[Patch] Add the __wchar_t type in MS-compatibility mode (PR15815)

[Hans Wennborg]

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On Mon, May 6, 2013 at 4:02 PM, Hans Wennborg <hans at chromium.org> wrote:
> Hello again,
>
> As it turned out, that commit broke test/Sema/wchar.c on Windows, and
> was reverted.
>
> The line that failed was this:
>
>   unsigned short s[] = L"something";
>
> The problem is that my patch was causing the type of the string
> literal to change to __wchar_t on Windows, and since that is a
> different type than unsigned short, the initialization doesn't work.
>
> I experimented some more with MSVC and learned that the code above
> does compile in C mode, but not in C++ mode. The following does not
> compile in C mode:
>
>   __wchar_t s[] = L"something";
>
> Which I found surprising.
>
> I think the semantics are like this:
>
> In C++, we have the wchar_t built-in type, and that's the type used
> for wide string literals. __wchar_t is the same as wchar_t.
>
> In C, __wchar_t is the same as the built-in wchar_t would have been if
> it were available. The type of wide string literals is array of
> unsigned short.
>
> I'm attaching a new patch that implements this behavior. Please take a
> look, and sorry again for the breakage.
>
> Thanks,
> Hans
>
> On Fri, May 3, 2013 at 10:16 AM, Hans Wennborg <hans at chromium.org> wrote:
>> Thanks! Committed r181004.
>>
>> On Thu, May 2, 2013 at 6:55 PM, Aaron Ballman <aaron at aaronballman.com> wrote:
>>> Patch LGTM!
>>>
>>> ~Aaron
>>>
>>> On Thu, May 2, 2013 at 1:38 PM, Hans Wennborg <hans at chromium.org> wrote:
>>>> On Tue, Apr 23, 2013 at 4:46 PM, Hans Wennborg <hans at chromium.org> wrote:
>>>>> On Tue, Apr 23, 2013 at 2:48 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>>>>>> Does the setup code in ASTContext::InitBuiltinTypes do the right thing here?
>>>>>
>>>>> Hmm, turns out it didn't.
>>>>>
>>>>> I guess it's not obvious what the right thing is here. From
>>>>> experimenting a bit, it seems that __wchar_t is always available, and
>>>>> is always a distinct builtin type in visual studio, even in C.
>>>>>
>>>>> New patch attached.
>>>>
>>>> Richard pointed out on IRC that we shouldn't change semantics in
>>>> -fms-extensions.
>>>>
>>>> I'm attaching a new patch. In -fms-extensions, __wchar_t is the same
>>>> as built-in wchar_t if available, otherwise it is the same as the
>>>> appropriate integer type.
>>>>
>>>> In -fms-compatibility we try to mimic MSVC exactly: there is always a
>>>> __wchar_t type, and it is always separate from the regular integer
>>>> types.
>>>>
>>>> There are a number of parameters here: C vs. C++, -fms-extensions vs.
>>>> -fms-compatibility, and -fno-wchar. The patch covers all of them and I
>>>> think the tests make it reasonably clear. If we think this is too
>>>> complicated, we could just use only the -fms-extensions part of the
>>>> patch.
>>>>
>>>> New patch attached, please take a look.
>>>>
>>>> Thanks,
>>>> Hans