patch, 4 partsUse tree_from_tree_or_commit() in diff-tree.

--- a/diff-tree.c
+++ b/diff-tree.c
@@ -160,18 +160,20 @@ static int diff_tree(void *tree1, unsign
 	return 0;
 }
 
-static int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base)
+static int diff_tree_sha1(const unsigned char *old,
+			  const unsigned char *new,
+			  const char *base)
 {
 	void *tree1, *tree2;
 	unsigned long size1, size2;
 	char type[20];
 	int retval;
 
-	tree1 = read_sha1_file(old, type, &size1);
-	if (!tree1 || strcmp(type, "tree"))
+	tree1 = tree_from_tree_or_commit(old, type, &size1);
+	if (!tree1)
 		die("unable to read source tree (%s)", sha1_to_hex(old));
-	tree2 = read_sha1_file(new, type, &size2);
-	if (!tree2 || strcmp(type, "tree"))
+	tree2 = tree_from_tree_or_commit(new, type, &size2);
+	if (!tree2)
 		die("unable to read destination tree (%s)", sha1_to_hex(new));
 	retval = diff_tree(tree1, size1, tree2, size2, base);
 	free(tree1);