Add Null class to dart:core.

tests/language/null_test.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2013, 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.
 // Second dart test program.
 
+import "dart:mirrors";
 import "package:expect/expect.dart";
 
-class NullTest {
-  static int foo(var obj) {
+class BadInherit
+  extends Null     /// 01: compile-time error
+  implements Null  /// 02: compile-time error
+  extends Object with Null  /// 03: compile-time error
+    {}
+
+class EqualsNotCalled {
+  int get hashCode => throw "And don't warn!";
+  bool operator==(Object other) {
+    throw "SHOULD NOT GET HERE";
+  }
+}
+
+class Generic<T> {
+  bool test(o) => o is T;
+  T cast(o) => o as T;
+  Type get type => T;
+}
+
+class Generic2<T, S> {
+  bool test(o) => new Generic<T>().test(o);
+  T cast(o) => new Generic<T>().cast(o);
+  Type get type => new Generic<T>().type;
+}
+
+// Magic incantation to avoid the compiler recognizing the constant values
+// at compile time. If the result is computed at compile time, the dynamic code
+// will not be tested.
+confuse(x) {
+  try { throw [x]; } catch (e) { return e[0]; }
+  return 42;
+}
+
+main() {
+  new BadInherit();  // Make sure class is referenced.
+
+  int foo(var obj) {
     Expect.equals(null, obj);
   }
 
-  static bool compareToNull(var value) {
+  bool compareToNull(var value) {
     return null == value;
   }
 
-  static bool compareWithNull(var value) {
+  bool compareWithNull(var value) {
     return value == null;
   }
 
-  static int testMain() {
-    var val = 1;
-    var obj = null;
+  var val = 1;
+  var obj = confuse(null);  // Null value that isn't known at compile-time.
+  Expect.isTrue(identical(obj, null), "identical");
 
-    Expect.equals(null, obj);
-    Expect.equals(null, null);
+  Expect.isTrue(null == null);
+  Expect.isTrue(null == obj);
+  Expect.isTrue(obj == null);
+  Expect.isTrue(obj == obj);
 
+  // Using  == null  or  null ==  will not call any equality method.
+  Expect.isFalse(new EqualsNotCalled() == null);
+  Expect.isFalse(null == new EqualsNotCalled());
+  Expect.isFalse(new EqualsNotCalled() == obj);
+  Expect.isFalse(obj == new EqualsNotCalled());
+
+  Expect.isFalse(null == false);
+  Expect.isFalse(null == 0);
+  Expect.isFalse(null == "");
+  Expect.isFalse(null == []);
+  Expect.isFalse(null == 0.0);
+  Expect.isFalse(null == -0.0);
+  Expect.isFalse(null == double.NAN);
+
+  Expect.isFalse(obj == false);
+  Expect.isFalse(obj == 0);
+  Expect.isFalse(obj == "");
+  Expect.isFalse(obj == []);
+  Expect.isFalse(obj == 0.0);
+  Expect.isFalse(obj == -0.0);
+  Expect.isFalse(obj == double.NAN);
+
+  // Explicit constant expressions.
+  const t1 = null == null;
+  const t2 = null == 0;
+  const t3 = false == null;
+  Expect.isTrue(t1);
+  Expect.isFalse(t2);
+  Expect.isFalse(t3);
+
+  foo(obj);
+  foo(null);
+  if (obj != null) {
+    foo(null);
+  } else {
     foo(obj);
-    foo(null);
+  }
 
-    if (obj != null) {
-      foo(null);
-    } else {
-      foo(obj);
-    }
+  // Test "is" operator.
+  Expect.isTrue(null is Null);
+  Expect.isTrue(obj is Null);
+  Expect.isTrue(null is Object);
+  Expect.isTrue(obj is Object);
+  Expect.isTrue(null is dynamic);
+  Expect.isTrue(obj is dynamic);
+  Expect.isFalse(null is String);
+  Expect.isFalse(obj is String);
+  Expect.isFalse(0 is Null);  // It's only assignable.
+  Expect.isFalse(null is! Null);
+  Expect.isFalse(obj is! Null);
+  Expect.isFalse(null is! Object);
+  Expect.isFalse(obj is! Object);
+  Expect.isFalse(null is! dynamic);
+  Expect.isFalse(obj is! dynamic);
+  Expect.isTrue(null is! String);
+  Expect.isTrue(obj is! String);
+  Expect.isTrue(0 is! Null);  // It's only assignable.
 
-    Expect.isFalse(compareToNull(val));
-    Expect.isTrue(compareToNull(obj));
-    Expect.isFalse(compareWithNull(val));
-    Expect.isTrue(compareWithNull(obj));
-    Expect.isTrue(obj is Object);
-    Expect.isFalse(obj is String);
-    Expect.isTrue(obj is !String);
-    Expect.isFalse(obj is !Object);
-    Expect.isFalse(val is !Object);
+  // Test "is" operator with generic type variable.
+  Expect.isTrue(new Generic<Null>().test(null));
+  Expect.isFalse(new Generic<Null>().test(42));
+  Expect.isTrue(new Generic2<Null, int>().test(null));
+  Expect.isFalse(new Generic2<Null, int>().test(42));
 
-    return 0;
-  }
+  // Test cast, "as", operator.
+  Expect.equals(null, null as Null);
+  Expect.equals(null, null as Object);
+  Expect.equals(null, null as int);
+  Expect.throws(() => 42 as Null, (e) => e is CastError);
+  Expect.equals(null, new Generic<Null>().cast(null));
+  Expect.equals(null, new Generic<Object>().cast(null));
+  Expect.equals(null, new Generic<int>().cast(null));
+
+  Expect.equals(null, obj as Null);
+  Expect.equals(null, obj as Object);
+  Expect.equals(null, obj as int);
+  Expect.equals(null, new Generic<Null>().cast(obj));
+  Expect.equals(null, new Generic<Object>().cast(obj));
+  Expect.equals(null, new Generic<int>().cast(obj));
+
+  Expect.equals("null", null.toString());
+  Expect.equals("null", "${null}");
+  Expect.equals("null", obj.toString());
+  Expect.equals("null", "${obj}");
+
+  Expect.equals(Null, null.runtimeType);
+  Expect.equals(Null, obj.runtimeType);
+  Expect.equals(Null, new Generic<Null>().type);
+  Expect.equals(Null, new Generic2<Null, int>().type);
+
+  Expect.isFalse(compareToNull(val));
+  Expect.isTrue(compareToNull(obj));
+  Expect.isFalse(compareWithNull(val));
+  Expect.isTrue(compareWithNull(obj));
+
+  ClassMirror cm = reflectClass(Null);
+
+  InstanceMirror im1 = reflect(null);
+  Expect.equals(cm, im1.type);
+  Expect.isTrue(im1.invoke(const Symbol("=="), [null]).reflectee);
+  Expect.isFalse(im1.invoke(const Symbol("=="), [42]).reflectee);
+
+  InstanceMirror im2 = reflect(obj);
+  Expect.equals(cm, im2.type);
+  Expect.isTrue(im2.invoke(const Symbol("=="), [null]).reflectee);
+  Expect.isFalse(im2.invoke(const Symbol("=="), [42]).reflectee);
+
+  // Method/value extraction. The runtimeType was checked above, and operator==
+  // cannot be extracted.
+  // Currently fails in VM.
+  // Expect.equals(null.toString, obj.toString);
+  // Expect.equals(null.noSuchMethod, obj.noSuchMethod);
+  Expect.equals(null.hashCode, obj.hashCode);
+
+  var toString = null.toString;
+  Expect.equals("null", toString());
+  Expect.equals("null", Function.apply(toString, []));
+
+  Expect.throws(() => null.notDeclared());
+  var noSuchMethod = null.noSuchMethod;
+  var mirror = new CaptureInvocationMirror().notDeclared();
+  Expect.throws(() => noSuchMethod(mirror));
+  Expect.throws(() => Function.apply(noSuchMethod, [mirror]));
 }
 
 
-main() {
-  NullTest.testMain();
+class CaptureInvocationMirror {
+  noSuchMethod(mirror) => mirror;
 }