git：使用父分支重置先前的提交

Question

Suppose I've a parent branch in my repository and I make another branch named derived from it.

git checkout -b derived

Now the derived branch contains all the commits of my parent branch. I add two more commits (commit D1 and D2) to my derived branch. My derived branch is two commits ahead of parent branch.

Now I amend some previous commits in the parent branch and add new commit "Pn". After this, for some reason I want my derived branch to exactly look like this

Amended commits from parent branch ---> Pn ---> D1 ----> D2

I tried git rebase parent from my derived branch but it is giving a lot of merge conflicts. Is there any easier way to just reset all the commits before D1 and D2 exactly as the parent branch.

Answer 1

You do want to use git rebase , you just want it to stop at the point where you used to share commits with the other branch.

That is, you had:

...--Pl--Pm--Pn   <-- parent
               \
                D1--D2  <-- derived

Since both amending and git rebase work by copying commits, what you have now is:

          Pn'--Po--Pp   <-- parent
         /
---Pl--Pm--Pn   <-- parent@{some-number}
             \
              D1--D2   <-- derived

where the memory that parent used to contain original commit Pn is in the reflog for parent (and probably in the reflog for HEAD ).

You can manually specify that git rebase should stop at Pn by using:

git rebase --onto parent <hash-of-Pn>

(ie, specify the stopping point for the <upstream> as a commit hash, and use --onto to make the copies go after the new tip of parent ). You can also use commit-relative syntax ( derived~ number ) as in jpaugh's answer to identify Pn . See the gitrevisions documentation for details.

Git also now has --fork-point . Using --fork-point , you can have Git automatically root around through the reflog for parent to attempt to locate Pn . Here you would run:

git rebase --fork-point parent

which tells Git to do this rooting-around, and rebase onto parent but drop commit Pn .

Exactly when and whether --fork-point works is a bit tricky since reflog entries expire (after 30 or 90 days by default).

Answer 2

Not as such. The commits D1 and D2 rely on every commit before them, including the ones you don't want. But, here are things you can try:

• git rebase --onto parent derived~3 derived

  Rebase derived onto the new parent. This sets the merge base explicitly to derived~3 , the commit that was the HEAD of parent when you created the derived branch. This will reduce the conflicts, and will avoid reintroducing the old changes.

  Normally, git figures this out automatically, but since you've amended these commits, git can't tell that any relationship exists between them — it can't tell that commit A' is an amended variant of commit A .

• Cherry pick D1 and D2 onto a new branch

   git branch derived-new parent git checkout derived-new git cherry-pick D1 D2 git branch -m derived derived-old # Save the old branch until you're ready to delete it git branch -m derived-new derived 

• Do an interactive rebase of the derived branch, removing the earlier commits that you don't want, and then seeing what happens. This may also generate a lot of extra conflicts, and force you to git rebase --abort , but if it doesn't, you're scott free... Just rebase onto the new parent again, as above

Answer 3

You should be able to follow these steps:

1. Check out your parent branch
   • git checkout parent
2. Create and check out new branch based off the parent branch
   • git checkout -b derived-modified
3. Use git cherry-pick with derived-modified checked out to move the new commits from derived to derived-modified (this will use the modified parent branch with the commits you have modified/added)
   • git cherry-pick 000aaaa
   • git cherry-pick 000bbbb
   • git cherry-pick 000cccc

This will take, for example, the 3 commits you've made to derived and move them to derived-modified , which contains the modified parent branch. Once you've verified the commits are on derived-modified , you can delete derived and rename derived-modified .

More information on git cherry-pick is available here .