[PATCH] Teach diff-cache about commit objects

Updates diff-cache.c to use read_tree_with_tree_or_commit_sha1()
function.  The end-user visible result is the same --- the command
takes either tree or commit ID.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff-cache.c

@@ -220,7 +220,6 @@ int main(int argc, char **argv)
 	unsigned char tree_sha1[20];
 	void *tree;
 	unsigned long size;
-	char type[20];
 
 	read_cache();
 	while (argc > 2) {
@@ -245,23 +244,9 @@ int main(int argc, char **argv)
 	if (argc != 2 || get_sha1_hex(argv[1], tree_sha1))
 		usage("diff-cache [-r] [-z] <tree sha1>");
 
-	tree = read_sha1_file(tree_sha1, type, &size);
+	tree = read_tree_with_tree_or_commit_sha1(tree_sha1, &size, 0);
 	if (!tree)
 		die("bad tree object %s", argv[1]);
 
-	/* We allow people to feed us a commit object, just because we're nice */
-	if (!strcmp(type, "commit")) {
-		/* tree sha1 is always at offset 5 ("tree ") */
-		if (get_sha1_hex(tree + 5, tree_sha1))
-			die("bad commit object %s", argv[1]);
-		free(tree);
-		tree = read_sha1_file(tree_sha1, type, &size);       
-		if (!tree)
-			die("unable to read tree object %s", sha1_to_hex(tree_sha1));
-	}
-
-	if (strcmp(type, "tree"))
-		die("bad tree object %s (%s)", sha1_to_hex(tree_sha1), type);
-
 	return diff_cache(tree, size, active_cache, active_nr, "");
 }