Make identical(a,b) a compile-time constant in dart2js.

tests/language/compile_time_constant10_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.
+
+// Test that 'identical(a,b)' is a compile-time constant.
+
+class C {
+  final x;
+  const C(this.x);
+  static f3(){}
+  static f4(){}
+}
+
+const i1 = 1;
+const i2 = 2;
+const d1 = 1.5;
+const d2 = 2.5;
+const b1 = true;
+const b2 = false;
+const s1 = "1";
+const s2 = "2";
+const l1 = const [1,2];
+const l2 = const [2,3];
+const m1 = const {"x": 1};
+const m2 = const {"x": 2};
+const c1 = const C(1);
+const c2 = const C(2);
+f1(){}
+f2(){}
+const id = identical;
+
+class CT {
+  final x1;
+  final x2;
+  bool id;
+  const CT(var x1, var x2)
+      : this.x1 = x1, this.x2 = x2, this.id = identical(x1, x2);
+  void test(void expect(a,b), name) {
+    expect(id, "$name: identical($x1,$x2)");
+  }
+}
+
+const trueTests = const [
+  const CT(2 - 1, i1),
+  const CT(1 + 1, i2),
+  const CT(2.5 - 1.0, d1),
+  const CT(1.5 + 1.0, d2),
+  const CT(false || true, b1),
+  const CT(true && false, b2),
+  const CT('$i1', s1),
+  const CT('$i2', s2),
+  const CT(const [i1, 2], l1),
+  const CT(const [i2, 3], l2),
+  const CT(const {"x": i1}, m1),
+  const CT(const {"x": i2}, m2),
+  const CT(const C(i1), c1),
+  const CT(const C(i2), c2),
+  const CT(f1, f1),
+  const CT(f2, f2),
+  const CT(C.f3, C.f3),
+  const CT(C.f4, C.f4),
+  const CT(id, identical),
+];
+
+const falseTests = const [
+  const CT(i1, i2),
+  const CT(d1, d2),
+  const CT(b1, b2),
+  const CT(s1, s2),
+  const CT(l1, l2),
+  const CT(m1, m2),
+  const CT(c1, c2),
+  const CT(f1, f2),
+  const CT(i1, d1),
+  const CT(d1, b1),
+  const CT(b1, s1),
+  const CT(s1, l1),
+  const CT(l1, m1),
+  const CT(m1, c1),
+  const CT(c1, f1),
+  const CT(f1, C.f3),
+  const CT(C.f3, identical),
+  const CT(identical, i1),
+];
+
+// Not a constant if it's not written 'identical'.
+const idtest = id(i1, i2);  /// 01: compile-time error
+
+// Not a constant if aliased? (Current interpretation, waiting for
+// confirmation).
+class T {                                     /// 02: compile-time error
+  static const identical = id;                /// 02: continued
+  static const idtest2 = identical(i1, i2);   /// 02: continued
+}                                             /// 02: continued
+
+main() {
+  for (int i = 0; i < trueTests.length; i++) {
+    trueTests[i].test(Expect.isTrue, "true[$i]");
+  }
+  for (int i = 0; i < falseTests.length; i++) {
+    falseTests[i].test(Expect.isFalse, "false[$i]");
+  }
+
+  var x = idtest;  /// 01: continued
+  var x = T.idtest2;  /// 02: continued
+}
+