How‑To: Rebasing GitHub Pull Requests

13 July 2019 Revision History

This is pretty esoteric but I keep forgetting how to do it so let’s put it here on the blog.

Situation

You’re maintaining a project on GitHub. A contributor has submitted a pull request. In the interim, the master branch has been updated and you want to bring the pull request up to date with the current version of master.

The best instructions I found were these ones on Stack Overflow. What I’m suggesting here is largely a simplification of what’s there so credit to Ryan Stewart for the answer.

Oh, and special thanks to Ash Maroli for being patient as I badgered him with e-mails asking for help (and who taught me the trick in step 2).

Steps

Step 1. Update `upstream`

git fetch upstream

This assumes you have a remote called upstream that’s pointed at the project’s repository.¹

Step 2. Checkout PR

git fetch upstream pull/<pr_number>/head:<local_branch_name>
git checkout <local_branch_name>

Step 3. Rebase PR

git rebase upstream/master

Step 4. Force Push PR

git push --force git@github.com:<contributor>/<project>.git <local_branch_name>:<remote_branch_name>

The <remote_branch_name> is the name of the branch on the contributor’s fork of the repository. The name of this branch is visible on the PR’s page.

And that’s it. As the Stack Overflow answer points out, one should always be careful with force pushing:²

…force pushing is dangerous, and you can lose commits with it. Only use it if you’re absolutely sure you know what you’re doing, like right here, where you intentionally want to drop the old, useless commits in the pre-rebase… branch.

I hope that’s useful for someone and/or me. ✺

Here’s some instructions on how to add an upstream remote. ↩
As Ash pointed out over e-mail, there are ways to recover from a lost commit occurring from a wayward git rebase. It’s beyond the scope of this article but git reflog and git reset are what you want to stick in your search engine. ↩