WARNING: treat this as alpha quality code - this was written quickly and hasn't been used much by anyone yet

It's often useful to create "WIP" (work-in-progress) commits while you're working on a branch, with the intention of rewriting the branch and commit messages later. Similarly, "fixup!" and "squash!" commits (created by git commit --fixup or git commit --squash) are useful to create are you're working, but should always be squashed out before merging the branch.

This little Flask app can be set up as a webhook handler that's listening for changes to pull requests, and it will create a GitHub status for the commit at the head of the pull request that success if the PR would introduce no such WIP commits, or fails it if finds any.

This code should be run with the following two environment variables set:

• GITHUB_SECRET: this value should be the same as the one you set in the webhook configuration on GitHub.
• GITHUB_ACCESS_TOKEN: this should be an access token that is allowed to create statuses for commits. If you want to set this up for a private repo, it will need the repo scope (which is very broad - it allows read and write access to the repository, so make sure you understand the implications). If you only want to use this for public repositories, however, the only scope that it needs is repo:status. You can create personal access tokens at: https://github.com/settings/tokens (Bear in mind you might want to create a new GitHub user account with access to the minimal repositories you need to check, since personal access tokens will have access to every repository the user can see.)

When setting up the webhook in GitHub you should use the following settings:

• Payload URL: this is the URL of wherever you're hosting this code. (Heroku works fine.)
• Content type: set this to application/json
• Secret: this should be the same as the value in the GITHUB_SECRET environment variable.
• Which events would you like to trigger the webhook? Select "Let me select individual events" and then make sure that only "Pull requests" is selected.

The idea from this code is from Matthew Somerville, who set up a Git hook to do the same check for mySociety's internal Git repositories while I worked there.