Github suggestion comments usually do this pretty easily. You can prompt the submitter to accept a diff. It does have two annoying problems though:

- You must use a browser editor, no attaching a diff you generated elsewhere. Anything more than 1 line is hell because Github's editor gives no fucks about running gofmt or whatever. - If you request a change, approve the PR, and then the submitter accepts your change, it dismisses your approval.