[Ada] Improve precision of Ada.Directories.Modification_Time

[Hans-Peter Nilsson]

On Wed, 21 Oct 2020, Iain Sandoe wrote:

> Arnaud Charlet <charlet@adacore.com> wrote:
>
> > > This patch breaks bootstrap on Darwin platforms.
> > >
> > > Pierre-Marie de Rodat <derodat@adacore.com> wrote:
> > >
> > > > The modification file time precision now defined by OS.
> > > >
> > > > Tested on x86_64-pc-linux-gnu, committed on trunk
> > > >
> > > > gcc/ada/
> > > >
> > > > 	* adaint.c (__gnat_file_time): New routine.
> > > > 	(__gnat_copy_attribs): Copy timestamps in nanoseconds.
> > > > 	* libgnat/a-direct.adb (C_Modification_Time): Bind to
> > > > 	__gnat_file_time.
> > > > 	(Modification_Time): Call to C_Modification_Time.<patch.diff>
> > >
> > > #if defined(st_mtime)
> > >
> > > is a necessary test - but the fields in the stat structure on Darwin
> > > platforms are
> > > named st_{a,c,m}timespec rather than the Linux st_{a,c,m}tim.
> >
> > What about instead putting above extern long long __gnat_file_time the
> > following:
> >
> > #if __APPLE__
> > #define st_mtim st_mtimespec
> > #define st_atim st_atimespec
> > #endif
> >
> > To avoid having the two (nested) #if __APPLE__ and keep the code easier
> > to follow?
>
> works for me (the test patch was drafted quickly to allow bootstrap to
> continue)
> - I can amend the patch and (re-)test more widely.
>
> Iain

For future reference, TRT for this kind of problem is to
autoconf for the right struct field name, using AC_CHECK_MEMBER
or AC_CHECK_MEMBERS (then use e.g. #if HAVE_STAT_ST_MTIM / #if
HAVE_STAT_ST_MTIMESPEC, definitely not #if __APPLE__).

brgds, H-P