[Language] Constants being the same iff equal

[DartBot]

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

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Spec ch. 10.1 says:
Let c1 and c2 be a pair of constants. Then c1 === c2 i� c1 == c2.

However, double.NAN and the following example seem to disagree with the above statement:

class C {
  final x;
  const C(this.x);

  // operator equals not supported by the VM yet
  bool operator==(C other) {
    return this.x != other.x;
  }
}

const C(1) != const C(1)
but const C(1) === const C(1)

[madsager]

Added Area-Language, Triaged labels.

[gbracha]

Set owner to @gbracha.
Added Accepted label.

[gbracha]

Yes, the definition in the spec assumes a sensible definition of equality, but users can define == to be arbitrary rubbish, and so can (and has) the IEEE. The point was to give a concise characterization of canonicalization, but it will have to be refined.

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Added this to the M1 milestone.

[gbracha]

Fixed in 0.11 draft:

Let c1 and c2 be a pair of constants. Then identical(c1, c2) iff:
• c1 evaluates to either null, a constant map, an constant list, an instance of bool, num, String or Type and c1 == c2, OR
• c1 and c2 are constant objects of the same class C and for each member field of c1 is identical to the corresponding field of c2.

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Added Done label.