Subject: Re: Git Evolve

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Tue, 02 Oct 2018 11:11:11 +0200

On Tue, Oct 02 2018, Taylor Blau wrote:

> Hi Stefan,
>
> On Sat, Sep 29, 2018 at 04:00:04PM -0700, Stefan Xenos wrote:
>> Hello, List!
>>
>> I'm interested in porting something like Mercurial's evolve command to
>> Git.
>
> Welcome to Git :-). I think that the discussion in this thread is good,
> but it's not why I'm replying. I have also wanted a Mercurial feature in
> Git, but a different one than yours.
>
> Specifically, I've wanted the 'hg absorb' command. My understanding of
> the commands functionality is that it builds a sort of flamegraph-esque
> view of the blame, and then cascades downwards parts of a change. I am
> sure that I'm not doing the command justice, so I'll defer to [1] where
> it is explained in more detail.
>
> The benefit of this command is that it gives you a way to--without
> ambiguity--absorb changes into earlier commits, and in fact, the
> earliest commit that they make sense to belong to.
>
> This would simplify my workflow greatly when re-rolling patches, as I
> often want to rewrite a part of an earlier commit. This is certainly
> possible by a number of different `git rebase` invocations (e.g., (1)
> create fixup commits, and then re-order them, or (2) mark points in your
> history as 'edit', and rewrite them in a detached state, and I'm sure
> many more).
>
> I'm curious if you or anyone else has thought about how this might work
> in Git.

I've wanted a "git absorb" for a while, but have done no actual work on
it, I just found out about it.

I think a combination of these two heuristics would probably do the
trick:

 1. If a change in your "git diff" output has a hunk whose lines overlap
    with an earlier commit in the @{u}.. range, we do the equivalent of
    "git add -p", select that hunk, and "git commit --fixup <that
    commit>". We fixup the most recent commit that matches (otherwise
    commit>we'd conflict).

 2. Have some mode where we fall back from #1 and consider changes to
    entire files, if that's unambiguous.

The neat thing about this would be that you could tweak how promiscuous
#1 would be via the -U option to git-diff, and #2 would just be a
special case of -U9999999999999 (we should really add a -Uinf...).

Then once you ran this you could run "git rebase -i --autosquash" to see
how the TODO list would look, and optionally have some "git absorb
--now" or whatever to do the "git add -p", "git commit --fixup" and "git
rebase --autosquash" all in one go.

> [1]: http://files.lihdd.net/hgabsorb-note.pdf