Auto merge of #123415 - petrochenkov:parenting, r=<try>

hir: Drop owner's own item-local id (zero) from parenting tables

I expect this to be a common case.

Author: bors

Diff for: compiler/rustc_ast_lowering/src/index.rs

@@ -112,7 +112,9 @@ impl<'a, 'hir> NodeCollector<'a, 'hir> {
     }
 
     fn insert_nested(&mut self, item: LocalDefId) {
-        self.parenting.insert(item, self.parent_node);
+        if self.parent_node.as_u32() != 0 {
+            self.parenting.insert(item, self.parent_node);
+        }
     }
 }
 

Diff for: compiler/rustc_middle/src/hir/mod.rs

@@ -174,8 +174,12 @@ pub fn provide(providers: &mut Providers) {
             let parent_owner_id = tcx.local_def_id_to_hir_id(parent_def_id).owner;
             HirId {
                 owner: parent_owner_id,
-                local_id: tcx.hir_crate(()).owners[parent_owner_id.def_id].unwrap().parenting
-                    [&owner_id.def_id],
+                local_id: tcx.hir_crate(()).owners[parent_owner_id.def_id]
+                    .unwrap()
+                    .parenting
+                    .get(&owner_id.def_id)
+                    .copied()
+                    .unwrap_or(ItemLocalId::from_u32(0)),
             }
         })
     };