[PATCH] SemaCXX: Support templates in availability attributes

[Duncan P. N. Exon Smith via cfe-commits]

> On 2016-Feb-24, at 10:01, Aaron Ballman <aaron at aaronballman.com> wrote:
> 
> On Tue, Feb 23, 2016 at 6:39 PM, Duncan P. N. Exon Smith
> <dexonsmith at apple.com> wrote:
>> 
>>> On 2016-Feb-23, at 11:18, Aaron Ballman <aaron at aaronballman.com> wrote:
>>> 
>>> On Tue, Feb 23, 2016 at 1:52 PM, Manman Ren <mren at apple.com> wrote:
>>>> This patch looks good to me. But I am not sure if Aaron has any comment.
>>>> 
>>>> On Feb 22, 2016, at 6:19 PM, Duncan P. N. Exon Smith <dexonsmith at apple.com>
>>>> wrote:
>>>> 
>>>> 
>>>> On 2016-Feb-22, at 17:24, Manman Ren <mren at apple.com> wrote:
>>>> 
>>>> 
>>>> 
>>>> On Feb 8, 2016, at 8:17 PM, Duncan P. N. Exon Smith <dexonsmith at apple.com>
>>>> wrote:
>>>> 
>>>> This patch adds support for templates in availability attributes.
>>>> - If the context for an availability diagnostic is a
>>>> `FunctionTemplateDecl`, look through it to the `FunctionDecl`.
>>>> 
>>>> 
>>>> AvailabilityResult Decl::getAvailability(std::string *Message) const {
>>>> +  if (auto *FTD = dyn_cast<FunctionTemplateDecl>(this))
>>>> +    return FTD->getTemplatedDecl()->getAvailability(Message);
>>>> +
>>>> AvailabilityResult Result = AR_Available;
>>>> 
>>>> 
>>>> This looks generally correct to me.
>>>> The UnavailableAttr is attached to the FunctionDecl, not the
>>>> FunctionTemplateDecl, so looking through sounds right.
>>>> 
>>>> - Add `__has_feature(attribute_availability_in_templates)`.
>>>> 
>>>> 
>>>> @Aaron, any comment on this?
>>>> This patch adds extra support for Availability attribute (similar to
>>>> attribute_availability_with_strict in r261548).
>>>> Not sure if has_attribute can be used for this purpose.
>>> 
>>> Given that we're already using __has_feature for the rest of the
>>> availability attribute stuff, I think it's better to keep it all
>>> grouped together instead of checking for some features with
>>> __has_feature and others with __has_attribute.
>> 
>> Besides that argument, this isn't adding any attributes, just checking
>> how they behave.
>> 
>>> If I understand
>>> properly, this is taking code that would have previously been
>>> ill-formed and making it well-formed, and that's why the feature
>>> testing macro is required?
>> 
>> Exactly.  Previously this was ill-formed:
>> ```
>> class Unavail __attribute__((unavailable));
>> 
>> template <class T>
>> void foo(Unavail&) __attribute__((unavailable));
>> ```
>> 
>> Same for `__attribute((availability(macosx,unavailable)))`, and other
>> triggers of "unavailable".
> 
> Okay, this makes sense to me, thank you for the explanation. LGTM!
> 

r262050.  Thanks!

> ~Aaron
>> 
>>> 
>>> Thanks!
>>> 
>>> ~Aaron
>>> 
>>>> 
>>>> Manman
>>>> 
>>>> 
>>>> Is there anything else I should be testing to be sure availability
>>>> works correctly in templates?
>>>> 
>>>> 
>>>> Maybe
>>>> test<UnavailableClass>()
>>>> calling unavailable function from an unavailable template function
>>>> calling an unavailable template function
>>>> 
>>>> I think these all work with the current compiler. But I am not sure if we
>>>> have existing test coverage.
>>>> 
>>>> 
>>>> Thanks for the ideas; let me know if you have any others.
>>>> 
>>>> Can you have a look at the new patch?
>>>> 
>>>> Cheers,
>>>> Manman
>>>> 
>>>> I'm working on a patch to add
>>>> availability markup to the libc++ headers, and this is the only
>>>> problem I've hit so far.  Anyone have thoughts on other things I
>>>> should test?
>>>> 
>>>> 
>>>> <0001-SemaCXX-Support-templates-in-availability-attributes.patch>