Evaluating variables (and viewing locals) in a frame behind (a few) async points doesn't work

[jensjoha]

Take this file for instance:

$ cat t.dart
import "dart:developer";

class Foo {
}

void main() async {
  Foo x = new Foo();
  await foo();
  print(x);
}

Future<void> foo() async {
  await null;
  await foo2();
}

Future<void> foo2() async {
  debugger();
  print("hello");
}

If I run as dart --enable-vm-service t.dart and go to observatory (or devtools for that matter) and try to evaluate x (or p x, or view the locals) in the main frame I'm being told org-dartlang-debug:synthetic_debug_expression:1:1: Error: Undefined name 'x'. (observatory), evaluateInFrame: (113) Expression compilation error; org-dartlang-debug:synthetic_debug_expression:1:1: Error: The getter 'x' isn't defined for the class '_FutureListener<S, T>'.; (DevTools), and presented with an empty list (locals listing).

That's not great.

If I go to the allocation profile I can find the Foo instance (having a retaining path like retained by [ 0 ] of Context (1) -> retained by [ 6 ] of Context (9) -> retained by a GC root (stack)), so it's definitely still there.

Why won't the debugger allow me to see it and evaluate it?

/cc @mkustermann

(to be fair this doesn't seem to have ever worked --- but it feels like a thing that should be possible)

[mkustermann]

There's currently work underway to change the way local variable state is stored async functions. It may not make sense to look into this issue before that work has been completed and/or may be done as part of that work.

/cc @alexmarkov

[dcharkes]

Duplicate of #51763 (which has more details than this issue).