[PATCH] Provide a dirname() function when NO_LIBGEN_H=YesPlease

[Johannes Schindelin <johannes.schindelin@gmx.de>]

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>
---

	I stumbled over the compile warning when upgrading Git for Windows
	to 2.6.0. There was a left-over NO_LIBGEN_H=YesPlease (which we
	no longer need in Git for Windows 2.x), but it did point to the
	fact that we use `dirname()` in builtin/am.c now, so we better
	have a fall-back implementation for platforms without libgen.h.

	I tested this implementation a bit, but I still would appreciate
	a few eye-balls to go over it.

 compat/basename.c | 26 ++++++++++++++++++++++++++
 git-compat-util.h |  2 ++
 2 files changed, 28 insertions(+)

diff --git a/compat/basename.c b/compat/basename.c
index d8f8a3c..10dba38 100644
--- a/compat/basename.c
+++ b/compat/basename.c
@@ -13,3 +13,29 @@ char *gitbasename (char *path)
 	}
 	return (char *)base;
 }
+
+char *gitdirname(char *path)
+{
+	char *p = path, *slash, c;
+
+	/* Skip over the disk name in MSDOS pathnames. */
+	if (has_dos_drive_prefix(p))
+		p += 2;
+	/* POSIX.1-2001 says dirname("/") should return "/" */
+	slash = is_dir_sep(*p) ? ++p : NULL;
+	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)
+		return ".";
+	*slash = '\0';
+	return path;
+}
diff --git a/git-compat-util.h b/git-compat-util.h
index f649e81..8b01aa5 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -253,6 +253,8 @@ struct itimerval {
 #else
 #define basename gitbasename
 extern char *gitbasename(char *);
+#define dirname gitdirname
+extern char *gitdirname(char *);
 #endif
 
 #ifndef NO_ICONV
-- 
2.5.3.windows.1.3.gc322723