find the "rebase -m" starting point

Question

Recently I am using

git checkout dev_branch -b merge_branch
git rebase -m merge_branch master
git checkout master
git rebase merge_branch

to do a merge rebase. As the help document indicates, merge_branch is first reset to HEAD of master and then the new commits in original dev_branch is played back one by one to the new branch.

Several days later I want to find where is the "starting point" of this rebase merge. I can find the first delta commit in dev_branch using

git merge-base master dev_branch // Get an SHA_root of the common ancestor
git log --reverse -1 <SHA_root>..dev_branch  // Get an SHA_delta of the first delta commit

But I don't find a way to locate where is the merged version of

git branch --contains <SHA_delta>

But find it is only in "dev_branch", not in "master_branch", though actually it has been merged.

In another word, the same commit with different parent (like the situation using cherry-pick) are with different SHA. Is there a way that git can recognize them as actually identical?

Answer 1

This is what git cherry does.

In a situation where topic consisted of three commits, and the maintainer applied two of them, the situation might look like:

$ git log --graph --oneline --decorate --boundary origin/master...topic
* 7654321 (origin/master) upstream tip commit
[... snip some other commits ...]
* cccc111 cherry-pick of C
* aaaa111 cherry-pick of A

[… snip a lot more that has happened …]

| * cccc000 (topic) commit C
| * bbbb000 commit B
| * aaaa000 commit A
|/
* 1234567 branch point

In such cases, git cherry shows a concise summary of what has yet to be applied:

$ git cherry origin/master topic
- cccc000... commit C
+ bbbb000... commit B
- aaaa000... commit A

Here, we see that the commits A and C (marked with -) can be dropped from your topic branch when you rebase it on top of origin/master, while the commit B (marked with +) still needs to be kept so that it will be sent to be applied to origin/master.