What are the git commands to rebase a child-branch whose parent branch has been rebased?

NOTE: This is different from the question here Is there a way to rebase a child branch after the parent has been rebased? in that the child-branch is not “up to date” with the parent branch at the time the parent is rebased.

Multiple git commit graphs shown to illustrate my question and understanding and the commands that I know to perform.

This has happened multiple times where we have a devel branch on which a large feature (feature/one branch) is being worked by multiple people. To maintain sanity, each developer branches off of feature/one and performs a sub-task. Periodically, the sub-tasks are merged into feature/one.

Initial Commit Graph. Branches are: devel is off of main, feature/one is off of devel, and more-work is off of feature/one. Since main has no impact on the remainder of this question it is not shown in any subsequent commit graphs.

o--o--o (main) 
        
        A---B---C (devel) 
              
              D---E---F (feature/one) 
                    
                    G---H (more-work) # one sub-task.

The feature/one branch is ready to be merged so it must first be rebased. To do this the git rebase command is used as follows:

git checkout devel 
git pull 
git checkout feature/one 
git rebase devel

These command ensure you have the latest devel branch and then you rebase onto it.
2. The resulting git commit graph is:

A---B---C (devel) 
         
         D2--E2--F2 (rebased feature/one) 
        
        D---E---F (original feature/one, now detached from feature/one branch) 
              
              G---H (more-work)

This gives the desired result and is the normal case I’ve used many times successfully.

NOTE: The hash D2 represents the commit D but with a new hash, similarly with E2 and F2.

Next, I want to merge more-work into feature/one.

IMPORTANT NOTE: IMO cherry-pick would be simpler to achieve the desired result.

What follows are the multiple (2 steps) required to allow git rebase –onto feature/one to be used. This means that more-work needs to be rebased onto original feature/one first (to include the F commit), and then onto rebased feature/one branch.

First rebase onto original feature/one to include the F commit. I’m not sure of the git command to do this so it is not shown, but the resulting git commit graph would look like this:

A---B---C (devel) 
    |    
    |    D2--E2--F2 (rebased feature/one) 
    |   
    |   D---E---F (original feature/one, now detached from feature/one branch) 
    |         
             G---H (more-work) 
         
      D3---E3---F3 (original feature/one rehashed a 2nd time) 
                  
                  G2---H2 (more-work (rebased))

At this point, the more-work rebased branch now includes the change made in hash F which allows the use of the git rebase --onto feature/one command as follows

git rebase --onto feature/one F3-hash more-work

After the above git command we have the following graph

A---B---C (devel) 
    |    
    |    D2--E2--F2 (feature/one after rebase) 
    |              
    |              G3---H3 (more-work (rebased-2nd-time)) 
    |      
    |     D---E---F (original feature/one, now detached from feature/one branch) 
    |           
               G---H (more-work) 
         
      D3---E3---F3 (original feature/one rehashed a 2nd time) 
                  
                  G2---H2 (more-work (rebased))

It’s that simple. ????

Is my understanding of how to rebase a child-branch who parent-branch has been rebased correct?

Searching for a solution

The following are relevant links I’ve found to form my understanding of how git rebase works.

Is there a way to rebase a child branch after the parent has been rebased? – This question/answer different from the question here in that the child-branch is not “up to date” with the parent branch at the time the parent is rebased. And my belief is the multiple rebases are needed as I illustrate in my commit graphs.
How can I change my parent branch? This is documented in the git documentation at https://git-scm.com/docs/git-rebase and shows how the topic branch can be moved from the next branch (aka devel in my example) to the master branch.

 o---o---o---o---o  master
         
          o---o---o---o---o  next
                           
                            o---o---o  topic

The biggest difference between this and my question is that my example does not have topic coming off of the HEAD of next.

The command to rebase onto master is simple.

git rebase --onto master next topic

which results in

    o---o---o---o---o  master
        |            
        |             o'--o'--o'  topic
         
          o---o---o---o---o  next

Other searches were answering other questions

Rebasing a branch that has been branched from – not relavent.
git rebase master with child branches – this appears different (to me)

Is my understanding of how to rebase a child-branch who’s parent-branch has been rebased correct?

Correct? kind of. Ideal? no.

The rebase of more-work onto rebased feature/one can and should be done in one pass. This is the exact scenario for which rebase --onto was created.

Initial situation

* 9a7c139 (HEAD -> more-work) H
* 922d375 G
| * 978c327 (feature/one) F
|/
* bce6cab E
* 3cf018e D
| * 9c2aeeb (devel) C
|/
* 0c5017f B
* 8914d3a A
* fbc5771 (master) Initial commit

Rebasing `feature/one` on `devel`

git switch feature/one && git rebase devel

* 6f50942 (HEAD -> feature/one) F
* 3cad97b E
* d0f8a97 D
* 9c2aeeb (devel) C
| * 9a7c139 (more-work) H
| * 922d375 G
| * bce6cab E
| * 3cf018e D
|/
* 0c5017f B
* 8914d3a A
* fbc5771 (master) Initial commit

Rebasing `more-work` onto `feature/one`

E_sha1=bce6cab 
git rebase --onto feature/one $E_sha1 more-work

* 6cb28df (HEAD -> more-work) H
* 1fc20f8 G
* 6f50942 (feature/one) F
* 3cad97b E
* d0f8a97 D
* 9c2aeeb (devel) C
* 0c5017f B
* 8914d3a A
* fbc5771 (master) Initial commit

Yes, git rebase --onto feature/one F3-hash more-work is the canonical way to do it. You might also try a simple git rebase feature/one more-work – Git is usually smart enough to figure out which commits are already part of the new parent.

The alternative is rebasing both branches at the same time, if you already know that one branch is a direct descendant of the other and you need them both rebased to a new upstream:

git rebase --update-refs devel more-work`

This will rebase all commits between devel and more-work, and update your feature/one ref (i.e. branch). The resulting history will be:

A---B---C (devel) 
          
          D2--E2--F2 (rebased feature/one) 
                     
                     G2---H2 (rebased more-work)

Filed under: Kiến thức lập trình - @ 22:04

Thẻ: gitrebase

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Danh mục

What are the git commands to rebase a child-branch whose parent branch has been rebased?

Searching for a solution

Initial situation

Rebasing `feature/one` on `devel`

Rebasing `more-work` onto `feature/one`

Danh mục

Searching for a solution

Initial situation

Rebasing feature/one on devel

Rebasing more-work onto feature/one

Rebasing `feature/one` on `devel`

Rebasing `more-work` onto `feature/one`