Implement new equality spec.

tests/language/equality_test.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+
+class A {
+  bool _result;
+  A(this._result);
+  operator ==(x) { return _result; }
+}
+
+tests() {
+  var alwaysTrue = new A(true);
+  var alwaysFalse = new A(false);
+  Expect.isFalse(alwaysFalse == alwaysFalse);
+  Expect.isTrue(alwaysFalse != alwaysFalse);
+  Expect.isTrue(alwaysTrue == alwaysTrue);
+  Expect.isTrue(alwaysTrue == 5);
+  Expect.isFalse(alwaysTrue == null);
+  Expect.isFalse(null == alwaysTrue);
+  Expect.isTrue(alwaysTrue != null);
+  Expect.isTrue(null != alwaysTrue);
+  Expect.isTrue(null == null);
+  Expect.isFalse(null != null);

[sra1, 2012/08/17 01:34:08]

Should also compare cases where both sides are expressions that are opaque to
the optimizer but one evaluates to 'null' (to avoid testing only code-gen for
comparison to constants).

E.g.


opaque(x) => [x,1,'y'][0];  // Whatever it takes to confuse the compiler, now
and in the foreseeable future.

class Death {
  operator ==(x) { throw 'Dead!'; }
}

death() => opaque(new Death());
nullFn() => opaque(null);

Expect.isFalse(death() == nullFn());
Expect.isFalse(nullFn() == death());
Expect.isTrue(nullFn() == nullFn());
Expect.throws(death() == 5);

+}
+
+main() {
+  for (int i = 0; i < 1000; i++) tests();
+}