+static int is_index_unchanged(void)
+{
+ unsigned char head_sha1[20];
+ struct commit *head_commit;
+
+ if (!resolve_ref_unsafe("HEAD", head_sha1, 1, NULL))
+ return error(_("Could not resolve HEAD commit\n"));
+
+ head_commit = lookup_commit(head_sha1);
+
+ /*
+ * If head_commit is NULL, check_commit, called from
+ * lookup_commit, would have indicated that head_commit is not
+ * a commit object already. parse_commit() will return failure
+ * without further complaints in such a case. Otherwise, if
+ * the commit is invalid, parse_commit() will complain. So
+ * there is nothing for us to say here. Just return failure.
+ */
+ if (parse_commit(head_commit))
+ return -1;
+
+ if (!active_cache_tree)
+ active_cache_tree = cache_tree();
+
+ if (!cache_tree_fully_valid(active_cache_tree))
+ if (cache_tree_update(active_cache_tree, active_cache,
+ active_nr, 0))
+ return error(_("Unable to update cache tree\n"));
+
+ return !hashcmp(active_cache_tree->sha1, head_commit->tree->object.sha1);
+}
+