Implement the `RegExp.prototype.flags` getter

src/regexp.js

Index: src/regexp.js
diff --git a/src/regexp.js b/src/regexp.js
index e1eac76c124dbda3bc0635466617d1887fd17775..bade7aadd29240880f576cc75ae7b4797013bda5 100644
--- a/src/regexp.js
+++ b/src/regexp.js
@@ -431,6 +431,29 @@ function SetUpRegExp() {
                                      DONT_DELETE);
   }
   %ToFastProperties($RegExp);
+
+
+  // ES6 draft 12-06-13, section 21.2.5.3
+  // + https://bugs.ecmascript.org/show_bug.cgi?id=3423
+  var RegExpGetFlags = function() {
+    if (!IS_SPEC_OBJECT(this)) {
+      throw MakeTypeError('home_object_non_object',
+                          'RegExp.prototype.flags',
+                          [%ToString(this)]);
+    }
+    var result = '';
+    if (this.global) result += 'g';
+    if (this.ignoreCase) result += 'i';
+    if (this.multiline) result += 'm';
+    if (this.unicode) result += 'u';
+    if (this.sticky) result += 'y';
+    return result;
+  };
+  //if (harmony_regexps) {

[Dmitry Lomov (no reviews), 2014/12/09 23:02:00]

harmony_regexps should not be used in bootstrapping code (code that executes on
loading natives).
[other uses in this file are ok since they are inside function bodies]

What we typically do is create a separate file, harmony-regexp.js, that is
loaded conditionally under FLAG_harmony_regexp.

+  %DefineAccessorPropertyUnchecked($RegExp.prototype, 'flags', RegExpGetFlags,
+                                   NoOpSetter, DONT_DELETE);
+  %SetNativeFlag(RegExpGetFlags);
+  //}

[mathias, 2014/12/09 22:50:48]

Uncommenting the `if` statement breaks the build. Am I doing something crazy
here?

 }
 
 SetUpRegExp();