How do I rewrite Git history to undo squashed merge commits?

Question

I've been working on a project that has recently migrated from Subversion to Git. I had been committing to the Subversion repo via git-svn prior to the migration. After the migration, I noticed a fair amount of history has been lost because each of my merge commits from topic branches have been squashed (either via the git-svn bridge, or due to the migration), losing some of the commit messages I want to keep. Is it possible to use my local copy of the pre-migration repo to unsquash the merge commits in the post-migration repo, perhaps via something like cherry-picking?

Answer 1

You can use git graft to augment squashed commits with another parent pointing to the real commit(s) that were merged in. Once you've added grafts for all squashed commits, you can permanently incorporate them by rewriting git history with git filter-branch

This SO answer provides details on how to do it: Setting git parent pointer to a different parent