Create def_id for async fns during lowering

Author: spastorino

compiler/rustc_ast_lowering/src/lib.rs

@@ -1839,9 +1839,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
         let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
 
-        let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
         let fn_def_id = self.local_def_id(fn_node_id);
 
+        let opaque_ty_def_id =
+            self.create_def(fn_def_id, opaque_ty_node_id, DefPathData::ImplTrait);
+
         // When we create the opaque type for this async fn, it is going to have
         // to capture all the lifetimes involved in the signature (including in the
         // return type). This is done by introducing lifetime parameters for:

compiler/rustc_resolve/src/def_collector.rs

@@ -131,22 +131,17 @@ impl<'a, 'b> visit::Visitor<'a> for DefCollector<'a, 'b> {
 
     fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
         if let FnKind::Fn(_, _, sig, _, generics, body) = fn_kind {
-            if let Async::Yes { closure_id, return_impl_trait_id, .. } = sig.header.asyncness {
+            if let Async::Yes { closure_id, .. } = sig.header.asyncness {
                 self.visit_generics(generics);
 
-                let return_impl_trait_id =
-                    self.create_def(return_impl_trait_id, DefPathData::ImplTrait, span);
-
                 // For async functions, we need to create their inner defs inside of a
                 // closure to match their desugared representation. Besides that,
                 // we must mirror everything that `visit::walk_fn` below does.
                 self.visit_fn_header(&sig.header);
                 for param in &sig.decl.inputs {
                     self.visit_param(param);
                 }
-                self.with_parent(return_impl_trait_id, |this| {
-                    this.visit_fn_ret_ty(&sig.decl.output)
-                });
+                self.visit_fn_ret_ty(&sig.decl.output);
                 // If this async fn has no body (i.e. it's an async fn signature in a trait)
                 // then the closure_def will never be used, and we should avoid generating a
                 // def-id for it.