branch - Git rebase subtree

Question

Suppose I have the following scenario:

    o (master)   
   /       o--o (WIP1)
  /       /
 o--o--o--o--o--o (WIP2)
(X)       
           o--o (WIP3)

Is there a git command which creates a new branch so that it contains the subtree after branch X? I want to perform a "large rebase", I want the three WIP branches rebased on master.

I know I can do that with some Bash scripting but I'd like to know how to do that using a git command.

Answer 1

There is no single git command for that. You will have to do some manual work. In your situation:

    o (master)   
   /        o--o (WIP1)
  /        /
 X--o--o--B--o--o (WIP2)
           
            o--o (WIP3)

You first rebase WIP1 onto master:

git rebase --onto master X WIP1

which will lead to this:

               o--o (WIP1)
 (master)     /
    o--o--o--B’
   /   
  /        
 X--o--o--B--o--o (WIP2)
           
            o--o (WIP3)

If you now run git rebase --onto master X WIP2, you get this structure:

                o--o (WIP1)
 (master)      /
     o--o--o--B’
    / 
   /   o--o--B’’--o--o (WIP2)
  /        
 X--o--o--B--o--o (WIP3)

This is probably not what you want, so now you should rebase WIP2 and WIP3 on B’:

git rebase --onto B’ B WIP2 
git rebase --onto B’ B WIP3 

which will lead to this:

                  o--o (WIP1)
(master)         /
    o--X--o--o--B’--o--o (WIP2)
                 
                  o--o (WIP3)