RFC: Default language standard mode policy

[Sean Silva via cfe-commits]

On Wed, Jun 29, 2016 at 12:51 PM, Richard Smith <richard at metafoo.co.uk>
wrote:

> On Wed, Jun 29, 2016 at 12:30 PM, Sean Silva <chisophugis at gmail.com>
> wrote:
>
>>
>>
>> On Wed, Jun 29, 2016 at 12:09 PM, Richard Smith via cfe-commits <
>> cfe-commits at lists.llvm.org> wrote:
>>
>>> Hi all!
>>>
>>> I'd like to establish a policy for Clang's default language standard (if
>>> none is specified with -std), as follows:
>>>
>>>   Clang defaults to the most recent published standard for the selected
>>> language that it fully implements.
>>>
>>> The practical impact of this is that clang++ will default to C++14 for
>>> C++ compilations (for version 3.9 onwards) and will default to C++17 once
>>> our implementation support is complete and the standard is published
>>> (whichever happens later).
>>>
>>> I'd suggest that we apply the same policy for clang-cl, but if it's
>>> important that we enable a not-yet-fully-implemented standard for cl
>>> compatibility, that seems reasonable.
>>>
>>> The question of whether the default mode for the GCC-compatible driver
>>> should be -std=gnuXXX or -std=cXXX is separate, but also likely worth
>>> discussing. Enabling GNU keywords by default is a very odd choice, and if
>>> we believe we can change our defaults without breaking the world then this
>>> seems like a good time to do so.
>>>
>>
>> Using cXXX instead of gnuXXX would break the world on PS4. So for sure
>> with `-std=c++latest` we would end up proposing a patch to change this for
>> the PS4 target to gnu++latest (or gnu++11 if gnu++latest is not feasible).
>>
>
> OK. Out of interest, is it the GNU keywords that you need, or some other
> effect of the difference between modes?
>

A quick check of two titles I have at hand shows that at least `typeof` is
in use.

-- Sean Silva


>
>
>> (As I'm sure you're aware, we have pending to upstream a patch that makes
>> -std=gnu++11 the default C++ language mode on PS4 (just blocked on fixing
>> tests to not assume the existing std)).
>>
>> It may be feasible for us to use a "-std=gnu++latest" behavior and not
>> have to have a PS4-specific default; CC'ing Warren and Paul.
>>
>> -- Sean Silva
>>
>>
>>>
>>> I also intend to make explicit in our documentation that our -std=XXX
>>> flag enables the selected standard, *plus all relevant issues in Defect
>>> Report status from the relevant language committee* (it doesn't make sense
>>> to support a language without its bugfixes).
>>>
>>> Thoughts?
>>>
>>> _______________________________________________
>>> cfe-commits mailing list
>>> cfe-commits at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
>>>
>>>
>>
>
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