Bug in VM async implementation

[sigurdm]

The program:

var p;

test(ex, o) {
  if (ex != o) throw "Error '$ex' != '$o'";
}

main() async {
  await 3;
  p = (i) async => "${await i}";
  test(await "1", (await (p(1))));
}

prints:

Unhandled exception:
Uncaught Error: Error '1' != '1'
Stack Trace:
...

[sigurdm]

Here is a simpler version, that might show more about what is going wrong:

test(ex, o) {
  if (ex != "1") throw "Error $ex '${ex.runtimeType}'";
}

main() async {
  await null;
  p(i) async => "${await i}";
  test(await "1", (await (p(2))));
}

Prints:
Uncaught Error: Error 2 'int'

[DartBot]

This comment was originally written by @mhausner

---

This could very well be the same root cause as issue #22858, because the bug goes away if I reorder some statements. I slightly simplified the example to this:

test(ex, o) {
  if (ex != "1") throw "Error $ex '${ex.runtimeType}'";
}

main() async {
  await null;
  p() async => await "2";
  test(await "1", await p());
}

[iposva-google]

cc @crelier.
Set owner to @sgmitrovic.
Added Accepted label.

[DartBot]

This comment was originally written by @mhausner

---

The bug was that the local function p() accidentally re-used a temporary variable from main. The effect was that the call to p() overwrote the value "1" saved from 'await "1"'

https://codereview.chromium.org/1007393004/

---

Added Started label.

[DartBot]

This comment was originally written by @mhausner

---

Fixed in r44526

---

Added Fixed label.