Test that we lint the awaited expression

Author: ebroto

tests/ui/used_underscore_binding.rs

@@ -87,11 +87,20 @@ fn non_variables() {
     let f = _fn_test;
     f();
 }
-// Tests that we do not lint if the binding comes from await desugaring.
-// See issue 5360.
+
+// Tests that we do not lint if the binding comes from await desugaring,
+// but we do lint the awaited expression. See issue 5360.
 async fn await_desugaring() {
     async fn foo() {}
+    fn uses_i(_i: i32) {}
+
     foo().await;
+    ({
+        let _i = 5;
+        uses_i(_i);
+        foo()
+    })
+    .await
 }
 
 fn main() {

tests/ui/used_underscore_binding.stderr

@@ -30,5 +30,11 @@ error: used binding `_underscore_field` which is prefixed with an underscore. A
 LL |     s._underscore_field += 1;
    |     ^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 5 previous errors
+error: used binding `_i` which is prefixed with an underscore. A leading underscore signals that a binding will not be used.
+  --> $DIR/used_underscore_binding.rs:100:16
+   |
+LL |         uses_i(_i);
+   |                ^^
+
+error: aborting due to 6 previous errors