Re: 2.19.0 regression: leaving editor with empty commit message doesn't stop rebase [was: Re: [RFC PATCH v5 9/9] git-rebase: make --allow-empty-message the default]

From: Elijah Newren <newren@gmail.com>
To: "SZEDER Gábor" <szeder.dev@gmail.com>
Cc: Junio C Hamano <gitster@pobox.com>,
	Git Mailing List <git@vger.kernel.org>,
	Phillip Wood <phillip.wood@dunelm.org.uk>,
	Johannes Schindelin <johannes.schindelin@gmx.de>,
	Eric Sunshine <sunshine@sunshineco.com>
Subject: Re: 2.19.0 regression: leaving editor with empty commit message doesn't stop rebase [was: Re: [RFC PATCH v5 9/9] git-rebase: make --allow-empty-message the default]
Date: Tue, 11 Sep 2018 23:21:07 -0700	[thread overview]
Message-ID: <CABPp-BEe=NCXhaCcbNQv6vxcuD2oWMvMfMMPv5+RVKfqarc0hA@mail.gmail.com> (raw)
In-Reply-To: <20180912024241.GA27036@localhost>

Hi,

On Tue, Sep 11, 2018 at 7:42 PM SZEDER Gábor <szeder.dev@gmail.com> wrote:
> Lately I noticed that occasionally I ended up with an empty commit
> message after an interactive rebase...those empty commit messages are the
> consequence of a regression in v2.19.0, which bisects down to this
> patch.
>
> To reproduce the issue, just start an interactive rebase, choose a
> commit to reword, save, delete all the commit message, save, and BAM!
> there is the commit with the empty message.
>
>
> On Wed, Jun 27, 2018 at 12:23:19AM -0700, Elijah Newren wrote:
> > rebase backends currently behave differently with empty commit messages,
> > largely as a side-effect of the different underlying commands on which
> > they are based.  am-based rebases apply commits with an empty commit
...
> I agree that this is an issue that should be addressed, and also agree
> that it's reasonable to accept an empty commit message, if the
> original commit already had an empty commit message.  (Though perhaps
> not completely silently, but with a warning?  Dunno.)
>
> However, this should only be the case for existing commit messages
> that are taken verbatim, but never in the case when the user is asked
> for a commit message.
...
>   # Please enter the commit message for your changes. Lines starting
>   # with '#' will be ignored, and an empty message aborts the commit.
...
> Let's suppose you start an interactive rebase, choose a commit to
> squash, save the instruction sheet, rebase fires up your editor, and
> then you notice that you mistakenly chose the wrong commit to squash.
> What do you do, how do you abort?

All sound like reasonable arguments to me to differentiate between
commit messages that started empty (which I admit was what I had in
mind) vs. ones where we asked for user input and it came out empty.

Are you cooking up a patch?  I might be able to find a little time to
dig into this tomorrow if no one else is working on it already by
then.  It'll probably conflict a bunch with all the
rewrite-rebase-in-C topics in flight in pu.  :-(