ES2015 web compat workaround: RegExp.prototype.flags => ""

It turns out that some old polyfill library uses
RegExp.prototype.flags as a way of feature testing. It's not clear
how widespread this is. For now, as a minimal workaround, we can
return undefined from getters like RegExp.prototype.global when
the receiver is RegExp.prototype. This patch implements that strategy
but omits a UseCounter to make backports easier.

R=adamk
CC=yangguo@chromium.org
BUG=chromium:581577
LOG=Y
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1640803003

Cr-Commit-Position: refs/heads/master@{#34201}

src/js/harmony-unicode-regexps.js

@@ -24,8 +24,10 @@ utils.Import(function(from) {
 // ES6 21.2.5.15.
 function RegExpGetUnicode() {
   if (!IS_REGEXP(this)) {
+    // TODO(littledan): Remove this RegExp compat workaround
     if (this === GlobalRegExpPrototype) {
       %IncrementUseCounter(kRegExpPrototypeUnicodeGetter);
+      return UNDEFINED;
     }
     throw MakeTypeError(kRegExpNonRegExp, "RegExp.prototype.unicode");
   }

src/js/regexp.js

@@ -642,6 +642,10 @@ function RegExpMakeCaptureGetter(n) {
 // ES6 21.2.5.4.
 function RegExpGetGlobal() {
   if (!IS_REGEXP(this)) {
+    // TODO(littledan): Remove this RegExp compat workaround
+    if (this === GlobalRegExpPrototype) {
+      return UNDEFINED;
+    }
     throw MakeTypeError(kRegExpNonRegExp, "RegExp.prototype.global");
   }
   return !!REGEXP_GLOBAL(this);
@@ -653,6 +657,10 @@ function RegExpGetGlobal() {
 // ES6 21.2.5.5.
 function RegExpGetIgnoreCase() {
   if (!IS_REGEXP(this)) {
+    // TODO(littledan): Remove this RegExp compat workaround
+    if (this === GlobalRegExpPrototype) {
+      return UNDEFINED;
+    }
     throw MakeTypeError(kRegExpNonRegExp, "RegExp.prototype.ignoreCase");
   }
   return !!REGEXP_IGNORE_CASE(this);
@@ -664,6 +672,10 @@ function RegExpGetIgnoreCase() {
 // ES6 21.2.5.7.
 function RegExpGetMultiline() {
   if (!IS_REGEXP(this)) {
+    // TODO(littledan): Remove this RegExp compat workaround
+    if (this === GlobalRegExpPrototype) {
+      return UNDEFINED;
+    }
     throw MakeTypeError(kRegExpNonRegExp, "RegExp.prototype.multiline");
   }
   return !!REGEXP_MULTILINE(this);
@@ -675,6 +687,10 @@ function RegExpGetMultiline() {
 // ES6 21.2.5.10.
 function RegExpGetSource() {
   if (!IS_REGEXP(this)) {
+    // TODO(littledan): Remove this RegExp compat workaround
+    if (this === GlobalRegExpPrototype) {
+      return UNDEFINED;
+    }
     throw MakeTypeError(kRegExpNonRegExp, "RegExp.prototype.source");
   }
   return REGEXP_SOURCE(this);

test/mjsunit/es6/regexp-flags.js

@@ -50,11 +50,9 @@ assertEquals(4, get_count);
 
 
 function testName(name) {
-  if (name === "sticky") {
-    assertEquals(undefined, RegExp.prototype[name]);
-  } else {
-    assertThrows(() => RegExp.prototype[name], TypeError);
-  }
+  // TODO(littledan): For web compatibility, we don't throw an exception,
+  // but ES2015 expects an exception to be thrown from this getter.
+  assertEquals(undefined, RegExp.prototype[name]);
   assertEquals(
       "get " + name,
       Object.getOwnPropertyDescriptor(RegExp.prototype, name).get.name);

test/mjsunit/regress/regress-crbug-581577.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.
+
+assertEquals("", RegExp.prototype.flags);

test/test262/test262.status

@@ -252,6 +252,12 @@
   'built-ins/Object/entries/*': [SKIP],
   'built-ins/Object/values/*': [SKIP],
 
+  # https://code.google.com/p/chromium/issues/detail?id=581577
+  'built-ins/RegExp/prototype/source/15.10.7.1-1': [FAIL],
+  'built-ins/RegExp/prototype/global/15.10.7.2-1': [FAIL],
+  'built-ins/RegExp/prototype/ignoreCase/15.10.7.3-1': [FAIL],
+  'built-ins/RegExp/prototype/multiline/15.10.7.4-1': [FAIL],
+
   ######################## NEEDS INVESTIGATION ###########################
 
   # These test failures are specific to the intl402 suite and need investigation

test/webkit/fast/regex/toString-expected.txt

@@ -28,7 +28,7 @@ On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE
 
 PASS RegExp('/').source is "\\/"
 PASS RegExp('').source is "(?:)"
-FAIL RegExp.prototype.source should be (?:). Threw exception TypeError: RegExp.prototype.source getter called on non-RegExp object
+FAIL RegExp.prototype.source should be (?:) (of type string). Was undefined (of type undefined).
 PASS RegExp('/').toString() is "/\\//"
 PASS RegExp('').toString() is "/(?:)/"
 PASS RegExp.prototype.toString() is "/(?:)/"