RFR: 1797: Add support for /backport pull request command

[Erik Duveblad]

> On 2 Feb 2023, at 09:28, Thomas Stüfe <thomas.stuefe at gmail.com> wrote:
> 
> > 1. If the `/backport` command is used in an **open** pull request, it adds a label `Backport=repo:branch` to the PR. If the PR is later integrated, the PR bot scans for backport labels and begins the backporting process. To cancel the backport, the user can use `/backport disable repo master` to remove the label before the PR is integrated.
> 
> This does not sound desirable. Fixes should undergo some bake time in 
> the primary repo before they get backported anywhere. With the current 
> situation it is up to the person doing the backport to go to the commit 
> in question and know that the commit has been suitable tested/baked.
> 
> David
> -----
> 
> 
> I agree with David. Making it easy to downport fresh changes right away is not something we should encourage.

Please do not jump to conclusions about what Zhao is proposing without understanding the patch :) Zhao’s patch is only making it easier to create a backport _pull request_, it will not automatically create any backport commits.

A user can already today type `/backport` in a commit comment for the commit a pull request resulted in once it was integrated. This can be done only seconds after the pull request was integrated and the Skara bots will then go ahead and create a “backport pull request” (see the Skara wiki on backports for more details [0]). Zhao’s patch only removes the manual step of having to navigate to the GitHub page for the resulting commit and add a commit comment. With Zhao’s patch a user can now instead type `/backport` in the pull request and the Skara bots will create the “backport pull request” once the pull request has been integrated.

So, this patch is not creating any new workflows, it is just removing a couple of manual steps needed today to create a "backport pull request". The "backport pull request" should of course not be integrated until the commit in mainline has received proper “soak time” and testing.

Thanks,
Erik

[0]: https://wiki.openjdk.org/display/SKARA/Backports