[proxies] Wire up Object.getOwnPropertyDescriptor

test/mjsunit/harmony/proxies-get-own-property-descriptor.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
+
+var target = {};
+var configurable_desc = {
+  value: 123,
+  configurable: true,
+  writable: true,
+  enumerable: false,
+};
+Object.defineProperty(target, "configurable", configurable_desc);
+var nonconfigurable_desc = {
+  value: 234,
+  configurable: false,
+  writable: false,
+  enumerable: true
+}
+Object.defineProperty(target, "nonconfigurable", nonconfigurable_desc);
+
+var proxied_desc = {
+  value: 345,
+  configurable: true
+};
+
+var handler = {
+  "getOwnPropertyDescriptor": function(target, name) {
+    if (name === "proxied") {
+      return proxied_desc;
+    }
+    if (name === "return_null") {
+      return null;
+    }
+    return Object.getOwnPropertyDescriptor(target, name);
+  }
+};
+
+var proxy = new Proxy(target, handler);
+var proxy_without_handler = new Proxy(target, {});
+
+// Checking basic functionality:
+
+assertEquals(configurable_desc,
+             Object.getOwnPropertyDescriptor(proxy, "configurable"));
+assertEquals(nonconfigurable_desc,
+             Object.getOwnPropertyDescriptor(proxy, "nonconfigurable"));
+assertEquals({ value: proxied_desc.value,
+               configurable: proxied_desc.configurable,
+               enumerable: false,
+               writable: false },
+             Object.getOwnPropertyDescriptor(proxy, "proxied"));
+assertEquals(configurable_desc,
+             Object.getOwnPropertyDescriptor(proxy_without_handler,
+                                             "configurable"));
+assertEquals(nonconfigurable_desc,
+             Object.getOwnPropertyDescriptor(proxy_without_handler,
+                                             "nonconfigurable"));
+
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "return_null")');
+
+handler.getOwnPropertyDescriptor = undefined;
+assertEquals(configurable_desc,
+             Object.getOwnPropertyDescriptor(proxy, "configurable"));
+
+// Checking invariants mentioned explicitly by the ES spec:
+
+// (Inv-1) "A property cannot be reported as non-existent, if it exists as a
+// non-configurable own property of the target object."
+handler.getOwnPropertyDescriptor = function(target, name) { return undefined; };
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "nonconfigurable")');
+assertEquals(undefined, Object.getOwnPropertyDescriptor(proxy, "configurable"));
+
+// (Inv-2) "A property cannot be reported as non-configurable, if it does not
+// exist as an own property of the target object or if it exists as a
+// configurable own property of the target object."
+handler.getOwnPropertyDescriptor = function(target, name) {
+  return {value: 234, configurable: false, enumerable: true};
+};
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "nonexistent")');
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "configurable")');
+assertEquals(
+    false,
+    Object.getOwnPropertyDescriptor(proxy, "nonconfigurable").configurable);
+
+// (Inv-3) "A property cannot be reported as non-existent, if it exists as an
+// own property of the target object and the target object is not extensible."
+Object.seal(target);
+handler.getOwnPropertyDescriptor = function(target, name) { return undefined; };
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "configurable")');
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "nonconfigurable")');
+assertEquals(undefined, Object.getOwnPropertyDescriptor(proxy, "nonexistent"));
+
+// (Inv-4) "A property cannot be reported as existent, if it does not exist as
+// an own property of the target object and the target object is not
+// extensible."
+var existent_desc = {value: "yes"};
+handler.getOwnPropertyDescriptor = function() { return existent_desc; };
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "nonexistent")');
+assertEquals(
+    {value: "yes", writable: false, enumerable: false, configurable: false},
+    Object.getOwnPropertyDescriptor(proxy, "configurable"));
+
+// Checking individual bailout points in the implementation:
+
+// Step 6: Trap is not callable.
+handler.getOwnPropertyDescriptor = {};
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "configurable")');
+
+// Step 8: Trap throws.
+handler.getOwnPropertyDescriptor = function() { throw "ball"; };
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "configurable")');
+
+// Step 9: Trap result is neither undefined nor an object.
+handler.getOwnPropertyDescriptor = function() { return 1; }
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "configurable")');
+
+// Step 11b: See (Inv-1) above.
+// Step 11e: See (Inv-3) above.
+
+// Step 16: Incompatible PropertyDescriptor; a non-configurable property
+// cannot be reported as configurable. (Inv-4) above checks more cases.
+handler.getOwnPropertyDescriptor = function(target, name) {
+  return {value: 456, configurable: true, writable: true}
+};
+assertThrows('Object.getOwnPropertyDescriptor(proxy, "nonconfigurable")');
+
+// Step 17: See (Inv-2) above.