Only store a LocalDefId in hir::ImplItem.

compiler/rustc_hir/src/hir.rs

@@ -1969,14 +1969,21 @@ pub enum TraitItemKind<'hir> {
 // so it can fetched later.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Encodable, Debug)]
 pub struct ImplItemId {
-    pub hir_id: HirId,
+    pub def_id: LocalDefId,
+}
+
+impl ImplItemId {
+    pub fn hir_id(&self) -> HirId {
+        // Items are always HIR owners.
+        HirId::make_owner(self.def_id)
+    }
 }
 
 /// Represents anything within an `impl` block.
 #[derive(Debug)]
 pub struct ImplItem<'hir> {
     pub ident: Ident,
-    pub hir_id: HirId,
+    pub def_id: LocalDefId,
     pub vis: Visibility<'hir>,
     pub defaultness: Defaultness,
     pub attrs: &'hir [Attribute],
@@ -1985,6 +1992,17 @@ pub struct ImplItem<'hir> {
     pub span: Span,
 }
 
+impl ImplItem<'_> {
+    pub fn hir_id(&self) -> HirId {
+        // Items are always HIR owners.
+        HirId::make_owner(self.def_id)
+    }
+
+    pub fn impl_item_id(&self) -> ImplItemId {
+        ImplItemId { def_id: self.def_id }
+    }
+}
+
 /// Represents various kinds of content within an `impl`.
 #[derive(Debug, HashStable_Generic)]
 pub enum ImplItemKind<'hir> {
@@ -2903,11 +2921,10 @@ impl<'hir> Node<'hir> {
 
     pub fn hir_id(&self) -> Option<HirId> {
         match self {
-            Node::Item(Item { def_id, .. }) | Node::TraitItem(TraitItem { def_id, .. }) => {
-                Some(HirId::make_owner(*def_id))
-            }
+            Node::Item(Item { def_id, .. })
+            | Node::TraitItem(TraitItem { def_id, .. })
+            | Node::ImplItem(ImplItem { def_id, .. }) => Some(HirId::make_owner(*def_id)),
             Node::ForeignItem(ForeignItem { hir_id, .. })
-            | Node::ImplItem(ImplItem { hir_id, .. })
             | Node::Field(StructField { hir_id, .. })
             | Node::AnonConst(AnonConst { hir_id, .. })
             | Node::Expr(Expr { hir_id, .. })

compiler/rustc_hir/src/intravisit.rs

@@ -1004,7 +1004,7 @@ pub fn walk_trait_item_ref<'v, V: Visitor<'v>>(visitor: &mut V, trait_item_ref:
 pub fn walk_impl_item<'v, V: Visitor<'v>>(visitor: &mut V, impl_item: &'v ImplItem<'v>) {
     // N.B., deliberately force a compilation error if/when new fields are added.
     let ImplItem {
-        hir_id: _,
+        def_id: _,
         ident,
         ref vis,
         ref defaultness,
@@ -1021,7 +1021,7 @@ pub fn walk_impl_item<'v, V: Visitor<'v>>(visitor: &mut V, impl_item: &'v ImplIt
     visitor.visit_generics(generics);
     match *kind {
         ImplItemKind::Const(ref ty, body) => {
-            visitor.visit_id(impl_item.hir_id);
+            visitor.visit_id(impl_item.hir_id());
             visitor.visit_ty(ty);
             visitor.visit_nested_body(body);
         }
@@ -1031,11 +1031,11 @@ pub fn walk_impl_item<'v, V: Visitor<'v>>(visitor: &mut V, impl_item: &'v ImplIt
                 &sig.decl,
                 body_id,
                 impl_item.span,
-                impl_item.hir_id,
+                impl_item.hir_id(),
             );
         }
         ImplItemKind::TyAlias(ref ty) => {
-            visitor.visit_id(impl_item.hir_id);
+            visitor.visit_id(impl_item.hir_id());
             visitor.visit_ty(ty);
         }
     }

compiler/rustc_hir/src/stable_hash_impls.rs

@@ -53,11 +53,11 @@ impl<HirCtx: crate::HashStableContext> ToStableHashKey<HirCtx> for TraitItemId {
 }
 
 impl<HirCtx: crate::HashStableContext> ToStableHashKey<HirCtx> for ImplItemId {
-    type KeyType = (DefPathHash, ItemLocalId);
+    type KeyType = DefPathHash;
 
     #[inline]
-    fn to_stable_hash_key(&self, hcx: &HirCtx) -> (DefPathHash, ItemLocalId) {
-        self.hir_id.to_stable_hash_key(hcx)
+    fn to_stable_hash_key(&self, hcx: &HirCtx) -> DefPathHash {
+        hcx.local_def_path_hash(self.def_id)
     }
 }
 
@@ -103,7 +103,7 @@ impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for ForeignItemId {
 
 impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for ImplItemId {
     fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
-        hcx.hash_reference_to_item(self.hir_id, hasher)
+        hcx.hash_reference_to_item(self.hir_id(), hasher)
     }
 }
 
@@ -154,7 +154,7 @@ impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for TraitItem<'_> {
 impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for ImplItem<'_> {
     fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
         let ImplItem {
-            hir_id: _,
+            def_id: _,
             ident,
             ref vis,
             defaultness,