git filter branch - Prune empty merge commits from history in Git repository

Question

I have cleaned up our Git repository quite a bit, we need to remove big parts from the history. I do this using:

git filter-branch --prune-empty --tree-filter 'rm -rf some_stuff'

The --prune-empty flag will remove commits that are left empty after the process, except commits with multiple parents (merge commits). Even if the branch being merged in contains absolutely nothing, and the merge adds nothing to the tree.

How do I also prune these empty merge commits from the history?

Answer 1

This is superior to the rebase solution because it preserves committer info, committer dates, and non-empty merges of the original history.

git filter-branch --prune-empty --parent-filter 
    'sed "s/-p //g" | xargs -r git show-branch --independent | sed "s/</-p /g"'

This is inspired by the same thread on the kernel mailing list than Lucas' solution. However it does not require Ruby and is a one-liner. It does require GNU versions of xargs and sed though.