Re: [PATCH v2] merge-ort: avoid assuming all renames detected

[Elijah Newren <newren@gmail.com>]

On Mon, Jan 17, 2022 at 11:33 AM Junio C Hamano <gitster@pobox.com> wrote:
>
> "Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
> > From: Elijah Newren <newren@gmail.com>
> >
> > 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 <me@ttaylorr.com>
> > Signed-off-by: Elijah Newren <newren@gmail.com>
> > ---
>
> Thanks.  An Ack?

Taylor told me the code change fixed his case, and that he'd review my
full patch with the testcase when I posted it.  Let's wait to hear
from him.