A Pull Request was created on GitHub targeting the wrong branch (let’s call it old-branch). We needed to change the target to good-branch. However, because old-branch had already been merged into our feature branch, cherry-picking individual commits was difficult. Let’s call the branch where the Pull Request is open pr-branch.

Rework strategy

At work, some Pull Requests are merged using a merge commit, but I much prefer Squash merges, as it allows us to worry less about the Pull Request’s internal commit history.

With that in mind, the rework strategy was simple:

• identify the diff between the original target branch and the PR branch
• export those changes into a patch file
• reset the current PR branch to the new desired target branch
• apply the patch
• commit and force-push to update the Pull Request
• change the Pull Request’s target branch in the GitHub UI

By following this process, the Pull Request ends up with a single, clean commit containing all the original changes.

Commands

Here is the Git workflow to execute this rewrite:

• switch to the PR branch: git switch pr-branch
• reset the branch to the new target: git reset --hard origin/good-branch (it will delete uncommitted changes)
• generate a diff between the old target and the original PR state: git diff origin/old-branch...origin/pr-branch > changes.patch (be careful of the 3 dots here to find the common ancestor between the two branches and start the diff from here)
• apply the patch to the local branch: git apply changes.patch (resolve any conflicts here)
• stage the changes: git add .
• create a new commit: git commit -m "feature description"
• overwrite the remote branch: git push --force
• update the target branch: go to the Pull Request on GitHub and edit the base branch to good-branch.

Using a Squash merge strategy provides more flexibility and makes manipulating Pull Requests much easier in scenarios like this.