How to change initial commit of branch after filter-branch

Question

After a filter-branch on master (to add sign-off), I have this :

A-B-C-D-E-F (master)

A'-X-Y-Z (branch xxx)

where A' is the old initial commit. I want to "reconnect" my branch "xxx" to master, to initial commit A to have something like this :

A-B-C-D-E-F (master)
 \
  X-Y-Z (branch xxx)

How to do that ? Thanks

Answer 1

3-steps solution with backup option included :

# create a backup for the branch
git checkout -b backup-xxx xxx

# force position of branch xxx at A
git branch -f xxx A

# get the commits you wanted from the backup branch
git checkout xxx
git cherry-pick X Y Z

You'll have backup-xxx in the state xxx was before the operations, just in case you regret your move later.

Backup plan :

# to restore branch xxx in its previous state
git branch -f xxx backup-xxx