dart:mirrors fails to find metadata on method parameters with --preview-dart-2

[itsjoeconway]

import 'dart:mirrors';

void main() {
  final m = reflectClass(T).declarations[#f] as MethodMirror;
  m.parameters.forEach((p) {
    print("${p.simpleName} -> ${p.metadata}");
  });
}

class T {
  void f(@U() int x) {}
}
class U {
  const U();
}

The expected behavior is that a list containing a single instance of U is printed, but the empty list is printed instead. The unexpected behavior is also true of top-level functions.

Related: metadata on class field declarations behaves correctly as far as I have seen.

[itsjoeconway]

@kmillikin Thank you for looking at this

[kmillikin]

@rmacnak-google it looks like we never added support in the VM for storing annotations on parameters (and also Kernel procedures). They seem to be skipped (looking at KernelLoader::LoadProcedure). The Kernel code for the example above has the annotation:

class T extends core::Object {
  synthetic constructor •() → void
    : super core::Object::•()
    ;
  method f(@self::U::•() core::int x) → void {}
}

I'm kicking it over to you for triage.

[itsjoeconway]

Hi all, just wanted to see if this issue is planning to land in 65? It's blocking right now and we're getting some confusion from users. I would like to be able to give them a rough timeline. Thanks!

[dgrove]

Hi Joe - We don't have an ETA yet, other than by Dart2Stable.

[thosakwe]

Also getting this bug. I have some code that reads ParameterMirror.metadata, but it always returns an empty list.