[PATCH] D32435: clang-cl: Add support for /permissive-

Tue Apr 25 11:42:02 PDT 2017

On Tue, Apr 25, 2017 at 2:06 PM, David Majnemer <david.majnemer at gmail.com>
wrote:

>
>
> On Tue, Apr 25, 2017 at 8:46 AM, Nico Weber <thakis at chromium.org> wrote:
>
>> On Mon, Apr 24, 2017 at 10:00 PM, David Majnemer <
>> david.majnemer at gmail.com> wrote:
>>
>>>
>>>
>>> On Mon, Apr 24, 2017 at 11:56 AM, Nico Weber <thakis at chromium.org>
>>> wrote:
>>>
>>>> "Opting into the conforming mode, /permissive-, during the series of VS
>>>> 2017 update is a commitment to keeping your code base clean and to fixing
>>>> non-conforming constructs we fix conformance issues in Visual C++." [...]
>>>> "By contrast /permissive- offers a useful conformance mode where input C++
>>>> code is interpreted according to ISO C++ rules but also allows conforming
>>>> extensions necessary to compile C++ on targets supported by Visual C++."
>>>>
>>>> I guess the second quote agrees with your interpretation.
>>>>
>>>> We already diag most of the things they already mention. The one thing
>>>> we don't diag by default is Wmicrosoft-enum-forward-reference since
>>>> that's only an Extension and not an ExtWarn. We don't expose -pedantic from
>>>> clang-cl, so this seemed like a somewhat natural mapping to me.
>>>>
>>>> Should /permissive- map to -Wmicrosoft instead and turn on the parts of
>>>> -Wmicrosoft that are Extensions?
>>>>
>>>
>>> Did you mean on or off?
>>>
>>
>> On.
>>
>>
>>> I think that their intent is that things like __declspec remain OK.
>>>
>>
>> Nothing in -Wmicrosoft warns on __declspec.
>>
>>
>>> They want to diagnose non-conforming extensions like crazy template
>>> stuff, bogus typedef syntax, bad main function definitions, etc.
>>>
>>
>> Right. The only thing it currently makes cl warn on that clang-cl doesn't
>> warn on by default is Wmicrosoft-enum-forward-reference, which is an
>> Extension warning, not an ExtWarn. So mapping /permissive- to -Wmicrosoft
>> would make clang-cl diagnose forward-declared enums like it does with 2017
>> cl.
>>
>
> Ok, sounds like it diagnoses the same sorts of things. They diagnose as
> error though, I think we should too. What about -fdelayed-template-parsing?
> Shouldn't that be disabled?
>

CL has added a /Zc:twoPhase for that (not yet released anywhere), and Hans
added support for that to clang-cl a while ago. Some blog post (maybe the
one I linked to?) says that they're thinking of possibly
enabling /Zc:twoPhase when /permissive- is passed, but at the moment it's
independent. (In part because /permissive- ships in VC2017 and /Zc:twoPhase
hasn't been shipped yet).

What's the advantage of making it an error? If it's a warning, you can pass
-Werror separately if you want. And SFINAE'ing on this seems like asking
for trouble.

>
>
>>
>>
>>>
>>>
>>>> Should we just ignore /permissive- and possibly make some of our
>>>> -Wmicrosoft Extensions ExtWarns instead?
>>>>
>>>> On Mon, Apr 24, 2017 at 2:10 PM, David Majnemer <
>>>> david.majnemer at gmail.com> wrote:
>>>>
>>>>> -pedantic means "Issue all the warnings demanded by strict ISO C and
>>>>> ISO C++; reject all programs that use forbidden extensions, and some other
>>>>> programs that do not follow ISO C and ISO C++."
>>>>> I believe it is more akin to -fno-ms-compatibility as it disables
>>>>> compatibility hacks.
>>>>>
>>>>> On Mon, Apr 24, 2017 at 11:02 AM, Nico Weber <thakis at chromium.org>
>>>>> wrote:
>>>>>
>>>>>> It does sound pretty similar to me from the blog post. I think this
>>>>>> is a decent place to start from.
>>>>>>
>>>>>> On Apr 24, 2017 11:55 AM, "David Majnemer via Phabricator via
>>>>>> cfe-commits" <cfe-commits at lists.llvm.org> wrote:
>>>>>>
>>>>>>> majnemer requested changes to this revision.
>>>>>>> majnemer added a comment.
>>>>>>> This revision now requires changes to proceed.
>>>>>>>
>>>>>>> I don't think this is correct. GDR (of Microsoft) says the behavior
>>>>>>> is different: https://www.reddit.com/r/cpp/comm
>>>>>>> <https://www.reddit.com/r/cpp/comments/5dh7j5/visual_c_introduces_permissive_for_conformance/da5fxjj/>
>>>>>>>               LOG(INFO) << "n_window_index: " << n_window_index;
>>>>>>> ents/5dh7j5/visual_c_introduces_permissive_for_conformance/da5fxjj/
>>>>>>> <https://www.reddit.com/r/cpp/comments/5dh7j5/visual_c_introduces_permissive_for_conformance/da5fxjj/>
>>>>>>>
>>>>>>>
>>>>>>> https://reviews.llvm.org/D32435
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> cfe-commits mailing list
>>>>>>> cfe-commits at lists.llvm.org
>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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