Re: [PATCH 2/2] checkout: introduce "--to-branch" option

From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: "ZheNing Hu" <adlternative@gmail.com>,
	"ZheNing Hu via GitGitGadget" <gitgitgadget@gmail.com>,
	"Git List" <git@vger.kernel.org>,
	"Christian Couder" <christian.couder@gmail.com>,
	"Hariom Verma" <hariom18599@gmail.com>,
	"brian m. carlson" <sandals@crustytoothpaste.net>,
	"Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>,
	"Eric Sunshine" <sunshine@sunshineco.com>
Subject: Re: [PATCH 2/2] checkout: introduce "--to-branch" option
Date: Mon, 13 Dec 2021 20:55:00 +0100	[thread overview]
Message-ID: <211213.86r1ag6ztx.gmgdl@evledraar.gmail.com> (raw)
In-Reply-To: <xmqqy24pk6f4.fsf@gitster.g>

On Sun, Dec 12 2021, Junio C Hamano wrote:

> ZheNing Hu <adlternative@gmail.com> writes:
>
>>> It is unclear if you mean "dev1" exactly point at the commit tagged
>>> as v1.1, or you want the branch "dev1" that is a descedanant of
>>> v1.1.  Without telling that to the reader, the above explanation is
>>> useless.
>>>
>>
>> I meant the former.
>>
>>> And whether you meant the former or the latter, neither use case does
>>> not make much sense.
>>> ...
>>> So, "--to-branch v1.1" that finds and checks out a branch whose tip
>>> exactly points at v1.1 would be pretty useless.
>> ...
>> "git branch --contains v1.1" can find all branches whose history contains the
>>  commit tagged as v1.1. So what if "git checkout --contains v1.1"?
>
> I already said, whether you meant "the only branch that points
> exactly at" or "the only branch that contains", the feature does not
> make sense.  Forcing users to keep only a single branch that either
> points at a given tag is simply impossible and also useless.  Once
> the branch gains even a single commit, it will no loger be pointing
> at the tag, so "let's prepare a branch pointing at v1.1 just in case
> when I want to start working from there" would not be a good
> workflow to begin with.  Forcing users to keep only a single branch
> that contains a given tag would encourage even a worse workflow to
> throw in unrelated things, whose only commonality is that they all
> want to fork from a single tag, into a single branch.
>
> IOW, there is nothing we want to add to "git checkout/switch" for
> this topic.  "git checkout --contains $tag" smells like a solution
> looking for a problem.

I don't see how it's fundimentally different than the DWIM logic of
taking "<name>" and seeing that there's only one "refs/heads/<name>",
and giving up in other cases where we get ambiguous reference names that
we can't resolve.

I.e. I think this is probably useful for some, it's a common workflow to
have a 1=1 relationship like this, and if it's 1=many we can just handle
it as we do with ambiguous ref, or ambiguous short OIDs for that matter.

But as I noted upthread I really don't see this making sense as a
per-command thing, as opposed to some extension of the "peel"
syntax. I.e. we should (or at least expose it as such to the user)
interpret that sort of argument/newx syntax before "git checkout" et al
get to it, so from a UX perspective you could feed a ^{oid2ref} (or
whatever it would be called) to rev-parse, checkout etc. etc.