r183883 - Implement core issue 903: only integer literals with value 0 and prvalues of

[Richard Smith]

On Mon, Jun 17, 2013 at 4:02 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> On Mon, Jun 17, 2013 at 2:37 PM, Sebastian Redl
> <sebastian.redl at getdesigned.at> wrote:
>>
>> On 17.06.2013, at 21:42, Richard Smith wrote:
>>
>>> On Mon, Jun 17, 2013 at 12:23 PM, Jordan Rose <jordan_rose at apple.com> wrote:
>>>>
>>>> On Jun 17, 2013, at 12:20 , Nico Weber <thakis at chromium.org> wrote:
>>>>
>>>> On Mon, Jun 17, 2013 at 9:38 AM, Jordan Rose <jordan_rose at apple.com> wrote:
>>>>>
>>>>> *sigh* I can't say this is the wrong thing to do—in fact, it's the kind of
>>>>> restriction I usually like—but for the record this breaks OS X's (ancient)
>>>>> libstdc++ implementation of <tr1/unordered_map> when compiling under
>>>>> -std=c++11. I don't think that's such an important configuration, though.
>>>>
>>>>
>>>> That means it breaks all programs that try to build in C++11 mode but still
>>>> need to ship to 10.6 (like, say, Chromium). Can this be worked around
>>>> somehow?
>>>>
>>>>
>>>> Will that still be true by the next Xcode release? It's not in 4.6.2, and I
>>>> can watch to make sure it stays out of Xcode 5. Do you really need to build
>>>> your 10.6-compatible binary with trunk Clang in C++11 mode?
>>>>
>>>> Richard, I suppose you could make it a warning...
>>>
>>> That's actually pretty tricky, due to its effects on SFINAE, overload
>>> resolution, and so on. But we should be able to add a more limited
>>> workaround which suffices for this specific libstdc++ issue.
>>
>> We had workarounds of the type "make this an error in SFINAE context and a warning otherwise" before.
>
> This is a much harder case, though, because of the effect on overload
> resolution (and more generally because the point where an error is
> detected can be distant from the point where we make the decision). If
> we only want to work around this one libstdc++ bug, we can just detect
> the case where a return statement's expression is the 'false' literal.

Sickening workaround hack deployed in r184395.