Re: [RFC PATCH 0/2] Introduce new merge-tree-ort command

From: Junio C Hamano <gitster@pobox.com>
To: Elijah Newren <newren@gmail.com>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Johannes Schindelin" <Johannes.Schindelin@gmx.de>,
	"Christian Couder" <christian.couder@gmail.com>,
	"Git Mailing List" <git@vger.kernel.org>,
	"Christian Couder" <chriscool@tuxfamily.org>,
	"Taylor Blau" <me@ttaylorr.com>
Subject: Re: [RFC PATCH 0/2] Introduce new merge-tree-ort command
Date: Wed, 12 Jan 2022 10:06:13 -0800	[thread overview]
Message-ID: <xmqqk0f4x20a.fsf@gitster.g> (raw)
In-Reply-To: <CABPp-BFei07srZBgyKs6HCm+G+hmPR-3_EkKjRK8WwGL1Uf2oA@mail.gmail.com> (Elijah Newren's message of "Tue, 11 Jan 2022 14:25:56 -0800")

Elijah Newren <newren@gmail.com> writes:

>> And isn't any doubt around that even more reason to just go with
>> Elijah's plan of introducing new plumbing? I.e. is it really costing us
>> to just leave these "legacy merge" plumbing built-ins
>
> I definitely think it's worth guiding users away from the old `git
> merge-tree` behavior in documentation (i.e. deprecating it).  That may
> also lead towards its eventual removal, but I'm not as worried about
> that.

Yup, promising users that we will remove it and telling them that
they should migrate away from it is necessary.  Doing anything else
is simply irresponsible.

I however suspect that Ævar didn't mean by "legacy merge plumbing
built-in" the strategy backends.  IOW, I had an impression that what
is on the chopping block is merge-tree and not merge-recursive.

But since you brought up deprecation of recursive, let's spend a few
minutes on the topic.

> `git merge-recursive` was actively used in various places, including
> in `git cherry-pick`.  I had used it a few times myself in a script.
> I don't see a need to deprecate it currently, which naturally would
> push its removal (if anyone is pushing for it) even further away.

I suspect that we may be able to just invoke ort when recursive is
invoked, and such a wrapping may even be easier than wrapping "git
blame" to replace "git annotate" (where a command line option or two
needs to change behaviour).  I doubt there is -X<strategy-option>
that affects recursive that ORT does not understand, so it may be
quite simple to deprecate "merge -s recursive".

As you say, replacing the internal implementation is a different
matter.

>   * `merge-recursive.c` is still hard-coded in three places in the
> code; you can't even set a configuration option to choose merge-ort.c
> in those places: builtin/am, builtin/merge-recursive, and
> builtin/stash.
>
> More details on that second point: All three of these use
> merge_recursive_generic() and need that usage to be replaced.  It's on
> my TODO list.

Yes, I do recall mentioning that when we were reviewing the series
that added ort.