Missing test for __APPLE__ chooses buggy SunOS/Solaris workaround in utc_minutes_offset

[toh-ableton]

spdlog uses the function utc_minutes_offset in the z_formatter to format the '%z'-part of a format string (UTC-offset) when logging time. The function has three implementations, one of which is chosen at compile time via marcro defines (Windows, SunOS/Solaris, default):

spdlog/include/spdlog/details/os-inl.h

Lines 268 to 271 in 3335c38

	#if defined(sun) || defined(__sun) || defined(_AIX) || \
	(defined(__NEWLIB__) && !defined(__TM_GMTOFF)) || \
	(!defined(_BSD_SOURCE) && !defined(_GNU_SOURCE))
	// 'tm_gmtoff' field is BSD extension and it's missing on SunOS/Solaris

This test doesn't detect Apple platforms, which have had the tm_gmtoff-field at least since Mac OS X 10.0, and also doesn't detect POSIX.1-2024 conforming systems, which are also required to support tm_gmtoff.

On Apple and POSIX1.-2024 platforms, this has the unfortunate effect to use the SunOS/Solaris fallback, which doesn't compute the correct value if the passed value of tm isn't the current system time, i.e. localtime(::time()) (#3351).

I suggest to fix this by changing the test to something like

    #if defined(sun) || defined(__sun) || defined(_AIX) || \
        (defined(__NEWLIB__) && !defined(__TM_GMTOFF)) ||  \
        (!defined(__APPLE__) && !defined(_BSD_SOURCE) && !defined(_GNU_SOURCE) && \
            (!defined(_POSIX_VERSION) || (_POSIX_VERSION < 202405L)))
    // 'tm_gmtoff' field is BSD extension and it's missing on SunOS/Solaris

[gabime]

Thanks for the report. Is there a test that can be added to tests/ to reproduce this?
PR is always welcome.

[toh-ableton]

Sure: #3353.