Auto merge of #90639 - matthewjasper:leaf-def-cache, r=cjgillot

Add a query for resolving an impl item from the trait item

This makes finding the item in an impl that implements a given trait item a query. This is for a few reasons:

- To slightly improve performance
- To avoid having to do name resolution during monomorphisation
- To make it easier to implement potential future features that create anonymous associated items

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -1008,6 +1008,10 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         self.get_impl_data(id).constness
     }
 
+    fn get_trait_item_def_id(&self, id: DefIndex) -> Option<DefId> {
+        self.root.tables.trait_item_def_id.get(self, id).map(|d| d.decode(self))
+    }
+
     fn get_coerce_unsized_info(&self, id: DefIndex) -> Option<ty::adjustment::CoerceUnsizedInfo> {
         self.get_impl_data(id).coerce_unsized_info
     }
@@ -1258,6 +1262,16 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
+    fn get_associated_item_def_ids(&self, tcx: TyCtxt<'tcx>, id: DefIndex) -> &'tcx [DefId] {
+        if let Some(children) = self.root.tables.children.get(self, id) {
+            tcx.arena.alloc_from_iter(
+                children.decode((self, tcx.sess)).map(|child_index| self.local_def_id(child_index)),
+            )
+        } else {
+            &[]
+        }
+    }
+
     fn get_associated_item(&self, id: DefIndex, sess: &Session) -> ty::AssocItem {
         let def_key = self.def_key(id);
         let parent = self.local_def_id(def_key.parent.unwrap());
@@ -1279,6 +1293,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             vis: self.get_visibility(id),
             defaultness: container.defaultness(),
             def_id: self.local_def_id(id),
+            trait_item_def_id: self.get_trait_item_def_id(id),
             container: container.with_def_id(parent),
             fn_has_self_parameter: has_self,
         }

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

@@ -103,12 +103,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
         tcx.calculate_dtor(def_id, |_,_| Ok(()))
     }
     variances_of => { tcx.arena.alloc_from_iter(cdata.get_item_variances(def_id.index)) }
-    associated_item_def_ids => {
-        let mut result = SmallVec::<[_; 8]>::new();
-        cdata.each_child_of_item(def_id.index,
-          |child| result.push(child.res.def_id()), tcx.sess);
-        tcx.arena.alloc_slice(&result)
-    }
+    associated_item_def_ids => { cdata.get_associated_item_def_ids(tcx, def_id.index) }
     associated_item => { cdata.get_associated_item(def_id.index, tcx.sess) }
     impl_trait_ref => { cdata.get_impl_trait(def_id.index, tcx) }
     impl_polarity => { cdata.get_impl_polarity(def_id.index) }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1294,6 +1294,9 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         }
         self.encode_ident_span(def_id, impl_item.ident);
         self.encode_item_type(def_id);
+        if let Some(trait_item_def_id) = impl_item.trait_item_def_id {
+            record!(self.tables.trait_item_def_id[def_id] <- trait_item_def_id);
+        }
         if impl_item.kind == ty::AssocKind::Fn {
             record!(self.tables.fn_sig[def_id] <- tcx.fn_sig(def_id));
         }

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -302,6 +302,7 @@ define_tables! {
     ty: Table<DefIndex, Lazy!(Ty<'tcx>)>,
     fn_sig: Table<DefIndex, Lazy!(ty::PolyFnSig<'tcx>)>,
     impl_trait_ref: Table<DefIndex, Lazy!(ty::TraitRef<'tcx>)>,
+    trait_item_def_id: Table<DefIndex, Lazy<DefId>>,
     inherent_impls: Table<DefIndex, Lazy<[DefIndex]>>,
     variances: Table<DefIndex, Lazy<[ty::Variance]>>,
     generics: Table<DefIndex, Lazy<ty::Generics>>,

compiler/rustc_middle/src/query/mod.rs

@@ -630,6 +630,32 @@ rustc_queries! {
         desc { |tcx| "collecting associated items of {}", tcx.def_path_str(key) }
     }
 
+    /// Maps from associated items on a trait to the corresponding associated
+    /// item on the impl specified by `impl_id`.
+    ///
+    /// For example, with the following code
+    ///
+    /// ```
+    /// struct Type {}
+    ///                         // DefId
+    /// trait Trait {           // trait_id
+    ///     fn f();             // trait_f
+    ///     fn g() {}           // trait_g
+    /// }
+    ///
+    /// impl Trait for Type {   // impl_id
+    ///     fn f() {}           // impl_f
+    ///     fn g() {}           // impl_g
+    /// }
+    /// ```
+    ///
+    /// The map returned for `tcx.impl_item_implementor_ids(impl_id)` would be
+    ///`{ trait_f: impl_f, trait_g: impl_g }`
+    query impl_item_implementor_ids(impl_id: DefId) -> FxHashMap<DefId, DefId> {
+        desc { |tcx| "comparing impl items against trait for {}", tcx.def_path_str(impl_id) }
+        storage(ArenaCacheSelector<'tcx>)
+    }
+
     /// Given an `impl_id`, return the trait it implements.
     /// Return `None` if this is an inherent impl.
     query impl_trait_ref(impl_id: DefId) -> Option<ty::TraitRef<'tcx>> {

compiler/rustc_middle/src/traits/specialization_graph.rs

@@ -4,7 +4,6 @@ use crate::ty::{self, TyCtxt};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::ErrorReported;
 use rustc_hir::def_id::{DefId, DefIdMap};
-use rustc_span::symbol::Ident;
 
 /// A per-trait graph of impls in specialization order. At the moment, this
 /// graph forms a tree rooted with the trait itself, with all other nodes
@@ -75,34 +74,28 @@ pub enum Node {
     Trait(DefId),
 }
 
-impl<'tcx> Node {
+impl Node {
     pub fn is_from_trait(&self) -> bool {
         matches!(self, Node::Trait(..))
     }
 
-    /// Iterate over the items defined directly by the given (impl or trait) node.
-    pub fn items(&self, tcx: TyCtxt<'tcx>) -> impl 'tcx + Iterator<Item = &'tcx ty::AssocItem> {
-        tcx.associated_items(self.def_id()).in_definition_order()
-    }
-
-    /// Finds an associated item defined in this node.
+    /// Trys to find the associated item that implements `trait_item_def_id`
+    /// defined in this node.
     ///
     /// If this returns `None`, the item can potentially still be found in
     /// parents of this node.
-    pub fn item(
+    pub fn item<'tcx>(
         &self,
         tcx: TyCtxt<'tcx>,
-        trait_item_name: Ident,
-        trait_item_kind: ty::AssocKind,
-        trait_def_id: DefId,
-    ) -> Option<ty::AssocItem> {
-        tcx.associated_items(self.def_id())
-            .filter_by_name_unhygienic(trait_item_name.name)
-            .find(move |impl_item| {
-                trait_item_kind == impl_item.kind
-                    && tcx.hygienic_eq(impl_item.ident, trait_item_name, trait_def_id)
-            })
-            .copied()
+        trait_item_def_id: DefId,
+    ) -> Option<&'tcx ty::AssocItem> {
+        match *self {
+            Node::Trait(_) => Some(tcx.associated_item(trait_item_def_id)),
+            Node::Impl(impl_def_id) => {
+                let id = tcx.impl_item_implementor_ids(impl_def_id).get(&trait_item_def_id)?;
+                Some(tcx.associated_item(*id))
+            }
+        }
     }
 
     pub fn def_id(&self) -> DefId {
@@ -181,17 +174,11 @@ impl LeafDef {
 impl<'tcx> Ancestors<'tcx> {
     /// Finds the bottom-most (ie. most specialized) definition of an associated
     /// item.
-    pub fn leaf_def(
-        mut self,
-        tcx: TyCtxt<'tcx>,
-        trait_item_name: Ident,
-        trait_item_kind: ty::AssocKind,
-    ) -> Option<LeafDef> {
-        let trait_def_id = self.trait_def_id;
+    pub fn leaf_def(mut self, tcx: TyCtxt<'tcx>, trait_item_def_id: DefId) -> Option<LeafDef> {
         let mut finalizing_node = None;
 
         self.find_map(|node| {
-            if let Some(item) = node.item(tcx, trait_item_name, trait_item_kind, trait_def_id) {
+            if let Some(item) = node.item(tcx, trait_item_def_id) {
                 if finalizing_node.is_none() {
                     let is_specializable = item.defaultness.is_default()
                         || tcx.impl_defaultness(node.def_id()).is_default();
@@ -201,7 +188,7 @@ impl<'tcx> Ancestors<'tcx> {
                     }
                 }
 
-                Some(LeafDef { item, defining_node: node, finalizing_node })
+                Some(LeafDef { item: *item, defining_node: node, finalizing_node })
             } else {
                 // Item not mentioned. This "finalizes" any defaulted item provided by an ancestor.
                 finalizing_node = Some(node);

compiler/rustc_middle/src/ty/assoc.rs

@@ -40,6 +40,7 @@ impl AssocItemContainer {
     }
 }
 
+/// Information about an associated item
 #[derive(Copy, Clone, Debug, PartialEq, HashStable, Eq, Hash)]
 pub struct AssocItem {
     pub def_id: DefId,
@@ -50,6 +51,10 @@ pub struct AssocItem {
     pub defaultness: hir::Defaultness,
     pub container: AssocItemContainer,
 
+    /// If this is an item in an impl of a trait then this is the `DefId` of
+    /// the associated item on the trait that this implements.
+    pub trait_item_def_id: Option<DefId>,
+
     /// Whether this is a method with an explicit self
     /// as its first parameter, allowing method calls.
     pub fn_has_self_parameter: bool,

compiler/rustc_monomorphize/src/collector.rs

@@ -1310,10 +1310,9 @@ fn create_mono_items_for_default_impls<'tcx>(
             if let Some(trait_ref) = tcx.impl_trait_ref(item.def_id) {
                 let param_env = ty::ParamEnv::reveal_all();
                 let trait_ref = tcx.normalize_erasing_regions(param_env, trait_ref);
-                let overridden_methods: FxHashSet<_> =
-                    impl_.items.iter().map(|iiref| iiref.ident.normalize_to_macros_2_0()).collect();
+                let overridden_methods = tcx.impl_item_implementor_ids(item.def_id);
                 for method in tcx.provided_trait_methods(trait_ref.def_id) {
-                    if overridden_methods.contains(&method.ident.normalize_to_macros_2_0()) {
+                    if overridden_methods.contains_key(&method.def_id) {
                         continue;
                     }
 

compiler/rustc_passes/src/check_const.rs

@@ -93,26 +93,29 @@ impl<'tcx> hir::itemlikevisit::ItemLikeVisitor<'tcx> for CheckConstTraitVisitor<
                     for trait_item in self.tcx.associated_items(trait_def_id).in_definition_order()
                     {
                         if let ty::AssocItem {
-                            kind: ty::AssocKind::Fn, ident, defaultness, ..
-                        } = trait_item
+                            kind: ty::AssocKind::Fn,
+                            defaultness,
+                            def_id: trait_item_id,
+                            ..
+                        } = *trait_item
                         {
                             // we can ignore functions that do not have default bodies:
                             // if those are unimplemented it will be catched by typeck.
                             if !defaultness.has_value()
                                 || self
                                     .tcx
-                                    .has_attr(trait_item.def_id, sym::default_method_body_is_const)
+                                    .has_attr(trait_item_id, sym::default_method_body_is_const)
                             {
                                 continue;
                             }
 
                             let is_implemented = ancestors
-                                .leaf_def(self.tcx, trait_item.ident, trait_item.kind)
+                                .leaf_def(self.tcx, trait_item_id)
                                 .map(|node_item| !node_item.defining_node.is_from_trait())
                                 .unwrap_or(false);
 
                             if !is_implemented {
-                                to_implement.push(ident.to_string());
+                                to_implement.push(self.tcx.item_name(trait_item_id).to_string());
                             }
                         }
                     }

compiler/rustc_passes/src/stability.rs

@@ -794,19 +794,12 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                     }
                 }
 
-                if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
-                    for impl_item_ref in items {
-                        let impl_item = self.tcx.hir().impl_item(impl_item_ref.id);
-                        let trait_item_def_id = self
-                            .tcx
-                            .associated_items(trait_did)
-                            .filter_by_name_unhygienic(impl_item.ident.name)
-                            .next()
-                            .map(|item| item.def_id);
-                        if let Some(def_id) = trait_item_def_id {
-                            // Pass `None` to skip deprecation warnings.
-                            self.tcx.check_stability(def_id, None, impl_item.span, None);
-                        }
+                for impl_item_ref in items {
+                    let impl_item = self.tcx.associated_item(impl_item_ref.id.def_id);
+
+                    if let Some(def_id) = impl_item.trait_item_def_id {
+                        // Pass `None` to skip deprecation warnings.
+                        self.tcx.check_stability(def_id, None, impl_item_ref.span, None);
                     }
                 }
             }

compiler/rustc_save_analysis/src/lib.rs

@@ -710,13 +710,11 @@ impl<'tcx> SaveContext<'tcx> {
             }
             Res::Def(HirDefKind::AssocFn, decl_id) => {
                 let def_id = if decl_id.is_local() {
-                    let ti = self.tcx.associated_item(decl_id);
-
-                    self.tcx
-                        .associated_items(ti.container.id())
-                        .filter_by_name_unhygienic(ti.ident.name)
-                        .find(|item| item.defaultness.has_value())
-                        .map(|item| item.def_id)
+                    if self.tcx.associated_item(decl_id).defaultness.has_value() {
+                        Some(decl_id)
+                    } else {
+                        None
+                    }
                 } else {
                     None
                 };

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1883,7 +1883,6 @@ fn assoc_ty_def(
     assoc_ty_def_id: DefId,
 ) -> Result<specialization_graph::LeafDef, ErrorReported> {
     let tcx = selcx.tcx();
-    let assoc_ty_name = tcx.associated_item(assoc_ty_def_id).ident;
     let trait_def_id = tcx.impl_trait_ref(impl_def_id).unwrap().def_id;
     let trait_def = tcx.trait_def(trait_def_id);
 
@@ -1893,21 +1892,18 @@ fn assoc_ty_def(
     // for the associated item at the given impl.
     // If there is no such item in that impl, this function will fail with a
     // cycle error if the specialization graph is currently being built.
-    let impl_node = specialization_graph::Node::Impl(impl_def_id);
-    for item in impl_node.items(tcx) {
-        if matches!(item.kind, ty::AssocKind::Type)
-            && tcx.hygienic_eq(item.ident, assoc_ty_name, trait_def_id)
-        {
-            return Ok(specialization_graph::LeafDef {
-                item: *item,
-                defining_node: impl_node,
-                finalizing_node: if item.defaultness.is_default() { None } else { Some(impl_node) },
-            });
-        }
+    if let Some(&impl_item_id) = tcx.impl_item_implementor_ids(impl_def_id).get(&assoc_ty_def_id) {
+        let item = tcx.associated_item(impl_item_id);
+        let impl_node = specialization_graph::Node::Impl(impl_def_id);
+        return Ok(specialization_graph::LeafDef {
+            item: *item,
+            defining_node: impl_node,
+            finalizing_node: if item.defaultness.is_default() { None } else { Some(impl_node) },
+        });
     }
 
     let ancestors = trait_def.ancestors(tcx, impl_def_id)?;
-    if let Some(assoc_item) = ancestors.leaf_def(tcx, assoc_ty_name, ty::AssocKind::Type) {
+    if let Some(assoc_item) = ancestors.leaf_def(tcx, assoc_ty_def_id) {
         Ok(assoc_item)
     } else {
         // This is saying that neither the trait nor
@@ -1916,7 +1912,11 @@ fn assoc_ty_def(
         // could only arise through a compiler bug --
         // if the user wrote a bad item name, it
         // should have failed in astconv.
-        bug!("No associated type `{}` for {}", assoc_ty_name, tcx.def_path_str(impl_def_id))
+        bug!(
+            "No associated type `{}` for {}",
+            tcx.item_name(assoc_ty_def_id),
+            tcx.def_path_str(impl_def_id)
+        )
     }
 }