Subject: Re: [PATCH] merge-ort: avoid assuming all renames detected

From: Junio C Hamano <[email-masked]>
Date: Sun, 16 Jan 2022 13:46:40 -0800

"Elijah Newren via GitGitGadget" <[email-masked]> writes:

> From: Elijah Newren <[email-masked]>
>
> In commit 8b09a900a1 ("merge-ort: restart merge with cached renames to
> reduce process entry cost", 2021-07-16), we noted that in the merge-ort
> steps of
>     collect_merge_info()
>     detect_and_process_renames()
>     process_entries()
> that process_entries() was expensive, and we could often make it cheaper
> by changing this to
>     collect_merge_info()
>     detect_and_process_renames()
>     <cache all the renames, and restart>
>     collect_merge_info()
>     detect_and_process_renames()
>     process_entries()
> because the second collect_merge_info() would be cheaper (we could avoid
> traversing into some directories), the second
> detect_and_process_renames() would be free since we had already detected
> all renames, and then process_entries() has far fewer entries to handle.
>
> However, this was built on the assumption that the first
> detect_and_process_renames() actually detected all potential renames.
> If someone has merge.renameLimit set to some small value, that
> assumption is violated which manifests later with the following message:
>
>     $ git -c merge.renameLimit=1 rebase upstream
>     ...
>     git: merge-ort.c:546: clear_or_reinit_internal_opts: Assertion
>     `renames->cached_pairs_valid_side == 0' failed.
>
> Turn off this cache-renames-and-restart whenever we cannot detect all
> renames, and add a testcase that would have caught this problem.
>
> Reported-by: Taylor Blau <[email-masked]>
> Signed-off-by: Elijah Newren <[email-masked]>
> ---

Thanks.  Will fork from maint-2.33 and park on 'seen' for now.