Re: [PATCH v3 3/4] Provide a dirname() function when NO_LIBGEN_H=YesPlease

> When there is no `libgen.h` to our disposal, we miss the `dirname()`
> function.
>
> So far, we only had one user of that function: credential-cache--daemon
> (which was only compiled when Unix sockets are available, anyway). But
> now we also have `builtin/am.c` as user, so we need it.
>
> Since `dirname()` is a sibling of `basename()`, we simply put our very
> own `gitdirname()` implementation next to `gitbasename()` and use it
> if `NO_LIBGEN_H` has been set.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
> diff --git a/compat/basename.c b/compat/basename.c
> @@ -25,3 +26,46 @@ char *gitbasename (char *path)
> +char *gitdirname(char *path)
> +{
> +       char *p = path, *slash = NULL, c;
> +       int dos_drive_prefix;
> +
> +       if (!p)
> +               return ".";
> +
> +       if ((dos_drive_prefix = skip_dos_drive_prefix(&p)) && !*p) {
> +               static struct strbuf buf = STRBUF_INIT;
> +
> +dot:
> +               strbuf_reset(&buf);
> +               strbuf_addf(&buf, "%.*s.", dos_drive_prefix, path);
> +               return buf.buf;
> +       }
> +
> +       /*
> +        * POSIX.1-2001 says dirname("/") should return "/", and dirname("//")
> +        * should return "//", but dirname("///") should return "/" again.
> +        */
> +       if (is_dir_sep(*p)) {
> +               if (!p[1] || (is_dir_sep(p[1]) && !p[2]))
> +                       return path;
> +               slash = ++p;
> +       }
> +       while ((c = *(p++)))
> +               if (is_dir_sep(c)) {
> +                       char *tentative = p - 1;
> +
> +                       /* POSIX.1-2001 says to ignore trailing slashes */
> +                       while (is_dir_sep(*p))
> +                               p++;
> +                       if (*p)
> +                               slash = tentative;
> +               }
> +
> +       if (!slash)
> +               goto dot;
> +       *slash = '\0';
> +       return path;
> +}