rustdoc/passes/

collect_intra_doc_links.rs

//! 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 std::borrow::Cow;
use std::fmt::Display;
use std::mem;
use std::ops::Range;

use rustc_ast::util::comments::may_have_doc_links;
use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet};
use rustc_data_structures::intern::Interned;
use rustc_errors::{Applicability, Diag, DiagMessage};
use rustc_hir::attrs::AttributeKind;
use rustc_hir::def::Namespace::*;
use rustc_hir::def::{DefKind, MacroKinds, Namespace, PerNS};
use rustc_hir::def_id::{CRATE_DEF_ID, DefId, LOCAL_CRATE};
use rustc_hir::{Attribute, Mutability, Safety, find_attr};
use rustc_middle::ty::{Ty, TyCtxt};
use rustc_middle::{bug, span_bug, ty};
use rustc_resolve::rustdoc::pulldown_cmark::LinkType;
use rustc_resolve::rustdoc::{
    MalformedGenerics, has_primitive_or_keyword_or_attribute_docs, prepare_to_doc_link_resolution,
    source_span_for_markdown_range, strip_generics_from_path,
};
use rustc_session::config::CrateType;
use rustc_session::lint::Lint;
use rustc_span::BytePos;
use rustc_span::symbol::{Ident, Symbol, sym};
use smallvec::{SmallVec, smallvec};
use tracing::{debug, info, instrument, trace};

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

pub(crate) const COLLECT_INTRA_DOC_LINKS: Pass =
    Pass { name: "collect-intra-doc-links", run: None, description: "resolves intra-doc links" };

pub(crate) fn collect_intra_doc_links<'a, 'tcx>(
    krate: Crate,
    cx: &'a mut DocContext<'tcx>,
) -> (Crate, LinkCollector<'a, 'tcx>) {
    let mut collector = LinkCollector {
        cx,
        visited_links: FxHashMap::default(),
        ambiguous_links: FxIndexMap::default(),
    };
    collector.visit_crate(&krate);
    (krate, collector)
}

fn filter_assoc_items_by_name_and_namespace(
    tcx: TyCtxt<'_>,
    assoc_items_of: DefId,
    ident: Ident,
    ns: Namespace,
) -> impl Iterator<Item = &ty::AssocItem> {
    tcx.associated_items(assoc_items_of).filter_by_name_unhygienic(ident.name).filter(move |item| {
        item.namespace() == ns && tcx.hygienic_eq(ident, item.ident(tcx), assoc_items_of)
    })
}

#[derive(Copy, Clone, Debug, Hash, PartialEq)]
pub(crate) 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(_) => "primitive 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,
        };

        let prefix = match kind {
            DefKind::Fn | DefKind::AssocFn => return Suggestion::Function,
            // FIXME: handle macros with multiple kinds, and attribute/derive macros that aren't
            // proc macros
            DefKind::Macro(MacroKinds::BANG) => return Suggestion::Macro,

            DefKind::Macro(MacroKinds::DERIVE) => "derive",
            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::Field => "field",
            DefKind::Variant | DefKind::Ctor(..) => "variant",
            DefKind::TyAlias => "tyalias",
            // 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]`
            ToolMod | 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: DefId,
    /// 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, 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),
}

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

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

pub(crate) struct OwnedDiagnosticInfo {
    item: Item,
    dox: String,
    ori_link: String,
    link_range: MarkdownLinkRange,
}

impl From<DiagnosticInfo<'_>> for OwnedDiagnosticInfo {
    fn from(f: DiagnosticInfo<'_>) -> Self {
        Self {
            item: f.item.clone(),
            dox: f.dox.to_string(),
            ori_link: f.ori_link.to_string(),
            link_range: f.link_range.clone(),
        }
    }
}

impl OwnedDiagnosticInfo {
    pub(crate) fn as_info(&self) -> DiagnosticInfo<'_> {
        DiagnosticInfo {
            item: &self.item,
            ori_link: &self.ori_link,
            dox: &self.dox,
            link_range: self.link_range.clone(),
        }
    }
}

pub(crate) struct LinkCollector<'a, 'tcx> {
    pub(crate) cx: &'a mut DocContext<'tcx>,
    /// 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).
    pub(crate) visited_links: FxHashMap<ResolutionInfo, Option<(Res, Option<UrlFragment>)>>,
    /// According to `rustc_resolve`, these links are ambiguous.
    ///
    /// However, we cannot link to an item that has been stripped from the documentation. If all
    /// but one of the "possibilities" are stripped, then there is no real ambiguity. To determine
    /// if an ambiguity is real, we delay resolving them until after `Cache::populate`, then filter
    /// every item that doesn't have a cached path.
    ///
    /// We could get correct results by simply delaying everything. This would have fewer happy
    /// codepaths, but we want to distinguish different kinds of error conditions, and this is easy
    /// to do by resolving links as soon as possible.
    pub(crate) ambiguous_links: FxIndexMap<(ItemId, String), Vec<AmbiguousLinks>>,
}

pub(crate) struct AmbiguousLinks {
    link_text: Box<str>,
    diag_info: OwnedDiagnosticInfo,
    resolved: Vec<(Res, Option<UrlFragment>)>,
}

impl<'tcx> LinkCollector<'_, '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: DefId,
        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 = Symbol::intern(split.next().unwrap());
        // 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.
        let variant_name = Symbol::intern(split.next().ok_or_else(no_res)?);

        // If there's no third component, we saw `[a::b]` before and it failed to resolve.
        // So there's no partial res.
        let path = split.next().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 | DefKind::TyAlias, did) => {
                match tcx.type_of(did).instantiate_identity().kind() {
                    ty::Adt(def, _) if def.is_enum() => {
                        if let Some(variant) =
                            def.variants().iter().find(|v| v.name == variant_name)
                            && let Some(field) =
                                variant.fields.iter().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(),
            }),
        }
    }

    /// Convenience wrapper around `doc_link_resolutions`.
    ///
    /// This also handles resolving `true` and `false` as booleans.
    /// NOTE: `doc_link_resolutions` 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: DefId,
        module_id: DefId,
    ) -> Option<Res> {
        if let res @ Some(..) = resolve_self_ty(self.cx.tcx, 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
            .tcx
            .doc_link_resolutions(module_id)
            .get(&(Symbol::intern(path_str), ns))
            .copied()
            // NOTE: do not remove this panic! Missing links should be recorded as `Res::Err`; if
            // `doc_link_resolutions` is missing a `path_str`, that means that there are valid links
            // that are being missed. To fix the ICE, change
            // `rustc_resolve::rustdoc::attrs_to_preprocessed_links` to cache the link.
            .unwrap_or_else(|| {
                span_bug!(
                    self.cx.tcx.def_span(item_id),
                    "no resolution for {path_str:?} {ns:?} {module_id:?}",
                )
            })
            .and_then(|res| res.try_into().ok())
            .or_else(|| resolve_primitive(path_str, ns));
        debug!("{path_str} resolved to {result:?} in namespace {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>(
        &self,
        path_str: &'path str,
        ns: Namespace,
        disambiguator: Option<Disambiguator>,
        item_id: DefId,
        module_id: DefId,
    ) -> Result<Vec<(Res, Option<DefId>)>, UnresolvedPath<'path>> {
        let tcx = self.cx.tcx;

        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,
                ) => {
                    vec![(Res::from_def_id(self.cx.tcx, self.cx.tcx.parent(def_id)), Some(def_id))]
                }
                _ => vec![(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.
        // NB: `path_root` could be empty when resolving in the root namespace (e.g. `::std`).
        let (path_root, item_str) = match path_str.rsplit_once("::") {
            Some(res @ (_path_root, item_str)) if !item_str.is_empty() => res,
            _ => {
                // If there's no `::`, or the `::` is at the end (e.g. `String::`) it's not an
                // associated item. So we can be sure that `rustc_resolve` was accurate when it
                // said it wasn't resolved.
                debug!("`::` missing or at end, assuming {path_str} was not in scope");
                return Err(UnresolvedPath {
                    item_id,
                    module_id,
                    partial_res: None,
                    unresolved: path_str.into(),
                });
            }
        };
        let item_name = Symbol::intern(item_str);

        // FIXME(#83862): this arbitrarily gives precedence to primitives over modules to support
        // links to primitives when `#[rustc_doc_primitive]` is present. It should give an ambiguity
        // error instead and special case *only* modules with `#[rustc_doc_primitive]`, not all
        // primitives.
        match resolve_primitive(path_root, TypeNS)
            .or_else(|| self.resolve_path(path_root, TypeNS, item_id, module_id))
            .map(|ty_res| {
                resolve_associated_item(tcx, ty_res, item_name, ns, disambiguator, module_id)
                    .into_iter()
                    .map(|(res, def_id)| (res, Some(def_id)))
                    .collect::<Vec<_>>()
            }) {
            Some(r) if !r.is_empty() => Ok(r),
            _ => {
                if ns == Namespace::ValueNS {
                    self.variant_field(path_str, item_id, module_id)
                        .map(|(res, def_id)| vec![(res, Some(def_id))])
                } else {
                    Err(UnresolvedPath {
                        item_id,
                        module_id,
                        partial_res: None,
                        unresolved: path_root.into(),
                    })
                }
            }
        }
    }
}

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))
}

/// Given a primitive type, try to resolve an associated item.
fn resolve_primitive_inherent_assoc_item<'tcx>(
    tcx: TyCtxt<'tcx>,
    prim_ty: PrimitiveType,
    ns: Namespace,
    item_ident: Ident,
) -> Vec<(Res, DefId)> {
    prim_ty
        .impls(tcx)
        .flat_map(|impl_| {
            filter_assoc_items_by_name_and_namespace(tcx, impl_, item_ident, ns)
                .map(|item| (Res::Primitive(prim_ty), item.def_id))
        })
        .collect::<Vec<_>>()
}

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

    let self_id = match tcx.def_kind(item_id) {
        def_kind @ (DefKind::AssocFn
        | DefKind::AssocConst { .. }
        | DefKind::AssocTy
        | DefKind::Variant
        | DefKind::Field) => {
            let parent_def_id = tcx.parent(item_id);
            if def_kind == DefKind::Field && tcx.def_kind(parent_def_id) == DefKind::Variant {
                tcx.parent(parent_def_id)
            } else {
                parent_def_id
            }
        }
        _ => item_id,
    };

    match tcx.def_kind(self_id) {
        DefKind::Impl { .. } => ty_to_res(tcx, tcx.type_of(self_id).instantiate_identity()),
        DefKind::Use => None,
        def_kind => Some(Res::Def(def_kind, self_id)),
    }
}

/// Convert a Ty to a Res, where possible.
///
/// This is used for resolving type aliases.
fn ty_to_res<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<Res> {
    use PrimitiveType::*;
    Some(match *ty.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::Pat(..) => Res::Primitive(Pat),
        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(tcx, did)
        }
        ty::Alias(..)
        | ty::Closure(..)
        | ty::CoroutineClosure(..)
        | ty::Coroutine(..)
        | ty::CoroutineWitness(..)
        | ty::Dynamic(..)
        | ty::UnsafeBinder(_)
        | 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<'tcx>(tcx: TyCtxt<'tcx>, prim: PrimitiveType) -> Option<Ty<'tcx>> {
    use PrimitiveType::*;

    // 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(match prim {
        Bool => tcx.types.bool,
        Str => tcx.types.str_,
        Char => tcx.types.char,
        Never => tcx.types.never,
        I8 => tcx.types.i8,
        I16 => tcx.types.i16,
        I32 => tcx.types.i32,
        I64 => tcx.types.i64,
        I128 => tcx.types.i128,
        Isize => tcx.types.isize,
        F16 => tcx.types.f16,
        F32 => tcx.types.f32,
        F64 => tcx.types.f64,
        F128 => tcx.types.f128,
        U8 => tcx.types.u8,
        U16 => tcx.types.u16,
        U32 => tcx.types.u32,
        U64 => tcx.types.u64,
        U128 => tcx.types.u128,
        Usize => tcx.types.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<'tcx>(
    tcx: TyCtxt<'tcx>,
    root_res: Res,
    item_name: Symbol,
    ns: Namespace,
    disambiguator: Option<Disambiguator>,
    module_id: DefId,
) -> Vec<(Res, DefId)> {
    let item_ident = Ident::with_dummy_span(item_name);

    match root_res {
        Res::Def(DefKind::TyAlias, alias_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 Some(aliased_res) = ty_to_res(tcx, tcx.type_of(alias_did).instantiate_identity())
            else {
                return vec![];
            };
            let aliased_items =
                resolve_associated_item(tcx, aliased_res, item_name, ns, disambiguator, module_id);
            aliased_items
                .into_iter()
                .map(|(res, assoc_did)| {
                    if is_assoc_item_on_alias_page(tcx, assoc_did) {
                        (root_res, assoc_did)
                    } else {
                        (res, assoc_did)
                    }
                })
                .collect()
        }
        Res::Primitive(prim) => resolve_assoc_on_primitive(tcx, prim, ns, item_ident, module_id),
        Res::Def(DefKind::Struct | DefKind::Union | DefKind::Enum, did) => {
            resolve_assoc_on_adt(tcx, did, item_ident, ns, disambiguator, module_id)
        }
        Res::Def(DefKind::ForeignTy, did) => {
            resolve_assoc_on_simple_type(tcx, did, item_ident, ns, module_id)
        }
        Res::Def(DefKind::Trait, did) => filter_assoc_items_by_name_and_namespace(
            tcx,
            did,
            Ident::with_dummy_span(item_name),
            ns,
        )
        .map(|item| (root_res, item.def_id))
        .collect::<Vec<_>>(),
        _ => Vec::new(),
    }
}

// FIXME: make this fully complete by also including ALL inherent impls
// and trait impls BUT ONLY if on alias directly
fn is_assoc_item_on_alias_page<'tcx>(tcx: TyCtxt<'tcx>, assoc_did: DefId) -> bool {
    match tcx.def_kind(assoc_did) {
        // Variants and fields always have docs on the alias page.
        DefKind::Variant | DefKind::Field => true,
        _ => false,
    }
}

fn resolve_assoc_on_primitive<'tcx>(
    tcx: TyCtxt<'tcx>,
    prim: PrimitiveType,
    ns: Namespace,
    item_ident: Ident,
    module_id: DefId,
) -> Vec<(Res, DefId)> {
    let root_res = Res::Primitive(prim);
    let items = resolve_primitive_inherent_assoc_item(tcx, prim, ns, item_ident);
    if !items.is_empty() {
        items
    // Inherent associated items take precedence over items that come from trait impls.
    } else {
        primitive_type_to_ty(tcx, prim)
            .map(|ty| {
                resolve_associated_trait_item(ty, module_id, item_ident, ns, tcx)
                    .iter()
                    .map(|item| (root_res, item.def_id))
                    .collect::<Vec<_>>()
            })
            .unwrap_or_default()
    }
}

fn resolve_assoc_on_adt<'tcx>(
    tcx: TyCtxt<'tcx>,
    adt_def_id: DefId,
    item_ident: Ident,
    ns: Namespace,
    disambiguator: Option<Disambiguator>,
    module_id: DefId,
) -> Vec<(Res, DefId)> {
    debug!("looking for associated item named {item_ident} for item {adt_def_id:?}");
    let root_res = Res::from_def_id(tcx, adt_def_id);
    let adt_ty = tcx.type_of(adt_def_id).instantiate_identity();
    let adt_def = adt_ty.ty_adt_def().expect("must be ADT");
    // Checks if item_name is a variant of the `SomeItem` enum
    if ns == TypeNS && adt_def.is_enum() {
        for variant in adt_def.variants() {
            if variant.name == item_ident.name {
                return vec![(root_res, variant.def_id)];
            }
        }
    }

    if let Some(Disambiguator::Kind(DefKind::Field)) = disambiguator
        && (adt_def.is_struct() || adt_def.is_union())
    {
        return resolve_structfield(adt_def, item_ident.name)
            .into_iter()
            .map(|did| (root_res, did))
            .collect();
    }

    let assoc_items = resolve_assoc_on_simple_type(tcx, adt_def_id, item_ident, ns, module_id);
    if !assoc_items.is_empty() {
        return assoc_items;
    }

    if ns == Namespace::ValueNS && (adt_def.is_struct() || adt_def.is_union()) {
        return resolve_structfield(adt_def, item_ident.name)
            .into_iter()
            .map(|did| (root_res, did))
            .collect();
    }

    vec![]
}

/// "Simple" i.e. an ADT, foreign type, etc. -- not a type alias, primitive type, or other trickier type.
fn resolve_assoc_on_simple_type<'tcx>(
    tcx: TyCtxt<'tcx>,
    ty_def_id: DefId,
    item_ident: Ident,
    ns: Namespace,
    module_id: DefId,
) -> Vec<(Res, DefId)> {
    let root_res = Res::from_def_id(tcx, ty_def_id);
    // Checks if item_name belongs to `impl SomeItem`
    let inherent_assoc_items: Vec<_> = tcx
        .inherent_impls(ty_def_id)
        .iter()
        .flat_map(|&imp| filter_assoc_items_by_name_and_namespace(tcx, imp, item_ident, ns))
        .map(|item| (root_res, item.def_id))
        .collect();
    debug!("got inherent assoc items {inherent_assoc_items:?}");
    if !inherent_assoc_items.is_empty() {
        return inherent_assoc_items;
    }

    // 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)
    let ty = tcx.type_of(ty_def_id).instantiate_identity();
    let trait_assoc_items = resolve_associated_trait_item(ty, module_id, item_ident, ns, tcx)
        .into_iter()
        .map(|item| (root_res, item.def_id))
        .collect::<Vec<_>>();
    debug!("got trait assoc items {trait_assoc_items:?}");
    trait_assoc_items
}

fn resolve_structfield<'tcx>(adt_def: ty::AdtDef<'tcx>, item_name: Symbol) -> Option<DefId> {
    debug!("looking for fields named {item_name} for {adt_def:?}");
    adt_def
        .non_enum_variant()
        .fields
        .iter()
        .find(|field| field.name == item_name)
        .map(|field| field.did)
}

/// 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<'tcx>(
    ty: Ty<'tcx>,
    module: DefId,
    item_ident: Ident,
    ns: Namespace,
    tcx: TyCtxt<'tcx>,
) -> Vec<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(tcx, ty, module);
    debug!("considering traits {traits:?}");
    let candidates = traits
        .iter()
        .flat_map(|&(impl_, trait_)| {
            filter_assoc_items_by_name_and_namespace(tcx, trait_, item_ident, ns).map(
                move |trait_assoc| {
                    trait_assoc_to_impl_assoc_item(tcx, impl_, trait_assoc.def_id)
                        .unwrap_or(*trait_assoc)
                },
            )
        })
        .collect::<Vec<_>>();
    // FIXME(#74563): warn about ambiguity
    debug!("the candidates were {candidates:?}");
    candidates
}

/// 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<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(tcx))]
fn trait_impls_for<'tcx>(
    tcx: TyCtxt<'tcx>,
    ty: Ty<'tcx>,
    module: DefId,
) -> FxIndexSet<(DefId, DefId)> {
    let mut impls = FxIndexSet::default();

    for &trait_ in tcx.doc_link_traits_in_scope(module) {
        tcx.for_each_relevant_impl(trait_, ty, |impl_| {
            let trait_ref = tcx.impl_trait_ref(impl_);
            // Check if these are the same type.
            let impl_type = trait_ref.skip_binder().self_ty();
            trace!(
                "comparing type {impl_type} with kind {kind:?} against type {ty:?}",
                kind = impl_type.kind(),
            );
            // 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 {
                impls.insert((impl_, trait_));
            }
        });
    }

    impls
}

/// 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<Vec<(Res, T)>, ResolutionFailure<'_>>>) -> bool {
    if let (Ok(type_ns), Ok(macro_ns)) = (&ns.type_ns, &ns.macro_ns) {
        type_ns.iter().any(|(res, _)| matches!(res, Res::Def(DefKind::Trait, _)))
            && macro_ns.iter().any(|(res, _)| {
                matches!(
                    res,
                    Res::Def(DefKind::Macro(kinds), _) if kinds.contains(MacroKinds::DERIVE)
                )
            })
    } else {
        false
    }
}

impl DocVisitor<'_> for LinkCollector<'_, '_> {
    fn visit_item(&mut self, item: &Item) {
        self.resolve_links(item);
        self.visit_item_recur(item)
    }
}

enum PreprocessingError {
    /// User error: `[std#x#y]` is not valid
    MultipleAnchors,
    Disambiguator(MarkdownLinkRange, 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.clone())
            }
            PreprocessingError::MalformedGenerics(err, path_str) => {
                report_malformed_generics(cx, diag_info, *err, path_str)
            }
        }
    }
}

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

// 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,
    dox: &str,
) -> Option<Result<PreprocessingInfo, PreprocessingError>> {
    // IMPORTANT: To be kept in sync with the corresponding function in `rustc_resolve::rustdoc`.
    // Namely, whenever this function returns a successful result for a given input,
    // the rustc counterpart *MUST* return a link that's equal to `PreprocessingInfo.path_str`!

    // certain link kinds cannot have their path be urls,
    // so they should not be ignored, no matter how much they look like urls.
    // e.g. [https://example.com/] is not a link to example.com.
    let can_be_url = !matches!(
        ori_link.kind,
        LinkType::ShortcutUnknown | LinkType::CollapsedUnknown | LinkType::ReferenceUnknown
    );

    // [] is mostly likely not supposed to be a link
    if ori_link.link.is_empty() {
        return None;
    }

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

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

    let link = parts.next().unwrap();
    let link = link.trim();
    if link.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, link),
        Err((err_msg, relative_range)) => {
            // Only report error if we would not have ignored this link. See issue #83859.
            if !(can_be_url && should_ignore_link_with_disambiguators(link)) {
                let disambiguator_range = match range_between_backticks(&ori_link.range, dox) {
                    MarkdownLinkRange::Destination(no_backticks_range) => {
                        MarkdownLinkRange::Destination(
                            (no_backticks_range.start + relative_range.start)
                                ..(no_backticks_range.start + relative_range.end),
                        )
                    }
                    mdlr @ MarkdownLinkRange::WholeLink(_) => mdlr,
                };
                return Some(Err(PreprocessingError::Disambiguator(disambiguator_range, err_msg)));
            } else {
                return None;
            }
        }
    };

    let is_shortcut_style = ori_link.kind == LinkType::ShortcutUnknown;
    // If there's no backticks, be lenient and revert to the old behavior.
    // This is to prevent churn by linting on stuff that isn't meant to be a link.
    // only shortcut links have simple enough syntax that they
    // are likely to be written accidentally, collapsed and reference links
    // need 4 metachars, and reference links will not usually use
    // backticks in the reference name.
    // therefore, only shortcut syntax gets the lenient behavior.
    //
    // here's a truth table for how link kinds that cannot be urls are handled:
    //
    // |-------------------------------------------------------|
    // |              |  is shortcut link  | not shortcut link |
    // |--------------|--------------------|-------------------|
    // | has backtick |    never ignore    |    never ignore   |
    // | no backtick  | ignore if url-like |    never ignore   |
    // |-------------------------------------------------------|
    let ignore_urllike = can_be_url || (is_shortcut_style && !ori_link.link.contains('`'));
    if ignore_urllike && should_ignore_link(path_str) {
        return None;
    }
    // If we have an intra-doc link starting with `!` (which isn't `[!]` because this is the never type), we ignore it
    // as it is never valid.
    //
    // The case is common enough because of cases like `#[doc = include_str!("../README.md")]` which often
    // uses GitHub-flavored Markdown (GFM) admonitions, such as `[!NOTE]`.
    if is_shortcut_style
        && let Some(suffix) = ori_link.link.strip_prefix('!')
        && !suffix.is_empty()
        && suffix.chars().all(|c| c.is_ascii_alphabetic())
    {
        return None;
    }

    // Strip generics from the path.
    let path_str = 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())));
        }
    };

    // 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: Box::<str>::from(link_text),
    }))
}

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

impl LinkCollector<'_, '_> {
    #[instrument(level = "debug", skip_all)]
    fn resolve_links(&mut self, item: &Item) {
        let tcx = self.cx.tcx;
        let document_private = self.cx.document_private();
        let effective_visibilities = tcx.effective_visibilities(());
        let should_skip_link_resolution = |item_id: DefId| {
            !document_private
                && item_id
                    .as_local()
                    .is_some_and(|local_def_id| !effective_visibilities.is_exported(local_def_id))
                && !has_primitive_or_keyword_or_attribute_docs(&item.attrs.other_attrs)
        };

        if let Some(def_id) = item.item_id.as_def_id()
            && should_skip_link_resolution(def_id)
        {
            // Skip link resolution for non-exported items.
            return;
        }

        let mut try_insert_links = |item_id, doc: &str| {
            if should_skip_link_resolution(item_id) {
                return;
            }
            let module_id = match tcx.def_kind(item_id) {
                DefKind::Mod if item.inner_docs(tcx) => item_id,
                _ => find_nearest_parent_module(tcx, item_id).unwrap(),
            };
            for md_link in preprocessed_markdown_links(&doc) {
                let link = self.resolve_link(&doc, item, item_id, module_id, &md_link);
                if let Some(link) = link {
                    self.cx
                        .cache
                        .intra_doc_links
                        .entry(item.item_or_reexport_id())
                        .or_default()
                        .insert(link);
                }
            }
        };

        // 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 (item_id, doc) in prepare_to_doc_link_resolution(&item.attrs.doc_strings) {
            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 item_id = item_id.unwrap_or_else(|| item.item_id.expect_def_id());
            try_insert_links(item_id, &doc)
        }

        // Also resolve links in the note text of `#[deprecated]`.
        for attr in &item.attrs.other_attrs {
            let Attribute::Parsed(AttributeKind::Deprecated { span: depr_span, deprecation }) =
                attr
            else {
                continue;
            };
            let Some(note_sym) = deprecation.note else { continue };
            let note = note_sym.as_str();

            if !may_have_doc_links(note) {
                continue;
            }

            debug!("deprecated_note={note}");
            // When resolving an intra-doc link inside a deprecation note that is on an inlined
            // `use` statement, we need to use the `def_id` of the `use` statement, not the
            // inlined item.
            // <https://github.com/rust-lang/rust/pull/151120>
            let item_id = if let Some(inline_stmt_id) = item.inline_stmt_id
                && find_attr!(tcx, inline_stmt_id, Deprecated { span, ..} if span == depr_span)
            {
                inline_stmt_id.to_def_id()
            } else {
                item.item_id.expect_def_id()
            };
            try_insert_links(item_id, note)
        }
    }

    pub(crate) fn save_link(&mut self, item_id: ItemId, link: ItemLink) {
        self.cx.cache.intra_doc_links.entry(item_id).or_default().insert(link);
    }

    /// This is the entry point for resolving an intra-doc link.
    ///
    /// FIXME(jynelson): this is way too many arguments
    fn resolve_link(
        &mut self,
        dox: &str,
        item: &Item,
        item_id: DefId,
        module_id: DefId,
        PreprocessedMarkdownLink(pp_link, ori_link): &PreprocessedMarkdownLink,
    ) -> Option<ItemLink> {
        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;

        let mut resolved = self.resolve_with_disambiguator_cached(
            ResolutionInfo {
                item_id,
                module_id,
                dis: disambiguator,
                path_str: path_str.clone(),
                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),
        )?;

        if resolved.len() > 1 {
            let links = AmbiguousLinks {
                link_text: link_text.clone(),
                diag_info: diag_info.into(),
                resolved,
            };

            self.ambiguous_links
                .entry((item.item_id, path_str.to_string()))
                .or_default()
                .push(links);
            None
        } else if let Some((res, fragment)) = resolved.pop() {
            self.compute_link(res, fragment, path_str, disambiguator, diag_info, link_text)
        } else {
            None
        }
    }

    /// Returns `true` if a link could be generated from the given intra-doc information.
    ///
    /// This is a very light version of `format::href_with_root_path` since we're only interested
    /// about whether we can generate a link to an item or not.
    ///
    /// * If `original_did` is local, then we check if the item is reexported or public.
    /// * If `original_did` is not local, then we check if the crate it comes from is a direct
    ///   public dependency.
    fn validate_link(&self, original_did: DefId) -> bool {
        let tcx = self.cx.tcx;
        let def_kind = tcx.def_kind(original_did);
        let did = match def_kind {
            DefKind::AssocTy | DefKind::AssocFn | DefKind::AssocConst { .. } | DefKind::Variant => {
                // documented on their parent's page
                tcx.parent(original_did)
            }
            // If this a constructor, we get the parent (either a struct or a variant) and then
            // generate the link for this item.
            DefKind::Ctor(..) => return self.validate_link(tcx.parent(original_did)),
            DefKind::ExternCrate => {
                // Link to the crate itself, not the `extern crate` item.
                if let Some(local_did) = original_did.as_local() {
                    tcx.extern_mod_stmt_cnum(local_did).unwrap_or(LOCAL_CRATE).as_def_id()
                } else {
                    original_did
                }
            }
            _ => original_did,
        };

        let cache = &self.cx.cache;
        if !original_did.is_local()
            && !cache.effective_visibilities.is_directly_public(tcx, did)
            && !cache.document_private
            && !cache.primitive_locations.values().any(|&id| id == did)
        {
            return false;
        }

        cache.paths.get(&did).is_some()
            || cache.external_paths.contains_key(&did)
            || !did.is_local()
    }

    pub(crate) fn resolve_ambiguities(&mut self) {
        let mut ambiguous_links = mem::take(&mut self.ambiguous_links);
        for ((item_id, path_str), info_items) in ambiguous_links.iter_mut() {
            for info in info_items {
                info.resolved.retain(|(res, _)| match res {
                    Res::Def(_, def_id) => self.validate_link(*def_id),
                    // Primitive types are always valid.
                    Res::Primitive(_) => true,
                });
                let diag_info = info.diag_info.as_info();
                match info.resolved.len() {
                    1 => {
                        let (res, fragment) = info.resolved.pop().unwrap();
                        if let Some(link) = self.compute_link(
                            res,
                            fragment,
                            path_str,
                            None,
                            diag_info,
                            &info.link_text,
                        ) {
                            self.save_link(*item_id, link);
                        }
                    }
                    0 => {
                        report_diagnostic(
                            self.cx.tcx,
                            BROKEN_INTRA_DOC_LINKS,
                            format!("all items matching `{path_str}` are private or doc(hidden)"),
                            &diag_info,
                            |diag, sp, _| {
                                if let Some(sp) = sp {
                                    diag.span_label(sp, "unresolved link");
                                } else {
                                    diag.note("unresolved link");
                                }
                            },
                        );
                    }
                    _ => {
                        let candidates = info
                            .resolved
                            .iter()
                            .map(|(res, fragment)| {
                                let def_id = if let Some(UrlFragment::Item(def_id)) = fragment {
                                    Some(*def_id)
                                } else {
                                    None
                                };
                                (*res, def_id)
                            })
                            .collect::<Vec<_>>();
                        ambiguity_error(self.cx, &diag_info, path_str, &candidates, true);
                    }
                }
            }
        }
    }

    fn compute_link(
        &mut self,
        mut res: Res,
        fragment: Option<UrlFragment>,
        path_str: &str,
        disambiguator: Option<Disambiguator>,
        diag_info: DiagnosticInfo<'_>,
        link_text: &Box<str>,
    ) -> Option<ItemLink> {
        // 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(_))
            && 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 = &[(res, res.def_id(self.cx.tcx)), (prim, None)];
                ambiguity_error(self.cx, &diag_info, path_str, candidates, true);
                return None;
            }
        }

        match res {
            Res::Primitive(_) => {
                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, kind, id, disambiguator, &diag_info)?;
                } else {
                    match disambiguator {
                        Some(Disambiguator::Primitive | Disambiguator::Namespace(_)) | None => {}
                        Some(other) => {
                            self.report_disambiguator_mismatch(path_str, other, res, &diag_info);
                            return None;
                        }
                    }
                }

                res.def_id(self.cx.tcx).map(|page_id| ItemLink {
                    link: Box::<str>::from(diag_info.ori_link),
                    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,
                    kind_for_dis,
                    id_for_dis,
                    disambiguator,
                    &diag_info,
                )?;

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

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

        // Disallow e.g. linking to enums with `struct@`
        debug!("saw kind {kind:?} with disambiguator {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, specified, Res::Def(kind, id), diag_info);
                    return None;
                }
            }

        // item can be non-local e.g. when using `#[rustc_doc_primitive = "pointer"]`
        if let Some(dst_id) = id.as_local()
            && let Some(src_id) = diag_info.item.item_id.expect_def_id().as_local()
            && 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,
        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 Diag<'_, ()>, sp: Option<rustc_span::Span>, link_range| {
            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, link_range, sp, diag_info);
        };
        report_diagnostic(self.cx.tcx, BROKEN_INTRA_DOC_LINKS, msg, diag_info, callback);
    }

    fn report_rawptr_assoc_feature_gate(
        &self,
        dox: &str,
        ori_link: &MarkdownLinkRange,
        item: &Item,
    ) {
        let span = match source_span_for_markdown_range(
            self.cx.tcx,
            dox,
            ori_link.inner_range(),
            &item.attrs.doc_strings,
        ) {
            Some((sp, _)) => sp,
            None => item.attr_span(self.cx.tcx),
        };
        rustc_session::parse::feature_err(
            self.cx.tcx.sess,
            sym::intra_doc_pointers,
            span,
            "linking to associated items of raw pointers is experimental",
        )
        .with_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<Vec<(Res, Option<UrlFragment>)>> {
        if let Some(res) = self.visited_links.get(&key)
            && (res.is_some() || cache_errors)
        {
            return res.clone().map(|r| vec![r]);
        }

        let mut candidates = self.resolve_with_disambiguator(&key, diag.clone());

        // 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 let Some(candidate) = candidates.first()
            && candidate.0 == Res::Primitive(PrimitiveType::RawPointer)
            && key.path_str.contains("::")
        // We only want to check this if this is an associated item.
        {
            if key.item_id.is_local() && !self.cx.tcx.features().intra_doc_pointers() {
                self.report_rawptr_assoc_feature_gate(diag.dox, &diag.link_range, diag.item);
                return None;
            } else {
                candidates = vec![*candidate];
            }
        }

        // If there are multiple items with the same "kind" (for example, both "associated types")
        // and after removing duplicated kinds, only one remains, the `ambiguity_error` function
        // won't emit an error. So at this point, we can just take the first candidate as it was
        // the first retrieved and use it to generate the link.
        if let [candidate, _candidate2, ..] = *candidates
            && !ambiguity_error(self.cx, &diag, &key.path_str, &candidates, false)
        {
            candidates = vec![candidate];
        }

        let mut out = Vec::with_capacity(candidates.len());
        for (res, def_id) in candidates {
            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,
            };
            out.push((res, fragment));
        }
        if let [r] = out.as_slice() {
            self.visited_links.insert(key, Some(r.clone()));
        } else if cache_errors {
            self.visited_links.insert(key, None);
        }
        Some(out)
    }

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

        match disambiguator.map(Disambiguator::ns) {
            Some(expected_ns) => {
                match self.resolve(path_str, expected_ns, disambiguator, item_id, module_id) {
                    Ok(candidates) => candidates,
                    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
                                && let Ok(&[res, ..]) = self
                                    .resolve(path_str, other_ns, None, item_id, module_id)
                                    .as_deref()
                            {
                                err = ResolutionFailure::WrongNamespace {
                                    res: full_res(self.cx.tcx, res),
                                    expected_ns,
                                };
                                break;
                            }
                        }
                        resolution_failure(self, diag, path_str, disambiguator, smallvec![err]);
                        vec![]
                    }
                }
            }
            None => {
                // Try everything!
                let candidate = |ns| {
                    self.resolve(path_str, ns, None, item_id, module_id)
                        .map_err(ResolutionFailure::NotResolved)
                };

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

                let len = candidates
                    .iter()
                    .fold(0, |acc, res| if let Ok(res) = res { acc + res.len() } else { acc });

                if len == 0 {
                    resolution_failure(
                        self,
                        diag,
                        path_str,
                        disambiguator,
                        candidates.into_iter().filter_map(|res| res.err()).collect(),
                    );
                    vec![]
                } else if len == 1 {
                    candidates.into_iter().filter_map(|res| res.ok()).flatten().collect::<Vec<_>>()
                } else {
                    let has_derive_trait_collision = is_derive_trait_collision(&candidates);
                    if len == 2 && has_derive_trait_collision {
                        candidates.type_ns.unwrap()
                    } else {
                        // If we're reporting an ambiguity, don't mention the namespaces that failed
                        let mut candidates = candidates.map(|candidate| candidate.ok());
                        // If there a collision between a trait and a derive, we ignore the derive.
                        if has_derive_trait_collision {
                            candidates.macro_ns = None;
                        }
                        candidates.into_iter().flatten().flatten().collect::<Vec<_>>()
                    }
                }
            }
        }
    }
}

/// Get the section of a link between the backticks,
/// or the whole link if there aren't any backticks.
///
/// For example:
///
/// ```text
/// [`Foo`]
///   ^^^
/// ```
///
/// This function does nothing if `ori_link.range` is a `MarkdownLinkRange::WholeLink`.
fn range_between_backticks(ori_link_range: &MarkdownLinkRange, dox: &str) -> MarkdownLinkRange {
    let range = match ori_link_range {
        mdlr @ MarkdownLinkRange::WholeLink(_) => return mdlr.clone(),
        MarkdownLinkRange::Destination(inner) => inner.clone(),
    };
    let ori_link_text = &dox[range.clone()];
    let after_first_backtick_group = ori_link_text.bytes().position(|b| b != b'`').unwrap_or(0);
    let before_second_backtick_group = ori_link_text
        .bytes()
        .skip(after_first_backtick_group)
        .position(|b| b == b'`')
        .unwrap_or(ori_link_text.len());
    MarkdownLinkRange::Destination(
        (range.start + after_first_backtick_group)..(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};

        let suffixes = [
            // If you update this list, please also update the relevant rustdoc book section!
            ("!()", DefKind::Macro(MacroKinds::BANG)),
            ("!{}", DefKind::Macro(MacroKinds::BANG)),
            ("![]", DefKind::Macro(MacroKinds::BANG)),
            ("()", DefKind::Fn),
            ("!", DefKind::Macro(MacroKinds::BANG)),
        ];

        if let Some(idx) = link.find('@') {
            let (prefix, rest) = link.split_at(idx);
            let d = match prefix {
                // If you update this list, please also update the relevant rustdoc book section!
                "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 { is_type_const: false }),
                "static" => Kind(DefKind::Static {
                    mutability: Mutability::Not,
                    nested: false,
                    safety: Safety::Safe,
                }),
                "function" | "fn" | "method" => Kind(DefKind::Fn),
                "derive" => Kind(DefKind::Macro(MacroKinds::DERIVE)),
                "field" => Kind(DefKind::Field),
                "variant" => Kind(DefKind::Variant),
                "type" => NS(Namespace::TypeNS),
                "value" => NS(Namespace::ValueNS),
                "macro" => NS(Namespace::MacroNS),
                "prim" | "primitive" => Primitive,
                "tyalias" | "typealias" => Kind(DefKind::TyAlias),
                _ => return Err((format!("unknown disambiguator `{prefix}`"), 0..idx)),
            };

            for (suffix, kind) in suffixes {
                if let Some(path_str) = rest.strip_suffix(suffix) {
                    if d.ns() != Kind(kind).ns() {
                        return Err((
                            format!("unmatched disambiguator `{prefix}` and suffix `{suffix}`"),
                            0..idx,
                        ));
                    } else if path_str.len() > 1 {
                        // path_str != "@"
                        return Ok(Some((d, &path_str[1..], &rest[1..])));
                    }
                }
            }

            Ok(Some((d, &rest[1..], &rest[1..])))
        } else {
            for (suffix, kind) in suffixes {
                // Avoid turning `!` or `()` into an empty string
                if let Some(path_str) = link.strip_suffix(suffix)
                    && !path_str.is_empty()
                {
                    return Ok(Some((Kind(kind), path_str, link)));
                }
            }
            Ok(None)
        }
    }

    fn ns(self) -> Namespace {
        match self {
            Self::Namespace(n) => n,
            // for purposes of link resolution, fields are in the value namespace.
            Self::Kind(DefKind::Field) => ValueNS,
            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,
}

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(),
        }
    }

    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}!"),
        }
    }

    fn as_help_span(
        &self,
        ori_link: &str,
        sp: rustc_span::Span,
    ) -> Vec<(rustc_span::Span, String)> {
        let inner_sp = match ori_link.find('(') {
            Some(index) if index != 0 && ori_link.as_bytes()[index - 1] == b'\\' => {
                sp.with_hi(sp.lo() + BytePos((index - 1) as _))
            }
            Some(index) => sp.with_hi(sp.lo() + BytePos(index as _)),
            None => sp,
        };
        let inner_sp = match ori_link.find('!') {
            Some(index) if index != 0 && ori_link.as_bytes()[index - 1] == b'\\' => {
                sp.with_hi(sp.lo() + BytePos((index - 1) as _))
            }
            Some(index) => inner_sp.with_hi(inner_sp.lo() + BytePos(index as _)),
            None => inner_sp,
        };
        let inner_sp = match ori_link.find('@') {
            Some(index) if index != 0 && ori_link.as_bytes()[index - 1] == b'\\' => {
                sp.with_hi(sp.lo() + BytePos((index - 1) as _))
            }
            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
            }
        }
    }
}

/// 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: impl Into<DiagMessage> + Display,
    DiagnosticInfo { item, ori_link: _, dox, link_range }: &DiagnosticInfo<'_>,
    decorate: impl FnOnce(&mut Diag<'_, ()>, Option<rustc_span::Span>, MarkdownLinkRange),
) {
    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.emit_node_span_lint(
        lint,
        hir_id,
        sp,
        rustc_errors::DiagDecorator(|lint| {
            lint.primary_message(msg);

            let (span, link_range) = match link_range {
                MarkdownLinkRange::Destination(md_range) => {
                    let mut md_range = md_range.clone();
                    let sp = source_span_for_markdown_range(
                        tcx,
                        dox,
                        &md_range,
                        &item.attrs.doc_strings,
                    )
                    .map(|(mut sp, _)| {
                        while dox.as_bytes().get(md_range.start) == Some(&b' ')
                            || dox.as_bytes().get(md_range.start) == Some(&b'`')
                        {
                            md_range.start += 1;
                            sp = sp.with_lo(sp.lo() + BytePos(1));
                        }
                        while dox.as_bytes().get(md_range.end - 1) == Some(&b' ')
                            || dox.as_bytes().get(md_range.end - 1) == Some(&b'`')
                        {
                            md_range.end -= 1;
                            sp = sp.with_hi(sp.hi() - BytePos(1));
                        }
                        sp
                    });
                    (sp, MarkdownLinkRange::Destination(md_range))
                }
                MarkdownLinkRange::WholeLink(md_range) => (
                    source_span_for_markdown_range(tcx, dox, md_range, &item.attrs.doc_strings)
                        .map(|(sp, _)| sp),
                    link_range.clone(),
                ),
            };

            if let Some(sp) = span {
                lint.span(sp);
            } else {
                // blah blah blah\nblah\nblah [blah] blah blah\nblah blah
                //                       ^     ~~~~
                //                       |     link_range
                //                       last_new_line_offset
                let md_range = link_range.inner_range().clone();
                let last_new_line_offset = dox[..md_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 `md_range` and manually mark it with '^'s.
                lint.note(format!(
                    "the link appears in this line:\n\n{line}\n\
                     {indicator: <before$}{indicator:^<found$}",
                    indicator = "",
                    before = md_range.start - last_new_line_offset,
                    found = md_range.len(),
                ));
            }

            decorate(lint, span, link_range);
        }),
    );
}

/// 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: &LinkCollector<'_, '_>,
    diag_info: DiagnosticInfo<'_>,
    path_str: &str,
    disambiguator: Option<Disambiguator>,
    kinds: SmallVec<[ResolutionFailure<'_>; 3]>,
) {
    let tcx = collector.cx.tcx;
    report_diagnostic(
        tcx,
        BROKEN_INTRA_DOC_LINKS,
        format!("unresolved link to `{path_str}`"),
        &diag_info,
        |diag, sp, link_range| {
            let item = |res: Res| format!("the {} `{}`", res.descr(), res.name(tcx));
            let assoc_item_not_allowed = |res: Res| {
                let name = res.name(tcx);
                format!(
                    "`{name}` is {} {}, not a module or type, and cannot have associated items",
                    res.article(),
                    res.descr()
                )
            };
            // ignore duplicates
            let mut variants_seen = SmallVec::<[_; 3]>::new();
            for mut failure in kinds {
                let variant = 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;

                    // 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 {
                        // FIXME(jynelson): this might conflict with my `Self` fix in #76467
                        let Some((start, end)) = name.rsplit_once("::") 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(v_res) =
                                collector.resolve(start, ns, None, item_id, module_id)
                            {
                                debug!("found partial_res={v_res:?}");
                                if let Some(&res) = v_res.first() {
                                    *partial_res = Some(full_res(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 `{unresolved}` in module `{module_name}`")
                        } else {
                            // None of the link resolved; e.g. `Notimported`
                            format!("no item named `{unresolved}` in scope")
                        };
                        if let Some(span) = sp {
                            diag.span_label(span, note);
                        } else {
                            diag.note(note);
                        }

                        if !path_str.contains("::") {
                            if disambiguator.is_none_or(|d| d.ns() == MacroNS)
                                && collector
                                    .cx
                                    .tcx
                                    .resolutions(())
                                    .all_macro_rules
                                    .contains(&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"
                                ));
                            } 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_did = match res {
                        Res::Def(kind, did) => Some((kind, did)),
                        Res::Primitive(_) => None,
                    };
                    let is_struct_variant = |did| {
                        if let ty::Adt(def, _) = tcx.type_of(did).instantiate_identity().kind()
                            && def.is_enum()
                            && let Some(variant) =
                                def.variants().iter().find(|v| v.name == res.name(tcx))
                        {
                            // ctor is `None` if variant is a struct
                            variant.ctor.is_none()
                        } else {
                            false
                        }
                    };
                    let path_description = if let Some((kind, did)) = kind_did {
                        match kind {
                            Mod | ForeignMod => "inner item",
                            Struct => "field or associated item",
                            Enum | Union => "variant or associated item",
                            Variant if is_struct_variant(did) => {
                                let variant = res.name(tcx);
                                let note = format!("variant `{variant}` has no such field");
                                if let Some(span) = sp {
                                    diag.span_label(span, note);
                                } else {
                                    diag.note(note);
                                }
                                return;
                            }
                            Variant
                            | Field
                            | Closure
                            | 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
                            | TraitAlias
                            | TyParam
                            | Static { .. } => "associated item",
                            Impl { .. } | GlobalAsm | SyntheticCoroutineBody => {
                                unreachable!("not a path")
                            }
                        }
                    } else {
                        "associated item"
                    };
                    let name = res.name(tcx);
                    let note = format!(
                        "the {res} `{name}` has no {disamb_res} named `{unresolved}`",
                        res = res.descr(),
                        disamb_res = disambiguator.map_or(path_description, |d| d.descr()),
                    );
                    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,
                            link_range.clone(),
                            sp,
                            &diag_info,
                        );

                        if let Some(disambiguator) = disambiguator
                            && !matches!(disambiguator, Disambiguator::Namespace(..))
                        {
                            format!(
                                "this link resolves to {}, which is not {} {}",
                                item(res),
                                disambiguator.article(),
                                disambiguator.descr()
                            )
                        } else {
                            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);
                }
            }
        },
    );
}

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: String,
    anchor_idx: usize,
) {
    report_diagnostic(cx.tcx, BROKEN_INTRA_DOC_LINKS, msg, &diag_info, |diag, sp, _link_range| {
        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: MarkdownLinkRange,
    msg: impl Into<DiagMessage> + Display,
) {
    diag_info.link_range = disambiguator_range;
    report_diagnostic(cx.tcx, BROKEN_INTRA_DOC_LINKS, msg, &diag_info, |diag, _sp, _link_range| {
        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_VERSION
        );
        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, _link_range| {
            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.
///
/// If all `candidates` have the same kind, it's not possible to disambiguate so in this case,
/// the function won't emit an error and will return `false`. Otherwise, it'll emit the error and
/// return `true`.
fn ambiguity_error(
    cx: &DocContext<'_>,
    diag_info: &DiagnosticInfo<'_>,
    path_str: &str,
    candidates: &[(Res, Option<DefId>)],
    emit_error: bool,
) -> bool {
    let mut descrs = FxHashSet::default();
    // proc macro can exist in multiple namespaces at once, so we need to compare `DefIds`
    //  to remove the candidate in the fn namespace.
    let mut possible_proc_macro_id = None;
    let is_proc_macro_crate = cx.tcx.crate_types() == [CrateType::ProcMacro];
    let mut kinds = candidates
        .iter()
        .map(|(res, def_id)| {
            let r =
                if let Some(def_id) = def_id { Res::from_def_id(cx.tcx, *def_id) } else { *res };
            if is_proc_macro_crate && let Res::Def(DefKind::Macro(_), id) = r {
                possible_proc_macro_id = Some(id);
            }
            r
        })
        .collect::<Vec<_>>();
    // In order to properly dedup proc macros, we have to do it in two passes:
    // 1. Completing the full traversal to find the possible duplicate in the macro namespace,
    // 2. Another full traversal to eliminate the candidate in the fn namespace.
    //
    // Thus, we have to do an iteration after collection is finished.
    //
    // As an optimization, we only deduplicate if we're in a proc-macro crate,
    // and only if we already found something that looks like a proc macro.
    if is_proc_macro_crate && let Some(macro_id) = possible_proc_macro_id {
        kinds.retain(|res| !matches!(res, Res::Def(DefKind::Fn, fn_id) if macro_id == *fn_id));
    }

    kinds.retain(|res| descrs.insert(res.descr()));

    if descrs.len() == 1 {
        // There is no way for users to disambiguate at this point, so better return the first
        // candidate and not show a warning.
        return false;
    } else if !emit_error {
        return true;
    }

    let mut msg = format!("`{path_str}` is ");
    match kinds.as_slice() {
        [res1, res2] => {
            msg += &format!(
                "both {} {} and {} {}",
                res1.article(),
                res1.descr(),
                res2.article(),
                res2.descr()
            );
        }
        _ => {
            let mut kinds = kinds.iter().peekable();
            while let Some(res) = kinds.next() {
                if kinds.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, link_range| {
        if let Some(sp) = sp {
            diag.span_label(sp, "ambiguous link");
        } else {
            diag.note("ambiguous link");
        }

        for res in kinds {
            suggest_disambiguator(res, diag, path_str, link_range.clone(), sp, diag_info);
        }
    });
    true
}

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

    let ori_link = match link_range {
        MarkdownLinkRange::Destination(range) => Some(&diag_info.dox[range]),
        MarkdownLinkRange::WholeLink(_) => None,
    };

    if let (Some(sp), Some(ori_link)) = (sp, ori_link) {
        let mut spans = suggestion.as_help_span(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 `{item_name}` links to private item `{path_str}`");

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

        let note_msg = if cx.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,
        "f16" => F16,
        "f32" => F32,
        "f64" => F64,
        "f128" => F128,
        "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))
}