diff --follow: do not waste cycles while recursing

The "--follow" logic is called from diff_tree_sha1() function, but the
input trees to diff_tree_sha1() are not necessarily the top-level trees
(compare_tree_entry() calls it while it recursively descends into
subtrees).  When a newly created path lives in somewhere deep in the
source hierarchy, e.g. "platform/", but the rename source is in a totally
different place in the destination hierarchy, e.g. "lang-api/src/com/...",
running "try_to_find_renames()" while base is set to "platform/" is a
wasted call.

We only need to run the rename following at the very top level.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/tree-diff.c b/tree-diff.c
index 1fb3e94614de4973a242b1f039ee7711a74fad9d..5b68c0864cac22d083228d5966487913df5c6be2 100644 (file)
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -412,7 +412,7 @@ int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const cha
        init_tree_desc(&t1, tree1, size1);
        init_tree_desc(&t2, tree2, size2);
        retval = diff_tree(&t1, &t2, base, opt);
-       if (DIFF_OPT_TST(opt, FOLLOW_RENAMES) && diff_might_be_rename()) {
+       if (!*base && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && diff_might_be_rename()) {
                init_tree_desc(&t1, tree1, size1);
                init_tree_desc(&t2, tree2, size2);
                try_to_follow_renames(&t1, &t2, base, opt);