Duplicate field initializers: compile error expected but doesn't occur

[DartBot]

This issue was originally filed by rodion...@unipro.ru

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Ran this on our latest VM build, no compile error.

Spec ch. 7.5.1 says: Let k be a generative constructor. [...] It is a compile-time error if more than one initializer corresponding to a given instance variable appears in k's initializer list.

However, in the following example:
class C {
  C() : x = 1, y = 2, this.x = 3;
  var x;
  var y;
}
main() {
  try {
    C c = new C();
    print(c.x);
  } catch(var x) {}
}

no compile-time error occurs and both initializers are executed, which is evident after print().

other constructor variations:
C() : x = 1, y = 2, x = 3;
C(x, y) : this.x = x, this.x = y;
demonstrate the same behaviour

[DartBot]

This comment was originally written by rodion...@unipro.ru

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Same for the next assertion:
It is a compile-time error if k's initializer list contains an initializer for a variable that is initialized by means of an initializing formal of k.

No compile-time error for constructors like
C(this.x, foo) : this.x = foo;
or C(this.x, foo) : x = foo;

[ghost]

Set owner to @mhausner.
Added Area-VM, Triaged labels.

[iposva-google]

Added Accepted label.

[DartBot]

This comment was originally written by @mhausner

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I have a review out to fix this.

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Added Started label.

[DartBot]

This comment was originally written by @mhausner

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Fixed at r10146

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Added Fixed label.