[PATCH 13 of 14] chg: extra the logic opening current directory to opencwdx()

[FUJIWARA Katsunori]

At Thu, 14 Apr 2016 09:59:06 -0700,
Sean Farley wrote:

> Yuya Nishihara <yuya at tcha.org> writes:
> 
> > On Wed, 13 Apr 2016 17:55:55 +0100, Jun Wu wrote:
> >> Do you think it's okay to have a marco for all "*x", or "*at" stuff? It will
> >> make the code shorter. Although I'm not a big fan of macros, I think current
> >> code duplication is a bit too much and macro can help.
> >
> > Using macros should be fine if that makes sense.
> 
> Agreed.
> 
> >> And about OS X feature detection. What do you think is the best way to do
> >> feature detection here? I personally dislike autoconf. But is compiling
> >> a dummy C program okay? Or should I use "#ifdef SYS_openat"? I think the
> >> C library and system header may not in sync though.
> >
> > No idea, and I don't like autoconf, too. It would be too complicated for small
> > tools like chg.
> 
> I, too, hate autotools.
> 
> > I think manually-set HAVE_OPENAT macro is good start. Then, we can add a dummy
> > C program later when we're sure it is the best way.
> 
> In our other C files, we have #ifdef for Mac OS X vs Windows vs Linux,
> so I'm ok with macros and preprocessors.

As far as I confirm actual header files, "#if defined(AT_FDCWD)" after
"#include <fcntl.h>" can detect availability of "openat()" on Linux,
(Open)Solaris, FreeBSD and MacOS X (10.10).

Defining HAVE_OPENAT macro according to existence of AT_FDCWD macro
can avoid manually-setting it on almost all platforms.

BTW, #3 of this series uses AT_FDCWD macro without any feature
examination. But for portability, it should examine availability of
AT_FDCWD, and define dummy AT_FDCWD if it isn't defined, shouldn't it ?

    https://www.mercurial-scm.org/repo/hg-committed/rev/7b5f5a1b4b41


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[FUJIWARA Katsunori]                             foozy at lares.dti.ne.jp