Re: [RFC PATCH 0/1] rebase --onto detection of already applied commits

[Junio C Hamano <gitster@pobox.com>]

Cristian Ciocaltea <cristian.ciocaltea@collabora.com> writes:

> Let's consider the following operation:
>
>   git rebase --onto new-base upstream feature
>
> where 'feature' contains a few commits on top of 'upstream' which need to be
> rebased onto 'new-base'.

Isn't it what "git rebase new-base feature" for?  "My 'feature'
forked from where 'new-base' came from but they updated 'new-base'
so I do not know if some of what I had in my 'feature' is in
theirs. Please forward port what is still left in 'feature' on top
of updated 'new-base' that I just got from them".

The primary reason why we have an explicit "--onto" is so that
"rebase" is used just like

	git checkout --detach new-base
	git cherry-pick upstream..feature
	git checkout -B feature

to deal with a different situation, i.e. "My 'feature' forked from
'upstream', and I have a commit 'new-base'.  Just transplant the
whole thing on top of it", without having to worry about "what is
already in new-base?" at all.  After all, 'new-base' may not have
ANY ancestry relationship with the 'upstream', so "inspect commits
in the range upstream..new-base to exclude those that are the same
as the ones in upstream..feature" is not a well defined operation.