How to squash/fixup commits very far apart? Non-interactive rebase

Question

Let's say I have commit 1, 2 ... 10.000.000, and I want to fixup commit 8.000.000 to 1.000, e.g sha2 is merged into sha1, keeping sha1's commit message, and keeping all other commits in order, where sha1 and sha2 are very far from each other and very far from HEAD.

This question has been asked several times, but every time it is assumed that the commits are close to each other and close to HEAD and git rebase -i HEAD~5 can be used. I just don't see how that is manageable as the number of commits scale.

I am hoping for an answer along the lines of git rebase --fixup sha2 --onto sha1

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Squash Git commits *non-interactively* with git rebase wants to squash all commits not shared between two branches. I want to squash/fixup 1 commit into 1 other commit, keeping all other commits the same.

Do I understand correctly: you want to squash the 8,000,000th commit into the 1,000th commit and keep the commit message of the 1,000th commit? (I am also assuming that 1 is the oldest commit and 10,000,000 is the youngest---most recent---commit.) — j6t, Feb 15 '22 at 07:27
Yes. 1 is the oldest commit, and 10.000.000 is the newest. I want to squash (or fixup) 8,000,000th into the 1,000th — Olsgaard, Feb 15 '22 at 09:57

score 2 · Answer 1 · answered Feb 15 '22 at 05:41

2

I would suggest the following solution.

git checkout <COMMIT_HASH YOU WANT TO BE SQUASHED>
git reset --soft HEAD~1
git stash

This will stash changes of commit you want to squash. Then:

git checkout master
git rebase -i <BASE COMMIT HASH -1>

In the opened editor

edit <COMMIT HASH YOU WANT TO MAKE BASIC>
...
drop <COMMIT HASH YOU WANT TO SQUASH>

After rebase process stops on the commit you marked as "edit", then:

git stash pop
git add -A
git commit
git rebase --continue

answered Feb 15 '22 at 05:41

Mike

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`git rebase -i ` won't this open a file with just under 8 million lines as there are millions of commits between sha1 and sha2? – Olsgaard Feb 15 '22 at 10:00
1

Yes, indeed, it will cause this behavior. – Mike Feb 15 '22 at 10:50

score 1 · Answer 2 · answered Feb 15 '22 at 11:18

You use git rebase -i and reorder the lines and mark the one you want to squash into the earlier one with fixup. Yes, this opens a file with millions of lines.

Instead of doing it interactively, you can set sequence.editor to a script that modifies the lines, for example:

git -c sequence.editor='f () {
   sed -i -e '1000a fixup abcde12345' -e '8000000d' "$1"
   }; f' rebase -i basecommit

Here, abcde12345 is the commit ID of the 8,000,000th commit.

If you do not want to depend on counts, but use commit IDs instead, you can do:

git -c sequence.editor='f () {
   sed -i -e '/pick 54ab32/a fixup abcde12345' -e '/pick abcde123/d' "$1"
   }; f' rebase -i basecommit

Note that the IDs after /pick must be given no longer than they appear in the file (typically only 6 characters, but probably more in your case where you have millions of objects).

How to squash/fixup commits very far apart? Non-interactive rebase

2 Answers2