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

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

3 files changed, 8497 insertions, 0 deletions

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);
+            }
+        }
+    }
+}