Put guards around timespec_get() decleration.

[brooks]

Summary

With a sufficiently low C standard version, struct timespec isn't
defined in time.h causing warnings. By adding guards for the version
in which timespec_get() was introduced we ensure that struct timespec
is defined.

These guards are based on the discussion in the origonal review:
https://reviews.freebsd.org/D16649

Test Plan

it builds and timespec_get() is new in 12

[brooks]

In CheriBSD, we have a copy of libpng in base that compiled with a low enough C standard that time.h breaks without this. I'm quite surprised the original change doesn't break some ports.

[kib]

I do not see when struct timespec could be not defined. Can you show an example of the program and compiler invocation to reproduce ?

[brooks]

Timespec defined by the include of sys/timespec.h IFF:

#if __POSIX_VISIBLE >= 199309

I don't fully understand how this can happen (and it wasn't obvious from the failing command line), but it did happen in our tree so I added the previously discussed guards.

[kib]

In D17174#366147, @brooks wrote:

Timespec defined by the include of sys/timespec.h IFF:

#if __POSIX_VISIBLE >= 199309

Where is this guard ? From my look at sys/time.h, sys/timespec.h is always included, and then sys/_timespec.h is also.

I don't fully understand how this can happen (and it wasn't obvious from the failing command line), but it did happen in our tree so I added the previously discussed guards.

[brooks]

This block of include/time.h at line 76:

#if __POSIX_VISIBLE >= 199309
/*
 * New in POSIX 1003.1b-1993.
 */
#ifndef _CLOCKID_T_DECLARED
typedef __clockid_t     clockid_t;
#define _CLOCKID_T_DECLARED
#endif

#ifndef _TIMER_T_DECLARED
typedef __timer_t       timer_t;
#define _TIMER_T_DECLARED
#endif

#include <sys/timespec.h>
#endif /* __POSIX_VISIBLE >= 199309 */

[kib]

In D17174#366160, @brooks wrote:

This block of include/time.h at line 76:

Now I understand, I looked at sys/time.h, sorry.

I think that STDC_VERSION should be replaced by ISO_C_VISIBLE check. And, instead of WANT_TIMESPEC_GET, wouldn't __BSD_VISIBLE check work ?

[kib]

And in fact our include/time.h is not C11 compatible, since C11 requires struct timespec to be defined.

[kib]

See also PR231425.

[brooks]

• Use ISO_C_VISIBLE and BSD_VISIBLE per @kib's suggestion.

[kib]

include/time.h

210

I do not see a need to check for the __ISO_C_VISIBLE defined. It should be there always, because sys/cdefs.h is included. This is how other headers use it as well.

[brooks]

• Check __ISO_C_VISIBLE unconditionally and rewrap.

[mjg]

Looks like these guards should be __cplusplus instead?

Spotted by Sascha Wildner <[e-mail]>

[pfg]

FWIW,
It looks like we should update
contrib/libc++/include/__config around line 348.

[kib]

head/include/time.h

211 ↗

(On Diff #48168)

Somebody pointed out that this should be spelled as __cplusplus.

[brooks]

Committed more or less as d02489d11aed2aa5410889f18f4fe8a356f4ca3b and fixed to actually work 8091b82e291642f3034dc3fdc8689a4f4ba027da