Make the coroutine def id of an async closure the child of the closure def id

compiler/rustc_resolve/src/def_collector.rs

@@ -289,12 +289,18 @@ fn visit_expr(&mut self, expr: &'a Expr) {
                 // we must create two defs.
                 let closure_def = self.create_def(expr.id, kw::Empty, DefKind::Closure, expr.span);
                 match closure.coroutine_kind {
-                    Some(coroutine_kind) => self.create_def(
-                        coroutine_kind.closure_id(),
-                        kw::Empty,
-                        DefKind::Closure,
-                        expr.span,
-                    ),
+                    Some(coroutine_kind) => {
+                        self.with_parent(closure_def, |this| {
+                            let coroutine_def = this.create_def(
+                                coroutine_kind.closure_id(),
+                                kw::Empty,
+                                DefKind::Closure,
+                                expr.span,
+                            );
+                            this.with_parent(coroutine_def, |this| visit::walk_expr(this, expr));
+                        });
+                        return;
+                    }
                     None => closure_def,
                 }
             }

tests/ui/async-await/async-closures/def-path.rs

@@ -0,0 +1,14 @@
+// compile-flags: -Zverbose-internals
+// edition:2021
+
+#![feature(async_closure)]
+
+fn main() {
+    let x = async || {};
+    //~^ NOTE the expected `async` closure body
+    let () = x();
+    //~^ ERROR mismatched types
+    //~| NOTE this expression has type `{static main::{closure#0}::{closure#0} upvar_tys=
+    //~| NOTE expected `async` closure body, found `()`
+    //~| NOTE expected `async` closure body `{static main::{closure#0}::{closure#0}
+}

tests/ui/async-await/async-closures/def-path.stderr

@@ -0,0 +1,17 @@
+error[E0308]: mismatched types
+  --> $DIR/def-path.rs:9:9
+   |
+LL |     let x = async || {};
+   |                      -- the expected `async` closure body
+LL |
+LL |     let () = x();
+   |         ^^   --- this expression has type `{static main::{closure#0}::{closure#0} upvar_tys=?7t witness=?8t}`
+   |         |
+   |         expected `async` closure body, found `()`
+   |
+   = note: expected `async` closure body `{static main::{closure#0}::{closure#0} upvar_tys=?7t witness=?8t}`
+                         found unit type `()`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.