Rebase onto branch without common ancestor

Question

I have a tree that looks as follows:

A--B (master)

C (newbase)

It contains two branches without common ancestor. Commit C is in fact a baseline for A, a guy who was importing it from old control version system just had forgotten to import it.

I would like to rebase branch so it would look as follows:

C--A--B

I tried

git checkout master
git rebase --onto newbase A -s recursive -Xtheirs

but it results in

C--B

Answer 1

You need to use git rebase --root (plus whatever additional options you like, in this case your --onto and strategy options).

(I have only tested this with interactive rebase, but it is documented as working with all forms of rebase.)