Populate labels from the PR to the backported PRs

[v1v]

What

#2288 added support for assigning labels to the backported PRs, I'd like to extend this functionality to populate the labels from the source PR to the backported PRs.

Proposal

Extend the backport action with a new list option, f.i: populate_labels (or something else)

See the below snippet as an example of how to configure mergify with it:

pull_request_rules:
  - name: backport patches to stable branch
    conditions:
      - base=main
      - label=backport-to-stable
    actions:
      backport:
        populate_labels: true
        branches:
          - stable

Therefore, given the PR-1 with the labels ['bug', 'customer', 'backport-to-stable' ] then when it gets merged the PR-2 is created with the labels ['bug', 'customer']

Thanks

[v1v]

To give more context with a real use case:

1. There is a hard requirement that each PR requires a team to be assigned, aka a label should be assigned.
2. Developers triage their PRs and assign those teams with the specific labels.
3. When a PR is merged and backported, those backported PRs don't contain the labels from the original PR.
4. Therefore there is a need to triage an existing triaged PR (well the initial PR)

If the above could be automated, then it can reduce the triaging and developers will be happy about it. :)

[Ryanf55]

Do you have any manual ways of doing this now? Perhaps in a workflow file?

[DouglasBlackwood]

You can't do it using Mergify for now.
But we do something similar with our merge queue. We created a GitHub Action to copy labels from a PR to the merge queue draft PR. https://github.com/Mergifyio/gha-mergify-merge-queue-labels-copier
You could probably do something similar for backports.