[PATCH] D59223: Objective-C++11: Support static_assert() in @interface/@implementation ivar lists and method declarations

[Erik Pilkington via Phabricator via cfe-commits]

erik.pilkington added inline comments.


================
Comment at: clang/include/clang/Basic/Features.def:121
 FEATURE(objc_class_property, LangOpts.ObjC)
+FEATURE(objc_c_static_assert, true)
+FEATURE(objc_cxx_static_assert, LangOpts.CPlusPlus11)
----------------
thakis wrote:
> erik.pilkington wrote:
> > We should only claim `_Static_assert` is a feature in languages where its actually a formal language feature (C11), you can also use EXTENSION to indicate what languages we accept it in (see the comment in the file header).
> Sorry, I don't follow. clang accepts `_Static_assert` in C89. You're saying you want `__has_feature(objc_c_static_assert)` to be false there? I'm guessing because -pedantic warns on it?
> 
> But if we do this, there's no way to differentiate clang-in-std=c89 mode with this patch from clang-without-this-patch, is there? Is that what you want? i.e. replace `true` with `LangOpts.C11`?
> 
> (For now, I updated the test to check the __has_feature() is true in c89 too.)
> 
> (That seems like another argument to restore the single feature to me since this working in objc is orthogonal on if the language version supports static asserts.)
> Sorry, I don't follow. clang accepts _Static_assert in C89. You're saying you want __has_feature(objc_c_static_assert) to be false there? I'm guessing because -pedantic warns on it?

Yeah, `__has_feature` is meant to check for standard language features. `__has_extension` checks whether clang will accept it, regardless of what respective standard says. So `_Static_assert` here is a "standard" language feature in ObjC + C11 and an extension in ObjC + C99. I'm suggesting you write this like:

```
FEATURE(objc_c_static_assert, LangOpts.C11)
FEATURE(objc_cxx_static_assert, LangOpts.CPlusPlus11)
EXTENSION(objc_c_static_assert, true)
```

Just like we do now for c_static_assert in general:
```
FEATURE(c_static_assert, LangOpts.C11)
EXTENSION(c_static_assert, true)
```

That way, `__has_extension(objc_c_static_assert)` is always true (with a new compiler), and `__has_feature` only deals with standard language features. Does that make sense?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D59223/new/

https://reviews.llvm.org/D59223