Auto merge of #74489 - jyn514:assoc-items, r=manishearth,petrochenkov

Fix intra-doc links for associated items

@Manishearth and I found that links of the following sort are broken:
```rust
$ cat str_from.rs
/// [`String::from`]
pub fn foo() {}
$ rustdoc str_from.rs
warning: `[String::from]` cannot be resolved, ignoring it.
 --> str_from.rs:4:6
  |
4 | /// [`String::from`]
  |      ^^^^^^^^^^^^^^ cannot be resolved, ignoring
```
It turns out this is because the current implementation only looks at inherent impls (`impl Bar {}`) and traits _for the item being documented_. Note that this is not the same as the item being _linked_ to. So this code would work:

```rust
pub trait T1 {
    fn method();
}

pub struct S;
impl T1 for S {
    /// [S::method] on method
    fn method() {}
}
```

but putting the documentation on `trait T1` would not.

~~I realized that writing it up that my fix is only partially correct: It removes the inherent impls code when it should instead remove the `trait_item` code.~~ Fixed.

Additionally, I discovered while writing this there is some ambiguity: you could have multiple methods with the same name, but for different traits:

```rust
pub trait T1 {
    fn method();
}

pub trait T2 {
    fn method();
}

/// See [S::method]
pub struct S;
```

Rustdoc should give an ambiguity error here, but since there is currently no way to disambiguate the traits (#74563) it does not (#74489 (comment)).

There is a _third_ ambiguity that pops up: What if the trait is generic and is implemented multiple times with different generic parameters? In this case, my fix does not do very well: it thinks there is only one trait instantiated and links to that trait:

```
/// [`String::from`] -- this resolves to https://doc.rust-lang.org/nightly/alloc/string/struct.String.html#method.from
pub fn foo() {}
```

However, every `From` implementation has a method called `from`! So the browser picks a random one. This is not the desired behavior, but it's not clear how to avoid it.

To be consistent with the rest of intra-doc links, this only resolves associated items from traits that are in scope. This required changes to rustc_resolve to work cross-crate; the relevant commits are prefixed with `resolve: `. As a bonus, considering only traits in scope is slightly faster. To avoid re-calculating the traits over and over, rustdoc uses a cache to store the traits in scope for a given module.

src/librustc_resolve/late.rs

@@ -8,7 +8,7 @@
 use RibKind::*;
 
 use crate::{path_names_to_string, BindingError, CrateLint, LexicalScopeBinding};
-use crate::{Module, ModuleOrUniformRoot, NameBindingKind, ParentScope, PathResult};
+use crate::{Module, ModuleOrUniformRoot, ParentScope, PathResult};
 use crate::{ResolutionError, Resolver, Segment, UseError};
 
 use rustc_ast::ptr::P;
@@ -24,7 +24,6 @@ use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
 use rustc_hir::TraitCandidate;
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
-use rustc_span::def_id::LocalDefId;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
 use smallvec::{smallvec, SmallVec};
@@ -2342,95 +2341,31 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         ident.span = ident.span.normalize_to_macros_2_0();
         let mut search_module = self.parent_scope.module;
         loop {
-            self.get_traits_in_module_containing_item(ident, ns, search_module, &mut found_traits);
+            self.r.get_traits_in_module_containing_item(
+                ident,
+                ns,
+                search_module,
+                &mut found_traits,
+                &self.parent_scope,
+            );
             search_module =
                 unwrap_or!(self.r.hygienic_lexical_parent(search_module, &mut ident.span), break);
         }
 
         if let Some(prelude) = self.r.prelude {
             if !search_module.no_implicit_prelude {
-                self.get_traits_in_module_containing_item(ident, ns, prelude, &mut found_traits);
+                self.r.get_traits_in_module_containing_item(
+                    ident,
+                    ns,
+                    prelude,
+                    &mut found_traits,
+                    &self.parent_scope,
+                );
             }
         }
 
         found_traits
     }
-
-    fn get_traits_in_module_containing_item(
-        &mut self,
-        ident: Ident,
-        ns: Namespace,
-        module: Module<'a>,
-        found_traits: &mut Vec<TraitCandidate>,
-    ) {
-        assert!(ns == TypeNS || ns == ValueNS);
-        let mut traits = module.traits.borrow_mut();
-        if traits.is_none() {
-            let mut collected_traits = Vec::new();
-            module.for_each_child(self.r, |_, name, ns, binding| {
-                if ns != TypeNS {
-                    return;
-                }
-                match binding.res() {
-                    Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
-                        collected_traits.push((name, binding))
-                    }
-                    _ => (),
-                }
-            });
-            *traits = Some(collected_traits.into_boxed_slice());
-        }
-
-        for &(trait_name, binding) in traits.as_ref().unwrap().iter() {
-            // Traits have pseudo-modules that can be used to search for the given ident.
-            if let Some(module) = binding.module() {
-                let mut ident = ident;
-                if ident.span.glob_adjust(module.expansion, binding.span).is_none() {
-                    continue;
-                }
-                if self
-                    .r
-                    .resolve_ident_in_module_unadjusted(
-                        ModuleOrUniformRoot::Module(module),
-                        ident,
-                        ns,
-                        &self.parent_scope,
-                        false,
-                        module.span,
-                    )
-                    .is_ok()
-                {
-                    let import_ids = self.find_transitive_imports(&binding.kind, trait_name);
-                    let trait_def_id = module.def_id().unwrap();
-                    found_traits.push(TraitCandidate { def_id: trait_def_id, import_ids });
-                }
-            } else if let Res::Def(DefKind::TraitAlias, _) = binding.res() {
-                // For now, just treat all trait aliases as possible candidates, since we don't
-                // know if the ident is somewhere in the transitive bounds.
-                let import_ids = self.find_transitive_imports(&binding.kind, trait_name);
-                let trait_def_id = binding.res().def_id();
-                found_traits.push(TraitCandidate { def_id: trait_def_id, import_ids });
-            } else {
-                bug!("candidate is not trait or trait alias?")
-            }
-        }
-    }
-
-    fn find_transitive_imports(
-        &mut self,
-        mut kind: &NameBindingKind<'_>,
-        trait_name: Ident,
-    ) -> SmallVec<[LocalDefId; 1]> {
-        let mut import_ids = smallvec![];
-        while let NameBindingKind::Import { import, binding, .. } = kind {
-            let id = self.r.local_def_id(import.id);
-            self.r.maybe_unused_trait_imports.insert(id);
-            self.r.add_to_glob_map(&import, trait_name);
-            import_ids.push(id);
-            kind = &binding.kind;
-        }
-        import_ids
-    }
 }
 
 impl<'a> Resolver<'a> {

src/librustc_resolve/lib.rs

@@ -43,9 +43,9 @@ use rustc_index::vec::IndexVec;
 use rustc_metadata::creader::{CStore, CrateLoader};
 use rustc_middle::hir::exports::ExportMap;
 use rustc_middle::middle::cstore::{CrateStore, MetadataLoaderDyn};
-use rustc_middle::span_bug;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, DefIdTree, ResolverOutputs};
+use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
 use rustc_session::lint::{BuiltinLintDiagnostics, LintBuffer};
 use rustc_session::Session;
@@ -54,6 +54,7 @@ use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 
+use smallvec::{smallvec, SmallVec};
 use std::cell::{Cell, RefCell};
 use std::collections::BTreeSet;
 use std::{cmp, fmt, iter, ptr};
@@ -521,6 +522,29 @@ impl<'a> ModuleData<'a> {
         }
     }
 
+    /// This modifies `self` in place. The traits will be stored in `self.traits`.
+    fn ensure_traits<R>(&'a self, resolver: &mut R)
+    where
+        R: AsMut<Resolver<'a>>,
+    {
+        let mut traits = self.traits.borrow_mut();
+        if traits.is_none() {
+            let mut collected_traits = Vec::new();
+            self.for_each_child(resolver, |_, name, ns, binding| {
+                if ns != TypeNS {
+                    return;
+                }
+                match binding.res() {
+                    Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
+                        collected_traits.push((name, binding))
+                    }
+                    _ => (),
+                }
+            });
+            *traits = Some(collected_traits.into_boxed_slice());
+        }
+    }
+
     fn res(&self) -> Option<Res> {
         match self.kind {
             ModuleKind::Def(kind, def_id, _) => Some(Res::Def(kind, def_id)),
@@ -1430,6 +1454,68 @@ impl<'a> Resolver<'a> {
         self.crate_loader.postprocess(krate);
     }
 
+    fn get_traits_in_module_containing_item(
+        &mut self,
+        ident: Ident,
+        ns: Namespace,
+        module: Module<'a>,
+        found_traits: &mut Vec<TraitCandidate>,
+        parent_scope: &ParentScope<'a>,
+    ) {
+        assert!(ns == TypeNS || ns == ValueNS);
+        module.ensure_traits(self);
+        let traits = module.traits.borrow();
+
+        for &(trait_name, binding) in traits.as_ref().unwrap().iter() {
+            // Traits have pseudo-modules that can be used to search for the given ident.
+            if let Some(module) = binding.module() {
+                let mut ident = ident;
+                if ident.span.glob_adjust(module.expansion, binding.span).is_none() {
+                    continue;
+                }
+                if self
+                    .resolve_ident_in_module_unadjusted(
+                        ModuleOrUniformRoot::Module(module),
+                        ident,
+                        ns,
+                        parent_scope,
+                        false,
+                        module.span,
+                    )
+                    .is_ok()
+                {
+                    let import_ids = self.find_transitive_imports(&binding.kind, trait_name);
+                    let trait_def_id = module.def_id().unwrap();
+                    found_traits.push(TraitCandidate { def_id: trait_def_id, import_ids });
+                }
+            } else if let Res::Def(DefKind::TraitAlias, _) = binding.res() {
+                // For now, just treat all trait aliases as possible candidates, since we don't
+                // know if the ident is somewhere in the transitive bounds.
+                let import_ids = self.find_transitive_imports(&binding.kind, trait_name);
+                let trait_def_id = binding.res().def_id();
+                found_traits.push(TraitCandidate { def_id: trait_def_id, import_ids });
+            } else {
+                bug!("candidate is not trait or trait alias?")
+            }
+        }
+    }
+
+    fn find_transitive_imports(
+        &mut self,
+        mut kind: &NameBindingKind<'_>,
+        trait_name: Ident,
+    ) -> SmallVec<[LocalDefId; 1]> {
+        let mut import_ids = smallvec![];
+        while let NameBindingKind::Import { import, binding, .. } = kind {
+            let id = self.local_def_id(import.id);
+            self.maybe_unused_trait_imports.insert(id);
+            self.add_to_glob_map(&import, trait_name);
+            import_ids.push(id);
+            kind = &binding.kind;
+        }
+        import_ids
+    }
+
     fn new_module(
         &self,
         parent: Module<'a>,
@@ -3039,6 +3125,34 @@ impl<'a> Resolver<'a> {
         })
     }
 
+    /// This is equivalent to `get_traits_in_module_containing_item`, but without filtering by the associated item.
+    ///
+    /// This is used by rustdoc for intra-doc links.
+    pub fn traits_in_scope(&mut self, module_id: DefId) -> Vec<TraitCandidate> {
+        let module = self.get_module(module_id);
+        module.ensure_traits(self);
+        let traits = module.traits.borrow();
+        let to_candidate =
+            |this: &mut Self, &(trait_name, binding): &(Ident, &NameBinding<'_>)| TraitCandidate {
+                def_id: binding.res().def_id(),
+                import_ids: this.find_transitive_imports(&binding.kind, trait_name),
+            };
+
+        let mut candidates: Vec<_> =
+            traits.as_ref().unwrap().iter().map(|x| to_candidate(self, x)).collect();
+
+        if let Some(prelude) = self.prelude {
+            if !module.no_implicit_prelude {
+                prelude.ensure_traits(self);
+                candidates.extend(
+                    prelude.traits.borrow().as_ref().unwrap().iter().map(|x| to_candidate(self, x)),
+                );
+            }
+        }
+
+        candidates
+    }
+
     /// Rustdoc uses this to resolve things in a recoverable way. `ResolutionError<'a>`
     /// isn't something that can be returned because it can't be made to live that long,
     /// and also it's a private type. Fortunately rustdoc doesn't need to know the error,

src/librustdoc/clean/types.rs

@@ -20,7 +20,7 @@ use rustc_hir::lang_items;
 use rustc_hir::Mutability;
 use rustc_index::vec::IndexVec;
 use rustc_middle::middle::stability;
-use rustc_middle::ty::TyCtxt;
+use rustc_middle::ty::{AssocKind, TyCtxt};
 use rustc_span::hygiene::MacroKind;
 use rustc_span::source_map::DUMMY_SP;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
@@ -282,12 +282,21 @@ pub enum ItemEnum {
 }
 
 impl ItemEnum {
-    pub fn is_associated(&self) -> bool {
+    pub fn is_type_alias(&self) -> bool {
         match *self {
             ItemEnum::TypedefItem(_, _) | ItemEnum::AssocTypeItem(_, _) => true,
             _ => false,
         }
     }
+
+    pub fn as_assoc_kind(&self) -> Option<AssocKind> {
+        match *self {
+            ItemEnum::AssocConstItem(..) => Some(AssocKind::Const),
+            ItemEnum::AssocTypeItem(..) => Some(AssocKind::Type),
+            ItemEnum::TyMethodItem(..) | ItemEnum::MethodItem(..) => Some(AssocKind::Fn),
+            _ => None,
+        }
+    }
 }
 
 #[derive(Clone, Debug)]

src/librustdoc/core.rs

@@ -69,6 +69,11 @@ pub struct DocContext<'tcx> {
     pub auto_traits: Vec<DefId>,
     /// The options given to rustdoc that could be relevant to a pass.
     pub render_options: RenderOptions,
+    /// The traits in scope for a given module.
+    ///
+    /// See `collect_intra_doc_links::traits_implemented_by` for more details.
+    /// `map<module, set<trait>>`
+    pub module_trait_cache: RefCell<FxHashMap<DefId, FxHashSet<DefId>>>,
 }
 
 impl<'tcx> DocContext<'tcx> {
@@ -510,6 +515,7 @@ pub fn run_core(options: RustdocOptions) -> (clean::Crate, RenderInfo, RenderOpt
                         .filter(|trait_def_id| tcx.trait_is_auto(*trait_def_id))
                         .collect(),
                     render_options,
+                    module_trait_cache: RefCell::new(FxHashMap::default()),
                 };
                 debug!("crate: {:?}", tcx.hir().krate());
 

src/librustdoc/html/render/mod.rs

@@ -3612,7 +3612,7 @@ fn render_impl(
         };
 
         let (is_hidden, extra_class) =
-            if (trait_.is_none() || item.doc_value().is_some() || item.inner.is_associated())
+            if (trait_.is_none() || item.doc_value().is_some() || item.inner.is_type_alias())
                 && !is_default_item
             {
                 (false, "")