Bug 134237

Consider this code in CrossOriginAccessControl.cpp (passesAccessControlCheck): if (accessControlOriginString == "*" && includeCredentials == DoNotAllowStoredCredentials) Amazingly, although includeCredentials is set to 'DoNotAllowStoredCredentials', this test failed: > p includeCredentials DoNotAllowStoredCredentials | -2 (-1) > p DoNotAllowStoredCredentials DoNotAllowStoredCredentials (1) > DoNotAllowStoredCredentials == includeCredentials false This change was introduced in http://trac.webkit.org/changeset/161958/trunk/Source/WebCore/loader/ResourceLoaderOptions.h. MSVC does strange things with bit fields containing enumerations. This has been documented in a few places: http://connect.microsoft.com/VisualStudio/feedback/details/828892/vc-2013-miscompilation-with-enums-and-bit-fields http://objectmix.com/c/749570-enum-bitfield-visual-studio-bug-not-3.html Small test case: #include <iostream> enum E { A = 0, B, C, D }; struct S { E e : 2; }; int main() { S s; s.e = D; std::cout << s.e << ' ' << (s.e == D) << std::endl; } Output on MSVC: -1 0 Output on G++/clang++ (correct according to the C++ standard): 3 1 Microsoft appears to think this behavior is within specification, since their enumerated type is based on int, not unsigned. They use a sign bit, which means our one-bit enum fields only ever hold the sign bit resulting in weird behavior.