ItemKind::Union(..),
+                    ..
+                }),
+                true, _
+            )
+            // Without the 2nd `true`, we'd suggest `impl <T>` for `impl T` when a type `T` isn't found
+            | (Some(Item { kind: kind @ ItemKind::Impl(..), .. }), true, true)
+            | (Some(Item { kind, .. }), false, _) => {
+                // Likely missing type parameter.
+                if let Some(generics) = kind.generics() {
+                    if span.overlaps(generics.span) {
+                        // Avoid the following:
+                        // error[E0405]: cannot find trait `A` in this scope
+                        //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
+                        //   |
+                        // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
+                        //   |           ^- help: you might be missing a type parameter: `, A`
+                        //   |           |
+                        //   |           not found in this scope
+                        return None;
+                    }
+                    let msg = "you might be missing a type parameter";
+                    let (span, sugg) = if let [.., param] = &generics.params[..] {
+                        let span = if let [.., bound] = &param.bounds[..] {
+                            bound.span()
+                        } else if let GenericParam {
+                            kind: GenericParamKind::Const { ty, kw_span: _, default  }, ..
+                        } = param {
+                            default.as_ref().map(|def| def.value.span).unwrap_or(ty.span)
+                        } else {
+                            param.ident.span
+                        };
+                        (span, format!(", {}", ident))
+                    } else {
+                        (generics.span, format!("<{}>", ident))
+                    };
+                    // Do not suggest if this is coming from macro expansion.
+                    if span.can_be_used_for_suggestions() {
+                        return Some((
+                            span.shrink_to_hi(),
+                            msg,
+                            sugg,
+                            Applicability::MaybeIncorrect,
+                        ));
+                    }
+                }
+            }
+            _ => {}
+        }
+        None
+    }
+
+    /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
+    /// optionally returning the closest match and whether it is reachable.
+    pub(crate) fn suggestion_for_label_in_rib(
+        &self,
+        rib_index: usize,
+        label: Ident,
+    ) -> Option<LabelSuggestion> {
+        // Are ribs from this `rib_index` within scope?
+        let within_scope = self.is_label_valid_from_rib(rib_index);
+
+        let rib = &self.label_ribs[rib_index];
+        let names = rib
+            .bindings
+            .iter()
+            .filter(|(id, _)| id.span.eq_ctxt(label.span))
+            .map(|(id, _)| id.name)
+            .collect::<Vec<Symbol>>();
+
+        find_best_match_for_name(&names, label.name, None).map(|symbol| {
+            // Upon finding a similar name, get the ident that it was from - the span
+            // contained within helps make a useful diagnostic. In addition, determine
+            // whether this candidate is within scope.
+            let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
+            (*ident, within_scope)
+        })
+    }
+
+    pub(crate) fn maybe_report_lifetime_uses(
+        &mut self,
+        generics_span: Span,
+        params: &[ast::GenericParam],
+    ) {
+        for (param_index, param) in params.iter().enumerate() {
+            let GenericParamKind::Lifetime = param.kind else { continue };
+
+            let def_id = self.r.local_def_id(param.id);
+
+            let use_set = self.lifetime_uses.remove(&def_id);
+            debug!(
+                "Use set for {:?}({:?} at {:?}) is {:?}",
+                def_id, param.ident, param.ident.span, use_set
+            );
+
+            let deletion_span = || {
+                if params.len() == 1 {
+                    // if sole lifetime, remove the entire `<>` brackets
+                    generics_span
+                } else if param_index == 0 {
+                    // if removing within `<>` brackets, we also want to
+                    // delete a leading or trailing comma as appropriate
+                    param.span().to(params[param_index + 1].span().shrink_to_lo())
+                } else {
+                    // if removing within `<>` brackets, we also want to
+                    // delete a leading or trailing comma as appropriate
+                    params[param_index - 1].span().shrink_to_hi().to(param.span())
+                }
+            };
+            match use_set {
+                Some(LifetimeUseSet::Many) => {}
+                Some(LifetimeUseSet::One { use_span, use_ctxt }) => {
+                    debug!(?param.ident, ?param.ident.span, ?use_span);
+
+                    let elidable = matches!(use_ctxt, LifetimeCtxt::Rptr);
+
+                    let deletion_span = deletion_span();
+                    self.r.lint_buffer.buffer_lint_with_diagnostic(
+                        lint::builtin::SINGLE_USE_LIFETIMES,
+                        param.id,
+                        param.ident.span,
+                        &format!("lifetime parameter `{}` only used once", param.ident),
+                        lint::BuiltinLintDiagnostics::SingleUseLifetime {
+                            param_span: param.ident.span,
+                            use_span: Some((use_span, elidable)),
+                            deletion_span,
+                        },
+                    );
+                }
+                None => {
+                    debug!(?param.ident, ?param.ident.span);
+
+                    let deletion_span = deletion_span();
+                    self.r.lint_buffer.buffer_lint_with_diagnostic(
+                        lint::builtin::UNUSED_LIFETIMES,
+                        param.id,
+                        param.ident.span,
+                        &format!("lifetime parameter `{}` never used", param.ident),
+                        lint::BuiltinLintDiagnostics::SingleUseLifetime {
+                            param_span: param.ident.span,
+                            use_span: None,
+                            deletion_span,
+                        },
+                    );
+                }
+            }
+        }
+    }
+
+    pub(crate) fn emit_undeclared_lifetime_error(
+        &self,
+        lifetime_ref: &ast::Lifetime,
+        outer_lifetime_ref: Option<Ident>,
+    ) {
+        debug_assert_ne!(lifetime_ref.ident.name, kw::UnderscoreLifetime);
+        let mut err = if let Some(outer) = outer_lifetime_ref {
+            let mut err = struct_span_err!(
+                self.r.session,
+                lifetime_ref.ident.span,
+                E0401,
+                "can't use generic parameters from outer item",
+            );
+            err.span_label(lifetime_ref.ident.span, "use of generic parameter from outer item");
+            err.span_label(outer.span, "lifetime parameter from outer item");
+            err
+        } else {
+            let mut err = struct_span_err!(
+                self.r.session,
+                lifetime_ref.ident.span,
+                E0261,
+                "use of undeclared lifetime name `{}`",
+                lifetime_ref.ident
+            );
+            err.span_label(lifetime_ref.ident.span, "undeclared lifetime");
+            err
+        };
+        self.suggest_introducing_lifetime(
+            &mut err,
+            Some(lifetime_ref.ident.name.as_str()),
+            |err, _, span, message, suggestion| {
+                err.span_suggestion(span, message, suggestion, Applicability::MaybeIncorrect);
+                true
+            },
+        );
+        err.emit();
+    }
+
+    fn suggest_introducing_lifetime(
+        &self,
+        err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
+        name: Option<&str>,
+        suggest: impl Fn(&mut DiagnosticBuilder<'_, ErrorGuaranteed>, bool, Span, &str, String) -> bool,
+    ) {
+        let mut suggest_note = true;
+        for rib in self.lifetime_ribs.iter().rev() {
+            let mut should_continue = true;
+            match rib.kind {
+                LifetimeRibKind::Generics { binder: _, span, kind } => {
+                    if !span.can_be_used_for_suggestions() && suggest_note && let Some(name) = name {
+                        suggest_note = false; // Avoid displaying the same help multiple times.
+                        err.span_label(
+                            span,
+                            &format!(
+                                "lifetime `{}` is missing in item created through this procedural macro",
+                                name,
+                            ),
+                        );
+                        continue;
+                    }
+
+                    let higher_ranked = matches!(
+                        kind,
+                        LifetimeBinderKind::BareFnType
+                            | LifetimeBinderKind::PolyTrait
+                            | LifetimeBinderKind::WhereBound
+                    );
+                    let (span, sugg) = if span.is_empty() {
+                        let sugg = format!(
+                            "{}<{}>{}",
+                            if higher_ranked { "for" } else { "" },
+                            name.unwrap_or("'a"),
+                            if higher_ranked { " " } else { "" },
+                        );
+                        (span, sugg)
+                    } else {
+                        let span =
+                            self.r.session.source_map().span_through_char(span, '<').shrink_to_hi();
+                        let sugg = format!("{}, ", name.unwrap_or("'a"));
+                        (span, sugg)
+                    };
+                    if higher_ranked {
+                        let message = format!(
+                            "consider making the {} lifetime-generic with a new `{}` lifetime",
+                            kind.descr(),
+                            name.unwrap_or("'a"),
+                        );
+                        should_continue = suggest(err, true, span, &message, sugg);
+                        err.note_once(
+                            "for more information on higher-ranked polymorphism, visit \
+                             https://doc.rust-lang.org/nomicon/hrtb.html",
+                        );
+                    } else if let Some(name) = name {
+                        let message = format!("consider introducing lifetime `{}` here", name);
+                        should_continue = suggest(err, false, span, &message, sugg);
+                    } else {
+                        let message = format!("consider introducing a named lifetime parameter");
+                        should_continue = suggest(err, false, span, &message, sugg);
+                    }
+                }
+                LifetimeRibKind::Item => break,
+                _ => {}
+            }
+            if !should_continue {
+                break;
+            }
+        }
+    }
+
+    pub(crate) fn emit_non_static_lt_in_const_generic_error(&self, lifetime_ref: &ast::Lifetime) {
+        struct_span_err!(
+            self.r.session,
+            lifetime_ref.ident.span,
+            E0771,
+            "use of non-static lifetime `{}` in const generic",
+            lifetime_ref.ident
+        )
+        .note(
+            "for more information, see issue #74052 \
+            <https://github.com/rust-lang/rust/issues/74052>",
+        )
+        .emit();
+    }
+
+    /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
+    /// This function will emit an error if `generic_const_exprs` is not enabled, the body identified by
+    /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
+    pub(crate) fn maybe_emit_forbidden_non_static_lifetime_error(
+        &self,
+        lifetime_ref: &ast::Lifetime,
+    ) {
+        let feature_active = self.r.session.features_untracked().generic_const_exprs;
+        if !feature_active {
+            feature_err(
+                &self.r.session.parse_sess,
+                sym::generic_const_exprs,
+                lifetime_ref.ident.span,
+                "a non-static lifetime is not allowed in a `const`",
+            )
+            .emit();
+        }
+    }
+
+    pub(crate) fn report_missing_lifetime_specifiers(
+        &mut self,
+        lifetime_refs: Vec<MissingLifetime>,
+        function_param_lifetimes: Option<(Vec<MissingLifetime>, Vec<ElisionFnParameter>)>,
+    ) -> ErrorGuaranteed {
+        let num_lifetimes: usize = lifetime_refs.iter().map(|lt| lt.count).sum();
+        let spans: Vec<_> = lifetime_refs.iter().map(|lt| lt.span).collect();
+
+        let mut err = struct_span_err!(
+            self.r.session,
+            spans,
+            E0106,
+            "missing lifetime specifier{}",
+            pluralize!(num_lifetimes)
+        );
+        self.add_missing_lifetime_specifiers_label(
+            &mut err,
+            lifetime_refs,
+            function_param_lifetimes,
+        );
+        err.emit()
+    }
+
+    pub(crate) fn add_missing_lifetime_specifiers_label(
+        &mut self,
+        err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
+        lifetime_refs: Vec<MissingLifetime>,
+        function_param_lifetimes: Option<(Vec<MissingLifetime>, Vec<ElisionFnParameter>)>,
+    ) {
+        for &lt in &lifetime_refs {
+            err.span_label(
+                lt.span,
+                format!(
+                    "expected {} lifetime parameter{}",
+                    if lt.count == 1 { "named".to_string() } else { lt.count.to_string() },
+                    pluralize!(lt.count),
+                ),
+            );
+        }
+
+        let mut in_scope_lifetimes: Vec<_> = self
+            .lifetime_ribs
+            .iter()
+            .rev()
+            .take_while(|rib| !matches!(rib.kind, LifetimeRibKind::Item))
+            .flat_map(|rib| rib.bindings.iter())
+            .map(|(&ident, &res)| (ident, res))
+            .filter(|(ident, _)| ident.name != kw::UnderscoreLifetime)
+            .collect();
+        debug!(?in_scope_lifetimes);
+
+        debug!(?function_param_lifetimes);
+        if let Some((param_lifetimes, params)) = &function_param_lifetimes {
+            let elided_len = param_lifetimes.len();
+            let num_params = params.len();
+
+            let mut m = String::new();
+
+            for (i, info) in params.iter().enumerate() {
+                let ElisionFnParameter { ident, index, lifetime_count, span } = *info;
+                debug_assert_ne!(lifetime_count, 0);
+
+                err.span_label(span, "");
+
+                if i != 0 {
+                    if i + 1 < num_params {
+                        m.push_str(", ");
+                    } else if num_params == 2 {
+                        m.push_str(" or ");
+                    } else {
+                        m.push_str(", or ");
+                    }
+                }
+
+                let help_name = if let Some(ident) = ident {
+                    format!("`{}`", ident)
+                } else {
+                    format!("argument {}", index + 1)
+                };
+
+                if lifetime_count == 1 {
+                    m.push_str(&help_name[..])
+                } else {
+                    m.push_str(&format!("one of {}'s {} lifetimes", help_name, lifetime_count)[..])
+                }
+            }
+
+            if num_params == 0 {
+                err.help(
+                    "this function's return type contains a borrowed value, \
+                 but there is no value for it to be borrowed from",
+                );
+                if in_scope_lifetimes.is_empty() {
+                    in_scope_lifetimes = vec![(
+                        Ident::with_dummy_span(kw::StaticLifetime),
+                        (DUMMY_NODE_ID, LifetimeRes::Static),
+                    )];
+                }
+            } else if elided_len == 0 {
+                err.help(
+                    "this function's return type contains a borrowed value with \
+                 an elided lifetime, but the lifetime cannot be derived from \
+                 the arguments",
+                );
+                if in_scope_lifetimes.is_empty() {
+                    in_scope_lifetimes = vec![(
+                        Ident::with_dummy_span(kw::StaticLifetime),
+                        (DUMMY_NODE_ID, LifetimeRes::Static),
+                    )];
+                }
+            } else if num_params == 1 {
+                err.help(&format!(
+                    "this function's return type contains a borrowed value, \
+                 but the signature does not say which {} it is borrowed from",
+                    m
+                ));
+            } else {
+                err.help(&format!(
+                    "this function's return type contains a borrowed value, \
+                 but the signature does not say whether it is borrowed from {}",
+                    m
+                ));
+            }
+        }
+
+        let existing_name = match &in_scope_lifetimes[..] {
+            [] => Symbol::intern("'a"),
+            [(existing, _)] => existing.name,
+            _ => Symbol::intern("'lifetime"),
+        };
+
+        let mut spans_suggs: Vec<_> = Vec::new();
+        let build_sugg = |lt: MissingLifetime| match lt.kind {
+            MissingLifetimeKind::Underscore => {
+                debug_assert_eq!(lt.count, 1);
+                (lt.span, existing_name.to_string())
+            }
+            MissingLifetimeKind::Ampersand => {
+                debug_assert_eq!(lt.count, 1);
+                (lt.span.shrink_to_hi(), format!("{} ", existing_name))
+            }
+            MissingLifetimeKind::Comma => {
+                let sugg: String = std::iter::repeat([existing_name.as_str(), ", "])
+                    .take(lt.count)
+                    .flatten()
+                    .collect();
+                (lt.span.shrink_to_hi(), sugg)
+            }
+            MissingLifetimeKind::Brackets => {
+                let sugg: String = std::iter::once("<")
+                    .chain(
+                        std::iter::repeat(existing_name.as_str()).take(lt.count).intersperse(", "),
+                    )
+                    .chain([">"])
+                    .collect();
+                (lt.span.shrink_to_hi(), sugg)
+            }
+        };
+        for &lt in &lifetime_refs {
+            spans_suggs.push(build_sugg(lt));
+        }
+        debug!(?spans_suggs);
+        match in_scope_lifetimes.len() {
+            0 => {
+                if let Some((param_lifetimes, _)) = function_param_lifetimes {
+                    for lt in param_lifetimes {
+                        spans_suggs.push(build_sugg(lt))
+                    }
+                }
+                self.suggest_introducing_lifetime(
+                    err,
+                    None,
+                    |err, higher_ranked, span, message, intro_sugg| {
+                        err.multipart_suggestion_verbose(
+                            message,
+                            std::iter::once((span, intro_sugg))
+                                .chain(spans_suggs.clone())
+                                .collect(),
+                            Applicability::MaybeIncorrect,
+                        );
+                        higher_ranked
+                    },
+                );
+            }
+            1 => {
+                err.multipart_suggestion_verbose(
+                    &format!("consider using the `{}` lifetime", existing_name),
+                    spans_suggs,
+                    Applicability::MaybeIncorrect,
+                );
+
+                // Record as using the suggested resolution.
+                let (_, (_, res)) = in_scope_lifetimes[0];
+                for &lt in &lifetime_refs {
+                    self.r.lifetimes_res_map.insert(lt.id, res);
+                }
+            }
+            _ => {
+                let lifetime_spans: Vec<_> =
+                    in_scope_lifetimes.iter().map(|(ident, _)| ident.span).collect();
+                err.span_note(lifetime_spans, "these named lifetimes are available to use");
+
+                if spans_suggs.len() > 0 {
+                    // This happens when we have `Foo<T>` where we point at the space before `T`,
+                    // but this can be confusing so we give a suggestion with placeholders.
+                    err.multipart_suggestion_verbose(
+                        "consider using one of the available lifetimes here",
+                        spans_suggs,
+                        Applicability::HasPlaceholders,
+                    );
+                }
+            }
+        }
+    }
+}
+
+/// Report lifetime/lifetime shadowing as an error.
+pub fn signal_lifetime_shadowing(sess: &Session, orig: Ident, shadower: Ident) {
+    let mut err = struct_span_err!(
+        sess,
+        shadower.span,
+        E0496,
+        "lifetime name `{}` shadows a lifetime name that is already in scope",
+        orig.name,
+    );
+    err.span_label(orig.span, "first declared here");
+    err.span_label(shadower.span, format!("lifetime `{}` already in scope", orig.name));
+    err.emit();
+}
+
+/// Shadowing involving a label is only a warning for historical reasons.
+//FIXME: make this a proper lint.
+pub fn signal_label_shadowing(sess: &Session, orig: Span, shadower: Ident) {
+    let name = shadower.name;
+    let shadower = shadower.span;
+    let mut err = sess.struct_span_warn(
+        shadower,
+        &format!("label name `{}` shadows a label name that is already in scope", name),
+    );
+    err.span_label(orig, "first declared here");
+    err.span_label(shadower, format!("label `{}` already in scope", name));
+    err.emit();
+}
diff --git a/compiler/rustc_resolve/src/late/lifetimes.rs b/compiler/rustc_resolve/src/late/lifetimes.rs
new file mode 100644
index 000000000..94460e33d
--- /dev/null
+++ b/compiler/rustc_resolve/src/late/lifetimes.rs
@@ -0,0 +1,2144 @@
+//! Resolution of early vs late bound lifetimes.
+//!
+//! Name resolution for lifetimes is performed on the AST and embedded into HIR.  From this
+//! information, typechecking needs to transform the lifetime parameters into bound lifetimes.
+//! Lifetimes can be early-bound or late-bound.  Construction of typechecking terms needs to visit
+//! the types in HIR to identify late-bound lifetimes and assign their Debruijn indices.  This file
+//! is also responsible for assigning their semantics to implicit lifetimes in trait objects.
+
+use rustc_ast::walk_list;
+use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
+use rustc_errors::struct_span_err;
+use rustc_hir as hir;
+use rustc_hir::def::{DefKind, Res};
+use rustc_hir::def_id::{DefIdMap, LocalDefId};
+use rustc_hir::intravisit::{self, Visitor};
+use rustc_hir::{GenericArg, GenericParam, GenericParamKind, HirIdMap, LifetimeName, Node};
+use rustc_middle::bug;
+use rustc_middle::hir::map::Map;
+use rustc_middle::hir::nested_filter;
+use rustc_middle::middle::resolve_lifetime::*;
+use rustc_middle::ty::{self, GenericParamDefKind, TyCtxt};
+use rustc_span::def_id::DefId;
+use rustc_span::symbol::{sym, Ident};
+use rustc_span::Span;
+use std::borrow::Cow;
+use std::fmt;
+use std::mem::take;
+
+trait RegionExt {
+    fn early(hir_map: Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (LocalDefId, Region);
+
+    fn late(index: u32, hir_map: Map<'_>, param: &GenericParam<'_>) -> (LocalDefId, Region);
+
+    fn id(&self) -> Option<DefId>;
+
+    fn shifted(self, amount: u32) -> Region;
+
+    fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region;
+
+    fn subst<'a, L>(self, params: L, map: &NamedRegionMap) -> Option<Region>
+    where
+        L: Iterator<Item = &'a hir::Lifetime>;
+}
+
+impl RegionExt for Region {
+    fn early(hir_map: Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (LocalDefId, Region) {
+        let i = *index;
+        *index += 1;
+        let def_id = hir_map.local_def_id(param.hir_id);
+        debug!("Region::early: index={} def_id={:?}", i, def_id);
+        (def_id, Region::EarlyBound(i, def_id.to_def_id()))
+    }
+
+    fn late(idx: u32, hir_map: Map<'_>, param: &GenericParam<'_>) -> (LocalDefId, Region) {
+        let depth = ty::INNERMOST;
+        let def_id = hir_map.local_def_id(param.hir_id);
+        debug!(
+            "Region::late: idx={:?}, param={:?} depth={:?} def_id={:?}",
+            idx, param, depth, def_id,
+        );
+        (def_id, Region::LateBound(depth, idx, def_id.to_def_id()))
+    }
+
+    fn id(&self) -> Option<DefId> {
+        match *self {
+            Region::Static => None,
+
+            Region::EarlyBound(_, id) | Region::LateBound(_, _, id) | Region::Free(_, id) => {
+                Some(id)
+            }
+        }
+    }
+
+    fn shifted(self, amount: u32) -> Region {
+        match self {
+            Region::LateBound(debruijn, idx, id) => {
+                Region::LateBound(debruijn.shifted_in(amount), idx, id)
+            }
+            _ => self,
+        }
+    }
+
+    fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
+        match self {
+            Region::LateBound(debruijn, index, id) => {
+                Region::LateBound(debruijn.shifted_out_to_binder(binder), index, id)
+            }
+            _ => self,
+        }
+    }
+
+    fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option<Region>
+    where
+        L: Iterator<Item = &'a hir::Lifetime>,
+    {
+        if let Region::EarlyBound(index, _) = self {
+            params.nth(index as usize).and_then(|lifetime| map.defs.get(&lifetime.hir_id).cloned())
+        } else {
+            Some(self)
+        }
+    }
+}
+
+/// Maps the id of each lifetime reference to the lifetime decl
+/// that it corresponds to.
+///
+/// FIXME. This struct gets converted to a `ResolveLifetimes` for
+/// actual use. It has the same data, but indexed by `LocalDefId`.  This
+/// is silly.
+#[derive(Debug, Default)]
+struct NamedRegionMap {
+    // maps from every use of a named (not anonymous) lifetime to a
+    // `Region` describing how that region is bound
+    defs: HirIdMap<Region>,
+
+    // Maps relevant hir items to the bound vars on them. These include:
+    // - function defs
+    // - function pointers
+    // - closures
+    // - trait refs
+    // - bound types (like `T` in `for<'a> T<'a>: Foo`)
+    late_bound_vars: HirIdMap<Vec<ty::BoundVariableKind>>,
+}
+
+pub(crate) struct LifetimeContext<'a, 'tcx> {
+    pub(crate) tcx: TyCtxt<'tcx>,
+    map: &'a mut NamedRegionMap,
+    scope: ScopeRef<'a>,
+
+    /// Indicates that we only care about the definition of a trait. This should
+    /// be false if the `Item` we are resolving lifetimes for is not a trait or
+    /// we eventually need lifetimes resolve for trait items.
+    trait_definition_only: bool,
+
+    /// Cache for cross-crate per-definition object lifetime defaults.
+    xcrate_object_lifetime_defaults: DefIdMap<Vec<ObjectLifetimeDefault>>,
+}
+
+#[derive(Debug)]
+enum Scope<'a> {
+    /// Declares lifetimes, and each can be early-bound or late-bound.
+    /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
+    /// it should be shifted by the number of `Binder`s in between the
+    /// declaration `Binder` and the location it's referenced from.
+    Binder {
+        /// We use an IndexMap here because we want these lifetimes in order
+        /// for diagnostics.
+        lifetimes: FxIndexMap<LocalDefId, Region>,
+
+        /// if we extend this scope with another scope, what is the next index
+        /// we should use for an early-bound region?
+        next_early_index: u32,
+
+        /// Whether or not this binder would serve as the parent
+        /// binder for opaque types introduced within. For example:
+        ///
+        /// ```text
+        ///     fn foo<'a>() -> impl for<'b> Trait<Item = impl Trait2<'a>>
+        /// ```
+        ///
+        /// Here, the opaque types we create for the `impl Trait`
+        /// and `impl Trait2` references will both have the `foo` item
+        /// as their parent. When we get to `impl Trait2`, we find
+        /// that it is nested within the `for<>` binder -- this flag
+        /// allows us to skip that when looking for the parent binder
+        /// of the resulting opaque type.
+        opaque_type_parent: bool,
+
+        scope_type: BinderScopeType,
+
+        /// The late bound vars for a given item are stored by `HirId` to be
+        /// queried later. However, if we enter an elision scope, we have to
+        /// later append the elided bound vars to the list and need to know what
+        /// to append to.
+        hir_id: hir::HirId,
+
+        s: ScopeRef<'a>,
+
+        /// If this binder comes from a where clause, specify how it was created.
+        /// This is used to diagnose inaccessible lifetimes in APIT:
+        /// ```ignore (illustrative)
+        /// fn foo(x: impl for<'a> Trait<'a, Assoc = impl Copy + 'a>) {}
+        /// ```
+        where_bound_origin: Option<hir::PredicateOrigin>,
+    },
+
+    /// Lifetimes introduced by a fn are scoped to the call-site for that fn,
+    /// if this is a fn body, otherwise the original definitions are used.
+    /// Unspecified lifetimes are inferred, unless an elision scope is nested,
+    /// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
+    Body {
+        id: hir::BodyId,
+        s: ScopeRef<'a>,
+    },
+
+    /// A scope which either determines unspecified lifetimes or errors
+    /// on them (e.g., due to ambiguity).
+    Elision {
+        s: ScopeRef<'a>,
+    },
+
+    /// Use a specific lifetime (if `Some`) or leave it unset (to be
+    /// inferred in a function body or potentially error outside one),
+    /// for the default choice of lifetime in a trait object type.
+    ObjectLifetimeDefault {
+        lifetime: Option<Region>,
+        s: ScopeRef<'a>,
+    },
+
+    /// When we have nested trait refs, we concatenate late bound vars for inner
+    /// trait refs from outer ones. But we also need to include any HRTB
+    /// lifetimes encountered when identifying the trait that an associated type
+    /// is declared on.
+    Supertrait {
+        lifetimes: Vec<ty::BoundVariableKind>,
+        s: ScopeRef<'a>,
+    },
+
+    TraitRefBoundary {
+        s: ScopeRef<'a>,
+    },
+
+    Root,
+}
+
+#[derive(Copy, Clone, Debug)]
+enum BinderScopeType {
+    /// Any non-concatenating binder scopes.
+    Normal,
+    /// Within a syntactic trait ref, there may be multiple poly trait refs that
+    /// are nested (under the `associated_type_bounds` feature). The binders of
+    /// the inner poly trait refs are extended from the outer poly trait refs
+    /// and don't increase the late bound depth. If you had
+    /// `T: for<'a>  Foo<Bar: for<'b> Baz<'a, 'b>>`, then the `for<'b>` scope
+    /// would be `Concatenating`. This also used in trait refs in where clauses
+    /// where we have two binders `for<> T: for<> Foo` (I've intentionally left
+    /// out any lifetimes because they aren't needed to show the two scopes).
+    /// The inner `for<>` has a scope of `Concatenating`.
+    Concatenating,
+}
+
+// A helper struct for debugging scopes without printing parent scopes
+struct TruncatedScopeDebug<'a>(&'a Scope<'a>);
+
+impl<'a> fmt::Debug for TruncatedScopeDebug<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.0 {
+            Scope::Binder {
+                lifetimes,
+                next_early_index,
+                opaque_type_parent,
+                scope_type,
+                hir_id,
+                where_bound_origin,
+                s: _,
+            } => f
+                .debug_struct("Binder")
+                .field("lifetimes", lifetimes)
+                .field("next_early_index", next_early_index)
+                .field("opaque_type_parent", opaque_type_parent)
+                .field("scope_type", scope_type)
+                .field("hir_id", hir_id)
+                .field("where_bound_origin", where_bound_origin)
+                .field("s", &"..")
+                .finish(),
+            Scope::Body { id, s: _ } => {
+                f.debug_struct("Body").field("id", id).field("s", &"..").finish()
+            }
+            Scope::Elision { s: _ } => f.debug_struct("Elision").field("s", &"..").finish(),
+            Scope::ObjectLifetimeDefault { lifetime, s: _ } => f
+                .debug_struct("ObjectLifetimeDefault")
+                .field("lifetime", lifetime)
+                .field("s", &"..")
+                .finish(),
+            Scope::Supertrait { lifetimes, s: _ } => f
+                .debug_struct("Supertrait")
+                .field("lifetimes", lifetimes)
+                .field("s", &"..")
+                .finish(),
+            Scope::TraitRefBoundary { s: _ } => f.debug_struct("TraitRefBoundary").finish(),
+            Scope::Root => f.debug_struct("Root").finish(),
+        }
+    }
+}
+
+type ScopeRef<'a> = &'a Scope<'a>;
+
+const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
+
+pub fn provide(providers: &mut ty::query::Providers) {
+    *providers = ty::query::Providers {
+        resolve_lifetimes_trait_definition,
+        resolve_lifetimes,
+
+        named_region_map: |tcx, id| resolve_lifetimes_for(tcx, id).defs.get(&id),
+        is_late_bound_map,
+        object_lifetime_defaults: |tcx, id| match tcx.hir().find_by_def_id(id) {
+            Some(Node::Item(item)) => compute_object_lifetime_defaults(tcx, item),
+            _ => None,
+        },
+        late_bound_vars_map: |tcx, id| resolve_lifetimes_for(tcx, id).late_bound_vars.get(&id),
+
+        ..*providers
+    };
+}
+
+/// Like `resolve_lifetimes`, but does not resolve lifetimes for trait items.
+/// Also does not generate any diagnostics.
+///
+/// This is ultimately a subset of the `resolve_lifetimes` work. It effectively
+/// resolves lifetimes only within the trait "header" -- that is, the trait
+/// and supertrait list. In contrast, `resolve_lifetimes` resolves all the
+/// lifetimes within the trait and its items. There is room to refactor this,
+/// for example to resolve lifetimes for each trait item in separate queries,
+/// but it's convenient to do the entire trait at once because the lifetimes
+/// from the trait definition are in scope within the trait items as well.
+///
+/// The reason for this separate call is to resolve what would otherwise
+/// be a cycle. Consider this example:
+///
+/// ```ignore UNSOLVED (maybe @jackh726 knows what lifetime parameter to give Sub)
+/// trait Base<'a> {
+///     type BaseItem;
+/// }
+/// trait Sub<'b>: for<'a> Base<'a> {
+///    type SubItem: Sub<BaseItem = &'b u32>;
+/// }
+/// ```
+///
+/// When we resolve `Sub` and all its items, we also have to resolve `Sub<BaseItem = &'b u32>`.
+/// To figure out the index of `'b`, we have to know about the supertraits
+/// of `Sub` so that we can determine that the `for<'a>` will be in scope.
+/// (This is because we -- currently at least -- flatten all the late-bound
+/// lifetimes into a single binder.) This requires us to resolve the
+/// *trait definition* of `Sub`; basically just enough lifetime information
+/// to look at the supertraits.
+#[tracing::instrument(level = "debug", skip(tcx))]
+fn resolve_lifetimes_trait_definition(
+    tcx: TyCtxt<'_>,
+    local_def_id: LocalDefId,
+) -> ResolveLifetimes {
+    convert_named_region_map(do_resolve(tcx, local_def_id, true))
+}
+
+/// Computes the `ResolveLifetimes` map that contains data for an entire `Item`.
+/// You should not read the result of this query directly, but rather use
+/// `named_region_map`, `is_late_bound_map`, etc.
+#[tracing::instrument(level = "debug", skip(tcx))]
+fn resolve_lifetimes(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> ResolveLifetimes {
+    convert_named_region_map(do_resolve(tcx, local_def_id, false))
+}
+
+fn do_resolve(
+    tcx: TyCtxt<'_>,
+    local_def_id: LocalDefId,
+    trait_definition_only: bool,
+) -> NamedRegionMap {
+    let item = tcx.hir().expect_item(local_def_id);
+    let mut named_region_map =
+        NamedRegionMap { defs: Default::default(), late_bound_vars: Default::default() };
+    let mut visitor = LifetimeContext {
+        tcx,
+        map: &mut named_region_map,
+        scope: ROOT_SCOPE,
+        trait_definition_only,
+        xcrate_object_lifetime_defaults: Default::default(),
+    };
+    visitor.visit_item(item);
+
+    named_region_map
+}
+
+fn convert_named_region_map(named_region_map: NamedRegionMap) -> ResolveLifetimes {
+    let mut rl = ResolveLifetimes::default();
+
+    for (hir_id, v) in named_region_map.defs {
+        let map = rl.defs.entry(hir_id.owner).or_default();
+        map.insert(hir_id.local_id, v);
+    }
+    for (hir_id, v) in named_region_map.late_bound_vars {
+        let map = rl.late_bound_vars.entry(hir_id.owner).or_default();
+        map.insert(hir_id.local_id, v);
+    }
+
+    debug!(?rl.defs);
+    rl
+}
+
+/// Given `any` owner (structs, traits, trait methods, etc.), does lifetime resolution.
+/// There are two important things this does.
+/// First, we have to resolve lifetimes for
+/// the entire *`Item`* that contains this owner, because that's the largest "scope"
+/// where we can have relevant lifetimes.
+/// Second, if we are asking for lifetimes in a trait *definition*, we use `resolve_lifetimes_trait_definition`
+/// instead of `resolve_lifetimes`, which does not descend into the trait items and does not emit diagnostics.
+/// This allows us to avoid cycles. Importantly, if we ask for lifetimes for lifetimes that have an owner
+/// other than the trait itself (like the trait methods or associated types), then we just use the regular
+/// `resolve_lifetimes`.
+fn resolve_lifetimes_for<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx ResolveLifetimes {
+    let item_id = item_for(tcx, def_id);
+    if item_id == def_id {
+        let item = tcx.hir().item(hir::ItemId { def_id: item_id });
+        match item.kind {
+            hir::ItemKind::Trait(..) => tcx.resolve_lifetimes_trait_definition(item_id),
+            _ => tcx.resolve_lifetimes(item_id),
+        }
+    } else {
+        tcx.resolve_lifetimes(item_id)
+    }
+}
+
+/// Finds the `Item` that contains the given `LocalDefId`
+fn item_for(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> LocalDefId {
+    match tcx.hir().find_by_def_id(local_def_id) {
+        Some(Node::Item(item)) => {
+            return item.def_id;
+        }
+        _ => {}
+    }
+    let item = {
+        let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
+        let mut parent_iter = tcx.hir().parent_iter(hir_id);
+        loop {
+            let node = parent_iter.next().map(|n| n.1);
+            match node {
+                Some(hir::Node::Item(item)) => break item.def_id,
+                Some(hir::Node::Crate(_)) | None => bug!("Called `item_for` on an Item."),
+                _ => {}
+            }
+        }
+    };
+    item
+}
+
+/// In traits, there is an implicit `Self` type parameter which comes before the generics.
+/// We have to account for this when computing the index of the other generic parameters.
+/// This function returns whether there is such an implicit parameter defined on the given item.
+fn sub_items_have_self_param(node: &hir::ItemKind<'_>) -> bool {
+    matches!(*node, hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..))
+}
+
+fn late_region_as_bound_region<'tcx>(tcx: TyCtxt<'tcx>, region: &Region) -> ty::BoundVariableKind {
+    match region {
+        Region::LateBound(_, _, def_id) => {
+            let name = tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id.expect_local()));
+            ty::BoundVariableKind::Region(ty::BrNamed(*def_id, name))
+        }
+        _ => bug!("{:?} is not a late region", region),
+    }
+}
+
+impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
+    /// Returns the binders in scope and the type of `Binder` that should be created for a poly trait ref.
+    fn poly_trait_ref_binder_info(&mut self) -> (Vec<ty::BoundVariableKind>, BinderScopeType) {
+        let mut scope = self.scope;
+        let mut supertrait_lifetimes = vec![];
+        loop {
+            match scope {
+                Scope::Body { .. } | Scope::Root => {
+                    break (vec![], BinderScopeType::Normal);
+                }
+
+                Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
+                    scope = s;
+                }
+
+                Scope::Supertrait { s, lifetimes } => {
+                    supertrait_lifetimes = lifetimes.clone();
+                    scope = s;
+                }
+
+                Scope::TraitRefBoundary { .. } => {
+                    // We should only see super trait lifetimes if there is a `Binder` above
+                    assert!(supertrait_lifetimes.is_empty());
+                    break (vec![], BinderScopeType::Normal);
+                }
+
+                Scope::Binder { hir_id, .. } => {
+                    // Nested poly trait refs have the binders concatenated
+                    let mut full_binders =
+                        self.map.late_bound_vars.entry(*hir_id).or_default().clone();
+                    full_binders.extend(supertrait_lifetimes.into_iter());
+                    break (full_binders, BinderScopeType::Concatenating);
+                }
+            }
+        }
+    }
+}
+impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
+    type NestedFilter = nested_filter::All;
+
+    fn nested_visit_map(&mut self) -> Self::Map {
+        self.tcx.hir()
+    }
+
+    // We want to nest trait/impl items in their parent, but nothing else.
+    fn visit_nested_item(&mut self, _: hir::ItemId) {}
+
+    fn visit_trait_item_ref(&mut self, ii: &'tcx hir::TraitItemRef) {
+        if !self.trait_definition_only {
+            intravisit::walk_trait_item_ref(self, ii)
+        }
+    }
+
+    fn visit_nested_body(&mut self, body: hir::BodyId) {
+        let body = self.tcx.hir().body(body);
+        self.with(Scope::Body { id: body.id(), s: self.scope }, |this| {
+            this.visit_body(body);
+        });
+    }
+
+    fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
+        if let hir::ExprKind::Closure(hir::Closure {
+            binder, bound_generic_params, fn_decl, ..
+        }) = e.kind
+        {
+            if let &hir::ClosureBinder::For { span: for_sp, .. } = binder {
+                fn span_of_infer(ty: &hir::Ty<'_>) -> Option<Span> {
+                    struct V(Option<Span>);
+
+                    impl<'v> Visitor<'v> for V {
+                        fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
+                            match t.kind {
+                                _ if self.0.is_some() => (),
+                                hir::TyKind::Infer => {
+                                    self.0 = Some(t.span);
+                                }
+                                _ => intravisit::walk_ty(self, t),
+                            }
+                        }
+                    }
+
+                    let mut v = V(None);
+                    v.visit_ty(ty);
+                    v.0
+                }
+
+                let infer_in_rt_sp = match fn_decl.output {
+                    hir::FnRetTy::DefaultReturn(sp) => Some(sp),
+                    hir::FnRetTy::Return(ty) => span_of_infer(ty),
+                };
+
+                let infer_spans = fn_decl
+                    .inputs
+                    .into_iter()
+                    .filter_map(span_of_infer)
+                    .chain(infer_in_rt_sp)
+                    .collect::<Vec<_>>();
+
+                if !infer_spans.is_empty() {
+                    self.tcx.sess
+                        .struct_span_err(
+                            infer_spans,
+                            "implicit types in closure signatures are forbidden when `for<...>` is present",
+                        )
+                        .span_label(for_sp, "`for<...>` is here")
+                        .emit();
+                }
+            }
+
+            let next_early_index = self.next_early_index();
+            let (lifetimes, binders): (FxIndexMap<LocalDefId, Region>, Vec<_>) =
+                bound_generic_params
+                    .iter()
+                    .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
+                    .enumerate()
+                    .map(|(late_bound_idx, param)| {
+                        let pair = Region::late(late_bound_idx as u32, self.tcx.hir(), param);
+                        let r = late_region_as_bound_region(self.tcx, &pair.1);
+                        (pair, r)
+                    })
+                    .unzip();
+
+            self.map.late_bound_vars.insert(e.hir_id, binders);
+            let scope = Scope::Binder {
+                hir_id: e.hir_id,
+                lifetimes,
+                s: self.scope,
+                next_early_index,
+                opaque_type_parent: false,
+                scope_type: BinderScopeType::Normal,
+                where_bound_origin: None,
+            };
+
+            self.with(scope, |this| {
+                // a closure has no bounds, so everything
+                // contained within is scoped within its binder.
+                intravisit::walk_expr(this, e)
+            });
+        } else {
+            intravisit::walk_expr(self, e)
+        }
+    }
+
+    fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
+        match &item.kind {
+            hir::ItemKind::Impl(hir::Impl { of_trait, .. }) => {
+                if let Some(of_trait) = of_trait {
+                    self.map.late_bound_vars.insert(of_trait.hir_ref_id, Vec::default());
+                }
+            }
+            _ => {}
+        }
+        match item.kind {
+            hir::ItemKind::Fn(_, ref generics, _) => {
+                self.visit_early_late(None, item.hir_id(), generics, |this| {
+                    intravisit::walk_item(this, item);
+                });
+            }
+
+            hir::ItemKind::ExternCrate(_)
+            | hir::ItemKind::Use(..)
+            | hir::ItemKind::Macro(..)
+            | hir::ItemKind::Mod(..)
+            | hir::ItemKind::ForeignMod { .. }
+            | hir::ItemKind::GlobalAsm(..) => {
+                // These sorts of items have no lifetime parameters at all.
+                intravisit::walk_item(self, item);
+            }
+            hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
+                // No lifetime parameters, but implied 'static.
+                self.with(Scope::Elision { s: self.scope }, |this| {
+                    intravisit::walk_item(this, item)
+                });
+            }
+            hir::ItemKind::OpaqueTy(hir::OpaqueTy { .. }) => {
+                // Opaque types are visited when we visit the
+                // `TyKind::OpaqueDef`, so that they have the lifetimes from
+                // their parent opaque_ty in scope.
+                //
+                // The core idea here is that since OpaqueTys are generated with the impl Trait as
+                // their owner, we can keep going until we find the Item that owns that. We then
+                // conservatively add all resolved lifetimes. Otherwise we run into problems in
+                // cases like `type Foo<'a> = impl Bar<As = impl Baz + 'a>`.
+                for (_hir_id, node) in
+                    self.tcx.hir().parent_iter(self.tcx.hir().local_def_id_to_hir_id(item.def_id))
+                {
+                    match node {
+                        hir::Node::Item(parent_item) => {
+                            let resolved_lifetimes: &ResolveLifetimes =
+                                self.tcx.resolve_lifetimes(item_for(self.tcx, parent_item.def_id));
+                            // We need to add *all* deps, since opaque tys may want them from *us*
+                            for (&owner, defs) in resolved_lifetimes.defs.iter() {
+                                defs.iter().for_each(|(&local_id, region)| {
+                                    self.map.defs.insert(hir::HirId { owner, local_id }, *region);
+                                });
+                            }
+                            for (&owner, late_bound_vars) in
+                                resolved_lifetimes.late_bound_vars.iter()
+                            {
+                                late_bound_vars.iter().for_each(|(&local_id, late_bound_vars)| {
+                                    self.map.late_bound_vars.insert(
+                                        hir::HirId { owner, local_id },
+                                        late_bound_vars.clone(),
+                                    );
+                                });
+                            }
+                            break;
+                        }
+                        hir::Node::Crate(_) => bug!("No Item about an OpaqueTy"),
+                        _ => {}
+                    }
+                }
+            }
+            hir::ItemKind::TyAlias(_, ref generics)
+            | hir::ItemKind::Enum(_, ref generics)
+            | hir::ItemKind::Struct(_, ref generics)
+            | hir::ItemKind::Union(_, ref generics)
+            | hir::ItemKind::Trait(_, _, ref generics, ..)
+            | hir::ItemKind::TraitAlias(ref generics, ..)
+            | hir::ItemKind::Impl(hir::Impl { ref generics, .. }) => {
+                // These kinds of items have only early-bound lifetime parameters.
+                let mut index = if sub_items_have_self_param(&item.kind) {
+                    1 // Self comes before lifetimes
+                } else {
+                    0
+                };
+                let mut non_lifetime_count = 0;
+                let lifetimes = generics
+                    .params
+                    .iter()
+                    .filter_map(|param| match param.kind {
+                        GenericParamKind::Lifetime { .. } => {
+                            Some(Region::early(self.tcx.hir(), &mut index, param))
+                        }
+                        GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
+                            non_lifetime_count += 1;
+                            None
+                        }
+                    })
+                    .collect();
+                self.map.late_bound_vars.insert(item.hir_id(), vec![]);
+                let scope = Scope::Binder {
+                    hir_id: item.hir_id(),
+                    lifetimes,
+                    next_early_index: index + non_lifetime_count,
+                    opaque_type_parent: true,
+                    scope_type: BinderScopeType::Normal,
+                    s: ROOT_SCOPE,
+                    where_bound_origin: None,
+                };
+                self.with(scope, |this| {
+                    let scope = Scope::TraitRefBoundary { s: this.scope };
+                    this.with(scope, |this| {
+                        intravisit::walk_item(this, item);
+                    });
+                });
+            }
+        }
+    }
+
+    fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
+        match item.kind {
+            hir::ForeignItemKind::Fn(_, _, ref generics) => {
+                self.visit_early_late(None, item.hir_id(), generics, |this| {
+                    intravisit::walk_foreign_item(this, item);
+                })
+            }
+            hir::ForeignItemKind::Static(..) => {
+                intravisit::walk_foreign_item(self, item);
+            }
+            hir::ForeignItemKind::Type => {
+                intravisit::walk_foreign_item(self, item);
+            }
+        }
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
+        match ty.kind {
+            hir::TyKind::BareFn(ref c) => {
+                let next_early_index = self.next_early_index();
+                let (lifetimes, binders): (FxIndexMap<LocalDefId, Region>, Vec<_>) = c
+                    .generic_params
+                    .iter()
+                    .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
+                    .enumerate()
+                    .map(|(late_bound_idx, param)| {
+                        let pair = Region::late(late_bound_idx as u32, self.tcx.hir(), param);
+                        let r = late_region_as_bound_region(self.tcx, &pair.1);
+                        (pair, r)
+                    })
+                    .unzip();
+                self.map.late_bound_vars.insert(ty.hir_id, binders);
+                let scope = Scope::Binder {
+                    hir_id: ty.hir_id,
+                    lifetimes,
+                    s: self.scope,
+                    next_early_index,
+                    opaque_type_parent: false,
+                    scope_type: BinderScopeType::Normal,
+                    where_bound_origin: None,
+                };
+                self.with(scope, |this| {
+                    // a bare fn has no bounds, so everything
+                    // contained within is scoped within its binder.
+                    intravisit::walk_ty(this, ty);
+                });
+            }
+            hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
+                debug!(?bounds, ?lifetime, "TraitObject");
+                let scope = Scope::TraitRefBoundary { s: self.scope };
+                self.with(scope, |this| {
+                    for bound in bounds {
+                        this.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
+                    }
+                });
+                match lifetime.name {
+                    LifetimeName::ImplicitObjectLifetimeDefault => {
+                        // If the user does not write *anything*, we
+                        // use the object lifetime defaulting
+                        // rules. So e.g., `Box<dyn Debug>` becomes
+                        // `Box<dyn Debug + 'static>`.
+                        self.resolve_object_lifetime_default(lifetime)
+                    }
+                    LifetimeName::Infer => {
+                        // If the user writes `'_`, we use the *ordinary* elision
+                        // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
+                        // resolved the same as the `'_` in `&'_ Foo`.
+                        //
+                        // cc #48468
+                    }
+                    LifetimeName::Param(..) | LifetimeName::Static => {
+                        // If the user wrote an explicit name, use that.
+                        self.visit_lifetime(lifetime);
+                    }
+                    LifetimeName::Error => {}
+                }
+            }
+            hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
+                self.visit_lifetime(lifetime_ref);
+                let scope = Scope::ObjectLifetimeDefault {
+                    lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
+                    s: self.scope,
+                };
+                self.with(scope, |this| this.visit_ty(&mt.ty));
+            }
+            hir::TyKind::OpaqueDef(item_id, lifetimes) => {
+                // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
+                // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
+                // `type MyAnonTy<'b> = impl MyTrait<'b>;`
+                //                 ^                  ^ this gets resolved in the scope of
+                //                                      the opaque_ty generics
+                let opaque_ty = self.tcx.hir().item(item_id);
+                let (generics, bounds) = match opaque_ty.kind {
+                    hir::ItemKind::OpaqueTy(hir::OpaqueTy {
+                        origin: hir::OpaqueTyOrigin::TyAlias,
+                        ..
+                    }) => {
+                        intravisit::walk_ty(self, ty);
+
+                        // Elided lifetimes are not allowed in non-return
+                        // position impl Trait
+                        let scope = Scope::TraitRefBoundary { s: self.scope };
+                        self.with(scope, |this| {
+                            let scope = Scope::Elision { s: this.scope };
+                            this.with(scope, |this| {
+                                intravisit::walk_item(this, opaque_ty);
+                            })
+                        });
+
+                        return;
+                    }
+                    hir::ItemKind::OpaqueTy(hir::OpaqueTy {
+                        origin: hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..),
+                        ref generics,
+                        bounds,
+                        ..
+                    }) => (generics, bounds),
+                    ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
+                };
+
+                // Resolve the lifetimes that are applied to the opaque type.
+                // These are resolved in the current scope.
+                // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
+                // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
+                //          ^                 ^this gets resolved in the current scope
+                for lifetime in lifetimes {
+                    let hir::GenericArg::Lifetime(lifetime) = lifetime else {
+                        continue
+                    };
+                    self.visit_lifetime(lifetime);
+
+                    // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
+                    // and ban them. Type variables instantiated inside binders aren't
+                    // well-supported at the moment, so this doesn't work.
+                    // In the future, this should be fixed and this error should be removed.
+                    let def = self.map.defs.get(&lifetime.hir_id).cloned();
+                    let Some(Region::LateBound(_, _, def_id)) = def else {
+                        continue
+                    };
+                    let Some(def_id) = def_id.as_local() else {
+                        continue
+                    };
+                    let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
+                    // Ensure that the parent of the def is an item, not HRTB
+                    let parent_id = self.tcx.hir().get_parent_node(hir_id);
+                    if !parent_id.is_owner() {
+                        if !self.trait_definition_only {
+                            struct_span_err!(
+                                self.tcx.sess,
+                                lifetime.span,
+                                E0657,
+                                "`impl Trait` can only capture lifetimes \
+                                    bound at the fn or impl level"
+                            )
+                            .emit();
+                        }
+                        self.uninsert_lifetime_on_error(lifetime, def.unwrap());
+                    }
+                    if let hir::Node::Item(hir::Item {
+                        kind: hir::ItemKind::OpaqueTy { .. }, ..
+                    }) = self.tcx.hir().get(parent_id)
+                    {
+                        if !self.trait_definition_only {
+                            let mut err = self.tcx.sess.struct_span_err(
+                                lifetime.span,
+                                "higher kinded lifetime bounds on nested opaque types are not supported yet",
+                            );
+                            err.span_note(self.tcx.def_span(def_id), "lifetime declared here");
+                            err.emit();
+                        }
+                        self.uninsert_lifetime_on_error(lifetime, def.unwrap());
+                    }
+                }
+
+                // We want to start our early-bound indices at the end of the parent scope,
+                // not including any parent `impl Trait`s.
+                let mut index = self.next_early_index_for_opaque_type();
+                debug!(?index);
+
+                let mut lifetimes = FxIndexMap::default();
+                let mut non_lifetime_count = 0;
+                debug!(?generics.params);
+                for param in generics.params {
+                    match param.kind {
+                        GenericParamKind::Lifetime { .. } => {
+                            let (def_id, reg) = Region::early(self.tcx.hir(), &mut index, &param);
+                            lifetimes.insert(def_id, reg);
+                        }
+                        GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
+                            non_lifetime_count += 1;
+                        }
+                    }
+                }
+                let next_early_index = index + non_lifetime_count;
+                self.map.late_bound_vars.insert(ty.hir_id, vec![]);
+
+                let scope = Scope::Binder {
+                    hir_id: ty.hir_id,
+                    lifetimes,
+                    next_early_index,
+                    s: self.scope,
+                    opaque_type_parent: false,
+                    scope_type: BinderScopeType::Normal,
+                    where_bound_origin: None,
+                };
+                self.with(scope, |this| {
+                    let scope = Scope::TraitRefBoundary { s: this.scope };
+                    this.with(scope, |this| {
+                        this.visit_generics(generics);
+                        for bound in bounds {
+                            this.visit_param_bound(bound);
+                        }
+                    })
+                });
+            }
+            _ => intravisit::walk_ty(self, ty),
+        }
+    }
+
+    fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
+        use self::hir::TraitItemKind::*;
+        match trait_item.kind {
+            Fn(_, _) => {
+                let tcx = self.tcx;
+                self.visit_early_late(
+                    Some(tcx.hir().get_parent_item(trait_item.hir_id())),
+                    trait_item.hir_id(),
+                    &trait_item.generics,
+                    |this| intravisit::walk_trait_item(this, trait_item),
+                );
+            }
+            Type(bounds, ref ty) => {
+                let generics = &trait_item.generics;
+                let mut index = self.next_early_index();
+                debug!("visit_ty: index = {}", index);
+                let mut non_lifetime_count = 0;
+                let lifetimes = generics
+                    .params
+                    .iter()
+                    .filter_map(|param| match param.kind {
+                        GenericParamKind::Lifetime { .. } => {
+                            Some(Region::early(self.tcx.hir(), &mut index, param))
+                        }
+                        GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
+                            non_lifetime_count += 1;
+                            None
+                        }
+                    })
+                    .collect();
+                self.map.late_bound_vars.insert(trait_item.hir_id(), vec![]);
+                let scope = Scope::Binder {
+                    hir_id: trait_item.hir_id(),
+                    lifetimes,
+                    next_early_index: index + non_lifetime_count,
+                    s: self.scope,
+                    opaque_type_parent: true,
+                    scope_type: BinderScopeType::Normal,
+                    where_bound_origin: None,
+                };
+                self.with(scope, |this| {
+                    let scope = Scope::TraitRefBoundary { s: this.scope };
+                    this.with(scope, |this| {
+                        this.visit_generics(generics);
+                        for bound in bounds {
+                            this.visit_param_bound(bound);
+                        }
+                        if let Some(ty) = ty {
+                            this.visit_ty(ty);
+                        }
+                    })
+                });
+            }
+            Const(_, _) => {
+                // Only methods and types support generics.
+                assert!(trait_item.generics.params.is_empty());
+                intravisit::walk_trait_item(self, trait_item);
+            }
+        }
+    }
+
+    fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
+        use self::hir::ImplItemKind::*;
+        match impl_item.kind {
+            Fn(..) => {
+                let tcx = self.tcx;
+                self.visit_early_late(
+                    Some(tcx.hir().get_parent_item(impl_item.hir_id())),
+                    impl_item.hir_id(),
+                    &impl_item.generics,
+                    |this| intravisit::walk_impl_item(this, impl_item),
+                );
+            }
+            TyAlias(ref ty) => {
+                let generics = &impl_item.generics;
+                let mut index = self.next_early_index();
+                let mut non_lifetime_count = 0;
+                debug!("visit_ty: index = {}", index);
+                let lifetimes: FxIndexMap<LocalDefId, Region> = generics
+                    .params
+                    .iter()
+                    .filter_map(|param| match param.kind {
+                        GenericParamKind::Lifetime { .. } => {
+                            Some(Region::early(self.tcx.hir(), &mut index, param))
+                        }
+                        GenericParamKind::Const { .. } | GenericParamKind::Type { .. } => {
+                            non_lifetime_count += 1;
+                            None
+                        }
+                    })
+                    .collect();
+                self.map.late_bound_vars.insert(ty.hir_id, vec![]);
+                let scope = Scope::Binder {
+                    hir_id: ty.hir_id,
+                    lifetimes,
+                    next_early_index: index + non_lifetime_count,
+                    s: self.scope,
+                    opaque_type_parent: true,
+                    scope_type: BinderScopeType::Normal,
+                    where_bound_origin: None,
+                };
+                self.with(scope, |this| {
+                    let scope = Scope::TraitRefBoundary { s: this.scope };
+                    this.with(scope, |this| {
+                        this.visit_generics(generics);
+                        this.visit_ty(ty);
+                    })
+                });
+            }
+            Const(_, _) => {
+                // Only methods and types support generics.
+                assert!(impl_item.generics.params.is_empty());
+                intravisit::walk_impl_item(self, impl_item);
+            }
+        }
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
+        match lifetime_ref.name {
+            hir::LifetimeName::Static => self.insert_lifetime(lifetime_ref, Region::Static),
+            hir::LifetimeName::Param(param_def_id, _) => {
+                self.resolve_lifetime_ref(param_def_id, lifetime_ref)
+            }
+            // If we've already reported an error, just ignore `lifetime_ref`.
+            hir::LifetimeName::Error => {}
+            // Those will be resolved by typechecking.
+            hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Infer => {}
+        }
+    }
+
+    fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) {
+        for (i, segment) in path.segments.iter().enumerate() {
+            let depth = path.segments.len() - i - 1;
+            if let Some(ref args) = segment.args {
+                self.visit_segment_args(path.res, depth, args);
+            }
+        }
+    }
+
+    fn visit_fn(
+        &mut self,
+        fk: intravisit::FnKind<'tcx>,
+        fd: &'tcx hir::FnDecl<'tcx>,
+        body_id: hir::BodyId,
+        _: Span,
+        _: hir::HirId,
+    ) {
+        let output = match fd.output {
+            hir::FnRetTy::DefaultReturn(_) => None,
+            hir::FnRetTy::Return(ref ty) => Some(&**ty),
+        };
+        self.visit_fn_like_elision(&fd.inputs, output, matches!(fk, intravisit::FnKind::Closure));
+        intravisit::walk_fn_kind(self, fk);
+        self.visit_nested_body(body_id)
+    }
+
+    fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
+        let scope = Scope::TraitRefBoundary { s: self.scope };
+        self.with(scope, |this| {
+            for param in generics.params {
+                match param.kind {
+                    GenericParamKind::Lifetime { .. } => {}
+                    GenericParamKind::Type { ref default, .. } => {
+                        if let Some(ref ty) = default {
+                            this.visit_ty(&ty);
+                        }
+                    }
+                    GenericParamKind::Const { ref ty, default } => {
+                        this.visit_ty(&ty);
+                        if let Some(default) = default {
+                            this.visit_body(this.tcx.hir().body(default.body));
+                        }
+                    }
+                }
+            }
+            for predicate in generics.predicates {
+                match predicate {
+                    &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
+                        ref bounded_ty,
+                        bounds,
+                        ref bound_generic_params,
+                        origin,
+                        ..
+                    }) => {
+                        let (lifetimes, binders): (FxIndexMap<LocalDefId, Region>, Vec<_>) =
+                            bound_generic_params
+                                .iter()
+                                .filter(|param| {
+                                    matches!(param.kind, GenericParamKind::Lifetime { .. })
+                                })
+                                .enumerate()
+                                .map(|(late_bound_idx, param)| {
+                                    let pair =
+                                        Region::late(late_bound_idx as u32, this.tcx.hir(), param);
+                                    let r = late_region_as_bound_region(this.tcx, &pair.1);
+                                    (pair, r)
+                                })
+                                .unzip();
+                        this.map.late_bound_vars.insert(bounded_ty.hir_id, binders.clone());
+                        let next_early_index = this.next_early_index();
+                        // Even if there are no lifetimes defined here, we still wrap it in a binder
+                        // scope. If there happens to be a nested poly trait ref (an error), that
+                        // will be `Concatenating` anyways, so we don't have to worry about the depth
+                        // being wrong.
+                        let scope = Scope::Binder {
+                            hir_id: bounded_ty.hir_id,
+                            lifetimes,
+                            s: this.scope,
+                            next_early_index,
+                            opaque_type_parent: false,
+                            scope_type: BinderScopeType::Normal,
+                            where_bound_origin: Some(origin),
+                        };
+                        this.with(scope, |this| {
+                            this.visit_ty(&bounded_ty);
+                            walk_list!(this, visit_param_bound, bounds);
+                        })
+                    }
+                    &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
+                        ref lifetime,
+                        bounds,
+                        ..
+                    }) => {
+                        this.visit_lifetime(lifetime);
+                        walk_list!(this, visit_param_bound, bounds);
+
+                        if lifetime.name != hir::LifetimeName::Static {
+                            for bound in bounds {
+                                let hir::GenericBound::Outlives(ref lt) = bound else {
+                                    continue;
+                                };
+                                if lt.name != hir::LifetimeName::Static {
+                                    continue;
+                                }
+                                this.insert_lifetime(lt, Region::Static);
+                                this.tcx
+                                    .sess
+                                    .struct_span_warn(
+                                        lifetime.span,
+                                        &format!(
+                                            "unnecessary lifetime parameter `{}`",
+                                            lifetime.name.ident(),
+                                        ),
+                                    )
+                                    .help(&format!(
+                                        "you can use the `'static` lifetime directly, in place of `{}`",
+                                        lifetime.name.ident(),
+                                    ))
+                                    .emit();
+                            }
+                        }
+                    }
+                    &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
+                        ref lhs_ty,
+                        ref rhs_ty,
+                        ..
+                    }) => {
+                        this.visit_ty(lhs_ty);
+                        this.visit_ty(rhs_ty);
+                    }
+                }
+            }
+        })
+    }
+
+    fn visit_param_bound(&mut self, bound: &'tcx hir::GenericBound<'tcx>) {
+        match bound {
+            hir::GenericBound::LangItemTrait(_, _, hir_id, _) => {
+                // FIXME(jackh726): This is pretty weird. `LangItemTrait` doesn't go
+                // through the regular poly trait ref code, so we don't get another
+                // chance to introduce a binder. For now, I'm keeping the existing logic
+                // of "if there isn't a Binder scope above us, add one", but I
+                // imagine there's a better way to go about this.
+                let (binders, scope_type) = self.poly_trait_ref_binder_info();
+
+                self.map.late_bound_vars.insert(*hir_id, binders);
+                let scope = Scope::Binder {
+                    hir_id: *hir_id,
+                    lifetimes: FxIndexMap::default(),
+                    s: self.scope,
+                    next_early_index: self.next_early_index(),
+                    opaque_type_parent: false,
+                    scope_type,
+                    where_bound_origin: None,
+                };
+                self.with(scope, |this| {
+                    intravisit::walk_param_bound(this, bound);
+                });
+            }
+            _ => intravisit::walk_param_bound(self, bound),
+        }
+    }
+
+    fn visit_poly_trait_ref(
+        &mut self,
+        trait_ref: &'tcx hir::PolyTraitRef<'tcx>,
+        _modifier: hir::TraitBoundModifier,
+    ) {
+        debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref);
+
+        let next_early_index = self.next_early_index();
+        let (mut binders, scope_type) = self.poly_trait_ref_binder_info();
+
+        let initial_bound_vars = binders.len() as u32;
+        let mut lifetimes: FxIndexMap<LocalDefId, Region> = FxIndexMap::default();
+        let binders_iter = trait_ref
+            .bound_generic_params
+            .iter()
+            .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
+            .enumerate()
+            .map(|(late_bound_idx, param)| {
+                let pair =
+                    Region::late(initial_bound_vars + late_bound_idx as u32, self.tcx.hir(), param);
+                let r = late_region_as_bound_region(self.tcx, &pair.1);
+                lifetimes.insert(pair.0, pair.1);
+                r
+            });
+        binders.extend(binders_iter);
+
+        debug!(?binders);
+        self.map.late_bound_vars.insert(trait_ref.trait_ref.hir_ref_id, binders);
+
+        // Always introduce a scope here, even if this is in a where clause and
+        // we introduced the binders around the bounded Ty. In that case, we
+        // just reuse the concatenation functionality also present in nested trait
+        // refs.
+        let scope = Scope::Binder {
+            hir_id: trait_ref.trait_ref.hir_ref_id,
+            lifetimes,
+            s: self.scope,
+            next_early_index,
+            opaque_type_parent: false,
+            scope_type,
+            where_bound_origin: None,
+        };
+        self.with(scope, |this| {
+            walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
+            this.visit_trait_ref(&trait_ref.trait_ref);
+        });
+    }
+}
+
+fn compute_object_lifetime_defaults<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    item: &hir::Item<'_>,
+) -> Option<&'tcx [ObjectLifetimeDefault]> {
+    match item.kind {
+        hir::ItemKind::Struct(_, ref generics)
+        | hir::ItemKind::Union(_, ref generics)
+        | hir::ItemKind::Enum(_, ref generics)
+        | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
+            ref generics,
+            origin: hir::OpaqueTyOrigin::TyAlias,
+            ..
+        })
+        | hir::ItemKind::TyAlias(_, ref generics)
+        | hir::ItemKind::Trait(_, _, ref generics, ..) => {
+            let result = object_lifetime_defaults_for_item(tcx, generics);
+
+            // Debugging aid.
+            let attrs = tcx.hir().attrs(item.hir_id());
+            if tcx.sess.contains_name(attrs, sym::rustc_object_lifetime_default) {
+                let object_lifetime_default_reprs: String = result
+                    .iter()
+                    .map(|set| match *set {
+                        Set1::Empty => "BaseDefault".into(),
+                        Set1::One(Region::Static) => "'static".into(),
+                        Set1::One(Region::EarlyBound(mut i, _)) => generics
+                            .params
+                            .iter()
+                            .find_map(|param| match param.kind {
+                                GenericParamKind::Lifetime { .. } => {
+                                    if i == 0 {
+                                        return Some(param.name.ident().to_string().into());
+                                    }
+                                    i -= 1;
+                                    None
+                                }
+                                _ => None,
+                            })
+                            .unwrap(),
+                        Set1::One(_) => bug!(),
+                        Set1::Many => "Ambiguous".into(),
+                    })
+                    .collect::<Vec<Cow<'static, str>>>()
+                    .join(",");
+                tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
+            }
+
+            Some(result)
+        }
+        _ => None,
+    }
+}
+
+/// Scan the bounds and where-clauses on parameters to extract bounds
+/// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
+/// for each type parameter.
+fn object_lifetime_defaults_for_item<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    generics: &hir::Generics<'_>,
+) -> &'tcx [ObjectLifetimeDefault] {
+    fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound<'_>]) {
+        for bound in bounds {
+            if let hir::GenericBound::Outlives(ref lifetime) = *bound {
+                set.insert(lifetime.name.normalize_to_macros_2_0());
+            }
+        }
+    }
+
+    let process_param = |param: &hir::GenericParam<'_>| match param.kind {
+        GenericParamKind::Lifetime { .. } => None,
+        GenericParamKind::Type { .. } => {
+            let mut set = Set1::Empty;
+
+            let param_def_id = tcx.hir().local_def_id(param.hir_id);
+            for predicate in generics.predicates {
+                // Look for `type: ...` where clauses.
+                let hir::WherePredicate::BoundPredicate(ref data) = *predicate else { continue };
+
+                // Ignore `for<'a> type: ...` as they can change what
+                // lifetimes mean (although we could "just" handle it).
+                if !data.bound_generic_params.is_empty() {
+                    continue;
+                }
+
+                let res = match data.bounded_ty.kind {
+                    hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.res,
+                    _ => continue,
+                };
+
+                if res == Res::Def(DefKind::TyParam, param_def_id.to_def_id()) {
+                    add_bounds(&mut set, &data.bounds);
+                }
+            }
+
+            Some(match set {
+                Set1::Empty => Set1::Empty,
+                Set1::One(name) => {
+                    if name == hir::LifetimeName::Static {
+                        Set1::One(Region::Static)
+                    } else {
+                        generics
+                            .params
+                            .iter()
+                            .filter_map(|param| match param.kind {
+                                GenericParamKind::Lifetime { .. } => {
+                                    let param_def_id = tcx.hir().local_def_id(param.hir_id);
+                                    Some((
+                                        param_def_id,
+                                        hir::LifetimeName::Param(param_def_id, param.name),
+                                    ))
+                                }
+                                _ => None,
+                            })
+                            .enumerate()
+                            .find(|&(_, (_, lt_name))| lt_name == name)
+                            .map_or(Set1::Many, |(i, (def_id, _))| {
+                                Set1::One(Region::EarlyBound(i as u32, def_id.to_def_id()))
+                            })
+                    }
+                }
+                Set1::Many => Set1::Many,
+            })
+        }
+        GenericParamKind::Const { .. } => {
+            // Generic consts don't impose any constraints.
+            //
+            // We still store a dummy value here to allow generic parameters
+            // in an arbitrary order.
+            Some(Set1::Empty)
+        }
+    };
+
+    tcx.arena.alloc_from_iter(generics.params.iter().filter_map(process_param))
+}
+
+impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
+    fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
+    where
+        F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
+    {
+        let LifetimeContext { tcx, map, .. } = self;
+        let xcrate_object_lifetime_defaults = take(&mut self.xcrate_object_lifetime_defaults);
+        let mut this = LifetimeContext {
+            tcx: *tcx,
+            map,
+            scope: &wrap_scope,
+            trait_definition_only: self.trait_definition_only,
+            xcrate_object_lifetime_defaults,
+        };
+        let span = tracing::debug_span!("scope", scope = ?TruncatedScopeDebug(&this.scope));
+        {
+            let _enter = span.enter();
+            f(&mut this);
+        }
+        self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
+    }
+
+    /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
+    ///
+    /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
+    /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
+    /// within type bounds; those are early bound lifetimes, and the rest are late bound.
+    ///
+    /// For example:
+    ///
+    ///    fn foo<'a,'b,'c,T:Trait<'b>>(...)
+    ///
+    /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
+    /// lifetimes may be interspersed together.
+    ///
+    /// If early bound lifetimes are present, we separate them into their own list (and likewise
+    /// for late bound). They will be numbered sequentially, starting from the lowest index that is
+    /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
+    /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
+    /// ordering is not important there.
+    fn visit_early_late<F>(
+        &mut self,
+        parent_id: Option<LocalDefId>,
+        hir_id: hir::HirId,
+        generics: &'tcx hir::Generics<'tcx>,
+        walk: F,
+    ) where
+        F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
+    {
+        // Find the start of nested early scopes, e.g., in methods.
+        let mut next_early_index = 0;
+        if let Some(parent_id) = parent_id {
+            let parent = self.tcx.hir().expect_item(parent_id);
+            if sub_items_have_self_param(&parent.kind) {
+                next_early_index += 1; // Self comes before lifetimes
+            }
+            match parent.kind {
+                hir::ItemKind::Trait(_, _, ref generics, ..)
+                | hir::ItemKind::Impl(hir::Impl { ref generics, .. }) => {
+                    next_early_index += generics.params.len() as u32;
+                }
+                _ => {}
+            }
+        }
+
+        let mut non_lifetime_count = 0;
+        let mut named_late_bound_vars = 0;
+        let lifetimes: FxIndexMap<LocalDefId, Region> = generics
+            .params
+            .iter()
+            .filter_map(|param| match param.kind {
+                GenericParamKind::Lifetime { .. } => {
+                    if self.tcx.is_late_bound(param.hir_id) {
+                        let late_bound_idx = named_late_bound_vars;
+                        named_late_bound_vars += 1;
+                        Some(Region::late(late_bound_idx, self.tcx.hir(), param))
+                    } else {
+                        Some(Region::early(self.tcx.hir(), &mut next_early_index, param))
+                    }
+                }
+                GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
+                    non_lifetime_count += 1;
+                    None
+                }
+            })
+            .collect();
+        let next_early_index = next_early_index + non_lifetime_count;
+
+        let binders: Vec<_> = generics
+            .params
+            .iter()
+            .filter(|param| {
+                matches!(param.kind, GenericParamKind::Lifetime { .. })
+                    && self.tcx.is_late_bound(param.hir_id)
+            })
+            .enumerate()
+            .map(|(late_bound_idx, param)| {
+                let pair = Region::late(late_bound_idx as u32, self.tcx.hir(), param);
+                late_region_as_bound_region(self.tcx, &pair.1)
+            })
+            .collect();
+        self.map.late_bound_vars.insert(hir_id, binders);
+        let scope = Scope::Binder {
+            hir_id,
+            lifetimes,
+            next_early_index,
+            s: self.scope,
+            opaque_type_parent: true,
+            scope_type: BinderScopeType::Normal,
+            where_bound_origin: None,
+        };
+        self.with(scope, walk);
+    }
+
+    fn next_early_index_helper(&self, only_opaque_type_parent: bool) -> u32 {
+        let mut scope = self.scope;
+        loop {
+            match *scope {
+                Scope::Root => return 0,
+
+                Scope::Binder { next_early_index, opaque_type_parent, .. }
+                    if (!only_opaque_type_parent || opaque_type_parent) =>
+                {
+                    return next_early_index;
+                }
+
+                Scope::Binder { s, .. }
+                | Scope::Body { s, .. }
+                | Scope::Elision { s, .. }
+                | Scope::ObjectLifetimeDefault { s, .. }
+                | Scope::Supertrait { s, .. }
+                | Scope::TraitRefBoundary { s, .. } => scope = s,
+            }
+        }
+    }
+
+    /// Returns the next index one would use for an early-bound-region
+    /// if extending the current scope.
+    fn next_early_index(&self) -> u32 {
+        self.next_early_index_helper(true)
+    }
+
+    /// Returns the next index one would use for an `impl Trait` that
+    /// is being converted into an opaque type alias `impl Trait`. This will be the
+    /// next early index from the enclosing item, for the most
+    /// part. See the `opaque_type_parent` field for more info.
+    fn next_early_index_for_opaque_type(&self) -> u32 {
+        self.next_early_index_helper(false)
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn resolve_lifetime_ref(
+        &mut self,
+        region_def_id: LocalDefId,
+        lifetime_ref: &'tcx hir::Lifetime,
+    ) {
+        // Walk up the scope chain, tracking the number of fn scopes
+        // that we pass through, until we find a lifetime with the
+        // given name or we run out of scopes.
+        // search.
+        let mut late_depth = 0;
+        let mut scope = self.scope;
+        let mut outermost_body = None;
+        let result = loop {
+            match *scope {
+                Scope::Body { id, s } => {
+                    outermost_body = Some(id);
+                    scope = s;
+                }
+
+                Scope::Root => {
+                    break None;
+                }
+
+                Scope::Binder { ref lifetimes, scope_type, s, where_bound_origin, .. } => {
+                    if let Some(&def) = lifetimes.get(&region_def_id) {
+                        break Some(def.shifted(late_depth));
+                    }
+                    match scope_type {
+                        BinderScopeType::Normal => late_depth += 1,
+                        BinderScopeType::Concatenating => {}
+                    }
+                    // Fresh lifetimes in APIT used to be allowed in async fns and forbidden in
+                    // regular fns.
+                    if let Some(hir::PredicateOrigin::ImplTrait) = where_bound_origin
+                        && let hir::LifetimeName::Param(_, hir::ParamName::Fresh) = lifetime_ref.name
+                        && let hir::IsAsync::NotAsync = self.tcx.asyncness(lifetime_ref.hir_id.owner)
+                        && !self.tcx.features().anonymous_lifetime_in_impl_trait
+                    {
+                        rustc_session::parse::feature_err(
+                            &self.tcx.sess.parse_sess,
+                            sym::anonymous_lifetime_in_impl_trait,
+                            lifetime_ref.span,
+                            "anonymous lifetimes in `impl Trait` are unstable",
+                        ).emit();
+                        return;
+                    }
+                    scope = s;
+                }
+
+                Scope::Elision { s, .. }
+                | Scope::ObjectLifetimeDefault { s, .. }
+                | Scope::Supertrait { s, .. }
+                | Scope::TraitRefBoundary { s, .. } => {
+                    scope = s;
+                }
+            }
+        };
+
+        if let Some(mut def) = result {
+            if let Region::EarlyBound(..) = def {
+                // Do not free early-bound regions, only late-bound ones.
+            } else if let Some(body_id) = outermost_body {
+                let fn_id = self.tcx.hir().body_owner(body_id);
+                match self.tcx.hir().get(fn_id) {
+                    Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. })
+                    | Node::TraitItem(&hir::TraitItem {
+                        kind: hir::TraitItemKind::Fn(..), ..
+                    })
+                    | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) => {
+                        let scope = self.tcx.hir().local_def_id(fn_id);
+                        def = Region::Free(scope.to_def_id(), def.id().unwrap());
+                    }
+                    _ => {}
+                }
+            }
+
+            self.insert_lifetime(lifetime_ref, def);
+            return;
+        }
+
+        // We may fail to resolve higher-ranked lifetimes that are mentionned by APIT.
+        // AST-based resolution does not care for impl-trait desugaring, which are the
+        // responibility of lowering.  This may create a mismatch between the resolution
+        // AST found (`region_def_id`) which points to HRTB, and what HIR allows.
+        // ```
+        // fn foo(x: impl for<'a> Trait<'a, Assoc = impl Copy + 'a>) {}
+        // ```
+        //
+        // In such case, walk back the binders to diagnose it properly.
+        let mut scope = self.scope;
+        loop {
+            match *scope {
+                Scope::Binder {
+                    where_bound_origin: Some(hir::PredicateOrigin::ImplTrait), ..
+                } => {
+                    let mut err = self.tcx.sess.struct_span_err(
+                        lifetime_ref.span,
+                        "`impl Trait` can only mention lifetimes bound at the fn or impl level",
+                    );
+                    err.span_note(self.tcx.def_span(region_def_id), "lifetime declared here");
+                    err.emit();
+                    return;
+                }
+                Scope::Root => break,
+                Scope::Binder { s, .. }
+                | Scope::Body { s, .. }
+                | Scope::Elision { s, .. }
+                | Scope::ObjectLifetimeDefault { s, .. }
+                | Scope::Supertrait { s, .. }
+                | Scope::TraitRefBoundary { s, .. } => {
+                    scope = s;
+                }
+            }
+        }
+
+        self.tcx.sess.delay_span_bug(
+            lifetime_ref.span,
+            &format!("Could not resolve {:?} in scope {:#?}", lifetime_ref, self.scope,),
+        );
+    }
+
+    fn visit_segment_args(
+        &mut self,
+        res: Res,
+        depth: usize,
+        generic_args: &'tcx hir::GenericArgs<'tcx>,
+    ) {
+        debug!(
+            "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})",
+            res, depth, generic_args,
+        );
+
+        if generic_args.parenthesized {
+            self.visit_fn_like_elision(
+                generic_args.inputs(),
+                Some(generic_args.bindings[0].ty()),
+                false,
+            );
+            return;
+        }
+
+        for arg in generic_args.args {
+            if let hir::GenericArg::Lifetime(lt) = arg {
+                self.visit_lifetime(lt);
+            }
+        }
+
+        // Figure out if this is a type/trait segment,
+        // which requires object lifetime defaults.
+        let parent_def_id = |this: &mut Self, def_id: DefId| {
+            let def_key = this.tcx.def_key(def_id);
+            DefId { krate: def_id.krate, index: def_key.parent.expect("missing parent") }
+        };
+        let type_def_id = match res {
+            Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
+            Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
+            Res::Def(
+                DefKind::Struct
+                | DefKind::Union
+                | DefKind::Enum
+                | DefKind::TyAlias
+                | DefKind::Trait,
+                def_id,
+            ) if depth == 0 => Some(def_id),
+            _ => None,
+        };
+
+        debug!("visit_segment_args: type_def_id={:?}", type_def_id);
+
+        // Compute a vector of defaults, one for each type parameter,
+        // per the rules given in RFCs 599 and 1156. Example:
+        //
+        // ```rust
+        // struct Foo<'a, T: 'a, U> { }
+        // ```
+        //
+        // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
+        // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
+        // and `dyn Baz` to `dyn Baz + 'static` (because there is no
+        // such bound).
+        //
+        // Therefore, we would compute `object_lifetime_defaults` to a
+        // vector like `['x, 'static]`. Note that the vector only
+        // includes type parameters.
+        let object_lifetime_defaults = type_def_id.map_or_else(Vec::new, |def_id| {
+            let in_body = {
+                let mut scope = self.scope;
+                loop {
+                    match *scope {
+                        Scope::Root => break false,
+
+                        Scope::Body { .. } => break true,
+
+                        Scope::Binder { s, .. }
+                        | Scope::Elision { s, .. }
+                        | Scope::ObjectLifetimeDefault { s, .. }
+                        | Scope::Supertrait { s, .. }
+                        | Scope::TraitRefBoundary { s, .. } => {
+                            scope = s;
+                        }
+                    }
+                }
+            };
+
+            let map = &self.map;
+            let set_to_region = |set: &ObjectLifetimeDefault| match *set {
+                Set1::Empty => {
+                    if in_body {
+                        None
+                    } else {
+                        Some(Region::Static)
+                    }
+                }
+                Set1::One(r) => {
+                    let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
+                        GenericArg::Lifetime(lt) => Some(lt),
+                        _ => None,
+                    });
+                    r.subst(lifetimes, map)
+                }
+                Set1::Many => None,
+            };
+            if let Some(def_id) = def_id.as_local() {
+                let id = self.tcx.hir().local_def_id_to_hir_id(def_id);
+                self.tcx
+                    .object_lifetime_defaults(id.owner)
+                    .unwrap()
+                    .iter()
+                    .map(set_to_region)
+                    .collect()
+            } else {
+                let tcx = self.tcx;
+                self.xcrate_object_lifetime_defaults
+                    .entry(def_id)
+                    .or_insert_with(|| {
+                        tcx.generics_of(def_id)
+                            .params
+                            .iter()
+                            .filter_map(|param| match param.kind {
+                                GenericParamDefKind::Type { object_lifetime_default, .. } => {
+                                    Some(object_lifetime_default)
+                                }
+                                GenericParamDefKind::Const { .. } => Some(Set1::Empty),
+                                GenericParamDefKind::Lifetime => None,
+                            })
+                            .collect()
+                    })
+                    .iter()
+                    .map(set_to_region)
+                    .collect()
+            }
+        });
+
+        debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
+
+        let mut i = 0;
+        for arg in generic_args.args {
+            match arg {
+                GenericArg::Lifetime(_) => {}
+                GenericArg::Type(ty) => {
+                    if let Some(&lt) = object_lifetime_defaults.get(i) {
+                        let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
+                        self.with(scope, |this| this.visit_ty(ty));
+                    } else {
+                        self.visit_ty(ty);
+                    }
+                    i += 1;
+                }
+                GenericArg::Const(ct) => {
+                    self.visit_anon_const(&ct.value);
+                    i += 1;
+                }
+                GenericArg::Infer(inf) => {
+                    self.visit_id(inf.hir_id);
+                    i += 1;
+                }
+            }
+        }
+
+        // Hack: when resolving the type `XX` in binding like `dyn
+        // Foo<'b, Item = XX>`, the current object-lifetime default
+        // would be to examine the trait `Foo` to check whether it has
+        // a lifetime bound declared on `Item`. e.g., if `Foo` is
+        // declared like so, then the default object lifetime bound in
+        // `XX` should be `'b`:
+        //
+        // ```rust
+        // trait Foo<'a> {
+        //   type Item: 'a;
+        // }
+        // ```
+        //
+        // but if we just have `type Item;`, then it would be
+        // `'static`. However, we don't get all of this logic correct.
+        //
+        // Instead, we do something hacky: if there are no lifetime parameters
+        // to the trait, then we simply use a default object lifetime
+        // bound of `'static`, because there is no other possibility. On the other hand,
+        // if there ARE lifetime parameters, then we require the user to give an
+        // explicit bound for now.
+        //
+        // This is intended to leave room for us to implement the
+        // correct behavior in the future.
+        let has_lifetime_parameter =
+            generic_args.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)));
+
+        // Resolve lifetimes found in the bindings, so either in the type `XX` in `Item = XX` or
+        // in the trait ref `YY<...>` in `Item: YY<...>`.
+        for binding in generic_args.bindings {
+            let scope = Scope::ObjectLifetimeDefault {
+                lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) },
+                s: self.scope,
+            };
+            if let Some(type_def_id) = type_def_id {
+                let lifetimes = LifetimeContext::supertrait_hrtb_lifetimes(
+                    self.tcx,
+                    type_def_id,
+                    binding.ident,
+                );
+                self.with(scope, |this| {
+                    let scope = Scope::Supertrait {
+                        lifetimes: lifetimes.unwrap_or_default(),
+                        s: this.scope,
+                    };
+                    this.with(scope, |this| this.visit_assoc_type_binding(binding));
+                });
+            } else {
+                self.with(scope, |this| this.visit_assoc_type_binding(binding));
+            }
+        }
+    }
+
+    /// Returns all the late-bound vars that come into scope from supertrait HRTBs, based on the
+    /// associated type name and starting trait.
+    /// For example, imagine we have
+    /// ```ignore (illustrative)
+    /// trait Foo<'a, 'b> {
+    ///   type As;
+    /// }
+    /// trait Bar<'b>: for<'a> Foo<'a, 'b> {}
+    /// trait Bar: for<'b> Bar<'b> {}
+    /// ```
+    /// In this case, if we wanted to the supertrait HRTB lifetimes for `As` on
+    /// the starting trait `Bar`, we would return `Some(['b, 'a])`.
+    fn supertrait_hrtb_lifetimes(
+        tcx: TyCtxt<'tcx>,
+        def_id: DefId,
+        assoc_name: Ident,
+    ) -> Option<Vec<ty::BoundVariableKind>> {
+        let trait_defines_associated_type_named = |trait_def_id: DefId| {
+            tcx.associated_items(trait_def_id)
+                .find_by_name_and_kind(tcx, assoc_name, ty::AssocKind::Type, trait_def_id)
+                .is_some()
+        };
+
+        use smallvec::{smallvec, SmallVec};
+        let mut stack: SmallVec<[(DefId, SmallVec<[ty::BoundVariableKind; 8]>); 8]> =
+            smallvec![(def_id, smallvec![])];
+        let mut visited: FxHashSet<DefId> = FxHashSet::default();
+        loop {
+            let Some((def_id, bound_vars)) = stack.pop() else {
+                break None;
+            };
+            // See issue #83753. If someone writes an associated type on a non-trait, just treat it as
+            // there being no supertrait HRTBs.
+            match tcx.def_kind(def_id) {
+                DefKind::Trait | DefKind::TraitAlias | DefKind::Impl => {}
+                _ => break None,
+            }
+
+            if trait_defines_associated_type_named(def_id) {
+                break Some(bound_vars.into_iter().collect());
+            }
+            let predicates =
+                tcx.super_predicates_that_define_assoc_type((def_id, Some(assoc_name)));
+            let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| {
+                let bound_predicate = pred.kind();
+                match bound_predicate.skip_binder() {
+                    ty::PredicateKind::Trait(data) => {
+                        // The order here needs to match what we would get from `subst_supertrait`
+                        let pred_bound_vars = bound_predicate.bound_vars();
+                        let mut all_bound_vars = bound_vars.clone();
+                        all_bound_vars.extend(pred_bound_vars.iter());
+                        let super_def_id = data.trait_ref.def_id;
+                        Some((super_def_id, all_bound_vars))
+                    }
+                    _ => None,
+                }
+            });
+
+            let obligations = obligations.filter(|o| visited.insert(o.0));
+            stack.extend(obligations);
+        }
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn visit_fn_like_elision(
+        &mut self,
+        inputs: &'tcx [hir::Ty<'tcx>],
+        output: Option<&'tcx hir::Ty<'tcx>>,
+        in_closure: bool,
+    ) {
+        self.with(Scope::Elision { s: self.scope }, |this| {
+            for input in inputs {
+                this.visit_ty(input);
+            }
+            if !in_closure && let Some(output) = output {
+                this.visit_ty(output);
+            }
+        });
+        if in_closure && let Some(output) = output {
+            self.visit_ty(output);
+        }
+    }
+
+    fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
+        debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref);
+        let mut late_depth = 0;
+        let mut scope = self.scope;
+        let lifetime = loop {
+            match *scope {
+                Scope::Binder { s, scope_type, .. } => {
+                    match scope_type {
+                        BinderScopeType::Normal => late_depth += 1,
+                        BinderScopeType::Concatenating => {}
+                    }
+                    scope = s;
+                }
+
+                Scope::Root | Scope::Elision { .. } => break Region::Static,
+
+                Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
+
+                Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
+
+                Scope::Supertrait { s, .. } | Scope::TraitRefBoundary { s, .. } => {
+                    scope = s;
+                }
+            }
+        };
+        self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
+    }
+
+    #[tracing::instrument(level = "debug", skip(self))]
+    fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
+        debug!(
+            node = ?self.tcx.hir().node_to_string(lifetime_ref.hir_id),
+            span = ?self.tcx.sess.source_map().span_to_diagnostic_string(lifetime_ref.span)
+        );
+        self.map.defs.insert(lifetime_ref.hir_id, def);
+    }
+
+    /// Sometimes we resolve a lifetime, but later find that it is an
+    /// error (esp. around impl trait). In that case, we remove the
+    /// entry into `map.defs` so as not to confuse later code.
+    fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
+        let old_value = self.map.defs.remove(&lifetime_ref.hir_id);
+        assert_eq!(old_value, Some(bad_def));
+    }
+}
+
+/// Detects late-bound lifetimes and inserts them into
+/// `late_bound`.
+///
+/// A region declared on a fn is **late-bound** if:
+/// - it is constrained by an argument type;
+/// - it does not appear in a where-clause.
+///
+/// "Constrained" basically means that it appears in any type but
+/// not amongst the inputs to a projection. In other words, `<&'a
+/// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
+fn is_late_bound_map(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<&FxIndexSet<LocalDefId>> {
+    let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
+    let decl = tcx.hir().fn_decl_by_hir_id(hir_id)?;
+    let generics = tcx.hir().get_generics(def_id)?;
+
+    let mut late_bound = FxIndexSet::default();
+
+    let mut constrained_by_input = ConstrainedCollector::default();
+    for arg_ty in decl.inputs {
+        constrained_by_input.visit_ty(arg_ty);
+    }
+
+    let mut appears_in_output = AllCollector::default();
+    intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
+
+    debug!(?constrained_by_input.regions);
+
+    // Walk the lifetimes that appear in where clauses.
+    //
+    // Subtle point: because we disallow nested bindings, we can just
+    // ignore binders here and scrape up all names we see.
+    let mut appears_in_where_clause = AllCollector::default();
+    appears_in_where_clause.visit_generics(generics);
+    debug!(?appears_in_where_clause.regions);
+
+    // Late bound regions are those that:
+    // - appear in the inputs
+    // - do not appear in the where-clauses
+    // - are not implicitly captured by `impl Trait`
+    for param in generics.params {
+        match param.kind {
+            hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
+
+            // Neither types nor consts are late-bound.
+            hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
+        }
+
+        let param_def_id = tcx.hir().local_def_id(param.hir_id);
+
+        // appears in the where clauses? early-bound.
+        if appears_in_where_clause.regions.contains(&param_def_id) {
+            continue;
+        }
+
+        // does not appear in the inputs, but appears in the return type? early-bound.
+        if !constrained_by_input.regions.contains(&param_def_id)
+            && appears_in_output.regions.contains(&param_def_id)
+        {
+            continue;
+        }
+
+        debug!("lifetime {:?} with id {:?} is late-bound", param.name.ident(), param.hir_id);
+
+        let inserted = late_bound.insert(param_def_id);
+        assert!(inserted, "visited lifetime {:?} twice", param.hir_id);
+    }
+
+    debug!(?late_bound);
+    return Some(tcx.arena.alloc(late_bound));
+
+    #[derive(Default)]
+    struct ConstrainedCollector {
+        regions: FxHashSet<LocalDefId>,
+    }
+
+    impl<'v> Visitor<'v> for ConstrainedCollector {
+        fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
+            match ty.kind {
+                hir::TyKind::Path(
+                    hir::QPath::Resolved(Some(_), _) | hir::QPath::TypeRelative(..),
+                ) => {
+                    // ignore lifetimes appearing in associated type
+                    // projections, as they are not *constrained*
+                    // (defined above)
+                }
+
+                hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
+                    // consider only the lifetimes on the final
+                    // segment; I am not sure it's even currently
+                    // valid to have them elsewhere, but even if it
+                    // is, those would be potentially inputs to
+                    // projections
+                    if let Some(last_segment) = path.segments.last() {
+                        self.visit_path_segment(path.span, last_segment);
+                    }
+                }
+
+                _ => {
+                    intravisit::walk_ty(self, ty);
+                }
+            }
+        }
+
+        fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
+            if let hir::LifetimeName::Param(def_id, _) = lifetime_ref.name {
+                self.regions.insert(def_id);
+            }
+        }
+    }
+
+    #[derive(Default)]
+    struct AllCollector {
+        regions: FxHashSet<LocalDefId>,
+    }
+
+    impl<'v> Visitor<'v> for AllCollector {
+        fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
+            if let hir::LifetimeName::Param(def_id, _) = lifetime_ref.name {
+                self.regions.insert(def_id);
+            }
+        }
+    }
+}
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
new file mode 100644
index 000000000..62843c651
--- /dev/null
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -0,0 +1,2089 @@
+//! This crate is responsible for the part of name resolution that doesn't require type checker.
+//!
+//! Module structure of the crate is built here.
+//! Paths in macros, imports, expressions, types, patterns are resolved here.
+//! Label and lifetime names are resolved here as well.
+//!
+//! Type-relative name resolution (methods, fields, associated items) happens in `rustc_typeck`.
+
+#![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
+#![feature(box_patterns)]
+#![feature(drain_filter)]
+#![feature(if_let_guard)]
+#![feature(iter_intersperse)]
+#![feature(let_chains)]
+#![feature(let_else)]
+#![feature(never_type)]
+#![recursion_limit = "256"]
+#![allow(rustdoc::private_intra_doc_links)]
+#![allow(rustc::potential_query_instability)]
+
+#[macro_use]
+extern crate tracing;
+
+pub use rustc_hir::def::{Namespace, PerNS};
+
+use rustc_arena::{DroplessArena, TypedArena};
+use rustc_ast::node_id::NodeMap;
+use rustc_ast::{self as ast, NodeId, CRATE_NODE_ID};
+use rustc_ast::{AngleBracketedArg, Crate, Expr, ExprKind, GenericArg, GenericArgs, LitKind, Path};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet};
+use rustc_data_structures::intern::Interned;
+use rustc_data_structures::sync::Lrc;
+use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed};
+use rustc_expand::base::{DeriveResolutions, SyntaxExtension, SyntaxExtensionKind};
+use rustc_hir::def::Namespace::*;
+use rustc_hir::def::{self, CtorOf, DefKind, LifetimeRes, PartialRes};
+use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId};
+use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE};
+use rustc_hir::definitions::{DefPathData, Definitions};
+use rustc_hir::TraitCandidate;
+use rustc_index::vec::IndexVec;
+use rustc_metadata::creader::{CStore, CrateLoader};
+use rustc_middle::metadata::ModChild;
+use rustc_middle::middle::privacy::AccessLevels;
+use rustc_middle::span_bug;
+use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::{self, DefIdTree, MainDefinition, RegisteredTools, ResolverOutputs};
+use rustc_query_system::ich::StableHashingContext;
+use rustc_session::cstore::{CrateStore, CrateStoreDyn, MetadataLoaderDyn};
+use rustc_session::lint::LintBuffer;
+use rustc_session::Session;
+use rustc_span::hygiene::{ExpnId, LocalExpnId, MacroKind, SyntaxContext, Transparency};
+use rustc_span::source_map::Spanned;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::{Span, DUMMY_SP};
+
+use smallvec::{smallvec, SmallVec};
+use std::cell::{Cell, RefCell};
+use std::collections::BTreeSet;
+use std::{cmp, fmt, ptr};
+use tracing::debug;
+
+use diagnostics::{ImportSuggestion, LabelSuggestion, Suggestion};
+use imports::{Import, ImportKind, ImportResolver, NameResolution};
+use late::{HasGenericParams, PathSource, PatternSource};
+use macros::{MacroRulesBinding, MacroRulesScope, MacroRulesScopeRef};
+
+use crate::access_levels::AccessLevelsVisitor;
+
+type Res = def::Res<NodeId>;
+
+mod access_levels;
+mod build_reduced_graph;
+mod check_unused;
+mod def_collector;
+mod diagnostics;
+mod ident;
+mod imports;
+mod late;
+mod macros;
+
+enum Weak {
+    Yes,
+    No,
+}
+
+#[derive(Copy, Clone, PartialEq, Debug)]
+pub enum Determinacy {
+    Determined,
+    Undetermined,
+}
+
+impl Determinacy {
+    fn determined(determined: bool) -> Determinacy {
+        if determined { Determinacy::Determined } else { Determinacy::Undetermined }
+    }
+}
+
+/// A specific scope in which a name can be looked up.
+/// This enum is currently used only for early resolution (imports and macros),
+/// but not for late resolution yet.
+#[derive(Clone, Copy)]
+enum Scope<'a> {
+    DeriveHelpers(LocalExpnId),
+    DeriveHelpersCompat,
+    MacroRules(MacroRulesScopeRef<'a>),
+    CrateRoot,
+    // The node ID is for reporting the `PROC_MACRO_DERIVE_RESOLUTION_FALLBACK`
+    // lint if it should be reported.
+    Module(Module<'a>, Option<NodeId>),
+    RegisteredAttrs,
+    MacroUsePrelude,
+    BuiltinAttrs,
+    ExternPrelude,
+    ToolPrelude,
+    StdLibPrelude,
+    BuiltinTypes,
+}
+
+/// Names from different contexts may want to visit different subsets of all specific scopes
+/// with different restrictions when looking up the resolution.
+/// This enum is currently used only for early resolution (imports and macros),
+/// but not for late resolution yet.
+#[derive(Clone, Copy)]
+enum ScopeSet<'a> {
+    /// All scopes with the given namespace.
+    All(Namespace, /*is_import*/ bool),
+    /// Crate root, then extern prelude (used for mixed 2015-2018 mode in macros).
+    AbsolutePath(Namespace),
+    /// All scopes with macro namespace and the given macro kind restriction.
+    Macro(MacroKind),
+    /// All scopes with the given namespace, used for partially performing late resolution.
+    /// The node id enables lints and is used for reporting them.
+    Late(Namespace, Module<'a>, Option<NodeId>),
+}
+
+/// Everything you need to know about a name's location to resolve it.
+/// Serves as a starting point for the scope visitor.
+/// This struct is currently used only for early resolution (imports and macros),
+/// but not for late resolution yet.
+#[derive(Clone, Copy, Debug)]
+pub struct ParentScope<'a> {
+    pub module: Module<'a>,
+    expansion: LocalExpnId,
+    pub macro_rules: MacroRulesScopeRef<'a>,
+    derives: &'a [ast::Path],
+}
+
+impl<'a> ParentScope<'a> {
+    /// Creates a parent scope with the passed argument used as the module scope component,
+    /// and other scope components set to default empty values.
+    pub fn module(module: Module<'a>, resolver: &Resolver<'a>) -> ParentScope<'a> {
+        ParentScope {
+            module,
+            expansion: LocalExpnId::ROOT,
+            macro_rules: resolver.arenas.alloc_macro_rules_scope(MacroRulesScope::Empty),
+            derives: &[],
+        }
+    }
+}
+
+#[derive(Copy, Debug, Clone)]
+enum ImplTraitContext {
+    Existential,
+    Universal(LocalDefId),
+}
+
+#[derive(Eq)]
+struct BindingError {
+    name: Symbol,
+    origin: BTreeSet<Span>,
+    target: BTreeSet<Span>,
+    could_be_path: bool,
+}
+
+impl PartialOrd for BindingError {
+    fn partial_cmp(&self, other: &BindingError) -> Option<cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl PartialEq for BindingError {
+    fn eq(&self, other: &BindingError) -> bool {
+        self.name == other.name
+    }
+}
+
+impl Ord for BindingError {
+    fn cmp(&self, other: &BindingError) -> cmp::Ordering {
+        self.name.cmp(&other.name)
+    }
+}
+
+enum ResolutionError<'a> {
+    /// Error E0401: can't use type or const parameters from outer function.
+    GenericParamsFromOuterFunction(Res, HasGenericParams),
+    /// Error E0403: the name is already used for a type or const parameter in this generic
+    /// parameter list.
+    NameAlreadyUsedInParameterList(Symbol, Span),
+    /// Error E0407: method is not a member of trait.
+    MethodNotMemberOfTrait(Ident, String, Option<Symbol>),
+    /// Error E0437: type is not a member of trait.
+    TypeNotMemberOfTrait(Ident, String, Option<Symbol>),
+    /// Error E0438: const is not a member of trait.
+    ConstNotMemberOfTrait(Ident, String, Option<Symbol>),
+    /// Error E0408: variable `{}` is not bound in all patterns.
+    VariableNotBoundInPattern(BindingError, ParentScope<'a>),
+    /// Error E0409: variable `{}` is bound in inconsistent ways within the same match arm.
+    VariableBoundWithDifferentMode(Symbol, Span),
+    /// Error E0415: identifier is bound more than once in this parameter list.
+    IdentifierBoundMoreThanOnceInParameterList(Symbol),
+    /// Error E0416: identifier is bound more than once in the same pattern.
+    IdentifierBoundMoreThanOnceInSamePattern(Symbol),
+    /// Error E0426: use of undeclared label.
+    UndeclaredLabel { name: Symbol, suggestion: Option<LabelSuggestion> },
+    /// Error E0429: `self` imports are only allowed within a `{ }` list.
+    SelfImportsOnlyAllowedWithin { root: bool, span_with_rename: Span },
+    /// Error E0430: `self` import can only appear once in the list.
+    SelfImportCanOnlyAppearOnceInTheList,
+    /// Error E0431: `self` import can only appear in an import list with a non-empty prefix.
+    SelfImportOnlyInImportListWithNonEmptyPrefix,
+    /// Error E0433: failed to resolve.
+    FailedToResolve { label: String, suggestion: Option<Suggestion> },
+    /// Error E0434: can't capture dynamic environment in a fn item.
+    CannotCaptureDynamicEnvironmentInFnItem,
+    /// Error E0435: attempt to use a non-constant value in a constant.
+    AttemptToUseNonConstantValueInConstant(
+        Ident,
+        /* suggestion */ &'static str,
+        /* current */ &'static str,
+    ),
+    /// Error E0530: `X` bindings cannot shadow `Y`s.
+    BindingShadowsSomethingUnacceptable {
+        shadowing_binding: PatternSource,
+        name: Symbol,
+        participle: &'static str,
+        article: &'static str,
+        shadowed_binding: Res,
+        shadowed_binding_span: Span,
+    },
+    /// Error E0128: generic parameters with a default cannot use forward-declared identifiers.
+    ForwardDeclaredGenericParam,
+    /// ERROR E0770: the type of const parameters must not depend on other generic parameters.
+    ParamInTyOfConstParam(Symbol),
+    /// generic parameters must not be used inside const evaluations.
+    ///
+    /// This error is only emitted when using `min_const_generics`.
+    ParamInNonTrivialAnonConst { name: Symbol, is_type: bool },
+    /// Error E0735: generic parameters with a default cannot use `Self`
+    SelfInGenericParamDefault,
+    /// Error E0767: use of unreachable label
+    UnreachableLabel { name: Symbol, definition_span: Span, suggestion: Option<LabelSuggestion> },
+    /// Error E0323, E0324, E0325: mismatch between trait item and impl item.
+    TraitImplMismatch {
+        name: Symbol,
+        kind: &'static str,
+        trait_path: String,
+        trait_item_span: Span,
+        code: rustc_errors::DiagnosticId,
+    },
+    /// Inline asm `sym` operand must refer to a `fn` or `static`.
+    InvalidAsmSym,
+}
+
+enum VisResolutionError<'a> {
+    Relative2018(Span, &'a ast::Path),
+    AncestorOnly(Span),
+    FailedToResolve(Span, String, Option<Suggestion>),
+    ExpectedFound(Span, String, Res),
+    Indeterminate(Span),
+    ModuleOnly(Span),
+}
+
+/// A minimal representation of a path segment. We use this in resolve because we synthesize 'path
+/// segments' which don't have the rest of an AST or HIR `PathSegment`.
+#[derive(Clone, Copy, Debug)]
+pub struct Segment {
+    ident: Ident,
+    id: Option<NodeId>,
+    /// Signals whether this `PathSegment` has generic arguments. Used to avoid providing
+    /// nonsensical suggestions.
+    has_generic_args: bool,
+    /// Signals whether this `PathSegment` has lifetime arguments.
+    has_lifetime_args: bool,
+    args_span: Span,
+}
+
+impl Segment {
+    fn from_path(path: &Path) -> Vec<Segment> {
+        path.segments.iter().map(|s| s.into()).collect()
+    }
+
+    fn from_ident(ident: Ident) -> Segment {
+        Segment {
+            ident,
+            id: None,
+            has_generic_args: false,
+            has_lifetime_args: false,
+            args_span: DUMMY_SP,
+        }
+    }
+
+    fn from_ident_and_id(ident: Ident, id: NodeId) -> Segment {
+        Segment {
+            ident,
+            id: Some(id),
+            has_generic_args: false,
+            has_lifetime_args: false,
+            args_span: DUMMY_SP,
+        }
+    }
+
+    fn names_to_string(segments: &[Segment]) -> String {
+        names_to_string(&segments.iter().map(|seg| seg.ident.name).collect::<Vec<_>>())
+    }
+}
+
+impl<'a> From<&'a ast::PathSegment> for Segment {
+    fn from(seg: &'a ast::PathSegment) -> Segment {
+        let has_generic_args = seg.args.is_some();
+        let (args_span, has_lifetime_args) = if let Some(args) = seg.args.as_deref() {
+            match args {
+                GenericArgs::AngleBracketed(args) => {
+                    let found_lifetimes = args
+                        .args
+                        .iter()
+                        .any(|arg| matches!(arg, AngleBracketedArg::Arg(GenericArg::Lifetime(_))));
+                    (args.span, found_lifetimes)
+                }
+                GenericArgs::Parenthesized(args) => (args.span, true),
+            }
+        } else {
+            (DUMMY_SP, false)
+        };
+        Segment {
+            ident: seg.ident,
+            id: Some(seg.id),
+            has_generic_args,
+            has_lifetime_args,
+            args_span,
+        }
+    }
+}
+
+/// An intermediate resolution result.
+///
+/// This refers to the thing referred by a name. The difference between `Res` and `Item` is that
+/// items are visible in their whole block, while `Res`es only from the place they are defined
+/// forward.
+#[derive(Debug)]
+enum LexicalScopeBinding<'a> {
+    Item(&'a NameBinding<'a>),
+    Res(Res),
+}
+
+impl<'a> LexicalScopeBinding<'a> {
+    fn res(self) -> Res {
+        match self {
+            LexicalScopeBinding::Item(binding) => binding.res(),
+            LexicalScopeBinding::Res(res) => res,
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+enum ModuleOrUniformRoot<'a> {
+    /// Regular module.
+    Module(Module<'a>),
+
+    /// Virtual module that denotes resolution in crate root with fallback to extern prelude.
+    CrateRootAndExternPrelude,
+
+    /// Virtual module that denotes resolution in extern prelude.
+    /// Used for paths starting with `::` on 2018 edition.
+    ExternPrelude,
+
+    /// Virtual module that denotes resolution in current scope.
+    /// Used only for resolving single-segment imports. The reason it exists is that import paths
+    /// are always split into two parts, the first of which should be some kind of module.
+    CurrentScope,
+}
+
+impl ModuleOrUniformRoot<'_> {
+    fn same_def(lhs: Self, rhs: Self) -> bool {
+        match (lhs, rhs) {
+            (ModuleOrUniformRoot::Module(lhs), ModuleOrUniformRoot::Module(rhs)) => {
+                ptr::eq(lhs, rhs)
+            }
+            (
+                ModuleOrUniformRoot::CrateRootAndExternPrelude,
+                ModuleOrUniformRoot::CrateRootAndExternPrelude,
+            )
+            | (ModuleOrUniformRoot::ExternPrelude, ModuleOrUniformRoot::ExternPrelude)
+            | (ModuleOrUniformRoot::CurrentScope, ModuleOrUniformRoot::CurrentScope) => true,
+            _ => false,
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
+enum PathResult<'a> {
+    Module(ModuleOrUniformRoot<'a>),
+    NonModule(PartialRes),
+    Indeterminate,
+    Failed {
+        span: Span,
+        label: String,
+        suggestion: Option<Suggestion>,
+        is_error_from_last_segment: bool,
+    },
+}
+
+impl<'a> PathResult<'a> {
+    fn failed(
+        span: Span,
+        is_error_from_last_segment: bool,
+        finalize: bool,
+        label_and_suggestion: impl FnOnce() -> (String, Option<Suggestion>),
+    ) -> PathResult<'a> {
+        let (label, suggestion) =
+            if finalize { label_and_suggestion() } else { (String::new(), None) };
+        PathResult::Failed { span, label, suggestion, is_error_from_last_segment }
+    }
+}
+
+#[derive(Debug)]
+enum ModuleKind {
+    /// An anonymous module; e.g., just a block.
+    ///
+    /// ```
+    /// fn main() {
+    ///     fn f() {} // (1)
+    ///     { // This is an anonymous module
+    ///         f(); // This resolves to (2) as we are inside the block.
+    ///         fn f() {} // (2)
+    ///     }
+    ///     f(); // Resolves to (1)
+    /// }
+    /// ```
+    Block,
+    /// Any module with a name.
+    ///
+    /// This could be:
+    ///
+    /// * A normal module – either `mod from_file;` or `mod from_block { }` –
+    ///   or the crate root (which is conceptually a top-level module).
+    ///   Note that the crate root's [name][Self::name] will be [`kw::Empty`].
+    /// * A trait or an enum (it implicitly contains associated types, methods and variant
+    ///   constructors).
+    Def(DefKind, DefId, Symbol),
+}
+
+impl ModuleKind {
+    /// Get name of the module.
+    pub fn name(&self) -> Option<Symbol> {
+        match self {
+            ModuleKind::Block => None,
+            ModuleKind::Def(.., name) => Some(*name),
+        }
+    }
+}
+
+/// A key that identifies a binding in a given `Module`.
+///
+/// Multiple bindings in the same module can have the same key (in a valid
+/// program) if all but one of them come from glob imports.
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+struct BindingKey {
+    /// The identifier for the binding, always the `normalize_to_macros_2_0` version of the
+    /// identifier.
+    ident: Ident,
+    ns: Namespace,
+    /// 0 if ident is not `_`, otherwise a value that's unique to the specific
+    /// `_` in the expanded AST that introduced this binding.
+    disambiguator: u32,
+}
+
+type Resolutions<'a> = RefCell<FxIndexMap<BindingKey, &'a RefCell<NameResolution<'a>>>>;
+
+/// One node in the tree of modules.
+///
+/// Note that a "module" in resolve is broader than a `mod` that you declare in Rust code. It may be one of these:
+///
+/// * `mod`
+/// * crate root (aka, top-level anonymous module)
+/// * `enum`
+/// * `trait`
+/// * curly-braced block with statements
+///
+/// You can use [`ModuleData::kind`] to determine the kind of module this is.
+pub struct ModuleData<'a> {
+    /// The direct parent module (it may not be a `mod`, however).
+    parent: Option<Module<'a>>,
+    /// What kind of module this is, because this may not be a `mod`.
+    kind: ModuleKind,
+
+    /// Mapping between names and their (possibly in-progress) resolutions in this module.
+    /// Resolutions in modules from other crates are not populated until accessed.
+    lazy_resolutions: Resolutions<'a>,
+    /// True if this is a module from other crate that needs to be populated on access.
+    populate_on_access: Cell<bool>,
+
+    /// Macro invocations that can expand into items in this module.
+    unexpanded_invocations: RefCell<FxHashSet<LocalExpnId>>,
+
+    /// Whether `#[no_implicit_prelude]` is active.
+    no_implicit_prelude: bool,
+
+    glob_importers: RefCell<Vec<&'a Import<'a>>>,
+    globs: RefCell<Vec<&'a Import<'a>>>,
+
+    /// Used to memoize the traits in this module for faster searches through all traits in scope.
+    traits: RefCell<Option<Box<[(Ident, &'a NameBinding<'a>)]>>>,
+
+    /// Span of the module itself. Used for error reporting.
+    span: Span,
+
+    expansion: ExpnId,
+}
+
+type Module<'a> = &'a ModuleData<'a>;
+
+impl<'a> ModuleData<'a> {
+    fn new(
+        parent: Option<Module<'a>>,
+        kind: ModuleKind,
+        expansion: ExpnId,
+        span: Span,
+        no_implicit_prelude: bool,
+    ) -> Self {
+        let is_foreign = match kind {
+            ModuleKind::Def(_, def_id, _) => !def_id.is_local(),
+            ModuleKind::Block => false,
+        };
+        ModuleData {
+            parent,
+            kind,
+            lazy_resolutions: Default::default(),
+            populate_on_access: Cell::new(is_foreign),
+            unexpanded_invocations: Default::default(),
+            no_implicit_prelude,
+            glob_importers: RefCell::new(Vec::new()),
+            globs: RefCell::new(Vec::new()),
+            traits: RefCell::new(None),
+            span,
+            expansion,
+        }
+    }
+
+    fn for_each_child<R, F>(&'a self, resolver: &mut R, mut f: F)
+    where
+        R: AsMut<Resolver<'a>>,
+        F: FnMut(&mut R, Ident, Namespace, &'a NameBinding<'a>),
+    {
+        for (key, name_resolution) in resolver.as_mut().resolutions(self).borrow().iter() {
+            if let Some(binding) = name_resolution.borrow().binding {
+                f(resolver, key.ident, key.ns, binding);
+            }
+        }
+    }
+
+    /// This modifies `self` in place. The traits will be stored in `self.traits`.
+    fn ensure_traits<R>(&'a self, resolver: &mut R)
+    where
+        R: AsMut<Resolver<'a>>,
+    {
+        let mut traits = self.traits.borrow_mut();
+        if traits.is_none() {
+            let mut collected_traits = Vec::new();
+            self.for_each_child(resolver, |_, name, ns, binding| {
+                if ns != TypeNS {
+                    return;
+                }
+                if let Res::Def(DefKind::Trait | DefKind::TraitAlias, _) = binding.res() {
+                    collected_traits.push((name, binding))
+                }
+            });
+            *traits = Some(collected_traits.into_boxed_slice());
+        }
+    }
+
+    fn res(&self) -> Option<Res> {
+        match self.kind {
+            ModuleKind::Def(kind, def_id, _) => Some(Res::Def(kind, def_id)),
+            _ => None,
+        }
+    }
+
+    // Public for rustdoc.
+    pub fn def_id(&self) -> DefId {
+        self.opt_def_id().expect("`ModuleData::def_id` is called on a block module")
+    }
+
+    fn opt_def_id(&self) -> Option<DefId> {
+        match self.kind {
+            ModuleKind::Def(_, def_id, _) => Some(def_id),
+            _ => None,
+        }
+    }
+
+    // `self` resolves to the first module ancestor that `is_normal`.
+    fn is_normal(&self) -> bool {
+        matches!(self.kind, ModuleKind::Def(DefKind::Mod, _, _))
+    }
+
+    fn is_trait(&self) -> bool {
+        matches!(self.kind, ModuleKind::Def(DefKind::Trait, _, _))
+    }
+
+    fn nearest_item_scope(&'a self) -> Module<'a> {
+        match self.kind {
+            ModuleKind::Def(DefKind::Enum | DefKind::Trait, ..) => {
+                self.parent.expect("enum or trait module without a parent")
+            }
+            _ => self,
+        }
+    }
+
+    /// The [`DefId`] of the nearest `mod` item ancestor (which may be this module).
+    /// This may be the crate root.
+    fn nearest_parent_mod(&self) -> DefId {
+        match self.kind {
+            ModuleKind::Def(DefKind::Mod, def_id, _) => def_id,
+            _ => self.parent.expect("non-root module without parent").nearest_parent_mod(),
+        }
+    }
+
+    fn is_ancestor_of(&self, mut other: &Self) -> bool {
+        while !ptr::eq(self, other) {
+            if let Some(parent) = other.parent {
+                other = parent;
+            } else {
+                return false;
+            }
+        }
+        true
+    }
+}
+
+impl<'a> fmt::Debug for ModuleData<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:?}", self.res())
+    }
+}
+
+/// Records a possibly-private value, type, or module definition.
+#[derive(Clone, Debug)]
+pub struct NameBinding<'a> {
+    kind: NameBindingKind<'a>,
+    ambiguity: Option<(&'a NameBinding<'a>, AmbiguityKind)>,
+    expansion: LocalExpnId,
+    span: Span,
+    vis: ty::Visibility,
+}
+
+pub trait ToNameBinding<'a> {
+    fn to_name_binding(self, arenas: &'a ResolverArenas<'a>) -> &'a NameBinding<'a>;
+}
+
+impl<'a> ToNameBinding<'a> for &'a NameBinding<'a> {
+    fn to_name_binding(self, _: &'a ResolverArenas<'a>) -> &'a NameBinding<'a> {
+        self
+    }
+}
+
+#[derive(Clone, Debug)]
+enum NameBindingKind<'a> {
+    Res(Res, /* is_macro_export */ bool),
+    Module(Module<'a>),
+    Import { binding: &'a NameBinding<'a>, import: &'a Import<'a>, used: Cell<bool> },
+}
+
+impl<'a> NameBindingKind<'a> {
+    /// Is this a name binding of an import?
+    fn is_import(&self) -> bool {
+        matches!(*self, NameBindingKind::Import { .. })
+    }
+}
+
+struct PrivacyError<'a> {
+    ident: Ident,
+    binding: &'a NameBinding<'a>,
+    dedup_span: Span,
+}
+
+struct UseError<'a> {
+    err: DiagnosticBuilder<'a, ErrorGuaranteed>,
+    /// Candidates which user could `use` to access the missing type.
+    candidates: Vec<ImportSuggestion>,
+    /// The `DefId` of the module to place the use-statements in.
+    def_id: DefId,
+    /// Whether the diagnostic should say "instead" (as in `consider importing ... instead`).
+    instead: bool,
+    /// Extra free-form suggestion.
+    suggestion: Option<(Span, &'static str, String, Applicability)>,
+    /// Path `Segment`s at the place of use that failed. Used for accurate suggestion after telling
+    /// the user to import the item directly.
+    path: Vec<Segment>,
+}
+
+#[derive(Clone, Copy, PartialEq, Debug)]
+enum AmbiguityKind {
+    Import,
+    BuiltinAttr,
+    DeriveHelper,
+    MacroRulesVsModularized,
+    GlobVsOuter,
+    GlobVsGlob,
+    GlobVsExpanded,
+    MoreExpandedVsOuter,
+}
+
+impl AmbiguityKind {
+    fn descr(self) -> &'static str {
+        match self {
+            AmbiguityKind::Import => "multiple potential import sources",
+            AmbiguityKind::BuiltinAttr => "a name conflict with a builtin attribute",
+            AmbiguityKind::DeriveHelper => "a name conflict with a derive helper attribute",
+            AmbiguityKind::MacroRulesVsModularized => {
+                "a conflict between a `macro_rules` name and a non-`macro_rules` name from another module"
+            }
+            AmbiguityKind::GlobVsOuter => {
+                "a conflict between a name from a glob import and an outer scope during import or macro resolution"
+            }
+            AmbiguityKind::GlobVsGlob => "multiple glob imports of a name in the same module",
+            AmbiguityKind::GlobVsExpanded => {
+                "a conflict between a name from a glob import and a macro-expanded name in the same module during import or macro resolution"
+            }
+            AmbiguityKind::MoreExpandedVsOuter => {
+                "a conflict between a macro-expanded name and a less macro-expanded name from outer scope during import or macro resolution"
+            }
+        }
+    }
+}
+
+/// Miscellaneous bits of metadata for better ambiguity error reporting.
+#[derive(Clone, Copy, PartialEq)]
+enum AmbiguityErrorMisc {
+    SuggestCrate,
+    SuggestSelf,
+    FromPrelude,
+    None,
+}
+
+struct AmbiguityError<'a> {
+    kind: AmbiguityKind,
+    ident: Ident,
+    b1: &'a NameBinding<'a>,
+    b2: &'a NameBinding<'a>,
+    misc1: AmbiguityErrorMisc,
+    misc2: AmbiguityErrorMisc,
+}
+
+impl<'a> NameBinding<'a> {
+    fn module(&self) -> Option<Module<'a>> {
+        match self.kind {
+            NameBindingKind::Module(module) => Some(module),
+            NameBindingKind::Import { binding, .. } => binding.module(),
+            _ => None,
+        }
+    }
+
+    fn res(&self) -> Res {
+        match self.kind {
+            NameBindingKind::Res(res, _) => res,
+            NameBindingKind::Module(module) => module.res().unwrap(),
+            NameBindingKind::Import { binding, .. } => binding.res(),
+        }
+    }
+
+    fn is_ambiguity(&self) -> bool {
+        self.ambiguity.is_some()
+            || match self.kind {
+                NameBindingKind::Import { binding, .. } => binding.is_ambiguity(),
+                _ => false,
+            }
+    }
+
+    fn is_possibly_imported_variant(&self) -> bool {
+        match self.kind {
+            NameBindingKind::Import { binding, .. } => binding.is_possibly_imported_variant(),
+            NameBindingKind::Res(
+                Res::Def(DefKind::Variant | DefKind::Ctor(CtorOf::Variant, ..), _),
+                _,
+            ) => true,
+            NameBindingKind::Res(..) | NameBindingKind::Module(..) => false,
+        }
+    }
+
+    fn is_extern_crate(&self) -> bool {
+        match self.kind {
+            NameBindingKind::Import {
+                import: &Import { kind: ImportKind::ExternCrate { .. }, .. },
+                ..
+            } => true,
+            NameBindingKind::Module(&ModuleData {
+                kind: ModuleKind::Def(DefKind::Mod, def_id, _),
+                ..
+            }) => def_id.is_crate_root(),
+            _ => false,
+        }
+    }
+
+    fn is_import(&self) -> bool {
+        matches!(self.kind, NameBindingKind::Import { .. })
+    }
+
+    fn is_glob_import(&self) -> bool {
+        match self.kind {
+            NameBindingKind::Import { import, .. } => import.is_glob(),
+            _ => false,
+        }
+    }
+
+    fn is_importable(&self) -> bool {
+        !matches!(
+            self.res(),
+            Res::Def(DefKind::AssocConst | DefKind::AssocFn | DefKind::AssocTy, _)
+        )
+    }
+
+    fn macro_kind(&self) -> Option<MacroKind> {
+        self.res().macro_kind()
+    }
+
+    // Suppose that we resolved macro invocation with `invoc_parent_expansion` to binding `binding`
+    // at some expansion round `max(invoc, binding)` when they both emerged from macros.
+    // Then this function returns `true` if `self` may emerge from a macro *after* that
+    // in some later round and screw up our previously found resolution.
+    // See more detailed explanation in
+    // https://github.com/rust-lang/rust/pull/53778#issuecomment-419224049
+    fn may_appear_after(
+        &self,
+        invoc_parent_expansion: LocalExpnId,
+        binding: &NameBinding<'_>,
+    ) -> bool {
+        // self > max(invoc, binding) => !(self <= invoc || self <= binding)
+        // Expansions are partially ordered, so "may appear after" is an inversion of
+        // "certainly appears before or simultaneously" and includes unordered cases.
+        let self_parent_expansion = self.expansion;
+        let other_parent_expansion = binding.expansion;
+        let certainly_before_other_or_simultaneously =
+            other_parent_expansion.is_descendant_of(self_parent_expansion);
+        let certainly_before_invoc_or_simultaneously =
+            invoc_parent_expansion.is_descendant_of(self_parent_expansion);
+        !(certainly_before_other_or_simultaneously || certainly_before_invoc_or_simultaneously)
+    }
+}
+
+#[derive(Debug, Default, Clone)]
+pub struct ExternPreludeEntry<'a> {
+    extern_crate_item: Option<&'a NameBinding<'a>>,
+    pub introduced_by_item: bool,
+}
+
+/// Used for better errors for E0773
+enum BuiltinMacroState {
+    NotYetSeen(SyntaxExtensionKind),
+    AlreadySeen(Span),
+}
+
+struct DeriveData {
+    resolutions: DeriveResolutions,
+    helper_attrs: Vec<(usize, Ident)>,
+    has_derive_copy: bool,
+}
+
+#[derive(Clone)]
+struct MacroData {
+    ext: Lrc<SyntaxExtension>,
+    macro_rules: bool,
+}
+
+/// The main resolver class.
+///
+/// This is the visitor that walks the whole crate.
+pub struct Resolver<'a> {
+    session: &'a Session,
+
+    definitions: Definitions,
+    /// Item with a given `LocalDefId` was defined during macro expansion with ID `ExpnId`.
+    expn_that_defined: FxHashMap<LocalDefId, ExpnId>,
+    /// Reference span for definitions.
+    source_span: IndexVec<LocalDefId, Span>,
+
+    graph_root: Module<'a>,
+
+    prelude: Option<Module<'a>>,
+    extern_prelude: FxHashMap<Ident, ExternPreludeEntry<'a>>,
+
+    /// N.B., this is used only for better diagnostics, not name resolution itself.
+    has_self: FxHashSet<DefId>,
+
+    /// Names of fields of an item `DefId` accessible with dot syntax.
+    /// Used for hints during error reporting.
+    field_names: FxHashMap<DefId, Vec<Spanned<Symbol>>>,
+
+    /// All imports known to succeed or fail.
+    determined_imports: Vec<&'a Import<'a>>,
+
+    /// All non-determined imports.
+    indeterminate_imports: Vec<&'a Import<'a>>,
+
+    // Spans for local variables found during pattern resolution.
+    // Used for suggestions during error reporting.
+    pat_span_map: NodeMap<Span>,
+
+    /// Resolutions for nodes that have a single resolution.
+    partial_res_map: NodeMap<PartialRes>,
+    /// Resolutions for import nodes, which have multiple resolutions in different namespaces.
+    import_res_map: NodeMap<PerNS<Option<Res>>>,
+    /// Resolutions for labels (node IDs of their corresponding blocks or loops).
+    label_res_map: NodeMap<NodeId>,
+    /// Resolutions for lifetimes.
+    lifetimes_res_map: NodeMap<LifetimeRes>,
+    /// Mapping from generics `def_id`s to TAIT generics `def_id`s.
+    /// For each captured lifetime (e.g., 'a), we create a new lifetime parameter that is a generic
+    /// defined on the TAIT, so we have type Foo<'a1> = ... and we establish a mapping in this
+    /// field from the original parameter 'a to the new parameter 'a1.
+    generics_def_id_map: Vec<FxHashMap<LocalDefId, LocalDefId>>,
+    /// Lifetime parameters that lowering will have to introduce.
+    extra_lifetime_params_map: NodeMap<Vec<(Ident, NodeId, LifetimeRes)>>,
+
+    /// `CrateNum` resolutions of `extern crate` items.
+    extern_crate_map: FxHashMap<LocalDefId, CrateNum>,
+    reexport_map: FxHashMap<LocalDefId, Vec<ModChild>>,
+    trait_map: NodeMap<Vec<TraitCandidate>>,
+
+    /// A map from nodes to anonymous modules.
+    /// Anonymous modules are pseudo-modules that are implicitly created around items
+    /// contained within blocks.
+    ///
+    /// For example, if we have this:
+    ///
+    ///  fn f() {
+    ///      fn g() {
+    ///          ...
+    ///      }
+    ///  }
+    ///
+    /// There will be an anonymous module created around `g` with the ID of the
+    /// entry block for `f`.
+    block_map: NodeMap<Module<'a>>,
+    /// A fake module that contains no definition and no prelude. Used so that
+    /// some AST passes can generate identifiers that only resolve to local or
+    /// language items.
+    empty_module: Module<'a>,
+    module_map: FxHashMap<DefId, Module<'a>>,
+    binding_parent_modules: FxHashMap<Interned<'a, NameBinding<'a>>, Module<'a>>,
+    underscore_disambiguator: u32,
+
+    /// Maps glob imports to the names of items actually imported.
+    glob_map: FxHashMap<LocalDefId, FxHashSet<Symbol>>,
+    /// Visibilities in "lowered" form, for all entities that have them.
+    visibilities: FxHashMap<LocalDefId, ty::Visibility>,
+    has_pub_restricted: bool,
+    used_imports: FxHashSet<NodeId>,
+    maybe_unused_trait_imports: FxIndexSet<LocalDefId>,
+    maybe_unused_extern_crates: Vec<(LocalDefId, Span)>,
+
+    /// Privacy errors are delayed until the end in order to deduplicate them.
+    privacy_errors: Vec<PrivacyError<'a>>,
+    /// Ambiguity errors are delayed for deduplication.
+    ambiguity_errors: Vec<AmbiguityError<'a>>,
+    /// `use` injections are delayed for better placement and deduplication.
+    use_injections: Vec<UseError<'a>>,
+    /// Crate-local macro expanded `macro_export` referred to by a module-relative path.
+    macro_expanded_macro_export_errors: BTreeSet<(Span, Span)>,
+
+    arenas: &'a ResolverArenas<'a>,
+    dummy_binding: &'a NameBinding<'a>,
+
+    crate_loader: CrateLoader<'a>,
+    macro_names: FxHashSet<Ident>,
+    builtin_macros: FxHashMap<Symbol, BuiltinMacroState>,
+    /// A small map keeping true kinds of built-in macros that appear to be fn-like on
+    /// the surface (`macro` items in libcore), but are actually attributes or derives.
+    builtin_macro_kinds: FxHashMap<LocalDefId, MacroKind>,
+    registered_attrs: FxHashSet<Ident>,
+    registered_tools: RegisteredTools,
+    macro_use_prelude: FxHashMap<Symbol, &'a NameBinding<'a>>,
+    macro_map: FxHashMap<DefId, MacroData>,
+    dummy_ext_bang: Lrc<SyntaxExtension>,
+    dummy_ext_derive: Lrc<SyntaxExtension>,
+    non_macro_attr: Lrc<SyntaxExtension>,
+    local_macro_def_scopes: FxHashMap<LocalDefId, Module<'a>>,
+    ast_transform_scopes: FxHashMap<LocalExpnId, Module<'a>>,
+    unused_macros: FxHashMap<LocalDefId, (NodeId, Ident)>,
+    unused_macro_rules: FxHashMap<(LocalDefId, usize), (Ident, Span)>,
+    proc_macro_stubs: FxHashSet<LocalDefId>,
+    /// Traces collected during macro resolution and validated when it's complete.
+    single_segment_macro_resolutions:
+        Vec<(Ident, MacroKind, ParentScope<'a>, Option<&'a NameBinding<'a>>)>,
+    multi_segment_macro_resolutions:
+        Vec<(Vec<Segment>, Span, MacroKind, ParentScope<'a>, Option<Res>)>,
+    builtin_attrs: Vec<(Ident, ParentScope<'a>)>,
+    /// `derive(Copy)` marks items they are applied to so they are treated specially later.
+    /// Derive macros cannot modify the item themselves and have to store the markers in the global
+    /// context, so they attach the markers to derive container IDs using this resolver table.
+    containers_deriving_copy: FxHashSet<LocalExpnId>,
+    /// Parent scopes in which the macros were invoked.
+    /// FIXME: `derives` are missing in these parent scopes and need to be taken from elsewhere.
+    invocation_parent_scopes: FxHashMap<LocalExpnId, ParentScope<'a>>,
+    /// `macro_rules` scopes *produced* by expanding the macro invocations,
+    /// include all the `macro_rules` items and other invocations generated by them.
+    output_macro_rules_scopes: FxHashMap<LocalExpnId, MacroRulesScopeRef<'a>>,
+    /// `macro_rules` scopes produced by `macro_rules` item definitions.
+    macro_rules_scopes: FxHashMap<LocalDefId, MacroRulesScopeRef<'a>>,
+    /// Helper attributes that are in scope for the given expansion.
+    helper_attrs: FxHashMap<LocalExpnId, Vec<Ident>>,
+    /// Ready or in-progress results of resolving paths inside the `#[derive(...)]` attribute
+    /// with the given `ExpnId`.
+    derive_data: FxHashMap<LocalExpnId, DeriveData>,
+
+    /// Avoid duplicated errors for "name already defined".
+    name_already_seen: FxHashMap<Symbol, Span>,
+
+    potentially_unused_imports: Vec<&'a Import<'a>>,
+
+    /// Table for mapping struct IDs into struct constructor IDs,
+    /// it's not used during normal resolution, only for better error reporting.
+    /// Also includes of list of each fields visibility
+    struct_constructors: DefIdMap<(Res, ty::Visibility, Vec<ty::Visibility>)>,
+
+    /// Features enabled for this crate.
+    active_features: FxHashSet<Symbol>,
+
+    lint_buffer: LintBuffer,
+
+    next_node_id: NodeId,
+
+    node_id_to_def_id: FxHashMap<ast::NodeId, LocalDefId>,
+    def_id_to_node_id: IndexVec<LocalDefId, ast::NodeId>,
+
+    /// Indices of unnamed struct or variant fields with unresolved attributes.
+    placeholder_field_indices: FxHashMap<NodeId, usize>,
+    /// When collecting definitions from an AST fragment produced by a macro invocation `ExpnId`
+    /// we know what parent node that fragment should be attached to thanks to this table,
+    /// and how the `impl Trait` fragments were introduced.
+    invocation_parents: FxHashMap<LocalExpnId, (LocalDefId, ImplTraitContext)>,
+
+    /// Some way to know that we are in a *trait* impl in `visit_assoc_item`.
+    /// FIXME: Replace with a more general AST map (together with some other fields).
+    trait_impl_items: FxHashSet<LocalDefId>,
+
+    legacy_const_generic_args: FxHashMap<DefId, Option<Vec<usize>>>,
+    /// Amount of lifetime parameters for each item in the crate.
+    item_generics_num_lifetimes: FxHashMap<LocalDefId, usize>,
+
+    main_def: Option<MainDefinition>,
+    trait_impls: FxIndexMap<DefId, Vec<LocalDefId>>,
+    /// A list of proc macro LocalDefIds, written out in the order in which
+    /// they are declared in the static array generated by proc_macro_harness.
+    proc_macros: Vec<NodeId>,
+    confused_type_with_std_module: FxHashMap<Span, Span>,
+
+    access_levels: AccessLevels,
+}
+
+/// Nothing really interesting here; it just provides memory for the rest of the crate.
+#[derive(Default)]
+pub struct ResolverArenas<'a> {
+    modules: TypedArena<ModuleData<'a>>,
+    local_modules: RefCell<Vec<Module<'a>>>,
+    imports: TypedArena<Import<'a>>,
+    name_resolutions: TypedArena<RefCell<NameResolution<'a>>>,
+    ast_paths: TypedArena<ast::Path>,
+    dropless: DroplessArena,
+}
+
+impl<'a> ResolverArenas<'a> {
+    fn new_module(
+        &'a self,
+        parent: Option<Module<'a>>,
+        kind: ModuleKind,
+        expn_id: ExpnId,
+        span: Span,
+        no_implicit_prelude: bool,
+        module_map: &mut FxHashMap<DefId, Module<'a>>,
+    ) -> Module<'a> {
+        let module =
+            self.modules.alloc(ModuleData::new(parent, kind, expn_id, span, no_implicit_prelude));
+        let def_id = module.opt_def_id();
+        if def_id.map_or(true, |def_id| def_id.is_local()) {
+            self.local_modules.borrow_mut().push(module);
+        }
+        if let Some(def_id) = def_id {
+            module_map.insert(def_id, module);
+        }
+        module
+    }
+    fn local_modules(&'a self) -> std::cell::Ref<'a, Vec<Module<'a>>> {
+        self.local_modules.borrow()
+    }
+    fn alloc_name_binding(&'a self, name_binding: NameBinding<'a>) -> &'a NameBinding<'a> {
+        self.dropless.alloc(name_binding)
+    }
+    fn alloc_import(&'a self, import: Import<'a>) -> &'a Import<'_> {
+        self.imports.alloc(import)
+    }
+    fn alloc_name_resolution(&'a self) -> &'a RefCell<NameResolution<'a>> {
+        self.name_resolutions.alloc(Default::default())
+    }
+    fn alloc_macro_rules_scope(&'a self, scope: MacroRulesScope<'a>) -> MacroRulesScopeRef<'a> {
+        Interned::new_unchecked(self.dropless.alloc(Cell::new(scope)))
+    }
+    fn alloc_macro_rules_binding(
+        &'a self,
+        binding: MacroRulesBinding<'a>,
+    ) -> &'a MacroRulesBinding<'a> {
+        self.dropless.alloc(binding)
+    }
+    fn alloc_ast_paths(&'a self, paths: &[ast::Path]) -> &'a [ast::Path] {
+        self.ast_paths.alloc_from_iter(paths.iter().cloned())
+    }
+    fn alloc_pattern_spans(&'a self, spans: impl Iterator<Item = Span>) -> &'a [Span] {
+        self.dropless.alloc_from_iter(spans)
+    }
+}
+
+impl<'a> AsMut<Resolver<'a>> for Resolver<'a> {
+    fn as_mut(&mut self) -> &mut Resolver<'a> {
+        self
+    }
+}
+
+impl<'a, 'b> DefIdTree for &'a Resolver<'b> {
+    #[inline]
+    fn opt_parent(self, id: DefId) -> Option<DefId> {
+        match id.as_local() {
+            Some(id) => self.definitions.def_key(id).parent,
+            None => self.cstore().def_key(id).parent,
+        }
+        .map(|index| DefId { index, ..id })
+    }
+}
+
+impl Resolver<'_> {
+    fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
+        self.node_id_to_def_id.get(&node).copied()
+    }
+
+    pub fn local_def_id(&self, node: NodeId) -> LocalDefId {
+        self.opt_local_def_id(node).unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
+    }
+
+    /// Adds a definition with a parent definition.
+    fn create_def(
+        &mut self,
+        parent: LocalDefId,
+        node_id: ast::NodeId,
+        data: DefPathData,
+        expn_id: ExpnId,
+        span: Span,
+    ) -> LocalDefId {
+        assert!(
+            !self.node_id_to_def_id.contains_key(&node_id),
+            "adding a def'n for node-id {:?} and data {:?} but a previous def'n exists: {:?}",
+            node_id,
+            data,
+            self.definitions.def_key(self.node_id_to_def_id[&node_id]),
+        );
+
+        let def_id = self.definitions.create_def(parent, data);
+
+        // Create the definition.
+        if expn_id != ExpnId::root() {
+            self.expn_that_defined.insert(def_id, expn_id);
+        }
+
+        // A relative span's parent must be an absolute span.
+        debug_assert_eq!(span.data_untracked().parent, None);
+        let _id = self.source_span.push(span);
+        debug_assert_eq!(_id, def_id);
+
+        // Some things for which we allocate `LocalDefId`s don't correspond to
+        // anything in the AST, so they don't have a `NodeId`. For these cases
+        // we don't need a mapping from `NodeId` to `LocalDefId`.
+        if node_id != ast::DUMMY_NODE_ID {
+            debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
+            self.node_id_to_def_id.insert(node_id, def_id);
+        }
+        assert_eq!(self.def_id_to_node_id.push(node_id), def_id);
+
+        def_id
+    }
+
+    fn item_generics_num_lifetimes(&self, def_id: DefId) -> usize {
+        if let Some(def_id) = def_id.as_local() {
+            self.item_generics_num_lifetimes[&def_id]
+        } else {
+            self.cstore().item_generics_num_lifetimes(def_id, self.session)
+        }
+    }
+}
+
+impl<'a> Resolver<'a> {
+    pub fn new(
+        session: &'a Session,
+        krate: &Crate,
+        crate_name: &str,
+        metadata_loader: Box<MetadataLoaderDyn>,
+        arenas: &'a ResolverArenas<'a>,
+    ) -> Resolver<'a> {
+        let root_def_id = CRATE_DEF_ID.to_def_id();
+        let mut module_map = FxHashMap::default();
+        let graph_root = arenas.new_module(
+            None,
+            ModuleKind::Def(DefKind::Mod, root_def_id, kw::Empty),
+            ExpnId::root(),
+            krate.spans.inner_span,
+            session.contains_name(&krate.attrs, sym::no_implicit_prelude),
+            &mut module_map,
+        );
+        let empty_module = arenas.new_module(
+            None,
+            ModuleKind::Def(DefKind::Mod, root_def_id, kw::Empty),
+            ExpnId::root(),
+            DUMMY_SP,
+            true,
+            &mut FxHashMap::default(),
+        );
+
+        let definitions = Definitions::new(session.local_stable_crate_id());
+
+        let mut visibilities = FxHashMap::default();
+        visibilities.insert(CRATE_DEF_ID, ty::Visibility::Public);
+
+        let mut def_id_to_node_id = IndexVec::default();
+        assert_eq!(def_id_to_node_id.push(CRATE_NODE_ID), CRATE_DEF_ID);
+        let mut node_id_to_def_id = FxHashMap::default();
+        node_id_to_def_id.insert(CRATE_NODE_ID, CRATE_DEF_ID);
+
+        let mut invocation_parents = FxHashMap::default();
+        invocation_parents.insert(LocalExpnId::ROOT, (CRATE_DEF_ID, ImplTraitContext::Existential));
+
+        let mut source_span = IndexVec::default();
+        let _id = source_span.push(krate.spans.inner_span);
+        debug_assert_eq!(_id, CRATE_DEF_ID);
+
+        let mut extern_prelude: FxHashMap<Ident, ExternPreludeEntry<'_>> = session
+            .opts
+            .externs
+            .iter()
+            .filter(|(_, entry)| entry.add_prelude)
+            .map(|(name, _)| (Ident::from_str(name), Default::default()))
+            .collect();
+
+        if !session.contains_name(&krate.attrs, sym::no_core) {
+            extern_prelude.insert(Ident::with_dummy_span(sym::core), Default::default());
+            if !session.contains_name(&krate.attrs, sym::no_std) {
+                extern_prelude.insert(Ident::with_dummy_span(sym::std), Default::default());
+            }
+        }
+
+        let (registered_attrs, registered_tools) =
+            macros::registered_attrs_and_tools(session, &krate.attrs);
+
+        let features = session.features_untracked();
+
+        let mut resolver = Resolver {
+            session,
+
+            definitions,
+            expn_that_defined: Default::default(),
+            source_span,
+
+            // The outermost module has def ID 0; this is not reflected in the
+            // AST.
+            graph_root,
+            prelude: None,
+            extern_prelude,
+
+            has_self: FxHashSet::default(),
+            field_names: FxHashMap::default(),
+
+            determined_imports: Vec::new(),
+            indeterminate_imports: Vec::new(),
+
+            pat_span_map: Default::default(),
+            partial_res_map: Default::default(),
+            import_res_map: Default::default(),
+            label_res_map: Default::default(),
+            lifetimes_res_map: Default::default(),
+            generics_def_id_map: Vec::new(),
+            extra_lifetime_params_map: Default::default(),
+            extern_crate_map: Default::default(),
+            reexport_map: FxHashMap::default(),
+            trait_map: NodeMap::default(),
+            underscore_disambiguator: 0,
+            empty_module,
+            module_map,
+            block_map: Default::default(),
+            binding_parent_modules: FxHashMap::default(),
+            ast_transform_scopes: FxHashMap::default(),
+
+            glob_map: Default::default(),
+            visibilities,
+            has_pub_restricted: false,
+            used_imports: FxHashSet::default(),
+            maybe_unused_trait_imports: Default::default(),
+            maybe_unused_extern_crates: Vec::new(),
+
+            privacy_errors: Vec::new(),
+            ambiguity_errors: Vec::new(),
+            use_injections: Vec::new(),
+            macro_expanded_macro_export_errors: BTreeSet::new(),
+
+            arenas,
+            dummy_binding: arenas.alloc_name_binding(NameBinding {
+                kind: NameBindingKind::Res(Res::Err, false),
+                ambiguity: None,
+                expansion: LocalExpnId::ROOT,
+                span: DUMMY_SP,
+                vis: ty::Visibility::Public,
+            }),
+
+            crate_loader: CrateLoader::new(session, metadata_loader, crate_name),
+            macro_names: FxHashSet::default(),
+            builtin_macros: Default::default(),
+            builtin_macro_kinds: Default::default(),
+            registered_attrs,
+            registered_tools,
+            macro_use_prelude: FxHashMap::default(),
+            macro_map: FxHashMap::default(),
+            dummy_ext_bang: Lrc::new(SyntaxExtension::dummy_bang(session.edition())),
+            dummy_ext_derive: Lrc::new(SyntaxExtension::dummy_derive(session.edition())),
+            non_macro_attr: Lrc::new(SyntaxExtension::non_macro_attr(session.edition())),
+            invocation_parent_scopes: Default::default(),
+            output_macro_rules_scopes: Default::default(),
+            macro_rules_scopes: Default::default(),
+            helper_attrs: Default::default(),
+            derive_data: Default::default(),
+            local_macro_def_scopes: FxHashMap::default(),
+            name_already_seen: FxHashMap::default(),
+            potentially_unused_imports: Vec::new(),
+            struct_constructors: Default::default(),
+            unused_macros: Default::default(),
+            unused_macro_rules: Default::default(),
+            proc_macro_stubs: Default::default(),
+            single_segment_macro_resolutions: Default::default(),
+            multi_segment_macro_resolutions: Default::default(),
+            builtin_attrs: Default::default(),
+            containers_deriving_copy: Default::default(),
+            active_features: features
+                .declared_lib_features
+                .iter()
+                .map(|(feat, ..)| *feat)
+                .chain(features.declared_lang_features.iter().map(|(feat, ..)| *feat))
+                .collect(),
+            lint_buffer: LintBuffer::default(),
+            next_node_id: CRATE_NODE_ID,
+            node_id_to_def_id,
+            def_id_to_node_id,
+            placeholder_field_indices: Default::default(),
+            invocation_parents,
+            trait_impl_items: Default::default(),
+            legacy_const_generic_args: Default::default(),
+            item_generics_num_lifetimes: Default::default(),
+            main_def: Default::default(),
+            trait_impls: Default::default(),
+            proc_macros: Default::default(),
+            confused_type_with_std_module: Default::default(),
+            access_levels: Default::default(),
+        };
+
+        let root_parent_scope = ParentScope::module(graph_root, &resolver);
+        resolver.invocation_parent_scopes.insert(LocalExpnId::ROOT, root_parent_scope);
+
+        resolver
+    }
+
+    fn new_module(
+        &mut self,
+        parent: Option<Module<'a>>,
+        kind: ModuleKind,
+        expn_id: ExpnId,
+        span: Span,
+        no_implicit_prelude: bool,
+    ) -> Module<'a> {
+        let module_map = &mut self.module_map;
+        self.arenas.new_module(parent, kind, expn_id, span, no_implicit_prelude, module_map)
+    }
+
+    pub fn next_node_id(&mut self) -> NodeId {
+        let start = self.next_node_id;
+        let next = start.as_u32().checked_add(1).expect("input too large; ran out of NodeIds");
+        self.next_node_id = ast::NodeId::from_u32(next);
+        start
+    }
+
+    pub fn next_node_ids(&mut self, count: usize) -> std::ops::Range<NodeId> {
+        let start = self.next_node_id;
+        let end = start.as_usize().checked_add(count).expect("input too large; ran out of NodeIds");
+        self.next_node_id = ast::NodeId::from_usize(end);
+        start..self.next_node_id
+    }
+
+    pub fn lint_buffer(&mut self) -> &mut LintBuffer {
+        &mut self.lint_buffer
+    }
+
+    pub fn arenas() -> ResolverArenas<'a> {
+        Default::default()
+    }
+
+    pub fn into_outputs(
+        self,
+    ) -> (Definitions, Box<CrateStoreDyn>, ResolverOutputs, ty::ResolverAstLowering) {
+        let proc_macros = self.proc_macros.iter().map(|id| self.local_def_id(*id)).collect();
+        let definitions = self.definitions;
+        let cstore = Box::new(self.crate_loader.into_cstore());
+        let source_span = self.source_span;
+        let expn_that_defined = self.expn_that_defined;
+        let visibilities = self.visibilities;
+        let has_pub_restricted = self.has_pub_restricted;
+        let extern_crate_map = self.extern_crate_map;
+        let reexport_map = self.reexport_map;
+        let maybe_unused_trait_imports = self.maybe_unused_trait_imports;
+        let maybe_unused_extern_crates = self.maybe_unused_extern_crates;
+        let glob_map = self.glob_map;
+        let main_def = self.main_def;
+        let confused_type_with_std_module = self.confused_type_with_std_module;
+        let access_levels = self.access_levels;
+        let resolutions = ResolverOutputs {
+            source_span,
+            expn_that_defined,
+            visibilities,
+            has_pub_restricted,
+            access_levels,
+            extern_crate_map,
+            reexport_map,
+            glob_map,
+            maybe_unused_trait_imports,
+            maybe_unused_extern_crates,
+            extern_prelude: self
+                .extern_prelude
+                .iter()
+                .map(|(ident, entry)| (ident.name, entry.introduced_by_item))
+                .collect(),
+            main_def,
+            trait_impls: self.trait_impls,
+            proc_macros,
+            confused_type_with_std_module,
+            registered_tools: self.registered_tools,
+        };
+        let resolutions_lowering = ty::ResolverAstLowering {
+            legacy_const_generic_args: self.legacy_const_generic_args,
+            partial_res_map: self.partial_res_map,
+            import_res_map: self.import_res_map,
+            label_res_map: self.label_res_map,
+            lifetimes_res_map: self.lifetimes_res_map,
+            generics_def_id_map: self.generics_def_id_map,
+            extra_lifetime_params_map: self.extra_lifetime_params_map,
+            next_node_id: self.next_node_id,
+            node_id_to_def_id: self.node_id_to_def_id,
+            def_id_to_node_id: self.def_id_to_node_id,
+            trait_map: self.trait_map,
+            builtin_macro_kinds: self.builtin_macro_kinds,
+        };
+        (definitions, cstore, resolutions, resolutions_lowering)
+    }
+
+    pub fn clone_outputs(
+        &self,
+    ) -> (Definitions, Box<CrateStoreDyn>, ResolverOutputs, ty::ResolverAstLowering) {
+        let proc_macros = self.proc_macros.iter().map(|id| self.local_def_id(*id)).collect();
+        let definitions = self.definitions.clone();
+        let cstore = Box::new(self.cstore().clone());
+        let resolutions = ResolverOutputs {
+            source_span: self.source_span.clone(),
+            expn_that_defined: self.expn_that_defined.clone(),
+            visibilities: self.visibilities.clone(),
+            has_pub_restricted: self.has_pub_restricted,
+            extern_crate_map: self.extern_crate_map.clone(),
+            reexport_map: self.reexport_map.clone(),
+            glob_map: self.glob_map.clone(),
+            maybe_unused_trait_imports: self.maybe_unused_trait_imports.clone(),
+            maybe_unused_extern_crates: self.maybe_unused_extern_crates.clone(),
+            extern_prelude: self
+                .extern_prelude
+                .iter()
+                .map(|(ident, entry)| (ident.name, entry.introduced_by_item))
+                .collect(),
+            main_def: self.main_def,
+            trait_impls: self.trait_impls.clone(),
+            proc_macros,
+            confused_type_with_std_module: self.confused_type_with_std_module.clone(),
+            registered_tools: self.registered_tools.clone(),
+            access_levels: self.access_levels.clone(),
+        };
+        let resolutions_lowering = ty::ResolverAstLowering {
+            legacy_const_generic_args: self.legacy_const_generic_args.clone(),
+            partial_res_map: self.partial_res_map.clone(),
+            import_res_map: self.import_res_map.clone(),
+            label_res_map: self.label_res_map.clone(),
+            lifetimes_res_map: self.lifetimes_res_map.clone(),
+            generics_def_id_map: self.generics_def_id_map.clone(),
+            extra_lifetime_params_map: self.extra_lifetime_params_map.clone(),
+            next_node_id: self.next_node_id.clone(),
+            node_id_to_def_id: self.node_id_to_def_id.clone(),
+            def_id_to_node_id: self.def_id_to_node_id.clone(),
+            trait_map: self.trait_map.clone(),
+            builtin_macro_kinds: self.builtin_macro_kinds.clone(),
+        };
+        (definitions, cstore, resolutions, resolutions_lowering)
+    }
+
+    fn create_stable_hashing_context(&self) -> StableHashingContext<'_> {
+        StableHashingContext::new(
+            self.session,
+            &self.definitions,
+            self.crate_loader.cstore(),
+            &self.source_span,
+        )
+    }
+
+    pub fn cstore(&self) -> &CStore {
+        self.crate_loader.cstore()
+    }
+
+    fn dummy_ext(&self, macro_kind: MacroKind) -> Lrc<SyntaxExtension> {
+        match macro_kind {
+            MacroKind::Bang => self.dummy_ext_bang.clone(),
+            MacroKind::Derive => self.dummy_ext_derive.clone(),
+            MacroKind::Attr => self.non_macro_attr.clone(),
+        }
+    }
+
+    /// Runs the function on each namespace.
+    fn per_ns<F: FnMut(&mut Self, Namespace)>(&mut self, mut f: F) {
+        f(self, TypeNS);
+        f(self, ValueNS);
+        f(self, MacroNS);
+    }
+
+    fn is_builtin_macro(&mut self, res: Res) -> bool {
+        self.get_macro(res).map_or(false, |macro_data| macro_data.ext.builtin_name.is_some())
+    }
+
+    fn macro_def(&self, mut ctxt: SyntaxContext) -> DefId {
+        loop {
+            match ctxt.outer_expn_data().macro_def_id {
+                Some(def_id) => return def_id,
+                None => ctxt.remove_mark(),
+            };
+        }
+    }
+
+    /// Entry point to crate resolution.
+    pub fn resolve_crate(&mut self, krate: &Crate) {
+        self.session.time("resolve_crate", || {
+            self.session.time("finalize_imports", || ImportResolver { r: self }.finalize_imports());
+            self.session.time("resolve_access_levels", || {
+                AccessLevelsVisitor::compute_access_levels(self, krate)
+            });
+            self.session.time("finalize_macro_resolutions", || self.finalize_macro_resolutions());
+            self.session.time("late_resolve_crate", || self.late_resolve_crate(krate));
+            self.session.time("resolve_main", || self.resolve_main());
+            self.session.time("resolve_check_unused", || self.check_unused(krate));
+            self.session.time("resolve_report_errors", || self.report_errors(krate));
+            self.session.time("resolve_postprocess", || self.crate_loader.postprocess(krate));
+        });
+    }
+
+    pub fn traits_in_scope(
+        &mut self,
+        current_trait: Option<Module<'a>>,
+        parent_scope: &ParentScope<'a>,
+        ctxt: SyntaxContext,
+        assoc_item: Option<(Symbol, Namespace)>,
+    ) -> Vec<TraitCandidate> {
+        let mut found_traits = Vec::new();
+
+        if let Some(module) = current_trait {
+            if self.trait_may_have_item(Some(module), assoc_item) {
+                let def_id = module.def_id();
+                found_traits.push(TraitCandidate { def_id, import_ids: smallvec![] });
+            }
+        }
+
+        self.visit_scopes(ScopeSet::All(TypeNS, false), parent_scope, ctxt, |this, scope, _, _| {
+            match scope {
+                Scope::Module(module, _) => {
+                    this.traits_in_module(module, assoc_item, &mut found_traits);
+                }
+                Scope::StdLibPrelude => {
+                    if let Some(module) = this.prelude {
+                        this.traits_in_module(module, assoc_item, &mut found_traits);
+                    }
+                }
+                Scope::ExternPrelude | Scope::ToolPrelude | Scope::BuiltinTypes => {}
+                _ => unreachable!(),
+            }
+            None::<()>
+        });
+
+        found_traits
+    }
+
+    fn traits_in_module(
+        &mut self,
+        module: Module<'a>,
+        assoc_item: Option<(Symbol, Namespace)>,
+        found_traits: &mut Vec<TraitCandidate>,
+    ) {
+        module.ensure_traits(self);
+        let traits = module.traits.borrow();
+        for (trait_name, trait_binding) in traits.as_ref().unwrap().iter() {
+            if self.trait_may_have_item(trait_binding.module(), assoc_item) {
+                let def_id = trait_binding.res().def_id();
+                let import_ids = self.find_transitive_imports(&trait_binding.kind, *trait_name);
+                found_traits.push(TraitCandidate { def_id, import_ids });
+            }
+        }
+    }
+
+    // List of traits in scope is pruned on best effort basis. We reject traits not having an
+    // associated item with the given name and namespace (if specified). This is a conservative
+    // optimization, proper hygienic type-based resolution of associated items is done in typeck.
+    // We don't reject trait aliases (`trait_module == None`) because we don't have access to their
+    // associated items.
+    fn trait_may_have_item(
+        &mut self,
+        trait_module: Option<Module<'a>>,
+        assoc_item: Option<(Symbol, Namespace)>,
+    ) -> bool {
+        match (trait_module, assoc_item) {
+            (Some(trait_module), Some((name, ns))) => {
+                self.resolutions(trait_module).borrow().iter().any(|resolution| {
+                    let (&BindingKey { ident: assoc_ident, ns: assoc_ns, .. }, _) = resolution;
+                    assoc_ns == ns && assoc_ident.name == name
+                })
+            }
+            _ => true,
+        }
+    }
+
+    fn find_transitive_imports(
+        &mut self,
+        mut kind: &NameBindingKind<'_>,
+        trait_name: Ident,
+    ) -> SmallVec<[LocalDefId; 1]> {
+        let mut import_ids = smallvec![];
+        while let NameBindingKind::Import { import, binding, .. } = kind {
+            let id = self.local_def_id(import.id);
+            self.maybe_unused_trait_imports.insert(id);
+            self.add_to_glob_map(&import, trait_name);
+            import_ids.push(id);
+            kind = &binding.kind;
+        }
+        import_ids
+    }
+
+    fn new_key(&mut self, ident: Ident, ns: Namespace) -> BindingKey {
+        let ident = ident.normalize_to_macros_2_0();
+        let disambiguator = if ident.name == kw::Underscore {
+            self.underscore_disambiguator += 1;
+            self.underscore_disambiguator
+        } else {
+            0
+        };
+        BindingKey { ident, ns, disambiguator }
+    }
+
+    fn resolutions(&mut self, module: Module<'a>) -> &'a Resolutions<'a> {
+        if module.populate_on_access.get() {
+            module.populate_on_access.set(false);
+            self.build_reduced_graph_external(module);
+        }
+        &module.lazy_resolutions
+    }
+
+    fn resolution(
+        &mut self,
+        module: Module<'a>,
+        key: BindingKey,
+    ) -> &'a RefCell<NameResolution<'a>> {
+        *self
+            .resolutions(module)
+            .borrow_mut()
+            .entry(key)
+            .or_insert_with(|| self.arenas.alloc_name_resolution())
+    }
+
+    fn record_use(
+        &mut self,
+        ident: Ident,
+        used_binding: &'a NameBinding<'a>,
+        is_lexical_scope: bool,
+    ) {
+        if let Some((b2, kind)) = used_binding.ambiguity {
+            self.ambiguity_errors.push(AmbiguityError {
+                kind,
+                ident,
+                b1: used_binding,
+                b2,
+                misc1: AmbiguityErrorMisc::None,
+                misc2: AmbiguityErrorMisc::None,
+            });
+        }
+        if let NameBindingKind::Import { import, binding, ref used } = used_binding.kind {
+            // Avoid marking `extern crate` items that refer to a name from extern prelude,
+            // but not introduce it, as used if they are accessed from lexical scope.
+            if is_lexical_scope {
+                if let Some(entry) = self.extern_prelude.get(&ident.normalize_to_macros_2_0()) {
+                    if let Some(crate_item) = entry.extern_crate_item {
+                        if ptr::eq(used_binding, crate_item) && !entry.introduced_by_item {
+                            return;
+                        }
+                    }
+                }
+            }
+            used.set(true);
+            import.used.set(true);
+            self.used_imports.insert(import.id);
+            self.add_to_glob_map(&import, ident);
+            self.record_use(ident, binding, false);
+        }
+    }
+
+    #[inline]
+    fn add_to_glob_map(&mut self, import: &Import<'_>, ident: Ident) {
+        if import.is_glob() {
+            let def_id = self.local_def_id(import.id);
+            self.glob_map.entry(def_id).or_default().insert(ident.name);
+        }
+    }
+
+    fn resolve_crate_root(&mut self, ident: Ident) -> Module<'a> {
+        debug!("resolve_crate_root({:?})", ident);
+        let mut ctxt = ident.span.ctxt();
+        let mark = if ident.name == kw::DollarCrate {
+            // When resolving `$crate` from a `macro_rules!` invoked in a `macro`,
+            // we don't want to pretend that the `macro_rules!` definition is in the `macro`
+            // as described in `SyntaxContext::apply_mark`, so we ignore prepended opaque marks.
+            // FIXME: This is only a guess and it doesn't work correctly for `macro_rules!`
+            // definitions actually produced by `macro` and `macro` definitions produced by
+            // `macro_rules!`, but at least such configurations are not stable yet.
+            ctxt = ctxt.normalize_to_macro_rules();
+            debug!(
+                "resolve_crate_root: marks={:?}",
+                ctxt.marks().into_iter().map(|(i, t)| (i.expn_data(), t)).collect::<Vec<_>>()
+            );
+            let mut iter = ctxt.marks().into_iter().rev().peekable();
+            let mut result = None;
+            // Find the last opaque mark from the end if it exists.
+            while let Some(&(mark, transparency)) = iter.peek() {
+                if transparency == Transparency::Opaque {
+                    result = Some(mark);
+                    iter.next();
+                } else {
+                    break;
+                }
+            }
+            debug!(
+                "resolve_crate_root: found opaque mark {:?} {:?}",
+                result,
+                result.map(|r| r.expn_data())
+            );
+            // Then find the last semi-transparent mark from the end if it exists.
+            for (mark, transparency) in iter {
+                if transparency == Transparency::SemiTransparent {
+                    result = Some(mark);
+                } else {
+                    break;
+                }
+            }
+            debug!(
+                "resolve_crate_root: found semi-transparent mark {:?} {:?}",
+                result,
+                result.map(|r| r.expn_data())
+            );
+            result
+        } else {
+            debug!("resolve_crate_root: not DollarCrate");
+            ctxt = ctxt.normalize_to_macros_2_0();
+            ctxt.adjust(ExpnId::root())
+        };
+        let module = match mark {
+            Some(def) => self.expn_def_scope(def),
+            None => {
+                debug!(
+                    "resolve_crate_root({:?}): found no mark (ident.span = {:?})",
+                    ident, ident.span
+                );
+                return self.graph_root;
+            }
+        };
+        let module = self.expect_module(
+            module.opt_def_id().map_or(LOCAL_CRATE, |def_id| def_id.krate).as_def_id(),
+        );
+        debug!(
+            "resolve_crate_root({:?}): got module {:?} ({:?}) (ident.span = {:?})",
+            ident,
+            module,
+            module.kind.name(),
+            ident.span
+        );
+        module
+    }
+
+    fn resolve_self(&mut self, ctxt: &mut SyntaxContext, module: Module<'a>) -> Module<'a> {
+        let mut module = self.expect_module(module.nearest_parent_mod());
+        while module.span.ctxt().normalize_to_macros_2_0() != *ctxt {
+            let parent = module.parent.unwrap_or_else(|| self.expn_def_scope(ctxt.remove_mark()));
+            module = self.expect_module(parent.nearest_parent_mod());
+        }
+        module
+    }
+
+    fn record_partial_res(&mut self, node_id: NodeId, resolution: PartialRes) {
+        debug!("(recording res) recording {:?} for {}", resolution, node_id);
+        if let Some(prev_res) = self.partial_res_map.insert(node_id, resolution) {
+            panic!("path resolved multiple times ({:?} before, {:?} now)", prev_res, resolution);
+        }
+    }
+
+    fn record_pat_span(&mut self, node: NodeId, span: Span) {
+        debug!("(recording pat) recording {:?} for {:?}", node, span);
+        self.pat_span_map.insert(node, span);
+    }
+
+    fn is_accessible_from(&self, vis: ty::Visibility, module: Module<'a>) -> bool {
+        vis.is_accessible_from(module.nearest_parent_mod(), self)
+    }
+
+    fn set_binding_parent_module(&mut self, binding: &'a NameBinding<'a>, module: Module<'a>) {
+        if let Some(old_module) =
+            self.binding_parent_modules.insert(Interned::new_unchecked(binding), module)
+        {
+            if !ptr::eq(module, old_module) {
+                span_bug!(binding.span, "parent module is reset for binding");
+            }
+        }
+    }
+
+    fn disambiguate_macro_rules_vs_modularized(
+        &self,
+        macro_rules: &'a NameBinding<'a>,
+        modularized: &'a NameBinding<'a>,
+    ) -> bool {
+        // Some non-controversial subset of ambiguities "modularized macro name" vs "macro_rules"
+        // is disambiguated to mitigate regressions from macro modularization.
+        // Scoping for `macro_rules` behaves like scoping for `let` at module level, in general.
+        match (
+            self.binding_parent_modules.get(&Interned::new_unchecked(macro_rules)),
+            self.binding_parent_modules.get(&Interned::new_unchecked(modularized)),
+        ) {
+            (Some(macro_rules), Some(modularized)) => {
+                macro_rules.nearest_parent_mod() == modularized.nearest_parent_mod()
+                    && modularized.is_ancestor_of(macro_rules)
+            }
+            _ => false,
+        }
+    }
+
+    fn extern_prelude_get(&mut self, ident: Ident, finalize: bool) -> Option<&'a NameBinding<'a>> {
+        if ident.is_path_segment_keyword() {
+            // Make sure `self`, `super` etc produce an error when passed to here.
+            return None;
+        }
+        self.extern_prelude.get(&ident.normalize_to_macros_2_0()).cloned().and_then(|entry| {
+            if let Some(binding) = entry.extern_crate_item {
+                if finalize && entry.introduced_by_item {
+                    self.record_use(ident, binding, false);
+                }
+                Some(binding)
+            } else {
+                let crate_id = if finalize {
+                    let Some(crate_id) =
+                        self.crate_loader.process_path_extern(ident.name, ident.span) else { return Some(self.dummy_binding); };
+                    crate_id
+                } else {
+                    self.crate_loader.maybe_process_path_extern(ident.name)?
+                };
+                let crate_root = self.expect_module(crate_id.as_def_id());
+                Some(
+                    (crate_root, ty::Visibility::Public, DUMMY_SP, LocalExpnId::ROOT)
+                        .to_name_binding(self.arenas),
+                )
+            }
+        })
+    }
+
+    /// Rustdoc uses this to resolve doc link paths in a recoverable way. `PathResult<'a>`
+    /// isn't something that can be returned because it can't be made to live that long,
+    /// and also it's a private type. Fortunately rustdoc doesn't need to know the error,
+    /// just that an error occurred.
+    pub fn resolve_rustdoc_path(
+        &mut self,
+        path_str: &str,
+        ns: Namespace,
+        mut parent_scope: ParentScope<'a>,
+    ) -> Option<Res> {
+        let mut segments =
+            Vec::from_iter(path_str.split("::").map(Ident::from_str).map(Segment::from_ident));
+        if let Some(segment) = segments.first_mut() {
+            if segment.ident.name == kw::Crate {
+                // FIXME: `resolve_path` always resolves `crate` to the current crate root, but
+                // rustdoc wants it to resolve to the `parent_scope`'s crate root. This trick of
+                // replacing `crate` with `self` and changing the current module should achieve
+                // the same effect.
+                segment.ident.name = kw::SelfLower;
+                parent_scope.module =
+                    self.expect_module(parent_scope.module.def_id().krate.as_def_id());
+            } else if segment.ident.name == kw::Empty {
+                segment.ident.name = kw::PathRoot;
+            }
+        }
+
+        match self.maybe_resolve_path(&segments, Some(ns), &parent_scope) {
+            PathResult::Module(ModuleOrUniformRoot::Module(module)) => Some(module.res().unwrap()),
+            PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
+                Some(path_res.base_res())
+            }
+            PathResult::Module(ModuleOrUniformRoot::ExternPrelude)
+            | PathResult::NonModule(..)
+            | PathResult::Failed { .. } => None,
+            PathResult::Module(..) | PathResult::Indeterminate => unreachable!(),
+        }
+    }
+
+    /// For rustdoc.
+    /// For local modules returns only reexports, for external modules returns all children.
+    pub fn module_children_or_reexports(&self, def_id: DefId) -> Vec<ModChild> {
+        if let Some(def_id) = def_id.as_local() {
+            self.reexport_map.get(&def_id).cloned().unwrap_or_default()
+        } else {
+            self.cstore().module_children_untracked(def_id, self.session)
+        }
+    }
+
+    /// For rustdoc.
+    pub fn macro_rules_scope(&self, def_id: LocalDefId) -> (MacroRulesScopeRef<'a>, Res) {
+        let scope = *self.macro_rules_scopes.get(&def_id).expect("not a `macro_rules` item");
+        match scope.get() {
+            MacroRulesScope::Binding(mb) => (scope, mb.binding.res()),
+            _ => unreachable!(),
+        }
+    }
+
+    /// Retrieves the span of the given `DefId` if `DefId` is in the local crate.
+    #[inline]
+    pub fn opt_span(&self, def_id: DefId) -> Option<Span> {
+        def_id.as_local().map(|def_id| self.source_span[def_id])
+    }
+
+    /// Checks if an expression refers to a function marked with
+    /// `#[rustc_legacy_const_generics]` and returns the argument index list
+    /// from the attribute.
+    pub fn legacy_const_generic_args(&mut self, expr: &Expr) -> Option<Vec<usize>> {
+        if let ExprKind::Path(None, path) = &expr.kind {
+            // Don't perform legacy const generics rewriting if the path already
+            // has generic arguments.
+            if path.segments.last().unwrap().args.is_some() {
+                return None;
+            }
+
+            let partial_res = self.partial_res_map.get(&expr.id)?;
+            if partial_res.unresolved_segments() != 0 {
+                return None;
+            }
+
+            if let Res::Def(def::DefKind::Fn, def_id) = partial_res.base_res() {
+                // We only support cross-crate argument rewriting. Uses
+                // within the same crate should be updated to use the new
+                // const generics style.
+                if def_id.is_local() {
+                    return None;
+                }
+
+                if let Some(v) = self.legacy_const_generic_args.get(&def_id) {
+                    return v.clone();
+                }
+
+                let attr = self
+                    .cstore()
+                    .item_attrs_untracked(def_id, self.session)
+                    .find(|a| a.has_name(sym::rustc_legacy_const_generics))?;
+                let mut ret = Vec::new();
+                for meta in attr.meta_item_list()? {
+                    match meta.literal()?.kind {
+                        LitKind::Int(a, _) => ret.push(a as usize),
+                        _ => panic!("invalid arg index"),
+                    }
+                }
+                // Cache the lookup to avoid parsing attributes for an iterm multiple times.
+                self.legacy_const_generic_args.insert(def_id, Some(ret.clone()));
+                return Some(ret);
+            }
+        }
+        None
+    }
+
+    fn resolve_main(&mut self) {
+        let module = self.graph_root;
+        let ident = Ident::with_dummy_span(sym::main);
+        let parent_scope = &ParentScope::module(module, self);
+
+        let Ok(name_binding) = self.maybe_resolve_ident_in_module(
+            ModuleOrUniformRoot::Module(module),
+            ident,
+            ValueNS,
+            parent_scope,
+        ) else {
+            return;
+        };
+
+        let res = name_binding.res();
+        let is_import = name_binding.is_import();
+        let span = name_binding.span;
+        if let Res::Def(DefKind::Fn, _) = res {
+            self.record_use(ident, name_binding, false);
+        }
+        self.main_def = Some(MainDefinition { res, is_import, span });
+    }
+}
+
+fn names_to_string(names: &[Symbol]) -> String {
+    let mut result = String::new();
+    for (i, name) in names.iter().filter(|name| **name != kw::PathRoot).enumerate() {
+        if i > 0 {
+            result.push_str("::");
+        }
+        if Ident::with_dummy_span(*name).is_raw_guess() {
+            result.push_str("r#");
+        }
+        result.push_str(name.as_str());
+    }
+    result
+}
+
+fn path_names_to_string(path: &Path) -> String {
+    names_to_string(&path.segments.iter().map(|seg| seg.ident.name).collect::<Vec<_>>())
+}
+
+/// A somewhat inefficient routine to obtain the name of a module.
+fn module_to_string(module: Module<'_>) -> Option<String> {
+    let mut names = Vec::new();
+
+    fn collect_mod(names: &mut Vec<Symbol>, module: Module<'_>) {
+        if let ModuleKind::Def(.., name) = module.kind {
+            if let Some(parent) = module.parent {
+                names.push(name);
+                collect_mod(names, parent);
+            }
+        } else {
+            names.push(Symbol::intern("<opaque>"));
+            collect_mod(names, module.parent.unwrap());
+        }
+    }
+    collect_mod(&mut names, module);
+
+    if names.is_empty() {
+        return None;
+    }
+    names.reverse();
+    Some(names_to_string(&names))
+}
+
+#[derive(Copy, Clone, Debug)]
+struct Finalize {
+    /// Node ID for linting.
+    node_id: NodeId,
+    /// Span of the whole path or some its characteristic fragment.
+    /// E.g. span of `b` in `foo::{a, b, c}`, or full span for regular paths.
+    path_span: Span,
+    /// Span of the path start, suitable for prepending something to to it.
+    /// E.g. span of `foo` in `foo::{a, b, c}`, or full span for regular paths.
+    root_span: Span,
+    /// Whether to report privacy errors or silently return "no resolution" for them,
+    /// similarly to speculative resolution.
+    report_private: bool,
+}
+
+impl Finalize {
+    fn new(node_id: NodeId, path_span: Span) -> Finalize {
+        Finalize::with_root_span(node_id, path_span, path_span)
+    }
+
+    fn with_root_span(node_id: NodeId, path_span: Span, root_span: Span) -> Finalize {
+        Finalize { node_id, path_span, root_span, report_private: true }
+    }
+}
+
+pub fn provide(providers: &mut Providers) {
+    late::lifetimes::provide(providers);
+}
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
new file mode 100644
index 000000000..070fb9c72
--- /dev/null
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -0,0 +1,921 @@
+//! A bunch of methods and structures more or less related to resolving macros and
+//! interface provided by `Resolver` to macro expander.
+
+use crate::imports::ImportResolver;
+use crate::Namespace::*;
+use crate::{BuiltinMacroState, Determinacy};
+use crate::{DeriveData, Finalize, ParentScope, ResolutionError, Resolver, ScopeSet};
+use crate::{ModuleKind, ModuleOrUniformRoot, NameBinding, PathResult, Segment};
+use rustc_ast::{self as ast, Inline, ItemKind, ModKind, NodeId};
+use rustc_ast_pretty::pprust;
+use rustc_attr::StabilityLevel;
+use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::intern::Interned;
+use rustc_data_structures::sync::Lrc;
+use rustc_errors::struct_span_err;
+use rustc_expand::base::{Annotatable, DeriveResolutions, Indeterminate, ResolverExpand};
+use rustc_expand::base::{SyntaxExtension, SyntaxExtensionKind};
+use rustc_expand::compile_declarative_macro;
+use rustc_expand::expand::{AstFragment, Invocation, InvocationKind, SupportsMacroExpansion};
+use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
+use rustc_hir::def_id::{CrateNum, LocalDefId};
+use rustc_middle::middle::stability;
+use rustc_middle::ty::RegisteredTools;
+use rustc_session::lint::builtin::{LEGACY_DERIVE_HELPERS, SOFT_UNSTABLE};
+use rustc_session::lint::builtin::{UNUSED_MACROS, UNUSED_MACRO_RULES};
+use rustc_session::lint::BuiltinLintDiagnostics;
+use rustc_session::parse::feature_err;
+use rustc_session::Session;
+use rustc_span::edition::Edition;
+use rustc_span::hygiene::{self, ExpnData, ExpnKind, LocalExpnId};
+use rustc_span::hygiene::{AstPass, MacroKind};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::{Span, DUMMY_SP};
+use std::cell::Cell;
+use std::mem;
+
+type Res = def::Res<NodeId>;
+
+/// Binding produced by a `macro_rules` item.
+/// Not modularized, can shadow previous `macro_rules` bindings, etc.
+#[derive(Debug)]
+pub struct MacroRulesBinding<'a> {
+    pub(crate) binding: &'a NameBinding<'a>,
+    /// `macro_rules` scope into which the `macro_rules` item was planted.
+    pub(crate) parent_macro_rules_scope: MacroRulesScopeRef<'a>,
+    pub(crate) ident: Ident,
+}
+
+/// The scope introduced by a `macro_rules!` macro.
+/// This starts at the macro's definition and ends at the end of the macro's parent
+/// module (named or unnamed), or even further if it escapes with `#[macro_use]`.
+/// Some macro invocations need to introduce `macro_rules` scopes too because they
+/// can potentially expand into macro definitions.
+#[derive(Copy, Clone, Debug)]
+pub enum MacroRulesScope<'a> {
+    /// Empty "root" scope at the crate start containing no names.
+    Empty,
+    /// The scope introduced by a `macro_rules!` macro definition.
+    Binding(&'a MacroRulesBinding<'a>),
+    /// The scope introduced by a macro invocation that can potentially
+    /// create a `macro_rules!` macro definition.
+    Invocation(LocalExpnId),
+}
+
+/// `macro_rules!` scopes are always kept by reference and inside a cell.
+/// The reason is that we update scopes with value `MacroRulesScope::Invocation(invoc_id)`
+/// in-place after `invoc_id` gets expanded.
+/// This helps to avoid uncontrollable growth of `macro_rules!` scope chains,
+/// which usually grow linearly with the number of macro invocations
+/// in a module (including derives) and hurt performance.
+pub(crate) type MacroRulesScopeRef<'a> = Interned<'a, Cell<MacroRulesScope<'a>>>;
+
+/// Macro namespace is separated into two sub-namespaces, one for bang macros and
+/// one for attribute-like macros (attributes, derives).
+/// We ignore resolutions from one sub-namespace when searching names in scope for another.
+pub(crate) fn sub_namespace_match(
+    candidate: Option<MacroKind>,
+    requirement: Option<MacroKind>,
+) -> bool {
+    #[derive(PartialEq)]
+    enum SubNS {
+        Bang,
+        AttrLike,
+    }
+    let sub_ns = |kind| match kind {
+        MacroKind::Bang => SubNS::Bang,
+        MacroKind::Attr | MacroKind::Derive => SubNS::AttrLike,
+    };
+    let candidate = candidate.map(sub_ns);
+    let requirement = requirement.map(sub_ns);
+    // "No specific sub-namespace" means "matches anything" for both requirements and candidates.
+    candidate.is_none() || requirement.is_none() || candidate == requirement
+}
+
+// We don't want to format a path using pretty-printing,
+// `format!("{}", path)`, because that tries to insert
+// line-breaks and is slow.
+fn fast_print_path(path: &ast::Path) -> Symbol {
+    if path.segments.len() == 1 {
+        path.segments[0].ident.name
+    } else {
+        let mut path_str = String::with_capacity(64);
+        for (i, segment) in path.segments.iter().enumerate() {
+            if i != 0 {
+                path_str.push_str("::");
+            }
+            if segment.ident.name != kw::PathRoot {
+                path_str.push_str(segment.ident.as_str())
+            }
+        }
+        Symbol::intern(&path_str)
+    }
+}
+
+/// The code common between processing `#![register_tool]` and `#![register_attr]`.
+fn registered_idents(
+    sess: &Session,
+    attrs: &[ast::Attribute],
+    attr_name: Symbol,
+    descr: &str,
+) -> FxHashSet<Ident> {
+    let mut registered = FxHashSet::default();
+    for attr in sess.filter_by_name(attrs, attr_name) {
+        for nested_meta in attr.meta_item_list().unwrap_or_default() {
+            match nested_meta.ident() {
+                Some(ident) => {
+                    if let Some(old_ident) = registered.replace(ident) {
+                        let msg = format!("{} `{}` was already registered", descr, ident);
+                        sess.struct_span_err(ident.span, &msg)
+                            .span_label(old_ident.span, "already registered here")
+                            .emit();
+                    }
+                }
+                None => {
+                    let msg = format!("`{}` only accepts identifiers", attr_name);
+                    let span = nested_meta.span();
+                    sess.struct_span_err(span, &msg).span_label(span, "not an identifier").emit();
+                }
+            }
+        }
+    }
+    registered
+}
+
+pub(crate) fn registered_attrs_and_tools(
+    sess: &Session,
+    attrs: &[ast::Attribute],
+) -> (FxHashSet<Ident>, FxHashSet<Ident>) {
+    let registered_attrs = registered_idents(sess, attrs, sym::register_attr, "attribute");
+    let mut registered_tools = registered_idents(sess, attrs, sym::register_tool, "tool");
+    // We implicitly add `rustfmt` and `clippy` to known tools,
+    // but it's not an error to register them explicitly.
+    let predefined_tools = [sym::clippy, sym::rustfmt];
+    registered_tools.extend(predefined_tools.iter().cloned().map(Ident::with_dummy_span));
+    (registered_attrs, registered_tools)
+}
+
+// Some feature gates for inner attributes are reported as lints for backward compatibility.
+fn soft_custom_inner_attributes_gate(path: &ast::Path, invoc: &Invocation) -> bool {
+    match &path.segments[..] {
+        // `#![test]`
+        [seg] if seg.ident.name == sym::test => return true,
+        // `#![rustfmt::skip]` on out-of-line modules
+        [seg1, seg2] if seg1.ident.name == sym::rustfmt && seg2.ident.name == sym::skip => {
+            if let InvocationKind::Attr { item, .. } = &invoc.kind {
+                if let Annotatable::Item(item) = item {
+                    if let ItemKind::Mod(_, ModKind::Loaded(_, Inline::No, _)) = item.kind {
+                        return true;
+                    }
+                }
+            }
+        }
+        _ => {}
+    }
+    false
+}
+
+impl<'a> ResolverExpand for Resolver<'a> {
+    fn next_node_id(&mut self) -> NodeId {
+        self.next_node_id()
+    }
+
+    fn invocation_parent(&self, id: LocalExpnId) -> LocalDefId {
+        self.invocation_parents[&id].0
+    }
+
+    fn resolve_dollar_crates(&mut self) {
+        hygiene::update_dollar_crate_names(|ctxt| {
+            let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));
+            match self.resolve_crate_root(ident).kind {
+                ModuleKind::Def(.., name) if name != kw::Empty => name,
+                _ => kw::Crate,
+            }
+        });
+    }
+
+    fn visit_ast_fragment_with_placeholders(
+        &mut self,
+        expansion: LocalExpnId,
+        fragment: &AstFragment,
+    ) {
+        // Integrate the new AST fragment into all the definition and module structures.
+        // We are inside the `expansion` now, but other parent scope components are still the same.
+        let parent_scope = ParentScope { expansion, ..self.invocation_parent_scopes[&expansion] };
+        let output_macro_rules_scope = self.build_reduced_graph(fragment, parent_scope);
+        self.output_macro_rules_scopes.insert(expansion, output_macro_rules_scope);
+
+        parent_scope.module.unexpanded_invocations.borrow_mut().remove(&expansion);
+    }
+
+    fn register_builtin_macro(&mut self, name: Symbol, ext: SyntaxExtensionKind) {
+        if self.builtin_macros.insert(name, BuiltinMacroState::NotYetSeen(ext)).is_some() {
+            self.session
+                .diagnostic()
+                .bug(&format!("built-in macro `{}` was already registered", name));
+        }
+    }
+
+    // Create a new Expansion with a definition site of the provided module, or
+    // a fake empty `#[no_implicit_prelude]` module if no module is provided.
+    fn expansion_for_ast_pass(
+        &mut self,
+        call_site: Span,
+        pass: AstPass,
+        features: &[Symbol],
+        parent_module_id: Option<NodeId>,
+    ) -> LocalExpnId {
+        let parent_module =
+            parent_module_id.map(|module_id| self.local_def_id(module_id).to_def_id());
+        let expn_id = LocalExpnId::fresh(
+            ExpnData::allow_unstable(
+                ExpnKind::AstPass(pass),
+                call_site,
+                self.session.edition(),
+                features.into(),
+                None,
+                parent_module,
+            ),
+            self.create_stable_hashing_context(),
+        );
+
+        let parent_scope =
+            parent_module.map_or(self.empty_module, |def_id| self.expect_module(def_id));
+        self.ast_transform_scopes.insert(expn_id, parent_scope);
+
+        expn_id
+    }
+
+    fn resolve_imports(&mut self) {
+        ImportResolver { r: self }.resolve_imports()
+    }
+
+    fn resolve_macro_invocation(
+        &mut self,
+        invoc: &Invocation,
+        eager_expansion_root: LocalExpnId,
+        force: bool,
+    ) -> Result<Lrc<SyntaxExtension>, Indeterminate> {
+        let invoc_id = invoc.expansion_data.id;
+        let parent_scope = match self.invocation_parent_scopes.get(&invoc_id) {
+            Some(parent_scope) => *parent_scope,
+            None => {
+                // If there's no entry in the table, then we are resolving an eagerly expanded
+                // macro, which should inherit its parent scope from its eager expansion root -
+                // the macro that requested this eager expansion.
+                let parent_scope = *self
+                    .invocation_parent_scopes
+                    .get(&eager_expansion_root)
+                    .expect("non-eager expansion without a parent scope");
+                self.invocation_parent_scopes.insert(invoc_id, parent_scope);
+                parent_scope
+            }
+        };
+
+        let (path, kind, inner_attr, derives) = match invoc.kind {
+            InvocationKind::Attr { ref attr, ref derives, .. } => (
+                &attr.get_normal_item().path,
+                MacroKind::Attr,
+                attr.style == ast::AttrStyle::Inner,
+                self.arenas.alloc_ast_paths(derives),
+            ),
+            InvocationKind::Bang { ref mac, .. } => (&mac.path, MacroKind::Bang, false, &[][..]),
+            InvocationKind::Derive { ref path, .. } => (path, MacroKind::Derive, false, &[][..]),
+        };
+
+        // Derives are not included when `invocations` are collected, so we have to add them here.
+        let parent_scope = &ParentScope { derives, ..parent_scope };
+        let supports_macro_expansion = invoc.fragment_kind.supports_macro_expansion();
+        let node_id = invoc.expansion_data.lint_node_id;
+        let (ext, res) = self.smart_resolve_macro_path(
+            path,
+            kind,
+            supports_macro_expansion,
+            inner_attr,
+            parent_scope,
+            node_id,
+            force,
+            soft_custom_inner_attributes_gate(path, invoc),
+        )?;
+
+        let span = invoc.span();
+        let def_id = res.opt_def_id();
+        invoc_id.set_expn_data(
+            ext.expn_data(
+                parent_scope.expansion,
+                span,
+                fast_print_path(path),
+                def_id,
+                def_id.map(|def_id| self.macro_def_scope(def_id).nearest_parent_mod()),
+            ),
+            self.create_stable_hashing_context(),
+        );
+
+        Ok(ext)
+    }
+
+    fn record_macro_rule_usage(&mut self, id: NodeId, rule_i: usize) {
+        let did = self.local_def_id(id);
+        self.unused_macro_rules.remove(&(did, rule_i));
+    }
+
+    fn check_unused_macros(&mut self) {
+        for (_, &(node_id, ident)) in self.unused_macros.iter() {
+            self.lint_buffer.buffer_lint(
+                UNUSED_MACROS,
+                node_id,
+                ident.span,
+                &format!("unused macro definition: `{}`", ident.name),
+            );
+        }
+        for (&(def_id, arm_i), &(ident, rule_span)) in self.unused_macro_rules.iter() {
+            if self.unused_macros.contains_key(&def_id) {
+                // We already lint the entire macro as unused
+                continue;
+            }
+            let node_id = self.def_id_to_node_id[def_id];
+            self.lint_buffer.buffer_lint(
+                UNUSED_MACRO_RULES,
+                node_id,
+                rule_span,
+                &format!(
+                    "{} rule of macro `{}` is never used",
+                    crate::diagnostics::ordinalize(arm_i + 1),
+                    ident.name
+                ),
+            );
+        }
+    }
+
+    fn has_derive_copy(&self, expn_id: LocalExpnId) -> bool {
+        self.containers_deriving_copy.contains(&expn_id)
+    }
+
+    fn resolve_derives(
+        &mut self,
+        expn_id: LocalExpnId,
+        force: bool,
+        derive_paths: &dyn Fn() -> DeriveResolutions,
+    ) -> Result<(), Indeterminate> {
+        // Block expansion of the container until we resolve all derives in it.
+        // This is required for two reasons:
+        // - Derive helper attributes are in scope for the item to which the `#[derive]`
+        //   is applied, so they have to be produced by the container's expansion rather
+        //   than by individual derives.
+        // - Derives in the container need to know whether one of them is a built-in `Copy`.
+        // Temporarily take the data to avoid borrow checker conflicts.
+        let mut derive_data = mem::take(&mut self.derive_data);
+        let entry = derive_data.entry(expn_id).or_insert_with(|| DeriveData {
+            resolutions: derive_paths(),
+            helper_attrs: Vec::new(),
+            has_derive_copy: false,
+        });
+        let parent_scope = self.invocation_parent_scopes[&expn_id];
+        for (i, (path, _, opt_ext)) in entry.resolutions.iter_mut().enumerate() {
+            if opt_ext.is_none() {
+                *opt_ext = Some(
+                    match self.resolve_macro_path(
+                        &path,
+                        Some(MacroKind::Derive),
+                        &parent_scope,
+                        true,
+                        force,
+                    ) {
+                        Ok((Some(ext), _)) => {
+                            if !ext.helper_attrs.is_empty() {
+                                let last_seg = path.segments.last().unwrap();
+                                let span = last_seg.ident.span.normalize_to_macros_2_0();
+                                entry.helper_attrs.extend(
+                                    ext.helper_attrs
+                                        .iter()
+                                        .map(|name| (i, Ident::new(*name, span))),
+                                );
+                            }
+                            entry.has_derive_copy |= ext.builtin_name == Some(sym::Copy);
+                            ext
+                        }
+                        Ok(_) | Err(Determinacy::Determined) => self.dummy_ext(MacroKind::Derive),
+                        Err(Determinacy::Undetermined) => {
+                            assert!(self.derive_data.is_empty());
+                            self.derive_data = derive_data;
+                            return Err(Indeterminate);
+                        }
+                    },
+                );
+            }
+        }
+        // Sort helpers in a stable way independent from the derive resolution order.
+        entry.helper_attrs.sort_by_key(|(i, _)| *i);
+        self.helper_attrs
+            .insert(expn_id, entry.helper_attrs.iter().map(|(_, ident)| *ident).collect());
+        // Mark this derive as having `Copy` either if it has `Copy` itself or if its parent derive
+        // has `Copy`, to support cases like `#[derive(Clone, Copy)] #[derive(Debug)]`.
+        if entry.has_derive_copy || self.has_derive_copy(parent_scope.expansion) {
+            self.containers_deriving_copy.insert(expn_id);
+        }
+        assert!(self.derive_data.is_empty());
+        self.derive_data = derive_data;
+        Ok(())
+    }
+
+    fn take_derive_resolutions(&mut self, expn_id: LocalExpnId) -> Option<DeriveResolutions> {
+        self.derive_data.remove(&expn_id).map(|data| data.resolutions)
+    }
+
+    // The function that implements the resolution logic of `#[cfg_accessible(path)]`.
+    // Returns true if the path can certainly be resolved in one of three namespaces,
+    // returns false if the path certainly cannot be resolved in any of the three namespaces.
+    // Returns `Indeterminate` if we cannot give a certain answer yet.
+    fn cfg_accessible(
+        &mut self,
+        expn_id: LocalExpnId,
+        path: &ast::Path,
+    ) -> Result<bool, Indeterminate> {
+        let span = path.span;
+        let path = &Segment::from_path(path);
+        let parent_scope = self.invocation_parent_scopes[&expn_id];
+
+        let mut indeterminate = false;
+        for ns in [TypeNS, ValueNS, MacroNS].iter().copied() {
+            match self.maybe_resolve_path(path, Some(ns), &parent_scope) {
+                PathResult::Module(ModuleOrUniformRoot::Module(_)) => return Ok(true),
+                PathResult::NonModule(partial_res) if partial_res.unresolved_segments() == 0 => {
+                    return Ok(true);
+                }
+                PathResult::NonModule(..) |
+                // HACK(Urgau): This shouldn't be necessary
+                PathResult::Failed { is_error_from_last_segment: false, .. } => {
+                    self.session
+                        .struct_span_err(span, "not sure whether the path is accessible or not")
+                        .note("the type may have associated items, but we are currently not checking them")
+                        .emit();
+
+                    // If we get a partially resolved NonModule in one namespace, we should get the
+                    // same result in any other namespaces, so we can return early.
+                    return Ok(false);
+                }
+                PathResult::Indeterminate => indeterminate = true,
+                // We can only be sure that a path doesn't exist after having tested all the
+                // posibilities, only at that time we can return false.
+                PathResult::Failed { .. } => {}
+                PathResult::Module(_) => panic!("unexpected path resolution"),
+            }
+        }
+
+        if indeterminate {
+            return Err(Indeterminate);
+        }
+
+        Ok(false)
+    }
+
+    fn get_proc_macro_quoted_span(&self, krate: CrateNum, id: usize) -> Span {
+        self.crate_loader.cstore().get_proc_macro_quoted_span_untracked(krate, id, self.session)
+    }
+
+    fn declare_proc_macro(&mut self, id: NodeId) {
+        self.proc_macros.push(id)
+    }
+
+    fn registered_tools(&self) -> &RegisteredTools {
+        &self.registered_tools
+    }
+}
+
+impl<'a> Resolver<'a> {
+    /// Resolve macro path with error reporting and recovery.
+    /// Uses dummy syntax extensions for unresolved macros or macros with unexpected resolutions
+    /// for better error recovery.
+    fn smart_resolve_macro_path(
+        &mut self,
+        path: &ast::Path,
+        kind: MacroKind,
+        supports_macro_expansion: SupportsMacroExpansion,
+        inner_attr: bool,
+        parent_scope: &ParentScope<'a>,
+        node_id: NodeId,
+        force: bool,
+        soft_custom_inner_attributes_gate: bool,
+    ) -> Result<(Lrc<SyntaxExtension>, Res), Indeterminate> {
+        let (ext, res) = match self.resolve_macro_path(path, Some(kind), parent_scope, true, force)
+        {
+            Ok((Some(ext), res)) => (ext, res),
+            Ok((None, res)) => (self.dummy_ext(kind), res),
+            Err(Determinacy::Determined) => (self.dummy_ext(kind), Res::Err),
+            Err(Determinacy::Undetermined) => return Err(Indeterminate),
+        };
+
+        // Report errors for the resolved macro.
+        for segment in &path.segments {
+            if let Some(args) = &segment.args {
+                self.session.span_err(args.span(), "generic arguments in macro path");
+            }
+            if kind == MacroKind::Attr && segment.ident.as_str().starts_with("rustc") {
+                self.session.span_err(
+                    segment.ident.span,
+                    "attributes starting with `rustc` are reserved for use by the `rustc` compiler",
+                );
+            }
+        }
+
+        match res {
+            Res::Def(DefKind::Macro(_), def_id) => {
+                if let Some(def_id) = def_id.as_local() {
+                    self.unused_macros.remove(&def_id);
+                    if self.proc_macro_stubs.contains(&def_id) {
+                        self.session.span_err(
+                            path.span,
+                            "can't use a procedural macro from the same crate that defines it",
+                        );
+                    }
+                }
+            }
+            Res::NonMacroAttr(..) | Res::Err => {}
+            _ => panic!("expected `DefKind::Macro` or `Res::NonMacroAttr`"),
+        };
+
+        self.check_stability_and_deprecation(&ext, path, node_id);
+
+        let unexpected_res = if ext.macro_kind() != kind {
+            Some((kind.article(), kind.descr_expected()))
+        } else if matches!(res, Res::Def(..)) {
+            match supports_macro_expansion {
+                SupportsMacroExpansion::No => Some(("a", "non-macro attribute")),
+                SupportsMacroExpansion::Yes { supports_inner_attrs } => {
+                    if inner_attr && !supports_inner_attrs {
+                        Some(("a", "non-macro inner attribute"))
+                    } else {
+                        None
+                    }
+                }
+            }
+        } else {
+            None
+        };
+        if let Some((article, expected)) = unexpected_res {
+            let path_str = pprust::path_to_string(path);
+            let msg = format!("expected {}, found {} `{}`", expected, res.descr(), path_str);
+            self.session
+                .struct_span_err(path.span, &msg)
+                .span_label(path.span, format!("not {} {}", article, expected))
+                .emit();
+            return Ok((self.dummy_ext(kind), Res::Err));
+        }
+
+        // We are trying to avoid reporting this error if other related errors were reported.
+        if res != Res::Err
+            && inner_attr
+            && !self.session.features_untracked().custom_inner_attributes
+        {
+            let msg = match res {
+                Res::Def(..) => "inner macro attributes are unstable",
+                Res::NonMacroAttr(..) => "custom inner attributes are unstable",
+                _ => unreachable!(),
+            };
+            if soft_custom_inner_attributes_gate {
+                self.session.parse_sess.buffer_lint(SOFT_UNSTABLE, path.span, node_id, msg);
+            } else {
+                feature_err(&self.session.parse_sess, sym::custom_inner_attributes, path.span, msg)
+                    .emit();
+            }
+        }
+
+        Ok((ext, res))
+    }
+
+    pub fn resolve_macro_path(
+        &mut self,
+        path: &ast::Path,
+        kind: Option<MacroKind>,
+        parent_scope: &ParentScope<'a>,
+        trace: bool,
+        force: bool,
+    ) -> Result<(Option<Lrc<SyntaxExtension>>, Res), Determinacy> {
+        let path_span = path.span;
+        let mut path = Segment::from_path(path);
+
+        // Possibly apply the macro helper hack
+        if kind == Some(MacroKind::Bang)
+            && path.len() == 1
+            && path[0].ident.span.ctxt().outer_expn_data().local_inner_macros
+        {
+            let root = Ident::new(kw::DollarCrate, path[0].ident.span);
+            path.insert(0, Segment::from_ident(root));
+        }
+
+        let res = if path.len() > 1 {
+            let res = match self.maybe_resolve_path(&path, Some(MacroNS), parent_scope) {
+                PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
+                    Ok(path_res.base_res())
+                }
+                PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
+                PathResult::NonModule(..)
+                | PathResult::Indeterminate
+                | PathResult::Failed { .. } => Err(Determinacy::Determined),
+                PathResult::Module(..) => unreachable!(),
+            };
+
+            if trace {
+                let kind = kind.expect("macro kind must be specified if tracing is enabled");
+                self.multi_segment_macro_resolutions.push((
+                    path,
+                    path_span,
+                    kind,
+                    *parent_scope,
+                    res.ok(),
+                ));
+            }
+
+            self.prohibit_imported_non_macro_attrs(None, res.ok(), path_span);
+            res
+        } else {
+            let scope_set = kind.map_or(ScopeSet::All(MacroNS, false), ScopeSet::Macro);
+            let binding = self.early_resolve_ident_in_lexical_scope(
+                path[0].ident,
+                scope_set,
+                parent_scope,
+                None,
+                force,
+                None,
+            );
+            if let Err(Determinacy::Undetermined) = binding {
+                return Err(Determinacy::Undetermined);
+            }
+
+            if trace {
+                let kind = kind.expect("macro kind must be specified if tracing is enabled");
+                self.single_segment_macro_resolutions.push((
+                    path[0].ident,
+                    kind,
+                    *parent_scope,
+                    binding.ok(),
+                ));
+            }
+
+            let res = binding.map(|binding| binding.res());
+            self.prohibit_imported_non_macro_attrs(binding.ok(), res.ok(), path_span);
+            res
+        };
+
+        res.map(|res| (self.get_macro(res).map(|macro_data| macro_data.ext), res))
+    }
+
+    pub(crate) fn finalize_macro_resolutions(&mut self) {
+        let check_consistency = |this: &mut Self,
+                                 path: &[Segment],
+                                 span,
+                                 kind: MacroKind,
+                                 initial_res: Option<Res>,
+                                 res: Res| {
+            if let Some(initial_res) = initial_res {
+                if res != initial_res {
+                    // Make sure compilation does not succeed if preferred macro resolution
+                    // has changed after the macro had been expanded. In theory all such
+                    // situations should be reported as errors, so this is a bug.
+                    this.session.delay_span_bug(span, "inconsistent resolution for a macro");
+                }
+            } else {
+                // It's possible that the macro was unresolved (indeterminate) and silently
+                // expanded into a dummy fragment for recovery during expansion.
+                // Now, post-expansion, the resolution may succeed, but we can't change the
+                // past and need to report an error.
+                // However, non-speculative `resolve_path` can successfully return private items
+                // even if speculative `resolve_path` returned nothing previously, so we skip this
+                // less informative error if the privacy error is reported elsewhere.
+                if this.privacy_errors.is_empty() {
+                    let msg = format!(
+                        "cannot determine resolution for the {} `{}`",
+                        kind.descr(),
+                        Segment::names_to_string(path)
+                    );
+                    let msg_note = "import resolution is stuck, try simplifying macro imports";
+                    this.session.struct_span_err(span, &msg).note(msg_note).emit();
+                }
+            }
+        };
+
+        let macro_resolutions = mem::take(&mut self.multi_segment_macro_resolutions);
+        for (mut path, path_span, kind, parent_scope, initial_res) in macro_resolutions {
+            // FIXME: Path resolution will ICE if segment IDs present.
+            for seg in &mut path {
+                seg.id = None;
+            }
+            match self.resolve_path(
+                &path,
+                Some(MacroNS),
+                &parent_scope,
+                Some(Finalize::new(ast::CRATE_NODE_ID, path_span)),
+                None,
+            ) {
+                PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
+                    let res = path_res.base_res();
+                    check_consistency(self, &path, path_span, kind, initial_res, res);
+                }
+                path_res @ PathResult::NonModule(..) | path_res @ PathResult::Failed { .. } => {
+                    let (span, label) = if let PathResult::Failed { span, label, .. } = path_res {
+                        (span, label)
+                    } else {
+                        (
+                            path_span,
+                            format!(
+                                "partially resolved path in {} {}",
+                                kind.article(),
+                                kind.descr()
+                            ),
+                        )
+                    };
+                    self.report_error(
+                        span,
+                        ResolutionError::FailedToResolve { label, suggestion: None },
+                    );
+                }
+                PathResult::Module(..) | PathResult::Indeterminate => unreachable!(),
+            }
+        }
+
+        let macro_resolutions = mem::take(&mut self.single_segment_macro_resolutions);
+        for (ident, kind, parent_scope, initial_binding) in macro_resolutions {
+            match self.early_resolve_ident_in_lexical_scope(
+                ident,
+                ScopeSet::Macro(kind),
+                &parent_scope,
+                Some(Finalize::new(ast::CRATE_NODE_ID, ident.span)),
+                true,
+                None,
+            ) {
+                Ok(binding) => {
+                    let initial_res = initial_binding.map(|initial_binding| {
+                        self.record_use(ident, initial_binding, false);
+                        initial_binding.res()
+                    });
+                    let res = binding.res();
+                    let seg = Segment::from_ident(ident);
+                    check_consistency(self, &[seg], ident.span, kind, initial_res, res);
+                    if res == Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat) {
+                        let node_id = self
+                            .invocation_parents
+                            .get(&parent_scope.expansion)
+                            .map_or(ast::CRATE_NODE_ID, |id| self.def_id_to_node_id[id.0]);
+                        self.lint_buffer.buffer_lint_with_diagnostic(
+                            LEGACY_DERIVE_HELPERS,
+                            node_id,
+                            ident.span,
+                            "derive helper attribute is used before it is introduced",
+                            BuiltinLintDiagnostics::LegacyDeriveHelpers(binding.span),
+                        );
+                    }
+                }
+                Err(..) => {
+                    let expected = kind.descr_expected();
+                    let msg = format!("cannot find {} `{}` in this scope", expected, ident);
+                    let mut err = self.session.struct_span_err(ident.span, &msg);
+                    self.unresolved_macro_suggestions(&mut err, kind, &parent_scope, ident);
+                    err.emit();
+                }
+            }
+        }
+
+        let builtin_attrs = mem::take(&mut self.builtin_attrs);
+        for (ident, parent_scope) in builtin_attrs {
+            let _ = self.early_resolve_ident_in_lexical_scope(
+                ident,
+                ScopeSet::Macro(MacroKind::Attr),
+                &parent_scope,
+                Some(Finalize::new(ast::CRATE_NODE_ID, ident.span)),
+                true,
+                None,
+            );
+        }
+    }
+
+    fn check_stability_and_deprecation(
+        &mut self,
+        ext: &SyntaxExtension,
+        path: &ast::Path,
+        node_id: NodeId,
+    ) {
+        let span = path.span;
+        if let Some(stability) = &ext.stability {
+            if let StabilityLevel::Unstable { reason, issue, is_soft, implied_by } = stability.level
+            {
+                let feature = stability.feature;
+
+                let is_allowed = |feature| {
+                    self.active_features.contains(&feature) || span.allows_unstable(feature)
+                };
+                let allowed_by_implication =
+                    implied_by.map(|feature| is_allowed(feature)).unwrap_or(false);
+                if !is_allowed(feature) && !allowed_by_implication {
+                    let lint_buffer = &mut self.lint_buffer;
+                    let soft_handler =
+                        |lint, span, msg: &_| lint_buffer.buffer_lint(lint, node_id, span, msg);
+                    stability::report_unstable(
+                        self.session,
+                        feature,
+                        reason.to_opt_reason(),
+                        issue,
+                        None,
+                        is_soft,
+                        span,
+                        soft_handler,
+                    );
+                }
+            }
+        }
+        if let Some(depr) = &ext.deprecation {
+            let path = pprust::path_to_string(&path);
+            let (message, lint) = stability::deprecation_message_and_lint(depr, "macro", &path);
+            stability::early_report_deprecation(
+                &mut self.lint_buffer,
+                &message,
+                depr.suggestion,
+                lint,
+                span,
+                node_id,
+            );
+        }
+    }
+
+    fn prohibit_imported_non_macro_attrs(
+        &self,
+        binding: Option<&'a NameBinding<'a>>,
+        res: Option<Res>,
+        span: Span,
+    ) {
+        if let Some(Res::NonMacroAttr(kind)) = res {
+            if kind != NonMacroAttrKind::Tool && binding.map_or(true, |b| b.is_import()) {
+                let msg =
+                    format!("cannot use {} {} through an import", kind.article(), kind.descr());
+                let mut err = self.session.struct_span_err(span, &msg);
+                if let Some(binding) = binding {
+                    err.span_note(binding.span, &format!("the {} imported here", kind.descr()));
+                }
+                err.emit();
+            }
+        }
+    }
+
+    pub(crate) fn check_reserved_macro_name(&mut self, ident: Ident, res: Res) {
+        // Reserve some names that are not quite covered by the general check
+        // performed on `Resolver::builtin_attrs`.
+        if ident.name == sym::cfg || ident.name == sym::cfg_attr {
+            let macro_kind = self.get_macro(res).map(|macro_data| macro_data.ext.macro_kind());
+            if macro_kind.is_some() && sub_namespace_match(macro_kind, Some(MacroKind::Attr)) {
+                self.session.span_err(
+                    ident.span,
+                    &format!("name `{}` is reserved in attribute namespace", ident),
+                );
+            }
+        }
+    }
+
+    /// Compile the macro into a `SyntaxExtension` and its rule spans.
+    ///
+    /// Possibly replace its expander to a pre-defined one for built-in macros.
+    pub(crate) fn compile_macro(
+        &mut self,
+        item: &ast::Item,
+        edition: Edition,
+    ) -> (SyntaxExtension, Vec<(usize, Span)>) {
+        let (mut result, mut rule_spans) = compile_declarative_macro(
+            &self.session,
+            self.session.features_untracked(),
+            item,
+            edition,
+        );
+
+        if let Some(builtin_name) = result.builtin_name {
+            // The macro was marked with `#[rustc_builtin_macro]`.
+            if let Some(builtin_macro) = self.builtin_macros.get_mut(&builtin_name) {
+                // The macro is a built-in, replace its expander function
+                // while still taking everything else from the source code.
+                // If we already loaded this builtin macro, give a better error message than 'no such builtin macro'.
+                match mem::replace(builtin_macro, BuiltinMacroState::AlreadySeen(item.span)) {
+                    BuiltinMacroState::NotYetSeen(ext) => {
+                        result.kind = ext;
+                        rule_spans = Vec::new();
+                        if item.id != ast::DUMMY_NODE_ID {
+                            self.builtin_macro_kinds
+                                .insert(self.local_def_id(item.id), result.macro_kind());
+                        }
+                    }
+                    BuiltinMacroState::AlreadySeen(span) => {
+                        struct_span_err!(
+                            self.session,
+                            item.span,
+                            E0773,
+                            "attempted to define built-in macro more than once"
+                        )
+                        .span_note(span, "previously defined here")
+                        .emit();
+                    }
+                }
+            } else {
+                let msg = format!("cannot find a built-in macro with name `{}`", item.ident);
+                self.session.span_err(item.span, &msg);
+            }
+        }
+
+        (result, rule_spans)
+    }
+}