Subject: Re: Idea: Add a filter option to 'git rebase'

From: Johannes Schindelin <[email-masked]>
Date: Mon, 23 Jan 2017 12:57:18 +0100 (CET)

Hi,

On Sat, 21 Jan 2017, Philip Oakley wrote:

> From: "Thomas Braun"  Friday, January 20, 2017 11:35 PM
> > Am 20.01.2017 um 23:28 schrieb Philip Oakley:
> > > A recent question on stackoverflow
> > > http://stackoverflow.com/questions/41753252/drop-commits-by-commit-message-in-git-rebase
> > > sought to remove automatically commits that could be identified by
> > > relevant words in the commit message.

Interesting. As long as those magic words appear in the oneline, I would
simply call the command ":%s/^pick.*<magic-word>/#&/".

But that is neither scripted nor does it work with magic words elsewhere
in the commit message (let alone more sophisticated filtering based on,
say, authorship or magic words in the diff's "+" lines).

> > > I had thought that the ubiquitous `git filter-branch` should be able
> > > to do this sort of thing. I was wrong. (It was pointed out to me
> > > that...) The man page notes that removing a commit via filter-branch
> > > does not remove the changes from following commits and directs
> > > readers to using `git rebase(1)`.

Right, filter-branch never cherry-picks patches, but instead complete
trees.

> > > However the rebase command does not have any filter option to allow
> > > the automatic population of its TODO list with the appropriate
> > > pick/edit/drop/etc. values.
> >
> > Well you can use an arbitrary shell command as editor, so something
> > like
> >
> > $ GIT_SEQUENCE_EDITOR="sed -i -re 's/^pick /edit /'" git rebase -i master
> >
> > will change pick to edit of all commits.
> >
> > Maybe that can be mentioned in the man page of rebase?

Please note that using a script instead of a command, you can do really
sophisticated things including sophisticated re-writing of the edit script
as well as calling the GIT_EDITOR in the end to re-establish
interactivity. I do exactly that in my Git garden shears [*1*].

> I had been more thinking of a process that passed single sha1's to the
> filter on each pass through the rebase list, so that the coding was
> simpler, plus the --interactive could be used, if required, for final
> refinement (gitk being handy for that).
> 
> However, a mention in the man pages would be zero code cost, and could
> help.

In the (frustratingly) long run, we will want to add a command-line option
that allows overriding the edit script generation, paired with a
command-line option that generates the current version of the edit script
(in my rebase--helper work that is still under review, the latter option
already exists).

That way, you have full flexibility and could even generate the entire
edit script from scratch, rather than letting rebase -i generate one and
then filtering it.

Ciao,
Johannes

Footnote *1*:
https://github.com/git-for-windows/build-extra/blob/master/shears.sh