feat(reword): Add --fixup flag to git branchless reword

[claytonrcarter]

This adds a --fixup option to git reword, providing a convenient way to turn existing commits into fixup! commit. With this, instead of doing something like git reword <commits to reword> -m 'fixup! <paste title of commit to fixup>', you can now do git reword <commits to reword> --fixup <commit to fixup> and reword will handle the rest, including some error checking.

I've been using this for a few weeks and it's been working well. My only remaining concern about this is that the CLI option docs and error messages feel a little clunky because it's hard to talk to about "the commit being fixed up" vs "the commits that will become fixup! commits". As usual, suggestions are welcome!

[claytonrcarter]

I suppose that instead of iter().any(...) I could instead just use a single dag query; perhaps like

commits.intersection(
    dag.query.descendents(
        commit_to_fixup.get_oid().into()
    )
) == commits

[claytonrcarter]

Nevermind this; I thought that NameSet allowed for ==/!= but it doesn't. I'll leave it as is unless you have a suggestion for a more intuitive way to check this.

[arxanas]

I think you could write this as dag.query().common_ancestors(CommitSet::from(commits))?.contains(commit_to_fixup)? or something like that. I don't know why there isn't a .equals() method or similar.

[arxanas]

I'm okay with merging this as-is for now, but maybe we should invent a more straightforward method to fixup commits? For example, it would be more direct if you could write git amend <target> --from <revs> or something like that. Now that we can move exact commits, it should be possible to move all of the <revs> right on top of <target>, and then create a RebaseCommand::Fixup to handle the fixing up. The implementation for in-memory rebases doesn't seem too bad: you would basically do a pick but call amend_commit instead of cherry_pick_fast.

[arxanas]

I think you could write this as dag.query().common_ancestors(CommitSet::from(commits))?.contains(commit_to_fixup)? or something like that. I don't know why there isn't a .equals() method or similar.

[arxanas]

I guess a theoretical fixup command should be part of git move; git amend should probably be for working copy changes only.

[claytonrcarter]

Thanks for the review, @arxanas!

maybe we should invent a more straightforward method to fixup commits?

Oh, I'm all over that idea. This just seemed like an easier place to start. 😄 I had been thinking about a separate git combine command, but seeing you mention in it the context of git move makes a lot of sense as all of the "move exact or subtree" plumbing is already in place there.