dart2js should provide reflective access to metadata

[peter-ahe-google]

dart2js should support this getter on DeclarationMirror:

/**
 * A list of the metadata associated with this declaration.
 */
List<InstanceMirror> get metadata;

See issue #6614.

[peter-ahe-google]

Removed this from the M5 milestone.
Added this to the M6 milestone.

[justinfagnani]

How will this work for compile-time mirrors? Will hasReflectee on the InstanceMirrors return true? If so, what type will it be and will there be a way visit the value?

[peter-ahe-google]

This bug is for runtime support, dart2js already supports metadata for source mirrors.

Some source-InstanceMirrors have a reflectee, but only simple values such as bool, int, String, etc. For lists and maps, Johnni added some convenience methods for accessing their elements. For more complex constants, you have to look at their fields. Take a look at dart/sdk/lib/_internal/compiler/implementation/mirrors/dart2js_mirror.dart. Feel free to ask additional questions about source mirrors at compiler-dev@dartlang.org.

[peter-ahe-google]

https://codereview.chromium.org/16101007/ implements LibraryMirror.metadata.

[peter-ahe-google]

CL 16101007 landed in r23406.

[peter-ahe-google]

https://codereview.chromium.org/15821011/ implements ClassMirror.metadata.

[peter-ahe-google]

CL 15821011 landed in r23457.

[peter-ahe-google]

https://codereview.chromium.org/15861028/ implements MethodMirror.metadata.

[peter-ahe-google]

CL 15861028 landed in r23529.

[peter-ahe-google]

https://codereview.chromium.org/16156013/ implements metadata on instance fields.

[peter-ahe-google]

CL 16156013 landed in r23580.

[sethladd]

Thanks Peter. Just tried a simple case and it worked!

import 'dart:mirrors';

const awesome = const Awesome('way cool');

class Awesome {
  final String msg;
  const Awesome(this.msg);
  
  String toString() => msg;
}

@awesome('it works!')
class Cool {
  
}

void main() {
  var classMirror = reflectClass(Cool);
  var metadata = classMirror.metadata;
  var obj = metadata.first.reflectee;
  print(metadata);
  print(obj);
}

Do you have an easy list of things you expect to work at this point?

[peter-ahe-google]

See this test for what works in both dart2js and the VM:
https://code.google.com/p/dart/source/browse/branches/bleeding_edge/dart/tests/lib/mirrors/metadata_test.dart

[peter-ahe-google]

Added Library-Mirrors label.

[peter-ahe-google]

Marked this as blocking #6490.