[PATCH] D34249: [libc++] Don't use UTIME_OMIT to detect utimensat on Apple

[Nico Weber via cfe-commits]

(To be clear, the patch as-is is 100% fine with me.)

On Thu, Feb 1, 2018 at 11:44 AM, Duncan P. N. Exon Smith via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Using runtime availability checking doesn't make sense for a system
> Libc++, as you point out.  If we add runtime checks they ought to be
> non-default, and hidden behind configuration flags.
>
> Also, do I remember correctly that __builtin_available requires linking
> against Foundation (and thus the Obj-C runtime) for NSProcessInfo, or has
> that dependency been removed/avoided?  It would be surprising for the C++
> standard library to pull in the Objective-C runtime.  A reasonable
> configuration option, but not a reasonable default behaviour IMO.
>
> > On Feb 1, 2018, at 05:52, Nico Weber via Phabricator <
> reviews at reviews.llvm.org> wrote:
> >
> > thakis added a comment.
> >
> > The powers that be updated the SDK on the chromium clang bots, so we
> need some solution for this issue soon.
> >
> > The approach in this patch should work, but it seems conservative. Now
> libc++ only uses utimesat() if it's built with a deployment target of macOS
> 10.13. But if we were to set a deployment target of 10.12 and then _run_ on
> 10.13, we could use utimesat() as well, even though this patch currently
> doesn't. (Apple bundles libc++ with the system, so it's not a meaningful
> difference for Apple-built libc++'s, but applications can build libc++
> themselves and statically link to it, and for those it would make a
> difference.)
> >
> > https://clang.llvm.org/docs/LanguageExtensions.html#
> objective-c-available has some words on it (except that `@available` is
> spelled `__builtin_available` in non-Objective-C code) -- thoughts on using
> runtime detection of utimes() instead? That's how things are supposed to
> work on the Apple platforms.
> >
> >
> > https://reviews.llvm.org/D34249
> >
> >
> >
>
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