Implement the `RegExp.prototype.flags` getter

test/mjsunit/harmony/regexp-flags.js

+// Copyright 2014 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-regexps

[Dmitry Lomov (no reviews), 2014/12/09 23:39:13]

Also add test that validates properties of Regexp.prototype.flag from its
property descriptor (has getter, has no setter)

+
+assertEquals('', RegExp.prototype.flags);

[arv (Not doing code reviews), 2014/12/10 02:54:50]

Shouldn't this throw since the prototype object does not have [[OriginalFlags]]?

I guess this is a really a bug in our implementation of RegExp.prototype.global.
But once/if we fix that then this test will start to fail.

+RegExp.prototype.flags = 'foo';

[arv (Not doing code reviews), 2014/12/10 02:54:50]

A better test is to get the descriptor and validate it.

+assertEquals('', RegExp.prototype.flags);
+delete RegExp.prototype.flags;
+assertEquals('', RegExp.prototype.flags);
+
+assertEquals('', RegExp('').flags);
+assertEquals('', /./.flags);
+assertEquals('gimy', RegExp('', 'ygmi').flags);
+assertEquals('gimy', /foo/ymig.flags);
+
+// When support for the `u` flag is added, uncomment the first line below and
+// remove the second line.
+//assertEquals(RegExp('', 'yumig').flags, 'gimuy');
+assertThrows(function() { RegExp('', 'yumig').flags; }, SyntaxError);
+
+// https://bugzilla.mozilla.org/show_bug.cgi?id=1108467#c0
+function testGenericFlags(object) {
+  return Object
+    .getOwnPropertyDescriptor(RegExp.prototype, 'flags')
+    .get.call(object);

[mathias, 2014/12/09 23:26:22]

Nit: +2 indent

Will fix in the next patch, along with any feedback.

+}
+
+assertEquals('', testGenericFlags({}));
+assertEquals('i', testGenericFlags({ ignoreCase: true }));
+assertEquals('uy', testGenericFlags({ global: 0, sticky: 1, unicode: 1 }));
+assertEquals('m', testGenericFlags({ __proto__: { multiline: true } }));
+assertThrows(function() { testGenericFlags(); }, TypeError);
+assertThrows(function() { testGenericFlags(undefined); }, TypeError);
+assertThrows(function() { testGenericFlags(null); }, TypeError);
+assertThrows(function() { testGenericFlags(true); }, TypeError);
+assertThrows(function() { testGenericFlags(false); }, TypeError);
+assertThrows(function() { testGenericFlags(''); }, TypeError);
+assertThrows(function() { testGenericFlags(42); }, TypeError);