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?

Solution 1

I found a very cute little wrapper script around filter-branch here:

https://github.com/pflanze/chj-bin/blob/master/cj-git-filter-branch

Preconds and background here:

http://lists.q42.co.uk/pipermail/git-announce/2011-September/000486.html

Solution 2

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.

Solution 3

I needed to do this after running filter-branch on a copy of ssokolow/profile to separate out ssokolow/lap.

This did a decent job as an automatic "collapse away anything left vestigial by --prune-empty" command:

git rebase --root HEAD

(I needed the --root so it would replace the now-empty initial commit with the oldest one that still had content.)

Solution 4

This looks like it worked for me: http://git.661346.n2.nabble.com/Removing-useless-merge-commit-with-quot-filter-branch-quot-td7356544.html

git filter-branch -f --prune-empty --parent-filter FULL_PATH_TO/rewrite_parent.rb master 

rewrite_parent.rb:

#!/usr/bin/ruby 
old_parents = gets.chomp.gsub('-p ', ' ') 

if old_parents.empty? then 
  new_parents = [] 
else 
  new_parents = `git show-branch --independent #{old_parents}`.split 
end 

puts new_parents.map{|p| '-p ' + p}.join(' ') 

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