Git: how to use rebase with theirs strategy

Question

Basically, I just want to (re)set the parent (let\'s say to commit A) of a specific commit (commit B) which is the root commit of some branch x

Answer 1

I'm not entirely sure I understand your question, but if your aim is to go from this:

o C (X)
|
o B

o A

to this:

o C' (X)
|
o B'
|
o A

then git replace --graft B A should do what you want.

N.B. B and B' have the same filetrees as each other, but different commit hashes because their parent commits are different. Likewise C and C'.

Why this has to be done via git replace --graft rather than git rebase -s theirs, I don't know. Presumably it is for hysterical raisins.

Also see: this answer to How do git grafts and replace differ? (Are grafts now deprecated?).

Answer 2

rebase isn't designed for what you want to do. The other poster was correct; what you want to do is set up a graft to attach B to A, then run git filter-branch to bake it into the commits. An example of this exact use case can be found in the git filter-branch manpage.