[libc][assert] provide `static_assert` macro pre-`__STDC_VERSION__ == 202311L`

[nickdesaulniers]

prior to C23, static_assert was a macro provided by assert.h.

I just hit this trying to build compiler-rt builtins against llvm-libc; we don't provide a definition of static_assert and compiler-rt uses the compiler default language standard (currently -std=c17).

We should add something along the lines of:

#if __STDC_VERSION__ < 202311L
#define static_assert(x, y) _Static_assert((x), y)
#endif

in libc/include/llvm-libc-macros/assert-macros.h. cc @frobtech

Link: #123848

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

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3. Fix the issue locally.
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If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

prior to C23, `static_assert` was a macro provided by assert.h.

I just hit this trying to build compiler-rt builtins against llvm-libc; we don't provide a definition of static_assert and compiler-rt uses the compiler default language standard (currently -std=c17).

We should add something along the lines of:

#if __STDC_VERSION__ < 202311L
#define static_assert(x, y) _Static_assert((x), y)
#endif

in libc/include/llvm-libc-macros/assert-macros.h. cc @frobtech

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Nick Desaulniers (nickdesaulniers)

prior to C23, `static_assert` was a macro provided by assert.h.

I just hit this trying to build compiler-rt builtins against llvm-libc; we don't provide a definition of static_assert and compiler-rt uses the compiler default language standard (currently -std=c17).

We should add something along the lines of:

#if __STDC_VERSION__ < 202311L
#define static_assert(x, y) _Static_assert((x), y)
#endif

in libc/include/llvm-libc-macros/assert-macros.h. cc @frobtech

[rajvgokidi]

Hi, I'm interested in this issue. Can I get assigned to it?

[nickdesaulniers]

Done; thanks for volunteering!

[frederick-vs-ja]

Just a question: was it intentional to provide static_assert in <assert.h> in C89/99 modes?

[frobtech]

We don't currently have a policy or a mechanism about limiting the visible declarations to the specific language mode. So at least for now, it is intentional that the libc headers may declare any and all C23 interfaces in all language modes.