[proxies] Implement Proxy.revocable.

For now, we revoke a proxy by setting its handler to null (as in the spec).

Change the "target" field from Object to JSReceiver as there's no point in
allowing more.

R=jkummerow@chromium.org, rossberg
BUG=v8:1543
LOG=n

Review URL: https://codereview.chromium.org/1496243003

Cr-Commit-Position: refs/heads/master@{#32608}

src/js/proxy.js

@@ -42,6 +42,11 @@ function ProxyCreateFunction(handler, callTrap, constructTrap) {
     {}, handler, callTrap, constructTrap, GlobalFunction.prototype)
 }
 
+function ProxyCreateRevocable(target, handler) {
+  var p = new GlobalProxy(target, handler);
+  return {proxy: p, revoke: () => %RevokeProxy(p)};
+}
+
 // -------------------------------------------------------------------
 // Proxy Builtins
 
@@ -144,6 +149,7 @@ function ProxyEnumerate(trap, handler, target) {
 
 //Set up non-enumerable properties of the Proxy object.
 utils.InstallFunctions(GlobalProxy, DONT_ENUM, [
+  "revocable", ProxyCreateRevocable,
   "createFunction", ProxyCreateFunction
 ]);
 

src/objects-inl.h

@@ -6336,10 +6336,12 @@ int JSFunction::NumberOfLiterals() {
 }
 
 
-ACCESSORS(JSProxy, target, Object, kTargetOffset)
 ACCESSORS(JSProxy, handler, Object, kHandlerOffset)
+ACCESSORS(JSProxy, target, JSReceiver, kTargetOffset)
 ACCESSORS(JSProxy, hash, Object, kHashOffset)
 
+bool JSProxy::IsRevoked() const { return !handler()->IsJSReceiver(); }
+
 ACCESSORS(JSFunctionProxy, call_trap, JSReceiver, kCallTrapOffset)
 ACCESSORS(JSFunctionProxy, construct_trap, Object, kConstructTrapOffset)
 

src/objects.h

@@ -9500,7 +9500,7 @@ class JSProxy: public JSReceiver {
   // [handler]: The handler property.
   DECL_ACCESSORS(handler, Object)
   // [target]: The target property.
-  DECL_ACCESSORS(target, Object)
+  DECL_ACCESSORS(target, JSReceiver)
   // [hash]: The hash code property (undefined if not initialized yet).
   DECL_ACCESSORS(hash, Object)
 
@@ -9508,7 +9508,8 @@ class JSProxy: public JSReceiver {
 
   DECLARE_CAST(JSProxy)
 
-  bool IsRevoked() const;
+  INLINE(bool IsRevoked() const);
+  static void Revoke(Handle<JSProxy> proxy);
 
   // ES6 9.5.1
   static MaybeHandle<Object> GetPrototype(Handle<JSProxy> receiver);

src/runtime/runtime-proxy.cc

@@ -65,5 +65,15 @@ RUNTIME_FUNCTION(Runtime_GetConstructTrap) {
   return proxy->construct_trap();
 }
 
+
+RUNTIME_FUNCTION(Runtime_RevokeProxy) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 1);
+  CONVERT_ARG_HANDLE_CHECKED(JSProxy, proxy, 0);
+  JSProxy::Revoke(proxy);
+  return isolate->heap()->undefined_value();
+}
+
+
 }  // namespace internal
 }  // namespace v8

src/runtime/runtime.h

@@ -547,7 +547,8 @@ namespace internal {
   F(IsJSFunctionProxy, 1, 1)        \
   F(GetHandler, 1, 1)               \
   F(GetCallTrap, 1, 1)              \
-  F(GetConstructTrap, 1, 1)
+  F(GetConstructTrap, 1, 1)         \
+  F(RevokeProxy, 1, 1)
 
 
 #define FOR_EACH_INTRINSIC_REGEXP(F)           \

test/mjsunit/harmony/proxies-revocable.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-proxies --harmony-reflect
+
+
+traps = [
+    "getPrototypeOf", "setPrototypeOf", "isExtensible", "preventExtensions",
+    "getOwnPropertyDescriptor", "has", "get", "set", "deleteProperty",
+    "defineProperty", "ownKeys", "apply", "construct"
+];
+// TODO(neis): Fix enumerate.
+
+var {proxy, revoke} = Proxy.revocable({}, {});
+assertEquals(0, revoke.length);
+
+assertEquals(undefined, revoke());
+for (var trap of traps) {
+  assertThrows(() => Reflect[trap](proxy), TypeError);
+}
+
+assertEquals(undefined, revoke());
+for (var trap of traps) {
+  assertThrows(() => Reflect[trap](proxy), TypeError);
+}