This is great, but as chrisseaton asked on Twitter [1], how does it interact with CI?

The trees in the rebased commits are new and may never have been tested. Is GitHub going to expose a `refs/pulls/123/rebase` ref (cf. the existing `refs/pulls/123/merge`) for running through CI before the button can be pressed?

EDIT: The docs [2] say:

  You aren't able to automatically rebase and merge on GitHub when:
  
  * Your pull request has merge conflicts.
  * Rebasing the commits from the base branch into the head branch
    runs into conflicts.
  * Rebasing your commits is considered "unsafe", such as when a
    rebase is possible without merge conflicts but would produce a
    different result than a merge would.

So I guess the point is moot. You can’t rebase a branch unless the resulting tree is identical to the one you’d get from a merge, and that’s the tree that runs through CI.

[1] https://twitter.com/ChrisGSeaton/status/780441251992731648

[2] https://help.github.com/articles/about-pull-request-merges/#...