[PATCH 1/2] patch-ids: turn off rename detection

[Jeff King <peff@peff.net>]

The patch-id code may be running inside another porcelain
like "git log" or "git format-patch", and therefore may have
set diff_detect_rename_default, either via the diff-ui
config, or by default since 5404c11 (diff: activate
diff.renames by default, 2016-02-25). This is the case even
if a command is run with `--no-renames`, as that is applied
only to the diff-options used by the command itself.

Rename detection doesn't help the patch-id results. It
_may_ actually hurt, as minor differences in the files that
would be overlooked by patch-id's canonicalization might
result in different renames (though I'd doubt that it ever
comes up in practice).

But mostly it is just a waste of CPU to compute these
renames.

Note that we don't have to worry about compatibility here.
This patch disables renames just for the internal patch-id
comparison run by "log --cherry-pick", etc. The user-visible
"git patch-id" output depends on the patch that it is fed
(so it is up to the diff generator to use --no-renames if
they wish).

Signed-off-by: Jeff King <peff@peff.net>
---
 patch-ids.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/patch-ids.c b/patch-ids.c
index 082412a..77e4663 100644
--- a/patch-ids.c
+++ b/patch-ids.c
@@ -45,6 +45,7 @@ int init_patch_ids(struct patch_ids *ids)
 {
 	memset(ids, 0, sizeof(*ids));
 	diff_setup(&ids->diffopts);
+	ids->diffopts.detect_rename = 0;
 	DIFF_OPT_SET(&ids->diffopts, RECURSIVE);
 	diff_setup_done(&ids->diffopts);
 	hashmap_init(&ids->patches, (hashmap_cmp_fn)patch_id_cmp, 256);
-- 
2.10.0.rc2.154.gb4a4b8b