[PATCH] D58149: [clang] Make sure C99/C11 features in <float.h> are provided in C++11

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added a comment.

In D58149#1397499 <https://reviews.llvm.org/D58149#1397499>, @ldionne wrote:

> In D58149#1397390 <https://reviews.llvm.org/D58149#1397390>, @jfb wrote:
>
> > In D58149#1397382 <https://reviews.llvm.org/D58149#1397382>, @efriedma wrote:
> >
> > > Formally, I don't think C11 is a normative reference for C++11 or C++14, only C++17 (see [intro.refs] in the standard).
> >
>
>
> You're right. I don't mind submitting a patch that enables it for C++17 and above only if that's what you want, however...
>
> > Right, this was changed in wg21.link/p0063r3
> >  That being said, we *can* offer these C11 features as extensions IIUC.
>
> ... I think it's also fine to have it in C++11.


In C++11, this is technically valid:

  #define FLT_TRUE_MIN 1
  #include <cfloat>
  #if FLT_TRUE_MIN != 1
  #error float.h redefined my macro
  #endif

and likewise

  #include <cfloat>
  constexpr float FLT_TRUE_MIN = 0.0001f;

... but both will fail with this patch, so providing these macros is technically non-conforming. I don't know to what extent we should care about such uses, though. We generally leak additional non-conforming names from the system `<*.h>` headers into the user's namespace if the libc headers put them there. This would, however, probably be the first time that we put them there ourselves.


Repository:
  rC Clang

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D58149/new/

https://reviews.llvm.org/D58149