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

Note that this does have one user-visible impact: the
prerequisite patches listed by "format-patch --base". There
may be some confusion between different versions of git as
older ones will enable renames, but newer ones will not.
However, this was already a problem, as people with
different settings for the "diff.renames" config would get
different results. After this patch, everyone should get the
same results, regardless of their config.

Signed-off-by: Jeff King <>
 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));
+       ids->diffopts.detect_rename = 0;
        DIFF_OPT_SET(&ids->diffopts, RECURSIVE);
        hashmap_init(&ids->patches, (hashmap_cmp_fn)patch_id_cmp, 256);

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