7

There seem to be some similar questions already, but none of them are exactly what I want.

Let's say I have commit history like this

* xxxxxxxH (HEAD -> B) Latest commit * (more commits) * xxxxxxxG (B) More commits * xxxxxxxF Merge branch 'master' into B |\ | * xxxxxxxE (master) Another commit on master | * (more commits here) | * xxxxxxxD Commit on master * | xxxxxxxC Another commit * | (more commits here) * | xxxxxxxB First commit on branch A |/ * xxxxxxxA (master) some commit

Now I want to rewrite the history of branch A, potentially merging or editing some commits, but I also want to change the first commit on branch A, and also I want to preserve merges, so that I keep the merge of master into A.

I first intuitively tried git rebase -i -p xxxxxxxB, but obviously that didn't include the xxxxxxxB commit itself. So another attempt was git rebase -i -p xxxxxxxB^ which did include that commit, but now it didn't actually to preserve merges.

Another option that looked promising was --root, but this one starts from the very first commit in the whole repository which is also not what I want.

Is there any way to do what I want?

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18

After longer than I considered reasonable, I was able to get a solution on irc:

git rebase -i -m -r firstCommitInBranch^ does exactly what I need.

From git documentation:

 -r, --rebase-merges[=(rebase-cousins|no-rebase-cousins)] By default, a rebase will simply drop merge commits from the todo list, and put the rebased commits into a single, linear branch. With --rebase-merges, the rebase will instead try to preserve the branching structure within the commits that are to be rebased, by recreating the merge commits. Any resolved merge conflicts or manual amendments in these merge commits will have to be resolved/re-applied manually. (...) The --rebase-merges mode is similar in spirit to --preserve-merges, but in contrast to that option works well in interactive rebases: commits can be reordered, inserted and dropped at will.

and

 -m, --merge Use merging strategies to rebase. When the recursive (default) merge strategy is used, this allows rebase to be aware of renames on the upstream side.

I also missed the part of documentation that said to not use -p together with -i:

 -p, --preserve-merges Recreate merge commits instead of flattening the history by replaying commits a merge commit introduces. Merge conflict resolutions or manual amendments to merge commits are not preserved. This uses the --interactive machinery internally, but combining it with the --interactive option explicitly is generally not a good idea unless you know what you are doing (see BUGS below).
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Note: --rebase-merges is new in Git 2.18.
And see this wonderful answer by VonC for a through story about the origin of --rebase-merges.
preserve-merges was deleted from Git at version 2.34. See Highlights from Git 2.34. Most attempts to use it will exit with a fatal error.

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