commit_lock_file(): use a strbuf to manage temporary space

Avoid relying on the filename length restrictions that are currently
checked by lock_file().

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

lockfile.c

@@ -319,7 +319,8 @@ int reopen_lock_file(struct lock_file *lk)
 
 int commit_lock_file(struct lock_file *lk)
 {
-	char result_file[PATH_MAX];
+	static struct strbuf result_file = STRBUF_INIT;
+	int err;
 
 	if (!lk->active)
 		die("BUG: attempt to commit unlocked object");
@@ -327,11 +328,12 @@ int commit_lock_file(struct lock_file *lk)
 	if (close_lock_file(lk))
 		return -1;
 
-	strcpy(result_file, lk->filename);
 	/* remove ".lock": */
-	result_file[strlen(result_file) - LOCK_SUFFIX_LEN] = 0;
-
-	if (rename(lk->filename, result_file)) {
+	strbuf_add(&result_file, lk->filename,
+		   strlen(lk->filename) - LOCK_SUFFIX_LEN);
+	err = rename(lk->filename, result_file.buf);
+	strbuf_reset(&result_file);
+	if (err) {
 		int save_errno = errno;
 		rollback_lock_file(lk);
 		errno = save_errno;