config.c: create missing parent directories when modifying config files

'git config' (--add / --unset etc.) automatically creates missing config
files. However, it fails with a misleading error message "could not lock
config file" if the parent directory doesn't exist.

Also create missing parent directories.

This is particularly important when calling

	git config -f /non/existing/directory/config ...

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: kblees

config.c

@@ -1924,6 +1924,24 @@ int git_config_parse_key(const char *key, char **store_key, int *baselen_)
 	return -CONFIG_INVALID_KEY;
 }
 
+static int lock_config_file(const char *config_filename,
+		struct lock_file **result)
+{
+	int fd;
+
+	/* make sure the parent directory exists */
+	if (safe_create_leading_directories_const(config_filename))
+		return error("could not create parent directory of %s",
+				config_filename);
+	*result = xcalloc(1, sizeof(struct lock_file));
+	fd = hold_lock_file_for_update(*result, config_filename, 0);
+	if (fd < 0)
+		error("could not lock config file %s: %s", config_filename,
+				strerror(errno));
+
+	return fd;
+}
+
 /*
  * If value==NULL, unset in (remove from) config,
  * if value_regex!=NULL, disregard key/value pairs where value does not match.
@@ -1974,10 +1992,8 @@ int git_config_set_multivar_in_file(const char *config_filename,
 	 * The lock serves a purpose in addition to locking: the new
 	 * contents of .git/config will be written into it.
 	 */
-	lock = xcalloc(1, sizeof(struct lock_file));
-	fd = hold_lock_file_for_update(lock, config_filename, 0);
+	fd = lock_config_file(config_filename, &lock);
 	if (fd < 0) {
-		error("could not lock config file %s: %s", config_filename, strerror(errno));
 		free(store.key);
 		ret = CONFIG_NO_LOCK;
 		goto out_free;
@@ -2256,12 +2272,9 @@ int git_config_rename_section_in_file(const char *config_filename,
 	if (!config_filename)
 		config_filename = filename_buf = git_pathdup("config");
 
-	lock = xcalloc(1, sizeof(struct lock_file));
-	out_fd = hold_lock_file_for_update(lock, config_filename, 0);
-	if (out_fd < 0) {
-		ret = error("could not lock config file %s", config_filename);
+	out_fd = lock_config_file(config_filename, &lock);
+	if (out_fd < 0)
 		goto out;
-	}
 
 	if (!(config_file = fopen(config_filename, "rb"))) {
 		/* no config file means nothing to rename, no error */