Add support for rebase --onto

[pkernevez]

Hi,

As explain in this ticket #126 it should be nice to add support for rebase --onto.
When working with a lot of stack branch it really efficient to use rebase --onto instead of cherry picking (more efficient in term of manual actions but also in term of conflict resolution).
This is a common need when working on big epics through several small feature branch and PR. In this case in conjunction with --update-ref all the bracnches build on top of the first are move at the same time.

In term of ui, I think it could be done by selecting a range (from::to) and right click on another commit (other).
In this case the associated git command should be:
git rebase --onto $other $from $to

We can also imagine to not start with a range but a single select commit (start) and right click on another commit (other).
In this case to command should be:
git rebase --onto $other $from $my_current_branch

[DanPristupov]

I think you can use interactive rebase and drop the undesired commits (usually, the bottom ones).

[pkernevez]

No you can't for my use case.

There are several specific use cases for rebase onto, but I will focus on my main one:
You are working (alone) on several chained branches:

You have to amend a commit a the first branch (let's say C1 becoming C1' in my example):

You now need to rebase commit C2 (included) to C3 onto C1.
If you try to use a classical rebase, you will have to solve the conflict between C1 and C1' because C1 and C1' modify the same files/lines (of course it's just an amendment).
With `git rebase --update-ref --onto C1' C1 feat3'

[DanPristupov]

If you try to use a classical rebase, you will have to solve the conflict between C1 and C1' because C1 and C1' modify the same files/lines (of course it's just an amendment).

As I said, use IR to rebase on C1' and drop the bottom commit (C1).

[pkernevez]

I can't use (or I don't knowh how) --update-ref with an IR

[DanPristupov]

No, Fork doesn't support --update-ref, but this is unrelated to --onto

[pkernevez]

It's already 'supported' by fork when you change your git conf like that:

[rebase]
        updateRefs = true

Rebase onto is quite fastidious to use because we need to retrieve the 3 relevant commits manually, it should be nice to have them filled by fork UI.