如何删除/替换 git subtree commit 及其合并提交？

Question

I have a history tree like this:

I found that I merged the wrong version of library in (2) commit and want to remove (2) and (3) from history to get that

and then create another subtree above (7) but ideally, I want to force replace commit (2) with another version of the library with forcefully rewritten history of my commits (Like if i did rebase -i and mark commits squash with replacement one)

Yellow commits are merge commits created by a subtree command
Red commits are squashed subtree commits

Answer 1

You can make a new commit 2' which contains the other version of the libray. Then merge it with 1. This makes a new commit 3'. Then you can rebase 5 and 7 onto 3' which makes new commits 5' and 7'. This gives you the desired result.

Of course, the commit IDs of 3', 5' and 7' are different from the IDs of 3, 5 and 7 as you cannot substitute one of the parents of a commit without changing its sha1 checksum.

Answer 2

Here is one way to replace the merge introduced in 2 with whatever commit you want :

• run git rebase --rebase-merges -i 1 (obviously : replace 1 with the sha for commit 1 ...)
• the scenario will be a bit more intricated than you may have seen for a simple rebase -i :

## here is a sample I got, from a history with two merges :
label onto

# Branch br2
reset [new root]
pick df98219 br2
label br2

# Branch br4
reset [new root]
pick 3a30d4d br4
label br4

## the linear history for master is described here :
reset onto
merge -C f47b992 br2 # Commit 3
merge -C e198adf br4 # Commit 5

• in the last section, replace the line mentionning your commit 3 with break :

...

reset onto
## remove this line to drop the faulty merge commit :
# merge -C f47b992 br2 # Commit 3
## add a 'break' instruction to stop for editing :
break
merge -C e198adf br4 # Commit 5

• when the rebasing pauses, create the commit you wish to have
• then run git rebase --continue

If you have any problem during the rebase, you can always run git rebase --abort , and restart from the beginning.