Dartc allows non-constant fields in a class with declared constant constructor

[DartBot]

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

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What steps will reproduce the problem?
Run the following test:
class A {
  const A();
  var x;
}

main() {
  var a = const A();
}

What is the expected output? What do you see instead?
Expected: compile-time error
Actual: test compiles without errors

What version of the product are you using? On what operating system?
dartc r2810, Ubuntu 10.04

Please provide any additional information below.

[dgrove]

Added Area-Compiler, Triaged labels.

[jtmcdole]

Set owner to @jtmcdole.
Added Accepted label.

[jtmcdole]

http://codereview.chromium.org/9122015

[DartBot]

This comment was originally written by zundel@google.com

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7.5.3 "It is a compile-time error if a constant constructor is declared by a class that has a non-final instance variable."

I agree that this fix is needed to comply with the spec, but it seems to me that creating a constant constructor creates a large set of constraints on the class hierarchy, thus, in practice, users are going to have to create an interface and two separate classes, neither of which can derive from the other, to implement the interface if they want to use constant constructors.

I am hoping with some thought we could we come up with a way to change the spec to allow one class to define both a const constructor and a non-constant version of the class in the same class definition.

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cc @gbracha.

[jtmcdole]

Fixed as per the spec for now:
http://code.google.com/p/dart/source/detail?r=3108

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Added Fixed label.