Update tests concerning null-extending classes (#658)

The latest revision of ECMA262 makes special provisions for classes
which extend the `null` value [1]. Update the relevant tests
accordingly.

[1] https://github.com/tc39/ecma262/issues/543

test/language/statements/class/subclass/class-definition-null-proto-contains-return-override.js

@@ -1,6 +1,7 @@
 // Copyright (C) 2014 the V8 project authors. All rights reserved.
 // This code is governed by the BSD license found in the LICENSE file.
 /*---
+esid: sec-runtime-semantics-classdefinitionevaluation
 es6id: 14.5.14
 description: >
     Runtime Semantics: ClassDefinitionEvaluation
@@ -8,8 +9,6 @@ description: >
     If superclass is null, then
       Let protoParent be null.
       Let constructorParent be the intrinsic object %FunctionPrototype%.
-
-    `extends null` requires return override in the constructor
 ---*/
 class Foo extends null {
   constructor() {

test/language/statements/class/subclass/class-definition-null-proto-missing-return-override.js

@@ -1,21 +1,43 @@
 // Copyright (C) 2014 the V8 project authors. All rights reserved.
 // This code is governed by the BSD license found in the LICENSE file.
 /*---
-es6id: 14.5.14
+esid: sec-runtime-semantics-classdefinitionevaluation
 description: >
-    Runtime Semantics: ClassDefinitionEvaluation
+  The `this` value of a null-extending class is automatically initialized,
+  obviating the need for an explicit return value in the constructor.
+info: |
+  The behavior under test was introduced in the "ES2017" revision of the
+  specification and conflicts with prior editions.
 
-    If superclass is null, then
-      Let protoParent be null.
-      Let constructorParent be the intrinsic object %FunctionPrototype%.
+  Runtime Semantics: ClassDefinitionEvaluation
 
-    `extends null` requires return override in the constructor
+  [...]
+  5. If ClassHeritageopt is not present, then
+     [...]
+  6. Else,
+     [...]
+     e. If superclass is null, then
+        i. Let protoParent be null.
+        ii. Let constructorParent be the intrinsic object %FunctionPrototype%.
+  [...]
+  15. If ClassHeritageopt is present and protoParent is not null, then set F's
+      [[ConstructorKind]] internal slot to "derived".
+  [...]
+
+  9.2.2 [[Construct]]
+
+  [...]
+  5. If kind is "base", then
+     a. Let thisArgument be ? OrdinaryCreateFromConstructor(newTarget,
+        "%ObjectPrototype%").
+  [...]
+  15. Return ? envRec.GetThisBinding().
 ---*/
+
 class Foo extends null {
   constructor() {}
 }
 
-assert.throws(ReferenceError, function() {
-  new Foo();
-});
+var foo = new Foo();
 
+assert.sameValue(Object.getPrototypeOf(foo), Foo);

test/language/statements/class/subclass/class-definition-null-proto-super.js

@@ -0,0 +1,67 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-runtime-semantics-classdefinitionevaluation
+description: >
+  The `this` value of a null-extending class is automatically initialized,
+  preventing the use of `super` from within the constructor.
+info: |
+  Runtime Semantics: ClassDefinitionEvaluation
+
+  [...]
+  5. If ClassHeritageopt is not present, then
+     [...]
+  6. Else,
+     [...]
+     e. If superclass is null, then
+        i. Let protoParent be null.
+        ii. Let constructorParent be the intrinsic object %FunctionPrototype%.
+  [...]
+  15. If ClassHeritageopt is present and protoParent is not null, then set F's
+      [[ConstructorKind]] internal slot to "derived".
+  [...]
+
+  9.2.2 [[Construct]]
+
+  [...]
+  5. If kind is "base", then
+     a. Let thisArgument be ? OrdinaryCreateFromConstructor(newTarget,
+        "%ObjectPrototype%").
+  [...]
+
+  12.3.5.1 Runtime Semantics: Evaluation
+
+  SuperCall : super Arguments
+
+  [...]
+  6. Let result be ? Construct(func, argList, newTarget).
+  7. Let thisER be GetThisEnvironment( ).
+  8. Return ? thisER.BindThisValue(result).
+
+  8.1.1.3.1 BindThisValue
+
+  [...]
+  3. If envRec.[[ThisBindingStatus]] is "initialized", throw a ReferenceError
+     exception.
+  4. Set envRec.[[ThisValue]] to V.
+  5. Set envRec.[[ThisBindingStatus]] to "initialized".
+  [...]
+---*/
+
+var unreachable = 0;
+var reachable = 0;
+
+class C extends null {
+  constructor() {
+    reachable += 1;
+    super();
+    unreachable += 1;
+  }
+}
+
+assert.throws(TypeError, function() {
+  new C();
+});
+
+assert.sameValue(reachable, 1);
+assert.sameValue(unreachable, 0);

test/language/statements/class/subclass/class-definition-null-proto-this.js

@@ -0,0 +1,46 @@
+// Copyright (C) 2014 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-runtime-semantics-classdefinitionevaluation
+description: >
+  The `this` value of a null-extending class is automatically initialized
+info: |
+  The behavior under test was introduced in the "ES2017" revision of the
+  specification and conflicts with prior editions.
+
+  Runtime Semantics: ClassDefinitionEvaluation
+
+  [...]
+  5. If ClassHeritageopt is not present, then
+     [...]
+  6. Else,
+     [...]
+     e. If superclass is null, then
+        i. Let protoParent be null.
+        ii. Let constructorParent be the intrinsic object %FunctionPrototype%.
+  [...]
+  15. If ClassHeritageopt is present and protoParent is not null, then set F's
+      [[ConstructorKind]] internal slot to "derived".
+  [...]
+
+  9.2.2 [[Construct]]
+
+  [...]
+  5. If kind is "base", then
+     a. Let thisArgument be ? OrdinaryCreateFromConstructor(newTarget,
+        "%ObjectPrototype%").
+  [...]
+---*/
+
+var thisVal, instance;
+
+class C extends null {
+  constructor() {
+    thisVal = this;
+  }
+}
+
+instance = new C();
+
+assert.sameValue(instance instanceof C, true);
+assert.sameValue(instance, thisVal);

test/language/statements/class/subclass/class-definition-null-proto.js

@@ -1,19 +1,41 @@
-// Copyright (C) 2014 the V8 project authors. All rights reserved.
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
 // This code is governed by the BSD license found in the LICENSE file.
 /*---
-es6id: 14.5.14_S6.e
+esid: sec-runtime-semantics-classdefinitionevaluation
+es6id: 14.5.14
 description: >
-    Runtime Semantics: ClassDefinitionEvaluation
+  When a null-extending class does not specify a `constructor` method
+  definition, a method with zero parameters and an empty body is used
+info: |
+  The behavior under test was introduced in the "ES2017" revision of the
+  specification and conflicts with prior editions.
 
-    If superclass is null, then
-      Let protoParent be null.
-      Let constructorParent be the intrinsic object %FunctionPrototype%.
+  Runtime Semantics: ClassDefinitionEvaluation
+
+  5. If ClassHeritageopt is not present, then
+     [...]
+  6. Else,
+     [...]
+     e. If superclass is null, then
+        i. Let protoParent be null.
+        ii. Let constructorParent be the intrinsic object %FunctionPrototype%.
+     [...]
+  7. Let proto be ObjectCreate(protoParent).
+  8. If ClassBodyopt is not present, let constructor be empty.
+  9. Else, let constructor be ConstructorMethod of ClassBody.
+  10. If constructor is empty, then
+      a. If ClassHeritageopt is present and protoParent is not null, then
+         [...]
+      b. Else,
+         i. Let constructor be the result of parsing the source text
+
+              constructor( ){ }
+
+            using the syntactic grammar with the goal symbol MethodDefinition.
+  [...]
 ---*/
-class Foo extends null {
-  constructor() {
-    return {};
-  }
-}
+
+class Foo extends null {}
 
 assert.sameValue(Object.getPrototypeOf(Foo.prototype), null);
 assert.sameValue(Object.getPrototypeOf(Foo.prototype.constructor), Function.prototype);