Re: [BUG] fixup commit is dropped during rebase if subject = branch name

[Erik Cervin Edin <erik@cervined.in>]

On Sat, Sep 17, 2022, 8:04 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> >   # failure
> >   seq 1 3 >> bar && git add bar && git commit -m main
> >   git tag -f x
> >   seq 4 6 >> bar && git add bar && git commit -m bar
> >   seq 7 9 >> bar && git add bar && git commit --fixup :/main
> >   git -c sequence.editor=: rebase --autosquash --interactive x
> >   git diff ORIG_HEAD
>
> So near the bottom there are "init", and "x".  The commit title of
> "x" is "main" and that is what the fix-up intends to amend.

Yes, sorry if that was unclear. So the branch looks like

  474b082 (HEAD -> main) fixup! main
  acd367f bar
  576294e (tag: x) main
  dd27847 (tag: init) init

so
  git -c sequence.editor rebase -i --autosquash x
should yield

  474b082 (HEAD -> main) fixup! main
  acd367f bar
  576294e (tag: x) main
  dd27847 (tag: init) init

ie. no change, but instead yields

  acd367f (HEAD -> main) bar
  576294e (tag: x) main
  dd27847 (tag: init) init

ie. it drops the fixup! main commit but only if it's the first commit, see
second example I posted

On Sat, Sep 17, 2022 at 4:45 PM Erik Cervin Edin <erik@cervined.in> wrote:
>   # normal
>   git reset --hard init
>   seq 1 3 >> bar && git add bar && git commit -m main
>   git tag -f x
>   seq 4 6 >> bar && git add bar && git commit --fixup :/main
>   seq 7 9 >> bar && git add bar && git commit -m bar
>   git -c sequence.editor=: rebase --autosquash --interactive x
>   git diff ORIG_HEAD

yields

  acd367f (HEAD -> main) bar
  474b082 fixup! main
  576294e (tag: x) main
  dd27847 (tag: init) init

as expected.

> But then I do not think there is any valid expectation if you say
> "keep x intact and rebase everything above", which is what the
> command line arguments tell the last command to do.  Perhaps we
> should keep all original commits up to that "fixup" one without any
> reordering or squashing?

I'm not sure I follow but the report is concerning the unexpected
behavior of dropping the commit under these specific conditions. I'm
not 100% sure but as I recall, this only happens in situation where
the fixup may not be applied (and in which case it should remain as
is).

> The title of your bug report is also curious.  What happens if you
> did
>
>     git branch -m master

that works as expected

  git reset --hard init
  seq 1 3 >> bar && git add bar && git commit -m main
  git tag -f x
  seq 4 6 >> bar && git add bar && git commit -m bar
  seq 7 9 >> bar && git add bar && git commit --fixup :/main
  git branch -m master
  git -c sequence.editor=: rebase --autosquash --interactive x

but changing branch -m to switch -c reproduces the bug

  6650ace (HEAD -> master) bar
  7835cd5 (tag: x) main
  368ed2f (tag: init) init

Hope this better clarifies what is going on!