Assert that HIR nodes are not their own parent.

compiler/rustc_ast_lowering/src/index.rs

@@ -69,6 +69,7 @@ impl<'a, 'hir> NodeCollector<'a, 'hir> {
     fn insert(&mut self, span: Span, hir_id: HirId, node: Node<'hir>) {
         debug_assert_eq!(self.owner, hir_id.owner);
         debug_assert_ne!(hir_id.local_id.as_u32(), 0);
+        debug_assert_ne!(hir_id.local_id, self.parent_node);
 
         // Make sure that the DepNode of some node coincides with the HirId
         // owner of that node.

compiler/rustc_ast_lowering/src/lib.rs

@@ -1256,7 +1256,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
             }
             TyKind::ImplicitSelf => {
-                let hir_id = self.lower_node_id(t.id);
+                let hir_id = self.next_id();
                 let res = self.expect_full_res(t.id);
                 let res = self.lower_res(res);
                 hir::TyKind::Path(hir::QPath::Resolved(

compiler/rustc_hir/src/hir.rs

@@ -835,7 +835,16 @@ impl<'tcx> OwnerNodes<'tcx> {
 impl fmt::Debug for OwnerNodes<'_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("OwnerNodes")
+            // Do not print all the pointers to all the nodes, as it would be unreadable.
             .field("node", &self.nodes[ItemLocalId::from_u32(0)])
+            .field(
+                "parents",
+                &self
+                    .nodes
+                    .iter_enumerated()
+                    .map(|(id, parented_node)| (id, parented_node.as_ref().map(|node| node.parent)))
+                    .collect::<Vec<_>>(),
+            )
             .field("bodies", &self.bodies)
             .field("local_id_to_def_id", &self.local_id_to_def_id)
             .field("hash_without_bodies", &self.hash_without_bodies)

compiler/rustc_middle/src/hir/map/mod.rs

@@ -301,6 +301,8 @@ impl<'hir> Map<'hir> {
             let owner = self.tcx.hir_owner_nodes(id.owner).as_owner()?;
             let node = owner.nodes[id.local_id].as_ref()?;
             let hir_id = HirId { owner: id.owner, local_id: node.parent };
+            // HIR indexing should have checked that.
+            debug_assert_ne!(id.local_id, node.parent);
             Some(hir_id)
         }
     }