[libc++] <ctime> std module on windows with ucrt

[Arthapz]

Hello, i tried to build std module on windows but it seems some of the ctime functions are marked static in ucrt so clang fail to export them

e.g

stdmodules/std/ctime.inc:20:14: error: using declaration referring to 'ctime' with internal linkage cannot be exported
   20 |   using std::ctime;
      |              ^
C:\Program Files (x86)\Windows Kits\10\Include\10.0.22621.0\ucrt\time.h:501:41: note: target of using declaration
  501 |         static __inline char* __CRTDECL ctime(

i got the module to build successfully with patching std/ctime.inc like this

export namespace std {
using std::clock_t;
using std::size_t;
using std::time_t;

using std::timespec;
using std::tm;

using std::asctime;
using std::clock;

#ifdef _UCRT
inline char* __CRTDECL ctime(_In_ time_t const* const _Time) {
  return _ctime64(_Time);
}

inline double __CRTDECL difftime(_In_ time_t const _Time1, _In_ time_t const _Time2) {
  return _difftime64(_Time1, _Time2);
}

inline struct tm* __CRTDECL gmtime(_In_ time_t const* const _Time) {
  return _gmtime64(_Time);
}

inline struct tm* __CRTDECL localtime(_In_ time_t const* const _Time) {
  return _localtime64(_Time);
}

inline time_t __CRTDECL mktime(_Inout_ struct tm* const _Tm) {
  return _mktime64(_Tm);
}
#else
using std::ctime;
using std::difftime;
using std::gmtime;
using std::localtime;
using std::mktime;
#endif

using std::strftime;
#ifdef _UCRT
inline time_t __CRTDECL time(_Out_opt_ time_t* const _Time) {
  return _time64(_Time);
}

inline int __CRTDECL timespec_get(_Out_ struct timespec* const _Ts, _In_ int const _Base) {
  return _timespec64_get((struct _timespec64*)_Ts, _Base);
}
#else
using std::time;
using std::timespec_get;
#endif
} // namespace std

here a self contained reproducer with full logs: https://github.com/Arthapz/libcpp-stdmodule-ctime-errors

[philnik777]

@StephanTLavavej @CaseyCarter Is this something that can be fixed in UCRT?

[llvmbot]

@llvm/issue-subscribers-clang-modules

[StephanTLavavej]

Yes, we've reported it to the UCRT (the internal bug number is OS-33790456 "static inline functions cannot be called when using modules") and they're planning to fix it, but there will be a significant delay in creating and shipping the fix.

MSVC's STL has a workaround for this; it's not perfect but it's the best we can do at this time. What we do is detect when we're building the std module, and instead of dragging ::time etc. into namespace std, we define a separate std::time function that calls ::time.

[philnik777]

Thanks for the info! Do you have some idea how long that delay would be? If it's fixed within six months or so it's probably not worth fixing for us, our modules support is still very much experimental.

[StephanTLavavej]

Lots more than 6 months, unfortunately.