In git, what's the simple way to squash mulitple commits in a head before rebasing it onto another head with ONLY 1 resolve conflict?

Question

I have the following 2 branches, A should be rebased on top of B:

(Ancestor) -> A1 -> A2 -> A3
          \
           -> B1

I'm trying to squash all commits in A into 1 commit:

(Ancestor) -> B1 -> A123

However when I use git rebase with squash commit command, git still tries to rebase one commit at a time, so it start rebasing A1, ask me to resolve conflict, then rebase A2, as resolve conflict again, ... This waste a lot of time in rebasing branches.

My idea rebase would be to squash A1, A2, A3, directly, then only ask to resolve conflict between A3 & another head. I can do it manually with 2 git commands, but this is also not convenient. Is it possible to do it automatically with one command?

Thanks a lot for your help

Answer 1

The number of commands is not really that important, I think, because you can always put however many commands it takes into a script or alias. What matters is the amount of interaction needed.

Thus, I think what you want is a soft reset style squash commit (see here and here) followed by a rebase. To get it down to one interaction, you will need to automate the message made for the first squash commit, probably by concatenating the three (or however many) to-be-squashed commits, and then use an interactive rebase with the sequence editor set to a script of your own that replaces the pick command with reword. Actually writing each of these pieces is something I leave to you, but I'll note that:

• git show --format=%B --no-patch --no-notes <commit> will get you the full commit message for the given commit.

• Replace show with log and a commit range to get several messages; or use git rev-list <range> to get the IDs printed to standard output, then loop using show, to allow you inject your own (varying) text between each. (For fixed text, possibly including additional % conversions, you can simply use the --format argument.)

• The sequence editor can be any script in any language; it just needs to open the interactive rebase commands file, modify it, and write it back out to the file.