[PATCH] Set up argv0_path correctly, even when argv[0] is just the basename

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

When the program 'git' is in the PATH, the argv[0] is set to the basename.
However, argv0_path needs the full path, so add a function to discover the
program by traversing the PATH manually.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---

	So it is not easily possible to reuse this function in 
	compat/mingw.c, as Junio said that compat/ should not depend
	(at least too much) on libgit.a.

	Of course, we could try to follow a symlinked git, too, but I 
	think this is overkill until someone proves me wrong.

 exec_cmd.c |   22 ++++++++++++++++++++++
 exec_cmd.h |    1 +
 git.c      |    6 ++++++
 3 files changed, 29 insertions(+), 0 deletions(-)

diff --git a/exec_cmd.c b/exec_cmd.c
index 0ed768d..048f3ca 100644
--- a/exec_cmd.c
+++ b/exec_cmd.c
@@ -125,3 +125,25 @@ int execl_git_cmd(const char *cmd,...)
 	argv[argc] = NULL;
 	return execv_git_cmd(argv);
 }
+
+char *lookup_program_in_path(const char *program)
+{
+	struct strbuf buf = STRBUF_INIT;
+	const char *path = getenv("PATH");
+
+	if (!path || !*path)
+		return NULL;
+
+	for (;;) {
+		const char *colon = strchrnul(path, PATH_SEP);
+
+		strbuf_setlen(&buf, 0);
+		strbuf_addf(&buf, "%.*s/%s",
+				(int)(colon - path), path, program);
+		if (!access(buf.buf, X_OK))
+			return strbuf_detach(&buf, NULL);
+		if (!*colon)
+			return NULL;
+		path = colon + 1;
+	}
+}
diff --git a/exec_cmd.h b/exec_cmd.h
index 0c46cd5..4548390 100644
--- a/exec_cmd.h
+++ b/exec_cmd.h
@@ -8,5 +8,6 @@ extern void setup_path(void);
 extern int execv_git_cmd(const char **argv); /* NULL terminated */
 extern int execl_git_cmd(const char *cmd, ...);
 extern const char *system_path(const char *path);
+extern char *lookup_program_in_path(const char *program);
 
 #endif /* GIT_EXEC_CMD_H */
diff --git a/git.c b/git.c
index 54c5bfa..0ec8ee1 100644
--- a/git.c
+++ b/git.c
@@ -428,6 +428,12 @@ int main(int argc, const char **argv)
 	do
 		--slash;
 	while (cmd <= slash && !is_dir_sep(*slash));
+	if (slash < cmd) {
+		cmd = lookup_program_in_path(cmd);
+		for (slash = (char *)cmd + strlen(cmd) - 1;
+				cmd <= slash && !is_dir_sep(*slash); slash--)
+			; /* do nothing */
+	}
 	if (cmd <= slash) {
 		*slash++ = 0;
 		git_set_argv0_path(cmd);
-- 
1.5.6.2.516.g22071