Tout se résume à un git reset --soft branch_b
au-dessus d'une branche temporaire basée sur la branche_a, et le résultat est renvoyé à la branche_b.
Il s'agit d'une marche à suivre, étape par étape, à travers le processus :
#Start out on the branch with the code we want
git checkout branch_a
#create tmp branch same as branch_a (so that we don't change our local branch_a state during the operation)
git branch tmp
#working directory has all the code that we want, on tmp branch
git checkout tmp
# Change the branch head to the branch we want to be on. All the delta
# between the current source code and branch_b is now staged for commit
git reset --soft branch_b
# Move away from tmp, so our commit will go directly to branch_b
git checkout branch_b
# Now you can examine the proposed commit
git status
# Add the delta we want to the branch
git commit
# Sanity check that the branches have the same content now (should return an empty line)
git diff branch_A..branch_b
# Remove tmp, we don't need it anymore
git branch -D tmp