一次性重新分支带有子分支的分支

Question

I often have sub-branches on a branch that I want to rebase onto the mainline. Consider this:

* (Mainline)
*
*
| * (topicA_Branch3)
| *
| *
| * (topicA_Branch2)
| *
| *
| * (topicA_Branch1)
| *
| *
|/
*
*

I want to move all three of these topicA branches onto mainline. Currently, I know two ways to do this:

1. While on topicA_Branch3 , execute the command, git rebase Mainline .

   a. At this point, I would have to delete topicA_Branch1 and 2 and manually re-create the branches on the correct commits on the now rebased topicA_Branch3 .

2. Another way would be to do three separate commands:

   a. While on topicA_Branch1 , do git rebase Mainline .

   b. git rebase --onto topicABranch1 <topicA_Branch1-old-SHA> topicABranch2

   c. git rebase --onto topicABranch2 <topicA_Branch2-old-SHA> topicABranch3

   d. This is kind of cumbersome...

Is there a command that I want that will rebase a branch and bring it's sub-branches with it?

To be clear, I want to end up with this:

* (topicA_Branch3)
*
*
* (topicA_Branch2)
*
*
* (topicA_Branch1)
*
*
* (Mainline)
*
*
*
*

Answer 1

I am afraid this is cumbersome, I am not aware of any existing do it all command. But it is scriptable. The commands to get from the first to second illustration are

for i in topicA_Branch1 topicA_Branch2 topicA_Branch3
do
    git branch $i._OrIg_ $i
done
# First branch directly
git rebase --onto Mainline topicA_Branch1
# Remaining branches
git rebase --onto topicA_Branch1 topicA_Branch1._OrIg_ topicA_Branch2
git rebase --onto topicA_Branch2 topicA_Branch2._OrIg_ topicA_Branch3

After you have verified things are correct you can delete the *._OrIg_ branches. With this you only have to keep the script up to date with the names and sequence of the branches.

Update: You can create a list of all the branches, in sequence, with

 git rev-list --reverse --simplify-by-decoration Mainline..topicA_BranchN \
 | git name-rev --stdin --name-only

Here you are only dependent on knowing the name of the last topicA_BranchN branch, eg topicA_Branch3 in your example.

Answer 2

You could use git filter-branch with an appropriate --parent-filter . Something like this:

git filter-branch --parent-filter 'sed -e "s/X/Y/"' --tag-name-filter cat -- branchA branchB branchC

Here X should be the hash of the first commit that is not on mainline but is on the other branches, and Y could just be HEAD or Mainline or the hash of the current head of Mainline ...

Answer 3

What about that:

 a. While on `topicA_Branch1`, do `git rebase Mainline`.

 b. `git rebase --onto topicABranch1 topicABranch1@{1} topicABranch2`

 c. `git rebase --onto topicABranch2 topicABranch2@{1} topicABranch3` 

 d. ...

This might easily be automated. The syntax topicABranch1@{1} means "the last known state of topicABranch1 before the rebase"