[cfe-commits] Rép: [PATCH] _has_feature support for new C1X?features.

[Jean-Daniel Dupas]

Le 30 avr. 2011 à 23:08, Peter Collingbourne a écrit :

> On Sat, Apr 30, 2011 at 08:08:06PM +0200, Jean-Daniel Dupas wrote:
>> 
>> Le 29 avr. 2011 à 20:07, Douglas Gregor a écrit :
>> 
>>> 
>>> On Apr 29, 2011, at 10:44 AM, Peter Collingbourne wrote:
>>>> OK, I am fine with introducing a c_ prefix, for the reasons you
>>>> point out.  But the way I understand it is that __has_feature in fact
>>>> has 2 semi-orthogonal purposes:
>>>> 
>>>> 1) To test for support for Clang-specific extensions to the language.
>>>> This is the purpose of the non-language-prefixed feature test
>>>> identifiers.
>>>> 
>>>> 2) To test for Clang support for language features which have been
>>>> standardised in the current language.  This is the purpose of the
>>>> language-prefixed feature test identifiers.
>>>> 
>>>> However, there is a gap here in that there is no way to test for
>>>> the existence of Clang-specific language extensions which have been
>>>> standardised in other languages.  For example, generic selections
>>>> can be used to implement an OpenCL runtime library using Clang.
>>>> Since OpenCL is based on C99, generic selections would be classified
>>>> as an extension.  This makes it impossible to test for that extension.
>>>> 
>>>> One solution to this problem is to have 2 feature test identifiers
>>>> for each standardised feature (e.g. "c_generic_selections" and
>>>> "generic_selections"), each serving the 2 purposes mentioned above.
>>>> The disadvantage of this approach would obviously be the doubling up of
>>>> language feature identifiers.  Also, as you point out "static_assert"
>>>> would be ambiguous.
>>>> 
>>>> An alternative solution would be to introduce another macro, say
>>>> __has_extension, which takes the same feature test identifiers
>>>> as __has_feature.  __has_extension would test the features of
>>>> the compiler alone (approximately serving purpose 1) while
>>>> __has_feature tests the features of the compiler together
>>>> with the current language (approximately serving purpose 2).
>>>> 
>>>> So for example __has_feature(c_generic_selections) could be
>>>> used to test for support for generic selections in C1X while
>>>> __has_extension(c_generic_selections) could be used in any language.
>>>> I would imagine that __has_extension should act identically to
>>>> __has_feature if -pedantic-errors (or perhaps -pedantic) is enabled.
>>>> 
>>>> Please let me know what you think.
>>> 
>>> I think that __has_extension is an *excellent* idea!
>> 
>> I tried to implements this new suggestion.
>> The has_feature variants are bound to the selected language and returns true only when compiling as C1X, and has_extension always returns true.
>> Is this what you had in mind ? 
> 
> __has_extension should be a superset of __has_feature, so it should
> also include the C++ and C++0x features, as well as the Clang specific
> extensions.  This can be done trivially by calling HasFeature from
> HasExtension.
> 
> I began an implementation (see patch), but this is incomplete since it
> includes no tests.  I also haven't surveyed all of the C++0x features
> to see which are supported as extensions to C++98.  If you like,
> you can extend the patch to add the correct set of C++0x features as
> well as tests.
> 

I'm not very familiar with C++0x features supported as extensions but a quick look in diagnostics gave 3 more features.
Someone familiar with this part should definitively review this list.

I also add a couple of simple tests, for c1X features and has_extensions.


-- Jean-Daniel


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