Named arguments don't work with constructor initializers

[nex3]

If a constructor has optional initializer arguments, as in Foo([int this.a = 1]), using those as named arguments as in new Foo(a: 2) fails:

An unhandled exception has been thrown
NoSuchMethodException - receiver: 'Instance of 'Foo'' function name: 'Foo.' arguments: [-3737570]]
 0. Function: 'Object.noSuchMethod' url: 'bootstrap' line:93 col:3
 1. Function: 'Foo.Foo.' url: '/usr/local/google-old/home/goog/dart/dart/test.dart' line:-1 col:-1
 2. Function: 'main' url: '/usr/local/google-old/home/goog/dart/dart/test.dart' line:7 col:13

[iposva-google]

This is actually a language question. Is Foo([int this.a = 1]) even allowed?

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Set owner to @gbracha.
Removed Area-VM label.
Added Area-Language, Accepted labels.

[gbracha]

The spec is buggy: it does not answer this question properly.

The construction is allowed by the syntax, but there is no way such a parameter could be used, as its name is undefined. The name of this.x could be x, which would mean that it introduced deliberate shadowing (something we warn about) so that is not desirable. It could be this.x, which exposes to the world an implementation detail about how you chose to do initialization, so that too is not desired. So we should leave it undefined, which means it cannot be called. In which case, the spec should clearly state that the an initializing formal cannot be used as an optional parameter to a constructor. This means that if you want an optional parameter, you will have to take the trouble of assigning it to the instance variable manually.

[gbracha]

Spec has been modified accordingly.

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Added Done label.