Re: [PATCH v3 0/2] fmt-merge-msg: selectively suppress "into <branch>"

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 31, 2020, 02:04 UTC
Message-ID: <xmqqy2n04ezk.fsf@gitster.c.googlers.com>
In-Reply-To: <20200731004202.GA240563@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

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> This version looks OK to me. The remaining issues that came up in
> earlier discussion but I didn't see you weigh in on are:
>
>   - what should happen with a detached HEAD? We'd match HEAD in the
>     suppressDest config, which I think is quite reasonable. Not sure if
>     it's worth documenting or testing that specifically.

I think what the code with posted patch happens to do is just fine. If you say "git -c merge.suppressDest=HEA? merge $topic" while on a detached HEAD, you'll get "into HEAD" omitted.

In a workflow where you'd do

	$ git co master^0
	... enumerate the topics merged in master..jch, and redo the
	... merge, but with updated versions of these topics
	$ git shortlog jch..HEAD
	$ git range-diff jch...HEAD
	$ git diff jch..HEAD
	... after inspection, find the result satisfactory, and ...
	$ git co -B jch

I would strongly suspect that hiding "into HEAD" is not enough, so I do not think HEAD is all that relevant in the first place.

You'd rather want to "lie" about the destination branch while redoing these merges, perhaps with

	$ git merge --pretend-dest=jch topic-name

with your HEAD detached, and tell fmt-merge-msg to pretend that the merge is being made into jch branch. And that is outside the scope of this patch, though it might be a good #leftoverbits candidate.

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>   - should "master" be in the list even if you configure a value? That
>     would do the wrong thing if you have a non-integration master, but
>     that seems unlikely. And it would do the right thing if somebody
>     later puts "main" in merge.suppressDest, but still occasionally
>     works with "master" repos (where "right" is defined as "what they
>     probably wanted", but it is perhaps a bit magical).

If you configure, you can configure it fully without manually clearing first. If you do not configure, you get a backward compatible default. I think that is the only sensible semantics.

Besides, I thought we were aiming to make 'master' less special. When a user already has a concrete list of things to use shorter merge title for, why should 'master' be magically added to the list and force the user to explicitly clear it? I do not think that makes much sense.

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>   - what's the plan if we do switch init.defaultBranch to "main"? Would
>     we add default_branch() to the list of defaults alongside "master",
>     or just add "main", or just leave it and let people configure
>     independently? It doesn't need to be decided now, but maybe worth
>     thinking about.

My understanding is that much more instances of repositories come to exist by cloning than running "git init". Hence, the value you set to the init.defaultBranch has no relevance to the name of the primary branch in majority of your repositories, whose primary branch is what their origin has designated before/when you cloned.

And the latter, "what is the primary branch name for this particular repository?", is what we want to ask here. The answer to "what is the first branch name for new repository I will create?" is not a good proxy for that.

I do not mind too much, even though I doubt it will be all that useful, if we taught "init" and "clone" to record which branch is the primary one in the repository they created. We'd need to add the repo_primary_branch_name() helper to allow this caller to replace the hardcoded 'master' in the patch with it, just like "init" and "clone" may ask the repo_default_branch_name() helper what the first branch name ought to be.

In any case, I do not think I want to see more reliance of the notion that there always is one and only one single special branch in the repository, so if we can get away without it, that would be more preferrable.

Thanks.