Auto merge of #88679 - petrochenkov:doctrscope, r=GuillaumeGomez

rustdoc: Pre-calculate traits that are in scope for doc links

This eliminates one more late use of resolver (part of #83761).
At early doc link resolution time we go through parent modules of items from the current crate, reexports of items from other crates, trait items, and impl items collected by `collect-intra-doc-links` pass, determine traits that are in scope in each such module, and put those traits into a map used by later rustdoc passes.
r? `@jyn514`

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -1373,11 +1373,15 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         self.root.traits.decode(self).map(move |index| self.local_def_id(index))
     }
 
-    fn get_trait_impls(self) -> impl Iterator<Item = (DefId, Option<SimplifiedType>)> + 'a {
-        self.cdata.trait_impls.values().flat_map(move |impls| {
-            impls
-                .decode(self)
-                .map(move |(idx, simplified_self_ty)| (self.local_def_id(idx), simplified_self_ty))
+    fn get_trait_impls(self) -> impl Iterator<Item = (DefId, DefId, Option<SimplifiedType>)> + 'a {
+        self.cdata.trait_impls.iter().flat_map(move |((trait_cnum_raw, trait_index), impls)| {
+            let trait_def_id = DefId {
+                krate: self.cnum_map[CrateNum::from_u32(*trait_cnum_raw)],
+                index: *trait_index,
+            };
+            impls.decode(self).map(move |(impl_index, simplified_self_ty)| {
+                (trait_def_id, self.local_def_id(impl_index), simplified_self_ty)
+            })
         })
     }
 

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -493,7 +493,7 @@ impl CStore {
     pub fn trait_impls_in_crate_untracked(
         &self,
         cnum: CrateNum,
-    ) -> impl Iterator<Item = (DefId, Option<SimplifiedType>)> + '_ {
+    ) -> impl Iterator<Item = (DefId, DefId, Option<SimplifiedType>)> + '_ {
         self.get_crate_data(cnum).get_trait_impls()
     }
 }

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -108,7 +108,7 @@ impl<'a> Resolver<'a> {
     /// Reachable macros with block module parents exist due to `#[macro_export] macro_rules!`,
     /// but they cannot use def-site hygiene, so the assumption holds
     /// (<https://github.com/rust-lang/rust/pull/77984#issuecomment-712445508>).
-    crate fn get_nearest_non_block_module(&mut self, mut def_id: DefId) -> Module<'a> {
+    pub fn get_nearest_non_block_module(&mut self, mut def_id: DefId) -> Module<'a> {
         loop {
             match self.get_module(def_id) {
                 Some(module) => return module,

compiler/rustc_resolve/src/lib.rs

@@ -614,7 +614,8 @@ impl<'a> ModuleData<'a> {
         }
     }
 
-    fn def_id(&self) -> DefId {
+    // Public for rustdoc.
+    pub fn def_id(&self) -> DefId {
         self.opt_def_id().expect("`ModuleData::def_id` is called on a block module")
     }
 
@@ -3407,6 +3408,16 @@ impl<'a> Resolver<'a> {
         &self.all_macros
     }
 
+    /// For rustdoc.
+    /// For local modules returns only reexports, for external modules returns all children.
+    pub fn module_children_or_reexports(&self, def_id: DefId) -> Vec<ModChild> {
+        if let Some(def_id) = def_id.as_local() {
+            self.reexport_map.get(&def_id).cloned().unwrap_or_default()
+        } else {
+            self.cstore().module_children_untracked(def_id, self.session)
+        }
+    }
+
     /// Retrieves the span of the given `DefId` if `DefId` is in the local crate.
     #[inline]
     pub fn opt_span(&self, def_id: DefId) -> Option<Span> {