//! This module implements [RFC 1946]: Intra-rustdoc-links
//!
//! [RFC 1946]: https://github.com/rust-lang/rfcs/blob/master/text/1946-intra-rustdoc-links.md

use pulldown_cmark::LinkType;
use rustc_ast::util::comments::may_have_doc_links;
use rustc_data_structures::{
    fx::{FxHashMap, FxHashSet},
    intern::Interned,
};
use rustc_errors::{Applicability, Diagnostic};
use rustc_hir::def::Namespace::*;
use rustc_hir::def::{DefKind, Namespace, PerNS};
use rustc_hir::def_id::{DefId, CRATE_DEF_ID};
use rustc_hir::Mutability;
use rustc_middle::ty::{DefIdTree, Ty, TyCtxt};
use rustc_middle::{bug, ty};
use rustc_resolve::ParentScope;
use rustc_session::lint::Lint;
use rustc_span::hygiene::MacroKind;
use rustc_span::symbol::{sym, Ident, Symbol};
use rustc_span::BytePos;
use smallvec::{smallvec, SmallVec};

use std::borrow::Cow;
use std::mem;
use std::ops::Range;

use crate::clean::{self, utils::find_nearest_parent_module};
use crate::clean::{Crate, Item, ItemId, ItemLink, PrimitiveType};
use crate::core::DocContext;
use crate::html::markdown::{markdown_links, MarkdownLink};
use crate::lint::{BROKEN_INTRA_DOC_LINKS, PRIVATE_INTRA_DOC_LINKS};
use crate::passes::Pass;
use crate::visit::DocVisitor;

mod early;
pub(crate) use early::early_resolve_intra_doc_links;

pub(crate) const COLLECT_INTRA_DOC_LINKS: Pass = Pass {
    name: "collect-intra-doc-links",
    run: collect_intra_doc_links,
    description: "resolves intra-doc links",
};

fn collect_intra_doc_links(krate: Crate, cx: &mut DocContext<'_>) -> Crate {
    let mut collector =
        LinkCollector { cx, mod_ids: Vec::new(), visited_links: FxHashMap::default() };
    collector.visit_crate(&krate);
    krate
}

#[derive(Copy, Clone, Debug, Hash)]
enum Res {
    Def(DefKind, DefId),
    Primitive(PrimitiveType),
}

type ResolveRes = rustc_hir::def::Res<rustc_ast::NodeId>;

impl Res {
    fn descr(self) -> &'static str {
        match self {
            Res::Def(kind, id) => ResolveRes::Def(kind, id).descr(),
            Res::Primitive(_) => "builtin type",
        }
    }

    fn article(self) -> &'static str {
        match self {
            Res::Def(kind, id) => ResolveRes::Def(kind, id).article(),
            Res::Primitive(_) => "a",
        }
    }

    fn name(self, tcx: TyCtxt<'_>) -> Symbol {
        match self {
            Res::Def(_, id) => tcx.item_name(id),
            Res::Primitive(prim) => prim.as_sym(),
        }
    }

    fn def_id(self, tcx: TyCtxt<'_>) -> Option<DefId> {
        match self {
            Res::Def(_, id) => Some(id),
            Res::Primitive(prim) => PrimitiveType::primitive_locations(tcx).get(&prim).copied(),
        }
    }

    fn from_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Res {
        Res::Def(tcx.def_kind(def_id), def_id)
    }

    /// Used for error reporting.
    fn disambiguator_suggestion(self) -> Suggestion {
        let kind = match self {
            Res::Primitive(_) => return Suggestion::Prefix("prim"),
            Res::Def(kind, _) => kind,
        };
        if kind == DefKind::Macro(MacroKind::Bang) {
            return Suggestion::Macro;
        } else if kind == DefKind::Fn || kind == DefKind::AssocFn {
            return Suggestion::Function;
        } else if kind == DefKind::Field {
            return Suggestion::RemoveDisambiguator;
        }

        let prefix = match kind {
            DefKind::Struct => "struct",
            DefKind::Enum => "enum",
            DefKind::Trait => "trait",
            DefKind::Union => "union",
            DefKind::Mod => "mod",
            DefKind::Const | DefKind::ConstParam | DefKind::AssocConst | DefKind::AnonConst => {
                "const"
            }
            DefKind::Static(_) => "static",
            DefKind::Macro(MacroKind::Derive) => "derive",
            // Now handle things that don't have a specific disambiguator
            _ => match kind
                .ns()
                .expect("tried to calculate a disambiguator for a def without a namespace?")
            {
                Namespace::TypeNS => "type",
                Namespace::ValueNS => "value",
                Namespace::MacroNS => "macro",
            },
        };

        Suggestion::Prefix(prefix)
    }
}

impl TryFrom<ResolveRes> for Res {
    type Error = ();

    fn try_from(res: ResolveRes) -> Result<Self, ()> {
        use rustc_hir::def::Res::*;
        match res {
            Def(kind, id) => Ok(Res::Def(kind, id)),
            PrimTy(prim) => Ok(Res::Primitive(PrimitiveType::from_hir(prim))),
            // e.g. `#[derive]`
            NonMacroAttr(..) | Err => Result::Err(()),
            other => bug!("unrecognized res {:?}", other),
        }
    }
}

/// The link failed to resolve. [`resolution_failure`] should look to see if there's
/// a more helpful error that can be given.
#[derive(Debug)]
struct UnresolvedPath<'a> {
    /// Item on which the link is resolved, used for resolving `Self`.
    item_id: ItemId,
    /// The scope the link was resolved in.
    module_id: DefId,
    /// If part of the link resolved, this has the `Res`.
    ///
    /// In `[std::io::Error::x]`, `std::io::Error` would be a partial resolution.
    partial_res: Option<Res>,
    /// The remaining unresolved path segments.
    ///
    /// In `[std::io::Error::x]`, `x` would be unresolved.
    unresolved: Cow<'a, str>,
}

#[derive(Debug)]
enum ResolutionFailure<'a> {
    /// This resolved, but with the wrong namespace.
    WrongNamespace {
        /// What the link resolved to.
        res: Res,
        /// The expected namespace for the resolution, determined from the link's disambiguator.
        ///
        /// E.g., for `[fn@Result]` this is [`Namespace::ValueNS`],
        /// even though `Result`'s actual namespace is [`Namespace::TypeNS`].
        expected_ns: Namespace,
    },
    NotResolved(UnresolvedPath<'a>),
}

#[derive(Clone, Copy, Debug)]
enum MalformedGenerics {
    /// This link has unbalanced angle brackets.
    ///
    /// For example, `Vec<T` should trigger this, as should `Vec<T>>`.
    UnbalancedAngleBrackets,
    /// The generics are not attached to a type.
    ///
    /// For example, `<T>` should trigger this.
    ///
    /// This is detected by checking if the path is empty after the generics are stripped.
    MissingType,
    /// The link uses fully-qualified syntax, which is currently unsupported.
    ///
    /// For example, `<Vec as IntoIterator>::into_iter` should trigger this.
    ///
    /// This is detected by checking if ` as ` (the keyword `as` with spaces around it) is inside
    /// angle brackets.
    HasFullyQualifiedSyntax,
    /// The link has an invalid path separator.
    ///
    /// For example, `Vec:<T>:new()` should trigger this. Note that `Vec:new()` will **not**
    /// trigger this because it has no generics and thus [`strip_generics_from_path`] will not be
    /// called.
    ///
    /// Note that this will also **not** be triggered if the invalid path separator is inside angle
    /// brackets because rustdoc mostly ignores what's inside angle brackets (except for
    /// [`HasFullyQualifiedSyntax`](MalformedGenerics::HasFullyQualifiedSyntax)).
    ///
    /// This is detected by checking if there is a colon followed by a non-colon in the link.
    InvalidPathSeparator,
    /// The link has too many angle brackets.
    ///
    /// For example, `Vec<<T>>` should trigger this.
    TooManyAngleBrackets,
    /// The link has empty angle brackets.
    ///
    /// For example, `Vec<>` should trigger this.
    EmptyAngleBrackets,
}

#[derive(Clone, Debug, Hash, PartialEq, Eq)]
pub(crate) enum UrlFragment {
    Item(DefId),
    /// A part of a page that isn't a rust item.
    ///
    /// Eg: `[Vector Examples](std::vec::Vec#examples)`
    UserWritten(String),
}

impl UrlFragment {
    /// Render the fragment, including the leading `#`.
    pub(crate) fn render(&self, s: &mut String, tcx: TyCtxt<'_>) {
        s.push('#');
        match self {
            &UrlFragment::Item(def_id) => {
                let kind = match tcx.def_kind(def_id) {
                    DefKind::AssocFn => {
                        if tcx.impl_defaultness(def_id).has_value() {
                            "method."
                        } else {
                            "tymethod."
                        }
                    }
                    DefKind::AssocConst => "associatedconstant.",
                    DefKind::AssocTy => "associatedtype.",
                    DefKind::Variant => "variant.",
                    DefKind::Field => {
                        let parent_id = tcx.parent(def_id);
                        if tcx.def_kind(parent_id) == DefKind::Variant {
                            s.push_str("variant.");
                            s.push_str(tcx.item_name(parent_id).as_str());
                            ".field."
                        } else {
                            "structfield."
                        }
                    }
                    kind => bug!("unexpected associated item kind: {:?}", kind),
                };
                s.push_str(kind);
                s.push_str(tcx.item_name(def_id).as_str());
            }
            UrlFragment::UserWritten(raw) => s.push_str(&raw),
        }
    }
}

#[derive(Clone, Debug, Hash, PartialEq, Eq)]
struct ResolutionInfo {
    item_id: ItemId,
    module_id: DefId,
    dis: Option<Disambiguator>,
    path_str: String,
    extra_fragment: Option<String>,
}

#[derive(Clone)]
struct DiagnosticInfo<'a> {
    item: &'a Item,
    dox: &'a str,
    ori_link: &'a str,
    link_range: Range<usize>,
}

struct LinkCollector<'a, 'tcx> {
    cx: &'a mut DocContext<'tcx>,
    /// A stack of modules used to decide what scope to resolve in.
    ///
    /// The last module will be used if the parent scope of the current item is
    /// unknown.
    mod_ids: Vec<DefId>,
    /// Cache the resolved links so we can avoid resolving (and emitting errors for) the same link.
    /// The link will be `None` if it could not be resolved (i.e. the error was cached).
    visited_links: FxHashMap<ResolutionInfo, Option<(Res, Option<UrlFragment>)>>,
}

impl<'a, 'tcx> LinkCollector<'a, 'tcx> {
    /// Given a full link, parse it as an [enum struct variant].
    ///
    /// In particular, this will return an error whenever there aren't three
    /// full path segments left in the link.
    ///
    /// [enum struct variant]: rustc_hir::VariantData::Struct
    fn variant_field<'path>(
        &self,
        path_str: &'path str,
        item_id: ItemId,
        module_id: DefId,
    ) -> Result<(Res, DefId), UnresolvedPath<'path>> {
        let tcx = self.cx.tcx;
        let no_res = || UnresolvedPath {
            item_id,
            module_id,
            partial_res: None,
            unresolved: path_str.into(),
        };

        debug!("looking for enum variant {}", path_str);
        let mut split = path_str.rsplitn(3, "::");
        let variant_field_name = split
            .next()
            .map(|f| Symbol::intern(f))
            .expect("fold_item should ensure link is non-empty");
        let variant_name =
            // we're not sure this is a variant at all, so use the full string
            // If there's no second component, the link looks like `[path]`.
            // So there's no partial res and we should say the whole link failed to resolve.
            split.next().map(|f|  Symbol::intern(f)).ok_or_else(no_res)?;
        let path = split
            .next()
            .map(|f| f.to_owned())
            // If there's no third component, we saw `[a::b]` before and it failed to resolve.
            // So there's no partial res.
            .ok_or_else(no_res)?;
        let ty_res = self.resolve_path(&path, TypeNS, item_id, module_id).ok_or_else(no_res)?;

        match ty_res {
            Res::Def(DefKind::Enum, did) => match tcx.type_of(did).kind() {
                ty::Adt(def, _) if def.is_enum() => {
                    if let Some(field) = def.all_fields().find(|f| f.name == variant_field_name) {
                        Ok((ty_res, field.did))
                    } else {
                        Err(UnresolvedPath {
                            item_id,
                            module_id,
                            partial_res: Some(Res::Def(DefKind::Enum, def.did())),
                            unresolved: variant_field_name.to_string().into(),
                        })
                    }
                }
                _ => unreachable!(),
            },
            _ => Err(UnresolvedPath {
                item_id,
                module_id,
                partial_res: Some(ty_res),
                unresolved: variant_name.to_string().into(),
            }),
        }
    }

    /// Given a primitive type, try to resolve an associated item.
    fn resolve_primitive_associated_item(
        &self,
        prim_ty: PrimitiveType,
        ns: Namespace,
        item_name: Symbol,
    ) -> Option<(Res, DefId)> {
        let tcx = self.cx.tcx;

        prim_ty.impls(tcx).find_map(|impl_| {
            tcx.associated_items(impl_)
                .find_by_name_and_namespace(tcx, Ident::with_dummy_span(item_name), ns, impl_)
                .map(|item| (Res::Primitive(prim_ty), item.def_id))
        })
    }

    fn resolve_self_ty(&self, path_str: &str, ns: Namespace, item_id: ItemId) -> Option<Res> {
        if ns != TypeNS || path_str != "Self" {
            return None;
        }

        let tcx = self.cx.tcx;
        item_id
            .as_def_id()
            .map(|def_id| match tcx.def_kind(def_id) {
                def_kind @ (DefKind::AssocFn
                | DefKind::AssocConst
                | DefKind::AssocTy
                | DefKind::Variant
                | DefKind::Field) => {
                    let parent_def_id = tcx.parent(def_id);
                    if def_kind == DefKind::Field && tcx.def_kind(parent_def_id) == DefKind::Variant
                    {
                        tcx.parent(parent_def_id)
                    } else {
                        parent_def_id
                    }
                }
                _ => def_id,
            })
            .and_then(|self_id| match tcx.def_kind(self_id) {
                DefKind::Impl => self.def_id_to_res(self_id),
                DefKind::Use => None,
                def_kind => Some(Res::Def(def_kind, self_id)),
            })
    }

    /// Convenience wrapper around `resolve_rustdoc_path`.
    ///
    /// This also handles resolving `true` and `false` as booleans.
    /// NOTE: `resolve_rustdoc_path` knows only about paths, not about types.
    /// Associated items will never be resolved by this function.
    fn resolve_path(
        &self,
        path_str: &str,
        ns: Namespace,
        item_id: ItemId,
        module_id: DefId,
    ) -> Option<Res> {
        if let res @ Some(..) = self.resolve_self_ty(path_str, ns, item_id) {
            return res;
        }

        // Resolver doesn't know about true, false, and types that aren't paths (e.g. `()`).
        let result = self
            .cx
            .resolver_caches
            .doc_link_resolutions
            .get(&(Symbol::intern(path_str), ns, module_id))
            .copied()
            .unwrap_or_else(|| {
                self.cx.enter_resolver(|resolver| {
                    let parent_scope =
                        ParentScope::module(resolver.expect_module(module_id), resolver);
                    resolver.resolve_rustdoc_path(path_str, ns, parent_scope)
                })
            })
            .and_then(|res| res.try_into().ok())
            .or_else(|| resolve_primitive(path_str, ns));
        debug!("{} resolved to {:?} in namespace {:?}", path_str, result, ns);
        result
    }

    /// Resolves a string as a path within a particular namespace. Returns an
    /// optional URL fragment in the case of variants and methods.
    fn resolve<'path>(
        &mut self,
        path_str: &'path str,
        ns: Namespace,
        item_id: ItemId,
        module_id: DefId,
    ) -> Result<(Res, Option<DefId>), UnresolvedPath<'path>> {
        if let Some(res) = self.resolve_path(path_str, ns, item_id, module_id) {
            return Ok(match res {
                Res::Def(
                    DefKind::AssocFn | DefKind::AssocConst | DefKind::AssocTy | DefKind::Variant,
                    def_id,
                ) => (Res::from_def_id(self.cx.tcx, self.cx.tcx.parent(def_id)), Some(def_id)),
                _ => (res, None),
            });
        } else if ns == MacroNS {
            return Err(UnresolvedPath {
                item_id,
                module_id,
                partial_res: None,
                unresolved: path_str.into(),
            });
        }

        // Try looking for methods and associated items.
        let mut split = path_str.rsplitn(2, "::");
        // NB: `split`'s first element is always defined, even if the delimiter was not present.
        // NB: `item_str` could be empty when resolving in the root namespace (e.g. `::std`).
        let item_str = split.next().unwrap();
        let item_name = Symbol::intern(item_str);
        let path_root = split
            .next()
            .map(|f| f.to_owned())
            // If there's no `::`, it's not an associated item.
            // So we can be sure that `rustc_resolve` was accurate when it said it wasn't resolved.
            .ok_or_else(|| {
                debug!("found no `::`, assuming {} was correctly not in scope", item_name);
                UnresolvedPath {
                    item_id,
                    module_id,
                    partial_res: None,
                    unresolved: item_str.into(),
                }
            })?;

        // FIXME(#83862): this arbitrarily gives precedence to primitives over modules to support
        // links to primitives when `#[doc(primitive)]` is present. It should give an ambiguity
        // error instead and special case *only* modules with `#[doc(primitive)]`, not all
        // primitives.
        resolve_primitive(&path_root, TypeNS)
            .or_else(|| self.resolve_path(&path_root, TypeNS, item_id, module_id))
            .and_then(|ty_res| {
                self.resolve_associated_item(ty_res, item_name, ns, module_id).map(Ok)
            })
            .unwrap_or_else(|| {
                if ns == Namespace::ValueNS {
                    self.variant_field(path_str, item_id, module_id)
                } else {
                    Err(UnresolvedPath {
                        item_id,
                        module_id,
                        partial_res: None,
                        unresolved: path_root.into(),
                    })
                }
            })
            .map(|(res, def_id)| (res, Some(def_id)))
    }

    /// Convert a DefId to a Res, where possible.
    ///
    /// This is used for resolving type aliases.
    fn def_id_to_res(&self, ty_id: DefId) -> Option<Res> {
        use PrimitiveType::*;
        Some(match *self.cx.tcx.type_of(ty_id).kind() {
            ty::Bool => Res::Primitive(Bool),
            ty::Char => Res::Primitive(Char),
            ty::Int(ity) => Res::Primitive(ity.into()),
            ty::Uint(uty) => Res::Primitive(uty.into()),
            ty::Float(fty) => Res::Primitive(fty.into()),
            ty::Str => Res::Primitive(Str),
            ty::Tuple(tys) if tys.is_empty() => Res::Primitive(Unit),
            ty::Tuple(_) => Res::Primitive(Tuple),
            ty::Array(..) => Res::Primitive(Array),
            ty::Slice(_) => Res::Primitive(Slice),
            ty::RawPtr(_) => Res::Primitive(RawPointer),
            ty::Ref(..) => Res::Primitive(Reference),
            ty::FnDef(..) => panic!("type alias to a function definition"),
            ty::FnPtr(_) => Res::Primitive(Fn),
            ty::Never => Res::Primitive(Never),
            ty::Adt(ty::AdtDef(Interned(&ty::AdtDefData { did, .. }, _)), _) | ty::Foreign(did) => {
                Res::from_def_id(self.cx.tcx, did)
            }
            ty::Alias(..)
            | ty::Closure(..)
            | ty::Generator(..)
            | ty::GeneratorWitness(_)
            | ty::Dynamic(..)
            | ty::Param(_)
            | ty::Bound(..)
            | ty::Placeholder(_)
            | ty::Infer(_)
            | ty::Error(_) => return None,
        })
    }

    /// Convert a PrimitiveType to a Ty, where possible.
    ///
    /// This is used for resolving trait impls for primitives
    fn primitive_type_to_ty(&mut self, prim: PrimitiveType) -> Option<Ty<'tcx>> {
        use PrimitiveType::*;
        let tcx = self.cx.tcx;

        // FIXME: Only simple types are supported here, see if we can support
        // other types such as Tuple, Array, Slice, etc.
        // See https://github.com/rust-lang/rust/issues/90703#issuecomment-1004263455
        Some(tcx.mk_ty(match prim {
            Bool => ty::Bool,
            Str => ty::Str,
            Char => ty::Char,
            Never => ty::Never,
            I8 => ty::Int(ty::IntTy::I8),
            I16 => ty::Int(ty::IntTy::I16),
            I32 => ty::Int(ty::IntTy::I32),
            I64 => ty::Int(ty::IntTy::I64),
            I128 => ty::Int(ty::IntTy::I128),
            Isize => ty::Int(ty::IntTy::Isize),
            F32 => ty::Float(ty::FloatTy::F32),
            F64 => ty::Float(ty::FloatTy::F64),
            U8 => ty::Uint(ty::UintTy::U8),
            U16 => ty::Uint(ty::UintTy::U16),
            U32 => ty::Uint(ty::UintTy::U32),
            U64 => ty::Uint(ty::UintTy::U64),
            U128 => ty::Uint(ty::UintTy::U128),
            Usize => ty::Uint(ty::UintTy::Usize),
            _ => return None,
        }))
    }

    /// Resolve an associated item, returning its containing page's `Res`
    /// and the fragment targeting the associated item on its page.
    fn resolve_associated_item(
        &mut self,
        root_res: Res,
        item_name: Symbol,
        ns: Namespace,
        module_id: DefId,
    ) -> Option<(Res, DefId)> {
        let tcx = self.cx.tcx;

        match root_res {
            Res::Primitive(prim) => {
                self.resolve_primitive_associated_item(prim, ns, item_name).or_else(|| {
                    self.primitive_type_to_ty(prim)
                        .and_then(|ty| {
                            resolve_associated_trait_item(ty, module_id, item_name, ns, self.cx)
                        })
                        .map(|item| (root_res, item.def_id))
                })
            }
            Res::Def(DefKind::TyAlias, did) => {
                // Resolve the link on the type the alias points to.
                // FIXME: if the associated item is defined directly on the type alias,
                // it will show up on its documentation page, we should link there instead.
                let res = self.def_id_to_res(did)?;
                self.resolve_associated_item(res, item_name, ns, module_id)
            }
            Res::Def(
                def_kind @ (DefKind::Struct | DefKind::Union | DefKind::Enum | DefKind::ForeignTy),
                did,
            ) => {
                debug!("looking for associated item named {} for item {:?}", item_name, did);
                // Checks if item_name is a variant of the `SomeItem` enum
                if ns == TypeNS && def_kind == DefKind::Enum {
                    match tcx.type_of(did).kind() {
                        ty::Adt(adt_def, _) => {
                            for variant in adt_def.variants() {
                                if variant.name == item_name {
                                    return Some((root_res, variant.def_id));
                                }
                            }
                        }
                        _ => unreachable!(),
                    }
                }

                // Checks if item_name belongs to `impl SomeItem`
                let assoc_item = tcx
                    .inherent_impls(did)
                    .iter()
                    .flat_map(|&imp| {
                        tcx.associated_items(imp).find_by_name_and_namespace(
                            tcx,
                            Ident::with_dummy_span(item_name),
                            ns,
                            imp,
                        )
                    })
                    .copied()
                    // There should only ever be one associated item that matches from any inherent impl
                    .next()
                    // Check if item_name belongs to `impl SomeTrait for SomeItem`
                    // FIXME(#74563): This gives precedence to `impl SomeItem`:
                    // Although having both would be ambiguous, use impl version for compatibility's sake.
                    // To handle that properly resolve() would have to support
                    // something like [`ambi_fn`](<SomeStruct as SomeTrait>::ambi_fn)
                    .or_else(|| {
                        resolve_associated_trait_item(
                            tcx.type_of(did),
                            module_id,
                            item_name,
                            ns,
                            self.cx,
                        )
                    });

                debug!("got associated item {:?}", assoc_item);

                if let Some(item) = assoc_item {
                    return Some((root_res, item.def_id));
                }

                if ns != Namespace::ValueNS {
                    return None;
                }
                debug!("looking for fields named {} for {:?}", item_name, did);
                // FIXME: this doesn't really belong in `associated_item` (maybe `variant_field` is better?)
                // NOTE: it's different from variant_field because it only resolves struct fields,
                // not variant fields (2 path segments, not 3).
                //
                // We need to handle struct (and union) fields in this code because
                // syntactically their paths are identical to associated item paths:
                // `module::Type::field` and `module::Type::Assoc`.
                //
                // On the other hand, variant fields can't be mistaken for associated
                // items because they look like this: `module::Type::Variant::field`.
                //
                // Variants themselves don't need to be handled here, even though
                // they also look like associated items (`module::Type::Variant`),
                // because they are real Rust syntax (unlike the intra-doc links
                // field syntax) and are handled by the compiler's resolver.
                let def = match tcx.type_of(did).kind() {
                    ty::Adt(def, _) if !def.is_enum() => def,
                    _ => return None,
                };
                let field =
                    def.non_enum_variant().fields.iter().find(|item| item.name == item_name)?;
                Some((root_res, field.did))
            }
            Res::Def(DefKind::Trait, did) => tcx
                .associated_items(did)
                .find_by_name_and_namespace(tcx, Ident::with_dummy_span(item_name), ns, did)
                .map(|item| {
                    let res = Res::Def(item.kind.as_def_kind(), item.def_id);
                    (res, item.def_id)
                }),
            _ => None,
        }
    }
}

fn full_res(tcx: TyCtxt<'_>, (base, assoc_item): (Res, Option<DefId>)) -> Res {
    assoc_item.map_or(base, |def_id| Res::from_def_id(tcx, def_id))
}

/// Look to see if a resolved item has an associated item named `item_name`.
///
/// Given `[std::io::Error::source]`, where `source` is unresolved, this would
/// find `std::error::Error::source` and return
/// `<io::Error as error::Error>::source`.
fn resolve_associated_trait_item<'a>(
    ty: Ty<'a>,
    module: DefId,
    item_name: Symbol,
    ns: Namespace,
    cx: &mut DocContext<'a>,
) -> Option<ty::AssocItem> {
    // FIXME: this should also consider blanket impls (`impl<T> X for T`). Unfortunately
    // `get_auto_trait_and_blanket_impls` is broken because the caching behavior is wrong. In the
    // meantime, just don't look for these blanket impls.

    // Next consider explicit impls: `impl MyTrait for MyType`
    // Give precedence to inherent impls.
    let traits = trait_impls_for(cx, ty, module);
    debug!("considering traits {:?}", traits);
    let mut candidates = traits.iter().filter_map(|&(impl_, trait_)| {
        cx.tcx
            .associated_items(trait_)
            .find_by_name_and_namespace(cx.tcx, Ident::with_dummy_span(item_name), ns, trait_)
            .map(|trait_assoc| {
                trait_assoc_to_impl_assoc_item(cx.tcx, impl_, trait_assoc.def_id)
                    .unwrap_or(trait_assoc)
            })
    });
    // FIXME(#74563): warn about ambiguity
    debug!("the candidates were {:?}", candidates.clone().collect::<Vec<_>>());
    candidates.next().copied()
}

/// Find the associated item in the impl `impl_id` that corresponds to the
/// trait associated item `trait_assoc_id`.
///
/// This function returns `None` if no associated item was found in the impl.
/// This can occur when the trait associated item has a default value that is
/// not overridden in the impl.
///
/// This is just a wrapper around [`TyCtxt::impl_item_implementor_ids()`] and
/// [`TyCtxt::associated_item()`] (with some helpful logging added).
#[instrument(level = "debug", skip(tcx), ret)]
fn trait_assoc_to_impl_assoc_item<'tcx>(
    tcx: TyCtxt<'tcx>,
    impl_id: DefId,
    trait_assoc_id: DefId,
) -> Option<&'tcx ty::AssocItem> {
    let trait_to_impl_assoc_map = tcx.impl_item_implementor_ids(impl_id);
    debug!(?trait_to_impl_assoc_map);
    let impl_assoc_id = *trait_to_impl_assoc_map.get(&trait_assoc_id)?;
    debug!(?impl_assoc_id);
    Some(tcx.associated_item(impl_assoc_id))
}

/// Given a type, return all trait impls in scope in `module` for that type.
/// Returns a set of pairs of `(impl_id, trait_id)`.
///
/// NOTE: this cannot be a query because more traits could be available when more crates are compiled!
/// So it is not stable to serialize cross-crate.
#[instrument(level = "debug", skip(cx))]
fn trait_impls_for<'a>(
    cx: &mut DocContext<'a>,
    ty: Ty<'a>,
    module: DefId,
) -> FxHashSet<(DefId, DefId)> {
    let tcx = cx.tcx;
    let iter = cx.resolver_caches.traits_in_scope[&module].iter().flat_map(|trait_candidate| {
        let trait_ = trait_candidate.def_id;
        trace!("considering explicit impl for trait {:?}", trait_);

        // Look at each trait implementation to see if it's an impl for `did`
        tcx.find_map_relevant_impl(trait_, ty, |impl_| {
            let trait_ref = tcx.impl_trait_ref(impl_).expect("this is not an inherent impl");
            // Check if these are the same type.
            let impl_type = trait_ref.skip_binder().self_ty();
            trace!(
                "comparing type {} with kind {:?} against type {:?}",
                impl_type,
                impl_type.kind(),
                ty
            );
            // Fast path: if this is a primitive simple `==` will work
            // NOTE: the `match` is necessary; see #92662.
            // this allows us to ignore generics because the user input
            // may not include the generic placeholders
            // e.g. this allows us to match Foo (user comment) with Foo<T> (actual type)
            let saw_impl = impl_type == ty
                || match (impl_type.kind(), ty.kind()) {
                    (ty::Adt(impl_def, _), ty::Adt(ty_def, _)) => {
                        debug!("impl def_id: {:?}, ty def_id: {:?}", impl_def.did(), ty_def.did());
                        impl_def.did() == ty_def.did()
                    }
                    _ => false,
                };

            if saw_impl { Some((impl_, trait_)) } else { None }
        })
    });
    iter.collect()
}

/// Check for resolve collisions between a trait and its derive.
///
/// These are common and we should just resolve to the trait in that case.
fn is_derive_trait_collision<T>(ns: &PerNS<Result<(Res, T), ResolutionFailure<'_>>>) -> bool {
    matches!(
        *ns,
        PerNS {
            type_ns: Ok((Res::Def(DefKind::Trait, _), _)),
            macro_ns: Ok((Res::Def(DefKind::Macro(MacroKind::Derive), _), _)),
            ..
        }
    )
}

impl<'a, 'tcx> DocVisitor for LinkCollector<'a, 'tcx> {
    fn visit_item(&mut self, item: &Item) {
        let parent_node =
            item.item_id.as_def_id().and_then(|did| find_nearest_parent_module(self.cx.tcx, did));
        if parent_node.is_some() {
            trace!("got parent node for {:?} {:?}, id {:?}", item.type_(), item.name, item.item_id);
        }

        let inner_docs = item.inner_docs(self.cx.tcx);

        if item.is_mod() && inner_docs {
            self.mod_ids.push(item.item_id.expect_def_id());
        }

        // We want to resolve in the lexical scope of the documentation.
        // In the presence of re-exports, this is not the same as the module of the item.
        // Rather than merging all documentation into one, resolve it one attribute at a time
        // so we know which module it came from.
        for (parent_module, doc) in item.attrs.prepare_to_doc_link_resolution() {
            if !may_have_doc_links(&doc) {
                continue;
            }
            debug!("combined_docs={}", doc);
            // NOTE: if there are links that start in one crate and end in another, this will not resolve them.
            // This is a degenerate case and it's not supported by rustdoc.
            let parent_node = parent_module.or(parent_node);
            let mut tmp_links = self
                .cx
                .resolver_caches
                .markdown_links
                .take()
                .expect("`markdown_links` are already borrowed");
            if !tmp_links.contains_key(&doc) {
                tmp_links.insert(doc.clone(), preprocessed_markdown_links(&doc));
            }
            for md_link in &tmp_links[&doc] {
                let link = self.resolve_link(item, &doc, parent_node, md_link);
                if let Some(link) = link {
                    self.cx.cache.intra_doc_links.entry(item.item_id).or_default().push(link);
                }
            }
            self.cx.resolver_caches.markdown_links = Some(tmp_links);
        }

        if item.is_mod() {
            if !inner_docs {
                self.mod_ids.push(item.item_id.expect_def_id());
            }

            self.visit_item_recur(item);
            self.mod_ids.pop();
        } else {
            self.visit_item_recur(item)
        }
    }
}

enum PreprocessingError {
    /// User error: `[std#x#y]` is not valid
    MultipleAnchors,
    Disambiguator(Range<usize>, String),
    MalformedGenerics(MalformedGenerics, String),
}

impl PreprocessingError {
    fn report(&self, cx: &DocContext<'_>, diag_info: DiagnosticInfo<'_>) {
        match self {
            PreprocessingError::MultipleAnchors => report_multiple_anchors(cx, diag_info),
            PreprocessingError::Disambiguator(range, msg) => {
                disambiguator_error(cx, diag_info, range.clone(), msg)
            }
            PreprocessingError::MalformedGenerics(err, path_str) => {
                report_malformed_generics(cx, diag_info, *err, path_str)
            }
        }
    }
}

#[derive(Clone)]
struct PreprocessingInfo {
    path_str: String,
    disambiguator: Option<Disambiguator>,
    extra_fragment: Option<String>,
    link_text: String,
}

// Not a typedef to avoid leaking several private structures from this module.
pub(crate) struct PreprocessedMarkdownLink(
    Result<PreprocessingInfo, PreprocessingError>,
    MarkdownLink,
);

/// Returns:
/// - `None` if the link should be ignored.
/// - `Some(Err)` if the link should emit an error
/// - `Some(Ok)` if the link is valid
///
/// `link_buffer` is needed for lifetime reasons; it will always be overwritten and the contents ignored.
fn preprocess_link(
    ori_link: &MarkdownLink,
) -> Option<Result<PreprocessingInfo, PreprocessingError>> {
    // [] is mostly likely not supposed to be a link
    if ori_link.link.is_empty() {
        return None;
    }

    // Bail early for real links.
    if ori_link.link.contains('/') {
        return None;
    }

    let stripped = ori_link.link.replace('`', "");
    let mut parts = stripped.split('#');

    let link = parts.next().unwrap();
    if link.trim().is_empty() {
        // This is an anchor to an element of the current page, nothing to do in here!
        return None;
    }
    let extra_fragment = parts.next();
    if parts.next().is_some() {
        // A valid link can't have multiple #'s
        return Some(Err(PreprocessingError::MultipleAnchors));
    }

    // Parse and strip the disambiguator from the link, if present.
    let (disambiguator, path_str, link_text) = match Disambiguator::from_str(link) {
        Ok(Some((d, path, link_text))) => (Some(d), path.trim(), link_text.trim()),
        Ok(None) => (None, link.trim(), link.trim()),
        Err((err_msg, relative_range)) => {
            // Only report error if we would not have ignored this link. See issue #83859.
            if !should_ignore_link_with_disambiguators(link) {
                let no_backticks_range = range_between_backticks(ori_link);
                let disambiguator_range = (no_backticks_range.start + relative_range.start)
                    ..(no_backticks_range.start + relative_range.end);
                return Some(Err(PreprocessingError::Disambiguator(disambiguator_range, err_msg)));
            } else {
                return None;
            }
        }
    };

    if should_ignore_link(path_str) {
        return None;
    }

    // Strip generics from the path.
    let path_str = if path_str.contains(['<', '>'].as_slice()) {
        match strip_generics_from_path(path_str) {
            Ok(path) => path,
            Err(err) => {
                debug!("link has malformed generics: {}", path_str);
                return Some(Err(PreprocessingError::MalformedGenerics(err, path_str.to_owned())));
            }
        }
    } else {
        path_str.to_owned()
    };

    // Sanity check to make sure we don't have any angle brackets after stripping generics.
    assert!(!path_str.contains(['<', '>'].as_slice()));

    // The link is not an intra-doc link if it still contains spaces after stripping generics.
    if path_str.contains(' ') {
        return None;
    }

    Some(Ok(PreprocessingInfo {
        path_str,
        disambiguator,
        extra_fragment: extra_fragment.map(|frag| frag.to_owned()),
        link_text: link_text.to_owned(),
    }))
}

fn preprocessed_markdown_links(s: &str) -> Vec<PreprocessedMarkdownLink> {
    markdown_links(s, |link| {
        preprocess_link(&link).map(|pp_link| PreprocessedMarkdownLink(pp_link, link))
    })
}

impl LinkCollector<'_, '_> {
    /// This is the entry point for resolving an intra-doc link.
    ///
    /// FIXME(jynelson): this is way too many arguments
    fn resolve_link(
        &mut self,
        item: &Item,
        dox: &str,
        parent_node: Option<DefId>,
        link: &PreprocessedMarkdownLink,
    ) -> Option<ItemLink> {
        let PreprocessedMarkdownLink(pp_link, ori_link) = link;
        trace!("considering link '{}'", ori_link.link);

        let diag_info = DiagnosticInfo {
            item,
            dox,
            ori_link: &ori_link.link,
            link_range: ori_link.range.clone(),
        };

        let PreprocessingInfo { path_str, disambiguator, extra_fragment, link_text } =
            pp_link.as_ref().map_err(|err| err.report(self.cx, diag_info.clone())).ok()?;
        let disambiguator = *disambiguator;

        // In order to correctly resolve intra-doc links we need to
        // pick a base AST node to work from.  If the documentation for
        // this module came from an inner comment (//!) then we anchor
        // our name resolution *inside* the module.  If, on the other
        // hand it was an outer comment (///) then we anchor the name
        // resolution in the parent module on the basis that the names
        // used are more likely to be intended to be parent names.  For
        // this, we set base_node to None for inner comments since
        // we've already pushed this node onto the resolution stack but
        // for outer comments we explicitly try and resolve against the
        // parent_node first.
        let inner_docs = item.inner_docs(self.cx.tcx);
        let base_node =
            if item.is_mod() && inner_docs { self.mod_ids.last().copied() } else { parent_node };
        let module_id = base_node.expect("doc link without parent module");

        let (mut res, fragment) = self.resolve_with_disambiguator_cached(
            ResolutionInfo {
                item_id: item.item_id,
                module_id,
                dis: disambiguator,
                path_str: path_str.to_owned(),
                extra_fragment: extra_fragment.clone(),
            },
            diag_info.clone(), // this struct should really be Copy, but Range is not :(
            // For reference-style links we want to report only one error so unsuccessful
            // resolutions are cached, for other links we want to report an error every
            // time so they are not cached.
            matches!(ori_link.kind, LinkType::Reference | LinkType::Shortcut),
        )?;

        // Check for a primitive which might conflict with a module
        // Report the ambiguity and require that the user specify which one they meant.
        // FIXME: could there ever be a primitive not in the type namespace?
        if matches!(
            disambiguator,
            None | Some(Disambiguator::Namespace(Namespace::TypeNS) | Disambiguator::Primitive)
        ) && !matches!(res, Res::Primitive(_))
        {
            if let Some(prim) = resolve_primitive(path_str, TypeNS) {
                // `prim@char`
                if matches!(disambiguator, Some(Disambiguator::Primitive)) {
                    res = prim;
                } else {
                    // `[char]` when a `char` module is in scope
                    let candidates = vec![res, prim];
                    ambiguity_error(self.cx, diag_info, path_str, candidates);
                    return None;
                }
            }
        }

        match res {
            Res::Primitive(prim) => {
                if let Some(UrlFragment::Item(id)) = fragment {
                    // We're actually resolving an associated item of a primitive, so we need to
                    // verify the disambiguator (if any) matches the type of the associated item.
                    // This case should really follow the same flow as the `Res::Def` branch below,
                    // but attempting to add a call to `clean::register_res` causes an ICE. @jyn514
                    // thinks `register_res` is only needed for cross-crate re-exports, but Rust
                    // doesn't allow statements like `use str::trim;`, making this a (hopefully)
                    // valid omission. See https://github.com/rust-lang/rust/pull/80660#discussion_r551585677
                    // for discussion on the matter.
                    let kind = self.cx.tcx.def_kind(id);
                    self.verify_disambiguator(
                        path_str,
                        ori_link,
                        kind,
                        id,
                        disambiguator,
                        item,
                        &diag_info,
                    )?;

                    // FIXME: it would be nice to check that the feature gate was enabled in the original crate, not just ignore it altogether.
                    // However I'm not sure how to check that across crates.
                    if prim == PrimitiveType::RawPointer
                        && item.item_id.is_local()
                        && !self.cx.tcx.features().intra_doc_pointers
                    {
                        self.report_rawptr_assoc_feature_gate(dox, ori_link, item);
                    }
                } else {
                    match disambiguator {
                        Some(Disambiguator::Primitive | Disambiguator::Namespace(_)) | None => {}
                        Some(other) => {
                            self.report_disambiguator_mismatch(
                                path_str, ori_link, other, res, &diag_info,
                            );
                            return None;
                        }
                    }
                }

                res.def_id(self.cx.tcx).map(|page_id| ItemLink {
                    link: ori_link.link.clone(),
                    link_text: link_text.clone(),
                    page_id,
                    fragment,
                })
            }
            Res::Def(kind, id) => {
                let (kind_for_dis, id_for_dis) = if let Some(UrlFragment::Item(id)) = fragment {
                    (self.cx.tcx.def_kind(id), id)
                } else {
                    (kind, id)
                };
                self.verify_disambiguator(
                    path_str,
                    ori_link,
                    kind_for_dis,
                    id_for_dis,
                    disambiguator,
                    item,
                    &diag_info,
                )?;

                let page_id = clean::register_res(self.cx, rustc_hir::def::Res::Def(kind, id));
                Some(ItemLink {
                    link: ori_link.link.clone(),
                    link_text: link_text.clone(),
                    page_id,
                    fragment,
                })
            }
        }
    }

    fn verify_disambiguator(
        &self,
        path_str: &str,
        ori_link: &MarkdownLink,
        kind: DefKind,
        id: DefId,
        disambiguator: Option<Disambiguator>,
        item: &Item,
        diag_info: &DiagnosticInfo<'_>,
    ) -> Option<()> {
        debug!("intra-doc link to {} resolved to {:?}", path_str, (kind, id));

        // Disallow e.g. linking to enums with `struct@`
        debug!("saw kind {:?} with disambiguator {:?}", kind, disambiguator);
        match (kind, disambiguator) {
                | (DefKind::Const | DefKind::ConstParam | DefKind::AssocConst | DefKind::AnonConst, Some(Disambiguator::Kind(DefKind::Const)))
                // NOTE: this allows 'method' to mean both normal functions and associated functions
                // This can't cause ambiguity because both are in the same namespace.
                | (DefKind::Fn | DefKind::AssocFn, Some(Disambiguator::Kind(DefKind::Fn)))
                // These are namespaces; allow anything in the namespace to match
                | (_, Some(Disambiguator::Namespace(_)))
                // If no disambiguator given, allow anything
                | (_, None)
                // All of these are valid, so do nothing
                => {}
                (actual, Some(Disambiguator::Kind(expected))) if actual == expected => {}
                (_, Some(specified @ Disambiguator::Kind(_) | specified @ Disambiguator::Primitive)) => {
                    self.report_disambiguator_mismatch(path_str,ori_link,specified, Res::Def(kind, id),diag_info);
                    return None;
                }
            }

        // item can be non-local e.g. when using #[doc(primitive = "pointer")]
        if let Some((src_id, dst_id)) = id
            .as_local()
            // The `expect_def_id()` should be okay because `local_def_id_to_hir_id`
            // would presumably panic if a fake `DefIndex` were passed.
            .and_then(|dst_id| {
                item.item_id.expect_def_id().as_local().map(|src_id| (src_id, dst_id))
            })
        {
            if self.cx.tcx.effective_visibilities(()).is_exported(src_id)
                && !self.cx.tcx.effective_visibilities(()).is_exported(dst_id)
            {
                privacy_error(self.cx, diag_info, path_str);
            }
        }

        Some(())
    }

    fn report_disambiguator_mismatch(
        &self,
        path_str: &str,
        ori_link: &MarkdownLink,
        specified: Disambiguator,
        resolved: Res,
        diag_info: &DiagnosticInfo<'_>,
    ) {
        // The resolved item did not match the disambiguator; give a better error than 'not found'
        let msg = format!("incompatible link kind for `{}`", path_str);
        let callback = |diag: &mut Diagnostic, sp: Option<rustc_span::Span>| {
            let note = format!(
                "this link resolved to {} {}, which is not {} {}",
                resolved.article(),
                resolved.descr(),
                specified.article(),
                specified.descr(),
            );
            if let Some(sp) = sp {
                diag.span_label(sp, &note);
            } else {
                diag.note(&note);
            }
            suggest_disambiguator(resolved, diag, path_str, &ori_link.link, sp);
        };
        report_diagnostic(self.cx.tcx, BROKEN_INTRA_DOC_LINKS, &msg, diag_info, callback);
    }

    fn report_rawptr_assoc_feature_gate(&self, dox: &str, ori_link: &MarkdownLink, item: &Item) {
        let span =
            super::source_span_for_markdown_range(self.cx.tcx, dox, &ori_link.range, &item.attrs)
                .unwrap_or_else(|| item.attr_span(self.cx.tcx));
        rustc_session::parse::feature_err(
            &self.cx.tcx.sess.parse_sess,
            sym::intra_doc_pointers,
            span,
            "linking to associated items of raw pointers is experimental",
        )
        .note("rustdoc does not allow disambiguating between `*const` and `*mut`, and pointers are unstable until it does")
        .emit();
    }

    fn resolve_with_disambiguator_cached(
        &mut self,
        key: ResolutionInfo,
        diag: DiagnosticInfo<'_>,
        // If errors are cached then they are only reported on first occurrence
        // which we want in some cases but not in others.
        cache_errors: bool,
    ) -> Option<(Res, Option<UrlFragment>)> {
        if let Some(res) = self.visited_links.get(&key) {
            if res.is_some() || cache_errors {
                return res.clone();
            }
        }

        let res = self.resolve_with_disambiguator(&key, diag.clone()).and_then(|(res, def_id)| {
            let fragment = match (&key.extra_fragment, def_id) {
                (Some(_), Some(def_id)) => {
                    report_anchor_conflict(self.cx, diag, def_id);
                    return None;
                }
                (Some(u_frag), None) => Some(UrlFragment::UserWritten(u_frag.clone())),
                (None, Some(def_id)) => Some(UrlFragment::Item(def_id)),
                (None, None) => None,
            };
            Some((res, fragment))
        });

        if res.is_some() || cache_errors {
            self.visited_links.insert(key, res.clone());
        }
        res
    }

    /// After parsing the disambiguator, resolve the main part of the link.
    // FIXME(jynelson): wow this is just so much
    fn resolve_with_disambiguator(
        &mut self,
        key: &ResolutionInfo,
        diag: DiagnosticInfo<'_>,
    ) -> Option<(Res, Option<DefId>)> {
        let disambiguator = key.dis;
        let path_str = &key.path_str;
        let item_id = key.item_id;
        let base_node = key.module_id;

        match disambiguator.map(Disambiguator::ns) {
            Some(expected_ns) => {
                match self.resolve(path_str, expected_ns, item_id, base_node) {
                    Ok(res) => Some(res),
                    Err(err) => {
                        // We only looked in one namespace. Try to give a better error if possible.
                        // FIXME: really it should be `resolution_failure` that does this, not `resolve_with_disambiguator`.
                        // See https://github.com/rust-lang/rust/pull/76955#discussion_r493953382 for a good approach.
                        let mut err = ResolutionFailure::NotResolved(err);
                        for other_ns in [TypeNS, ValueNS, MacroNS] {
                            if other_ns != expected_ns {
                                if let Ok(res) =
                                    self.resolve(path_str, other_ns, item_id, base_node)
                                {
                                    err = ResolutionFailure::WrongNamespace {
                                        res: full_res(self.cx.tcx, res),
                                        expected_ns,
                                    };
                                    break;
                                }
                            }
                        }
                        resolution_failure(self, diag, path_str, disambiguator, smallvec![err])
                    }
                }
            }
            None => {
                // Try everything!
                let mut candidate = |ns| {
                    self.resolve(path_str, ns, item_id, base_node)
                        .map_err(ResolutionFailure::NotResolved)
                };

                let candidates = PerNS {
                    macro_ns: candidate(MacroNS),
                    type_ns: candidate(TypeNS),
                    value_ns: candidate(ValueNS).and_then(|(res, def_id)| {
                        match res {
                            // Constructors are picked up in the type namespace.
                            Res::Def(DefKind::Ctor(..), _) => {
                                Err(ResolutionFailure::WrongNamespace { res, expected_ns: TypeNS })
                            }
                            _ => Ok((res, def_id)),
                        }
                    }),
                };

                let len = candidates.iter().filter(|res| res.is_ok()).count();

                if len == 0 {
                    return resolution_failure(
                        self,
                        diag,
                        path_str,
                        disambiguator,
                        candidates.into_iter().filter_map(|res| res.err()).collect(),
                    );
                }

                if len == 1 {
                    Some(candidates.into_iter().find_map(|res| res.ok()).unwrap())
                } else if len == 2 && is_derive_trait_collision(&candidates) {
                    Some(candidates.type_ns.unwrap())
                } else {
                    let ignore_macro = is_derive_trait_collision(&candidates);
                    // If we're reporting an ambiguity, don't mention the namespaces that failed
                    let mut candidates =
                        candidates.map(|candidate| candidate.ok().map(|(res, _)| res));
                    if ignore_macro {
                        candidates.macro_ns = None;
                    }
                    ambiguity_error(self.cx, diag, path_str, candidates.present_items().collect());
                    None
                }
            }
        }
    }
}

/// Get the section of a link between the backticks,
/// or the whole link if there aren't any backticks.
///
/// For example:
///
/// ```text
/// [`Foo`]
///   ^^^
/// ```
fn range_between_backticks(ori_link: &MarkdownLink) -> Range<usize> {
    let after_first_backtick_group = ori_link.link.bytes().position(|b| b != b'`').unwrap_or(0);
    let before_second_backtick_group = ori_link
        .link
        .bytes()
        .skip(after_first_backtick_group)
        .position(|b| b == b'`')
        .unwrap_or(ori_link.link.len());
    (ori_link.range.start + after_first_backtick_group)
        ..(ori_link.range.start + before_second_backtick_group)
}

/// Returns true if we should ignore `link` due to it being unlikely
/// that it is an intra-doc link. `link` should still have disambiguators
/// if there were any.
///
/// The difference between this and [`should_ignore_link()`] is that this
/// check should only be used on links that still have disambiguators.
fn should_ignore_link_with_disambiguators(link: &str) -> bool {
    link.contains(|ch: char| !(ch.is_alphanumeric() || ":_<>, !*&;@()".contains(ch)))
}

/// Returns true if we should ignore `path_str` due to it being unlikely
/// that it is an intra-doc link.
fn should_ignore_link(path_str: &str) -> bool {
    path_str.contains(|ch: char| !(ch.is_alphanumeric() || ":_<>, !*&;".contains(ch)))
}

#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
/// Disambiguators for a link.
enum Disambiguator {
    /// `prim@`
    ///
    /// This is buggy, see <https://github.com/rust-lang/rust/pull/77875#discussion_r503583103>
    Primitive,
    /// `struct@` or `f()`
    Kind(DefKind),
    /// `type@`
    Namespace(Namespace),
}

impl Disambiguator {
    /// Given a link, parse and return `(disambiguator, path_str, link_text)`.
    ///
    /// This returns `Ok(Some(...))` if a disambiguator was found,
    /// `Ok(None)` if no disambiguator was found, or `Err(...)`
    /// if there was a problem with the disambiguator.
    fn from_str(link: &str) -> Result<Option<(Self, &str, &str)>, (String, Range<usize>)> {
        use Disambiguator::{Kind, Namespace as NS, Primitive};

        if let Some(idx) = link.find('@') {
            let (prefix, rest) = link.split_at(idx);
            let d = match prefix {
                "struct" => Kind(DefKind::Struct),
                "enum" => Kind(DefKind::Enum),
                "trait" => Kind(DefKind::Trait),
                "union" => Kind(DefKind::Union),
                "module" | "mod" => Kind(DefKind::Mod),
                "const" | "constant" => Kind(DefKind::Const),
                "static" => Kind(DefKind::Static(Mutability::Not)),
                "function" | "fn" | "method" => Kind(DefKind::Fn),
                "derive" => Kind(DefKind::Macro(MacroKind::Derive)),
                "type" => NS(Namespace::TypeNS),
                "value" => NS(Namespace::ValueNS),
                "macro" => NS(Namespace::MacroNS),
                "prim" | "primitive" => Primitive,
                _ => return Err((format!("unknown disambiguator `{}`", prefix), 0..idx)),
            };
            Ok(Some((d, &rest[1..], &rest[1..])))
        } else {
            let suffixes = [
                ("!()", DefKind::Macro(MacroKind::Bang)),
                ("!{}", DefKind::Macro(MacroKind::Bang)),
                ("![]", DefKind::Macro(MacroKind::Bang)),
                ("()", DefKind::Fn),
                ("!", DefKind::Macro(MacroKind::Bang)),
            ];
            for (suffix, kind) in suffixes {
                if let Some(path_str) = link.strip_suffix(suffix) {
                    // Avoid turning `!` or `()` into an empty string
                    if !path_str.is_empty() {
                        return Ok(Some((Kind(kind), path_str, link)));
                    }
                }
            }
            Ok(None)
        }
    }

    fn ns(self) -> Namespace {
        match self {
            Self::Namespace(n) => n,
            Self::Kind(k) => {
                k.ns().expect("only DefKinds with a valid namespace can be disambiguators")
            }
            Self::Primitive => TypeNS,
        }
    }

    fn article(self) -> &'static str {
        match self {
            Self::Namespace(_) => panic!("article() doesn't make sense for namespaces"),
            Self::Kind(k) => k.article(),
            Self::Primitive => "a",
        }
    }

    fn descr(self) -> &'static str {
        match self {
            Self::Namespace(n) => n.descr(),
            // HACK(jynelson): the source of `DefKind::descr` only uses the DefId for
            // printing "module" vs "crate" so using the wrong ID is not a huge problem
            Self::Kind(k) => k.descr(CRATE_DEF_ID.to_def_id()),
            Self::Primitive => "builtin type",
        }
    }
}

/// A suggestion to show in a diagnostic.
enum Suggestion {
    /// `struct@`
    Prefix(&'static str),
    /// `f()`
    Function,
    /// `m!`
    Macro,
    /// `foo` without any disambiguator
    RemoveDisambiguator,
}

impl Suggestion {
    fn descr(&self) -> Cow<'static, str> {
        match self {
            Self::Prefix(x) => format!("prefix with `{}@`", x).into(),
            Self::Function => "add parentheses".into(),
            Self::Macro => "add an exclamation mark".into(),
            Self::RemoveDisambiguator => "remove the disambiguator".into(),
        }
    }

    fn as_help(&self, path_str: &str) -> String {
        // FIXME: if this is an implied shortcut link, it's bad style to suggest `@`
        match self {
            Self::Prefix(prefix) => format!("{}@{}", prefix, path_str),
            Self::Function => format!("{}()", path_str),
            Self::Macro => format!("{}!", path_str),
            Self::RemoveDisambiguator => path_str.into(),
        }
    }

    fn as_help_span(
        &self,
        path_str: &str,
        ori_link: &str,
        sp: rustc_span::Span,
    ) -> Vec<(rustc_span::Span, String)> {
        let inner_sp = match ori_link.find('(') {
            Some(index) => sp.with_hi(sp.lo() + BytePos(index as _)),
            None => sp,
        };
        let inner_sp = match ori_link.find('!') {
            Some(index) => inner_sp.with_hi(inner_sp.lo() + BytePos(index as _)),
            None => inner_sp,
        };
        let inner_sp = match ori_link.find('@') {
            Some(index) => inner_sp.with_lo(inner_sp.lo() + BytePos(index as u32 + 1)),
            None => inner_sp,
        };
        match self {
            Self::Prefix(prefix) => {
                // FIXME: if this is an implied shortcut link, it's bad style to suggest `@`
                let mut sugg = vec![(sp.with_hi(inner_sp.lo()), format!("{}@", prefix))];
                if sp.hi() != inner_sp.hi() {
                    sugg.push((inner_sp.shrink_to_hi().with_hi(sp.hi()), String::new()));
                }
                sugg
            }
            Self::Function => {
                let mut sugg = vec![(inner_sp.shrink_to_hi().with_hi(sp.hi()), "()".to_string())];
                if sp.lo() != inner_sp.lo() {
                    sugg.push((inner_sp.shrink_to_lo().with_lo(sp.lo()), String::new()));
                }
                sugg
            }
            Self::Macro => {
                let mut sugg = vec![(inner_sp.shrink_to_hi(), "!".to_string())];
                if sp.lo() != inner_sp.lo() {
                    sugg.push((inner_sp.shrink_to_lo().with_lo(sp.lo()), String::new()));
                }
                sugg
            }
            Self::RemoveDisambiguator => vec![(sp, path_str.into())],
        }
    }
}

/// Reports a diagnostic for an intra-doc link.
///
/// If no link range is provided, or the source span of the link cannot be determined, the span of
/// the entire documentation block is used for the lint. If a range is provided but the span
/// calculation fails, a note is added to the diagnostic pointing to the link in the markdown.
///
/// The `decorate` callback is invoked in all cases to allow further customization of the
/// diagnostic before emission. If the span of the link was able to be determined, the second
/// parameter of the callback will contain it, and the primary span of the diagnostic will be set
/// to it.
fn report_diagnostic(
    tcx: TyCtxt<'_>,
    lint: &'static Lint,
    msg: &str,
    DiagnosticInfo { item, ori_link: _, dox, link_range }: &DiagnosticInfo<'_>,
    decorate: impl FnOnce(&mut Diagnostic, Option<rustc_span::Span>),
) {
    let Some(hir_id) = DocContext::as_local_hir_id(tcx, item.item_id)
    else {
        // If non-local, no need to check anything.
        info!("ignoring warning from parent crate: {}", msg);
        return;
    };

    let sp = item.attr_span(tcx);

    tcx.struct_span_lint_hir(lint, hir_id, sp, msg, |lint| {
        let span =
            super::source_span_for_markdown_range(tcx, dox, link_range, &item.attrs).map(|sp| {
                if dox.as_bytes().get(link_range.start) == Some(&b'`')
                    && dox.as_bytes().get(link_range.end - 1) == Some(&b'`')
                {
                    sp.with_lo(sp.lo() + BytePos(1)).with_hi(sp.hi() - BytePos(1))
                } else {
                    sp
                }
            });

        if let Some(sp) = span {
            lint.set_span(sp);
        } else {
            // blah blah blah\nblah\nblah [blah] blah blah\nblah blah
            //                       ^     ~~~~
            //                       |     link_range
            //                       last_new_line_offset
            let last_new_line_offset = dox[..link_range.start].rfind('\n').map_or(0, |n| n + 1);
            let line = dox[last_new_line_offset..].lines().next().unwrap_or("");

            // Print the line containing the `link_range` and manually mark it with '^'s.
            lint.note(&format!(
                "the link appears in this line:\n\n{line}\n\
                     {indicator: <before$}{indicator:^<found$}",
                line = line,
                indicator = "",
                before = link_range.start - last_new_line_offset,
                found = link_range.len(),
            ));
        }

        decorate(lint, span);

        lint
    });
}

/// Reports a link that failed to resolve.
///
/// This also tries to resolve any intermediate path segments that weren't
/// handled earlier. For example, if passed `Item::Crate(std)` and `path_str`
/// `std::io::Error::x`, this will resolve `std::io::Error`.
fn resolution_failure(
    collector: &mut LinkCollector<'_, '_>,
    diag_info: DiagnosticInfo<'_>,
    path_str: &str,
    disambiguator: Option<Disambiguator>,
    kinds: SmallVec<[ResolutionFailure<'_>; 3]>,
) -> Option<(Res, Option<DefId>)> {
    let tcx = collector.cx.tcx;
    let mut recovered_res = None;
    report_diagnostic(
        tcx,
        BROKEN_INTRA_DOC_LINKS,
        &format!("unresolved link to `{}`", path_str),
        &diag_info,
        |diag, sp| {
            let item = |res: Res| format!("the {} `{}`", res.descr(), res.name(tcx),);
            let assoc_item_not_allowed = |res: Res| {
                let name = res.name(tcx);
                format!(
                    "`{}` is {} {}, not a module or type, and cannot have associated items",
                    name,
                    res.article(),
                    res.descr()
                )
            };
            // ignore duplicates
            let mut variants_seen = SmallVec::<[_; 3]>::new();
            for mut failure in kinds {
                let variant = std::mem::discriminant(&failure);
                if variants_seen.contains(&variant) {
                    continue;
                }
                variants_seen.push(variant);

                if let ResolutionFailure::NotResolved(UnresolvedPath {
                    item_id,
                    module_id,
                    partial_res,
                    unresolved,
                }) = &mut failure
                {
                    use DefKind::*;

                    let item_id = *item_id;
                    let module_id = *module_id;
                    // FIXME(jynelson): this might conflict with my `Self` fix in #76467
                    // FIXME: maybe use itertools `collect_tuple` instead?
                    fn split(path: &str) -> Option<(&str, &str)> {
                        let mut splitter = path.rsplitn(2, "::");
                        splitter.next().and_then(|right| splitter.next().map(|left| (left, right)))
                    }

                    // Check if _any_ parent of the path gets resolved.
                    // If so, report it and say the first which failed; if not, say the first path segment didn't resolve.
                    let mut name = path_str;
                    'outer: loop {
                        let Some((start, end)) = split(name) else {
                            // avoid bug that marked [Quux::Z] as missing Z, not Quux
                            if partial_res.is_none() {
                                *unresolved = name.into();
                            }
                            break;
                        };
                        name = start;
                        for ns in [TypeNS, ValueNS, MacroNS] {
                            if let Ok(res) = collector.resolve(start, ns, item_id, module_id) {
                                debug!("found partial_res={:?}", res);
                                *partial_res = Some(full_res(collector.cx.tcx, res));
                                *unresolved = end.into();
                                break 'outer;
                            }
                        }
                        *unresolved = end.into();
                    }

                    let last_found_module = match *partial_res {
                        Some(Res::Def(DefKind::Mod, id)) => Some(id),
                        None => Some(module_id),
                        _ => None,
                    };
                    // See if this was a module: `[path]` or `[std::io::nope]`
                    if let Some(module) = last_found_module {
                        let note = if partial_res.is_some() {
                            // Part of the link resolved; e.g. `std::io::nonexistent`
                            let module_name = tcx.item_name(module);
                            format!("no item named `{}` in module `{}`", unresolved, module_name)
                        } else {
                            // None of the link resolved; e.g. `Notimported`
                            format!("no item named `{}` in scope", unresolved)
                        };
                        if let Some(span) = sp {
                            diag.span_label(span, &note);
                        } else {
                            diag.note(&note);
                        }

                        if !path_str.contains("::") {
                            if disambiguator.map_or(true, |d| d.ns() == MacroNS)
                                && let Some(&res) = collector.cx.resolver_caches.all_macro_rules
                                                             .get(&Symbol::intern(path_str))
                            {
                                diag.note(format!(
                                    "`macro_rules` named `{path_str}` exists in this crate, \
                                     but it is not in scope at this link's location"
                                ));
                                recovered_res = res.try_into().ok().map(|res| (res, None));
                            } else {
                                // If the link has `::` in it, assume it was meant to be an
                                // intra-doc link. Otherwise, the `[]` might be unrelated.
                                diag.help("to escape `[` and `]` characters, \
                                           add '\\' before them like `\\[` or `\\]`");
                            }
                        }

                        continue;
                    }

                    // Otherwise, it must be an associated item or variant
                    let res = partial_res.expect("None case was handled by `last_found_module`");
                    let kind = match res {
                        Res::Def(kind, _) => Some(kind),
                        Res::Primitive(_) => None,
                    };
                    let path_description = if let Some(kind) = kind {
                        match kind {
                            Mod | ForeignMod => "inner item",
                            Struct => "field or associated item",
                            Enum | Union => "variant or associated item",
                            Variant
                            | Field
                            | Closure
                            | Generator
                            | AssocTy
                            | AssocConst
                            | AssocFn
                            | Fn
                            | Macro(_)
                            | Const
                            | ConstParam
                            | ExternCrate
                            | Use
                            | LifetimeParam
                            | Ctor(_, _)
                            | AnonConst
                            | InlineConst => {
                                let note = assoc_item_not_allowed(res);
                                if let Some(span) = sp {
                                    diag.span_label(span, &note);
                                } else {
                                    diag.note(&note);
                                }
                                return;
                            }
                            Trait | TyAlias | ForeignTy | OpaqueTy | ImplTraitPlaceholder
                            | TraitAlias | TyParam | Static(_) => "associated item",
                            Impl | GlobalAsm => unreachable!("not a path"),
                        }
                    } else {
                        "associated item"
                    };
                    let name = res.name(tcx);
                    let note = format!(
                        "the {} `{}` has no {} named `{}`",
                        res.descr(),
                        name,
                        disambiguator.map_or(path_description, |d| d.descr()),
                        unresolved,
                    );
                    if let Some(span) = sp {
                        diag.span_label(span, &note);
                    } else {
                        diag.note(&note);
                    }

                    continue;
                }
                let note = match failure {
                    ResolutionFailure::NotResolved { .. } => unreachable!("handled above"),
                    ResolutionFailure::WrongNamespace { res, expected_ns } => {
                        suggest_disambiguator(res, diag, path_str, diag_info.ori_link, sp);

                        format!(
                            "this link resolves to {}, which is not in the {} namespace",
                            item(res),
                            expected_ns.descr()
                        )
                    }
                };
                if let Some(span) = sp {
                    diag.span_label(span, &note);
                } else {
                    diag.note(&note);
                }
            }
        },
    );

    recovered_res
}

fn report_multiple_anchors(cx: &DocContext<'_>, diag_info: DiagnosticInfo<'_>) {
    let msg = format!("`{}` contains multiple anchors", diag_info.ori_link);
    anchor_failure(cx, diag_info, &msg, 1)
}

fn report_anchor_conflict(cx: &DocContext<'_>, diag_info: DiagnosticInfo<'_>, def_id: DefId) {
    let (link, kind) = (diag_info.ori_link, Res::from_def_id(cx.tcx, def_id).descr());
    let msg = format!("`{link}` contains an anchor, but links to {kind}s are already anchored");
    anchor_failure(cx, diag_info, &msg, 0)
}

/// Report an anchor failure.
fn anchor_failure(
    cx: &DocContext<'_>,
    diag_info: DiagnosticInfo<'_>,
    msg: &str,
    anchor_idx: usize,
) {
    report_diagnostic(cx.tcx, BROKEN_INTRA_DOC_LINKS, msg, &diag_info, |diag, sp| {
        if let Some(mut sp) = sp {
            if let Some((fragment_offset, _)) =
                diag_info.ori_link.char_indices().filter(|(_, x)| *x == '#').nth(anchor_idx)
            {
                sp = sp.with_lo(sp.lo() + BytePos(fragment_offset as _));
            }
            diag.span_label(sp, "invalid anchor");
        }
    });
}

/// Report an error in the link disambiguator.
fn disambiguator_error(
    cx: &DocContext<'_>,
    mut diag_info: DiagnosticInfo<'_>,
    disambiguator_range: Range<usize>,
    msg: &str,
) {
    diag_info.link_range = disambiguator_range;
    report_diagnostic(cx.tcx, BROKEN_INTRA_DOC_LINKS, msg, &diag_info, |diag, _sp| {
        let msg = format!(
            "see {}/rustdoc/write-documentation/linking-to-items-by-name.html#namespaces-and-disambiguators for more info about disambiguators",
            crate::DOC_RUST_LANG_ORG_CHANNEL
        );
        diag.note(&msg);
    });
}

fn report_malformed_generics(
    cx: &DocContext<'_>,
    diag_info: DiagnosticInfo<'_>,
    err: MalformedGenerics,
    path_str: &str,
) {
    report_diagnostic(
        cx.tcx,
        BROKEN_INTRA_DOC_LINKS,
        &format!("unresolved link to `{}`", path_str),
        &diag_info,
        |diag, sp| {
            let note = match err {
                MalformedGenerics::UnbalancedAngleBrackets => "unbalanced angle brackets",
                MalformedGenerics::MissingType => "missing type for generic parameters",
                MalformedGenerics::HasFullyQualifiedSyntax => {
                    diag.note(
                        "see https://github.com/rust-lang/rust/issues/74563 for more information",
                    );
                    "fully-qualified syntax is unsupported"
                }
                MalformedGenerics::InvalidPathSeparator => "has invalid path separator",
                MalformedGenerics::TooManyAngleBrackets => "too many angle brackets",
                MalformedGenerics::EmptyAngleBrackets => "empty angle brackets",
            };
            if let Some(span) = sp {
                diag.span_label(span, note);
            } else {
                diag.note(note);
            }
        },
    );
}

/// Report an ambiguity error, where there were multiple possible resolutions.
fn ambiguity_error(
    cx: &DocContext<'_>,
    diag_info: DiagnosticInfo<'_>,
    path_str: &str,
    candidates: Vec<Res>,
) {
    let mut msg = format!("`{}` is ", path_str);

    match candidates.as_slice() {
        [first_def, second_def] => {
            msg += &format!(
                "both {} {} and {} {}",
                first_def.article(),
                first_def.descr(),
                second_def.article(),
                second_def.descr(),
            );
        }
        _ => {
            let mut candidates = candidates.iter().peekable();
            while let Some(res) = candidates.next() {
                if candidates.peek().is_some() {
                    msg += &format!("{} {}, ", res.article(), res.descr());
                } else {
                    msg += &format!("and {} {}", res.article(), res.descr());
                }
            }
        }
    }

    report_diagnostic(cx.tcx, BROKEN_INTRA_DOC_LINKS, &msg, &diag_info, |diag, sp| {
        if let Some(sp) = sp {
            diag.span_label(sp, "ambiguous link");
        } else {
            diag.note("ambiguous link");
        }

        for res in candidates {
            suggest_disambiguator(res, diag, path_str, diag_info.ori_link, sp);
        }
    });
}

/// In case of an ambiguity or mismatched disambiguator, suggest the correct
/// disambiguator.
fn suggest_disambiguator(
    res: Res,
    diag: &mut Diagnostic,
    path_str: &str,
    ori_link: &str,
    sp: Option<rustc_span::Span>,
) {
    let suggestion = res.disambiguator_suggestion();
    let help = format!("to link to the {}, {}", res.descr(), suggestion.descr());

    if let Some(sp) = sp {
        let mut spans = suggestion.as_help_span(path_str, ori_link, sp);
        if spans.len() > 1 {
            diag.multipart_suggestion(&help, spans, Applicability::MaybeIncorrect);
        } else {
            let (sp, suggestion_text) = spans.pop().unwrap();
            diag.span_suggestion_verbose(sp, &help, suggestion_text, Applicability::MaybeIncorrect);
        }
    } else {
        diag.help(&format!("{}: {}", help, suggestion.as_help(path_str)));
    }
}

/// Report a link from a public item to a private one.
fn privacy_error(cx: &DocContext<'_>, diag_info: &DiagnosticInfo<'_>, path_str: &str) {
    let sym;
    let item_name = match diag_info.item.name {
        Some(name) => {
            sym = name;
            sym.as_str()
        }
        None => "<unknown>",
    };
    let msg =
        format!("public documentation for `{}` links to private item `{}`", item_name, path_str);

    report_diagnostic(cx.tcx, PRIVATE_INTRA_DOC_LINKS, &msg, diag_info, |diag, sp| {
        if let Some(sp) = sp {
            diag.span_label(sp, "this item is private");
        }

        let note_msg = if cx.render_options.document_private {
            "this link resolves only because you passed `--document-private-items`, but will break without"
        } else {
            "this link will resolve properly if you pass `--document-private-items`"
        };
        diag.note(note_msg);
    });
}

/// Resolve a primitive type or value.
fn resolve_primitive(path_str: &str, ns: Namespace) -> Option<Res> {
    if ns != TypeNS {
        return None;
    }
    use PrimitiveType::*;
    let prim = match path_str {
        "isize" => Isize,
        "i8" => I8,
        "i16" => I16,
        "i32" => I32,
        "i64" => I64,
        "i128" => I128,
        "usize" => Usize,
        "u8" => U8,
        "u16" => U16,
        "u32" => U32,
        "u64" => U64,
        "u128" => U128,
        "f32" => F32,
        "f64" => F64,
        "char" => Char,
        "bool" | "true" | "false" => Bool,
        "str" | "&str" => Str,
        // See #80181 for why these don't have symbols associated.
        "slice" => Slice,
        "array" => Array,
        "tuple" => Tuple,
        "unit" => Unit,
        "pointer" | "*const" | "*mut" => RawPointer,
        "reference" | "&" | "&mut" => Reference,
        "fn" => Fn,
        "never" | "!" => Never,
        _ => return None,
    };
    debug!("resolved primitives {:?}", prim);
    Some(Res::Primitive(prim))
}

fn strip_generics_from_path(path_str: &str) -> Result<String, MalformedGenerics> {
    let mut stripped_segments = vec![];
    let mut path = path_str.chars().peekable();
    let mut segment = Vec::new();

    while let Some(chr) = path.next() {
        match chr {
            ':' => {
                if path.next_if_eq(&':').is_some() {
                    let stripped_segment =
                        strip_generics_from_path_segment(mem::take(&mut segment))?;
                    if !stripped_segment.is_empty() {
                        stripped_segments.push(stripped_segment);
                    }
                } else {
                    return Err(MalformedGenerics::InvalidPathSeparator);
                }
            }
            '<' => {
                segment.push(chr);

                match path.next() {
                    Some('<') => {
                        return Err(MalformedGenerics::TooManyAngleBrackets);
                    }
                    Some('>') => {
                        return Err(MalformedGenerics::EmptyAngleBrackets);
                    }
                    Some(chr) => {
                        segment.push(chr);

                        while let Some(chr) = path.next_if(|c| *c != '>') {
                            segment.push(chr);
                        }
                    }
                    None => break,
                }
            }
            _ => segment.push(chr),
        }
        trace!("raw segment: {:?}", segment);
    }

    if !segment.is_empty() {
        let stripped_segment = strip_generics_from_path_segment(segment)?;
        if !stripped_segment.is_empty() {
            stripped_segments.push(stripped_segment);
        }
    }

    debug!("path_str: {:?}\nstripped segments: {:?}", path_str, &stripped_segments);

    let stripped_path = stripped_segments.join("::");

    if !stripped_path.is_empty() { Ok(stripped_path) } else { Err(MalformedGenerics::MissingType) }
}

fn strip_generics_from_path_segment(segment: Vec<char>) -> Result<String, MalformedGenerics> {
    let mut stripped_segment = String::new();
    let mut param_depth = 0;

    let mut latest_generics_chunk = String::new();

    for c in segment {
        if c == '<' {
            param_depth += 1;
            latest_generics_chunk.clear();
        } else if c == '>' {
            param_depth -= 1;
            if latest_generics_chunk.contains(" as ") {
                // The segment tries to use fully-qualified syntax, which is currently unsupported.
                // Give a helpful error message instead of completely ignoring the angle brackets.
                return Err(MalformedGenerics::HasFullyQualifiedSyntax);
            }
        } else {
            if param_depth == 0 {
                stripped_segment.push(c);
            } else {
                latest_generics_chunk.push(c);
            }
        }
    }

    if param_depth == 0 {
        Ok(stripped_segment)
    } else {
        // The segment has unbalanced angle brackets, e.g. `Vec<T` or `Vec<T>>`
        Err(MalformedGenerics::UnbalancedAngleBrackets)
    }
}