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From: Jakub Narebski <jnareb@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Giuseppe Crinò" <giuscri@gmail.com>,
	git@vger.kernel.org
Subject: Re: Feature request: Allow to update commit ID in messages when rebasing
Date: Thu, 18 Apr 2019 19:32:26 +0200	[thread overview]
Message-ID: <86o953z0b9.fsf@gmail.com> (raw)
In-Reply-To: <xmqqtvewgj4c.fsf@gitster-ct.c.googlers.com> (Junio C. Hamano's message of "Thu, 18 Apr 2019 11:08:51 +0900")

Junio C Hamano <gitster@pobox.com> writes:
> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>> On Wed, Apr 17 2019, Giuseppe Crinò wrote:
>>
>>> The feature I'm asking is to add an extra-step during rebasing,
>>> checking whether there's a reference to a commit that's not going to
>>> be included in history and asks the user whether the heuristics is
>>> correct and if she wants to update those references.
>>>
>>> Scenario: it can happen for a commit message to contain the ID of an
>>> ancestor commit. A typical example is a commit with the message
>>> "revert 01a9fe8". If 01a9fe8 and the commit that reverts it are
>>> involved in a rebase the message "revert 01a9fe8" is no longer valid
>>> -- the old 01a9fe8 has now a different hash. This will most likely be
>>> ignored by the person who's rebasing but will let the other people
>>> reading history confused.
>>
>> This would be useful. Done properly we'd need some machinery/command to
>> extract the commit id parts from the free-text of the commit
>> message. That would be useful for other parts of git, e.g. as discussed
>> here:
>> https://public-inbox.org/git/xmqqvaxp9oyp.fsf@gitster.mtv.corp.google.com/
>
> That's a helpful input.
>
> But in general we do not have an infrastructure to systematically
> keep track of "this commit was rewritten to produce that other
> commit", so even if a mention of an old/superseded commit can be
> identified reliably, there is no reliable source to rewrite it to
> the name of the corresponding commit in the new world.
>
> For that mapping, we'd need something like the "git change/evolve"
> Stefan Xenos was working on, which hasn't materialized.

Well, what about limiting changes and rewriting only to the commits
being rewritten by [interactive] rebase?  I mean that we would rewrite
"revert 01a9fe8" only if:

a.) the commit with this message is undergoing rewrite
b.) the commit 01a9fe8 is undergoing rewrite in the same command

We could use the infrastructure from git-filter-branch for this.

It is serious limitation, but that might be good enough for Giuseppe
Crinò use case.  Though for example there is a question what to do if
referred-to commit (01a9fe8 in the example) is simply dropped, or is
gets split in two?  Ask user?


Another possibility would be to provide a command line option to rebase
which would automatically generate replacements (in git-replace meaning)
from old pre-rebase name to new post-rebase name (assuming no splitting,
no dropping commits).  This would make references just work... well, as
long as refs/replace/* are in place (they are not copied by default).

On the other hand some of our performance-improving features, like the
commit-graph, do not work if there are replacements.


Best,
--
Jakub Narębski

  reply	other threads:[~2019-04-18 17:32 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-17 20:35 Giuseppe Crinò
2019-04-17 20:56 ` Ævar Arnfjörð Bjarmason
2019-04-18  2:08   ` Junio C Hamano
2019-04-18 17:32     ` Jakub Narebski [this message]
2019-04-18 17:58       ` Giuseppe Crinò
2019-04-19 10:44         ` Jakub Narebski
2019-04-18 18:00       ` Phil Hord

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