[PATCH] allow git to use the PATH for finding subcommands and help docs

[Scott Parish <sRp@srparish.net>]

I have a situation where software for a distribution is installed
into a fake "prefix" and then moved to one of several potential
places to be used by users. Given that the final location isn't
static, i can't depend on builtin_exec_path. I'd really like users
to be able to get started with git as easily as possible. With the
current setup, they would have to create and maintain either an
GIT_EXEC_PATH or an alias for including --exec-path, as well as a
MANPATH and PERL5LIB. This seem like an unnessisary burden.

I'd like to make it so that git works equally well when it is ran
via an absolute path (already partially works), relative path, or
from the PATH. (in saying "equally well" i'm including perl commands
and help commands)

To do this i've had to make the following changes:

 + check PATH for the location of git
 + the checking of argv[0] was restricted to absolute paths; remove
   that restriction so it also works when called with a relative
   path (eg ../../otheruser/usr/bin/git)
 + try to guess and set the env for the typical relative locations for
   MANPATH and PERL5LIB based off exec_path

Signed-off-by: Scott R Parish <srp@srparish.net>
---
 exec_cmd.c |   50 ++++++++++++++++++++++++++++++++++++++-
 git.c      |   76 +++++++++++++++++++++++++++++++++++++++++------------------
 2 files changed, 102 insertions(+), 24 deletions(-)

diff --git a/exec_cmd.c b/exec_cmd.c
index 9b74ed2..c6ecca9 100644
--- a/exec_cmd.c
+++ b/exec_cmd.c
@@ -13,19 +13,67 @@ void git_set_exec_path(const char *exec_path)
 }
 
 
+/* Return the first path in PATH that git is found in or NULL if not found */
+char *git_path_from_env(void)
+{
+	const char *env_paths = getenv("PATH");
+	const char *git = "/git";
+	int git_len = strlen(git);
+	char *paths, *path, *colon, *git_path;
+	int path_len;
+	struct stat st;
+
+	if (!env_paths)
+		return NULL;
+
+	path_len = strlen(env_paths);
+	path = paths = xmalloc(path_len + 1);
+	memcpy(paths, env_paths, path_len + 1);
+
+	while ((char *)1 != path) {
+		if ((colon = strchr(path, ':')))
+		    *colon = 0;
+
+		path_len = strlen(path);
+		git_path = xmalloc(path_len + git_len + 1);
+		memcpy(git_path, path, path_len);
+		memcpy(git_path + path_len, git, git_len + 1);
+
+		if (!stat(git_path, &st)) { /* found */
+			free(paths);
+			git_path[path_len] = 0;
+			return git_path;
+		}
+
+		free(git_path);
+		path = colon + 1;
+	}
+
+	free(paths);
+	return NULL;
+}
+
+
 /* Returns the highest-priority, location to look for git programs. */
 const char *git_exec_path(void)
 {
-	const char *env;
+	const char *env, *path;
 
 	if (current_exec_path)
 		return current_exec_path;
 
 	env = getenv(EXEC_PATH_ENVIRONMENT);
 	if (env && *env) {
+		current_exec_path = env;
 		return env;
 	}
 
+	if ((path = git_path_from_env())) {
+		current_exec_path = path;
+		return path;
+	}
+
+	current_exec_path = builtin_exec_path;
 	return builtin_exec_path;
 }
 
diff --git a/git.c b/git.c
index 9eaca1d..252ee7c 100644
--- a/git.c
+++ b/git.c
@@ -6,26 +6,56 @@
 const char git_usage_string[] =
 	"git [--version] [--exec-path[=GIT_EXEC_PATH]] [-p|--paginate|--no-pager] [--bare] [--git-dir=GIT_DIR] [--work-tree=GIT_WORK_TREE] [--help] COMMAND [ARGS]";
 
-static void prepend_to_path(const char *dir, int len)
+static void prepend_to_env(const char *env, const char *basedir,
+			   const char *subdir, const char *env_default)
 {
-	const char *old_path = getenv("PATH");
-	char *path;
-	int path_len = len;
-
-	if (!old_path)
-		old_path = "/usr/local/bin:/usr/bin:/bin";
-
-	path_len = len + strlen(old_path) + 1;
-
-	path = xmalloc(path_len + 1);
+	const char *old = getenv(env);
+	int basedir_len = strlen(basedir);
+	int subdir_len = strlen(subdir);
+	char *new;
+	int old_len;
+	
+	if (!old)
+		old = env_default;
+
+	old_len = strlen(old);
+
+	new = xmalloc(basedir_len + subdir_len + old_len + 1);
+	
+	memcpy(new, basedir, basedir_len);
+	memcpy(new + basedir_len, subdir, subdir_len);
+	memcpy(new + basedir_len + subdir_len, old, old_len + 1);
+	
+	if (setenv(env, new, 1))
+		fprintf(stderr, "Setenv failed: %s\n", strerror(errno));
+
+	free(new);
+}
 
-	memcpy(path, dir, len);
-	path[len] = ':';
-	memcpy(path + len + 1, old_path, path_len - len);
+static void prepend_to_envs(const char *dir, int len)
+{
+	char *slash;
+	char *basedir;
+
+	/* basedir is dir with "/bin" stripped off */
+	basedir = xmalloc(len + 1);
+	memcpy(basedir, dir, len + 1);
+	
+	if ((slash = strrchr(basedir, '/'))) {
+		*slash = 0;
+		while (slash == basedir + --len) /* found trailing slash */
+			if ((slash = strrchr(basedir, '/')))
+				*slash = 0;
+	}
 
-	setenv("PATH", path, 1);
+	prepend_to_env("PATH", basedir, "/bin:",
+		       "/usr/local/bin:/usr/bin:/bin");
+	prepend_to_env("MANPATH", basedir, "/share/man:",
+		       "/usr/local/share/man:/usr/share/man");
+	prepend_to_env("PERL5LIB", basedir, "/lib/perl5:",
+		       "/usr/lib/perl5");
 
-	free(path);
+	free(basedir);
 }
 
 static int handle_options(const char*** argv, int* argc, int* envchanged)
@@ -414,8 +444,7 @@ int main(int argc, const char **argv)
 	 */
 	if (slash) {
 		*slash++ = 0;
-		if (*cmd == '/')
-			exec_path = cmd;
+		exec_path = cmd;
 		cmd = slash;
 	}
 
@@ -453,14 +482,15 @@ int main(int argc, const char **argv)
 	/*
 	 * We execute external git command via execv_git_cmd(),
 	 * which looks at "--exec-path" option, GIT_EXEC_PATH
-	 * environment, and $(gitexecdir) in Makefile while built,
-	 * in this order.  For scripted commands, we prepend
-	 * the value of the exec_path variable to the PATH.
+	 * environment, PATH environment, and $(gitexecdir) in
+	 * Makefile while built, in this order.  For scripted
+	 * commands, we prepend the value of the exec_path
+	 * variable to the PATH.
 	 */
 	if (exec_path)
-		prepend_to_path(exec_path, strlen(exec_path));
+		prepend_to_envs(exec_path, strlen(exec_path));
 	exec_path = git_exec_path();
-	prepend_to_path(exec_path, strlen(exec_path));
+	prepend_to_envs(exec_path, strlen(exec_path));
 
 	while (1) {
 		/* See if it's an internal command */
-- 
1.5.3.4.206.g58ba4-dirty