Git Squash by author - All author commits into a single commit

Question

I am trying squash many commits into a single one, the problem is that I need do that by author (name or email).

The case:

Lets say I have a branch called feature-a, in this branch I have many commits for many authors. How can I squash all commits by author (email for example) into a single commit. I want do that to be able to merge all author commits into master.

Any help here?

Thanks in advance

Answer 1

Be careful rewriting history

The end result you want might be possible if you create branches for each author, cherry-pick the commits from each author into the right branch, then squash those changes. However, I don't think that will work if these commits meaningfully depend on each other.

If you have a series of commits:

            Author1                Author2                Author1
version1 ---commit---> version2 ---commit---> version3 ---commit--->...

If you were to try to extract the changes from Author2, and apply them to version1, there's a good chance it won't make sense (For example, if Author2 modifies code that Author1 created).

Answer 2

With Kenkron 's caveats in mind, you could do a:

SORTED_GIT_LOGS=$(git log --pretty="format:%an %H" master..feature_a | sort -g | cut -d' ' -f2); \
IFS=$(echo -en "\n\b"); for LOG in $SORTED_GIT_LOGS; do \
    git cherry-pick $LOG; \
done | less

The git log --pretty="format:%an %H" master..feature_a | sort -g git log --pretty="format:%an %H" master..feature_a | sort -g would sort the logs of the feature_a commits (not the ones from master because of the master..feature_a syntax)

You would still need to do an interactive rebase to squash the (now ordered by author) commits on master .

Answer 3

I needed to do a similar rewrite on an unnecessarily large repository while the repo was offline. The approach I took was trying automated 'interactive' rebase using GIT_SEQUENCE_EDITOR which is covered in this answer by @james-foucar & @pfalcon.

For this to work well, I found it better to first remove the merges from the section of the history being rewritten. For my own case, this was done using lots of git rebase --onto which is covered amply in other questions on StackOverflow.

I created a small script generate-similiar-commit-squashes.sh to generate the pick & squash commands so that consecutive similar commits would be squashed. I used author-date-and-shortlog to match similar commits, but you only need author (my gist has a comment about how to make it match only on author).

$ generate-similiar-commit-squashes.sh > /tmp/git-rebase-todo-list

The output looks like

...
pick aaff1c556004539a54a7a33ce2fb859af0c4238c foo@example.com-2015-01-01-Update-head.html
squash aa190ea2323ece42f1cd212041bf61b94d751d5c foo@example.com-2015-01-01-Update-head.html
pick aab8c98981a8d824d2bc0d5278d59bc1a22cc7b0 foo2@example.com-2015-01-28-Update-_config.yml

The repository was also full of self-reverts with the same style 'Update xyz' commit messages. When squashed, they resulted in empty commits.

The commits I was merging had identical commit messages. git rebase -i offers a revised commit message with all squashed commit messages appended, which would have been repetitive. To address that, I used a small perl script from this answer to remove duplicate lines from the commit message offered by git rebase . It is better in a file, as it will be used in a shell variable.

$ echo 'print if ! $x{$_}++' > /tmp/strip-seen-lines.pl

Now for the final step:

$ GIT_EDITOR='perl -i -n -f /tmp/strip-seen-lines.pl ' \
  GIT_SEQUENCE_EDITOR='cat /tmp/git-rebase-todo-list >' \
  git rebase --keep-empty -i $(git rev-list --max-parents=0 HEAD)

Despite using --keep-empty , git complained a few times through this process about empty commits. It would dump me out to the console with an incomplete git rebase . To skip the empty commit and resume processing, the following two commands were needed (rather frequently in my case).

$ git reset HEAD^
$ GIT_EDITOR='perl -i -n -f /tmp/strip-seen-lines.pl ' git rebase --continue

Again despite --keep-empty , I found I had no empty commits in the final git history, so the resets above had removed them all. I assume something is wrong with my git, version 2.14.1 . Processing ~10000 commits like this took just over 10 minutes on a crappy laptop.