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

Tue Apr 25 13:14:48 PDT 2017

On Tue, Apr 25, 2017 at 11:42 AM, Nico Weber <thakis at chromium.org> wrote:

> 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).
>

Ok.

>
> What's the advantage of making it an error?
>

All the diagnostics they show in
https://blogs.msdn.microsoft.com/vcblog/2016/11/16/permissive-switch/
diagnose as errors.

> If it's a warning, you can pass -Werror separately if you want. And
> SFINAE'ing on this seems like asking for trouble.
>

I said nothing about permitting SFINAE on these errors.

>
>
>>
>>
>>>
>>>
>>>>
>>>>
>>>>> 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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