Re: Bug with fixup and autosquash

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Feb 9, 2017, 20:55 UTC
Message-ID: <alpine.DEB.2.20.1702092142020.3496@virtualbox>
In-Reply-To: <xmqqbmucuwb0.fsf@gitster.mtv.corp.google.com>

Hi Ashutosh and Junio,

On Wed, 8 Feb 2017, Junio C Hamano wrote:

Show 32 quoted lines

> Ashutosh Bapat <ashutosh.bapat@enterprisedb.com> writes:
> 
> > I have been using git rebase heavily these days and seem to have found
> > a bug.
> >
> > If there are two commit messages which have same prefix e.g.
> > yyyyyy This is prefix
> > xxxxxx This is prefix and message
> >
> > xxxxxx comitted before yyyyyy
> >
> > Now I commit a fixup to yyyyyy using git commit --fixup yyyyyy
> > zzzzzz fixup! This is prefix
> >
> > When I run git rebase -i --autosquash, the script it shows me looks like
> > pick xxxxxx This is prefix and message
> > fixup zzzzzz fixup! This is prefix
> > pick yyyyyy This is prefix
> >
> > I think the correct order is
> > pick xxxxxx This is prefix and message
> > pick yyyyyy This is prefix
> > fixup zzzzzz fixup! This is prefix
> >
> > Is that right?
> 
> [...]
> 
> Unfortunately, "rebase -i --autosquash" reorders the entries by
> identifying the commit by its title, and it goes with prefix match so
> that fix-up commits created without using --fixup option but manually
> records the title's prefix substring can also work.

This prefix match also happens to introduce a serious performance problem, which is why I "fixed" this issue in the rebase--helper already (which is the case if you are using Git for Windows, whose master branch builds on Linux and MacOSX as well). I quoted "fix" because my motivation was to fix the performance problem, not the "incorrect match" problem.

The rebase--helper code (specifically, the patch moving autosquash logic into it: https://github.com/dscho/git/commit/7d0831637f) tries to match exact onelines first, and falls back to prefix matching only after that.

Now that the sequencer-i patch series is in `master`, the next step is to send the patch series introducing the rebase--helper. The patch series including the fix discussed above relies on that one. Meaning that it will take a while to get through the mill.

So please do not hold your breath until this feature/fix hits an official Git version. If you need it[*1*] faster, feel free to build Git for Windows' master and run with that for a while.

Ciao, Johannes

Footnote: By "it" I mean "the feature/fix", not "an official Git version"
nor "your breath".