builtin/commit: fix memory leak in prepare_index()

Release `pathspec` and the string list `partial`.

When we clear the string list, make sure we do not free the `util`
pointers. That would result in double-freeing, since we set them up as
`item->util = item` in `list_paths()`.

Initialize the string list early, so that we can always release it. That
introduces some unnecessary overhead in various code paths, but means
there is one and only one way out of the function. If we ever accumulate
more things we need to free, it should be straightforward to do so.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Martin Ågren

builtin/commit.c

@@ -336,7 +336,7 @@ static void refresh_cache_or_die(int refresh_flags)
 static const char *prepare_index(int argc, const char **argv, const char *prefix,
 				 const struct commit *current_head, int is_status)
 {
-	struct string_list partial;
+	struct string_list partial = STRING_LIST_INIT_DUP;
 	struct pathspec pathspec;
 	int refresh_flags = REFRESH_QUIET;
 	const char *ret;
@@ -381,7 +381,8 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 			warning(_("Failed to update main cache tree"));
 
 		commit_style = COMMIT_NORMAL;
-		return get_lock_file_path(&index_lock);
+		ret = get_lock_file_path(&index_lock);
+		goto out;
 	}
 
 	/*
@@ -404,7 +405,8 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 		if (write_locked_index(&the_index, &index_lock, CLOSE_LOCK))
 			die(_("unable to write new_index file"));
 		commit_style = COMMIT_NORMAL;
-		return get_lock_file_path(&index_lock);
+		ret = get_lock_file_path(&index_lock);
+		goto out;
 	}
 
 	/*
@@ -430,7 +432,8 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 			rollback_lock_file(&index_lock);
 		}
 		commit_style = COMMIT_AS_IS;
-		return get_index_file();
+		ret = get_index_file();
+		goto out;
 	}
 
 	/*
@@ -461,7 +464,6 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 			die(_("cannot do a partial commit during a cherry-pick."));
 	}
 
-	string_list_init(&partial, 1);
 	if (list_paths(&partial, !current_head ? NULL : "HEAD", prefix, &pathspec))
 		exit(1);
 
@@ -491,6 +493,9 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 	discard_cache();
 	ret = get_lock_file_path(&false_lock);
 	read_cache_from(ret);
+out:
+	string_list_clear(&partial, 0);
+	clear_pathspec(&pathspec);
 	return ret;
 }