To set up Regression Sniffer, we need three files:

• Workflow that captures Pull Request metadata (number and commit metadata) and uploads this data as an artifact
• Workflow that runs on workflow-run trigger, downloads artifact, and runs regression-sniffer GitHub Action
• And we need to set up regression-sniffer.yml configuration file

name: Gather Pull Request Metadata
on:
  pull_request:
    types: [ opened, reopened, synchronize ]
    branches: [ main ]

permissions:
  contents: read

jobs:
  gather-metadata:
    runs-on: ubuntu-latest

    steps:
      - name: Repository checkout
        uses: actions/checkout@v3

      - id: Metadata
        name: Gather Pull Request Metadata
        uses: redhat-plumbers-in-action/gather-pull-request-metadata@v1

      - name: Upload artifact with gathered metadata
        uses: actions/upload-artifact@v3
        with:
          name: pr-metadata
          path: ${{ steps.Metadata.outputs.metadata-file }}

name: Regression Sniffer
on:
  workflow_run:
    workflows: [ Gather Pull Request Metadata ]
    types:
      - completed

permissions:
  contents: read

jobs:
  download-metadata:
    if: >
      github.event.workflow_run.event == 'pull_request' &&
      github.event.workflow_run.conclusion == 'success'
    runs-on: ubuntu-latest

    outputs:
      pr-metadata: ${{ steps.Artifact.outputs.pr-metadata-json }}

    steps:
      - id: Artifact
        name: Download Artifact
        uses: redhat-plumbers-in-action/download-artifact@v1
        with:
          name: pr-metadata

  regression-sniffer:
    needs: [ download-metadata ]
    runs-on: ubuntu-latest

    permissions:
      # required for setting labels
      pull-requests: write

    steps:
      - name: Regression Sniffer
        uses: redhat-plumbers-in-action/regression-sniffer@v1
        with:
          pr-metadata: ${{ needs.download-metadata.outputs.pr-metadata }}
          token: ${{ secrets.GITHUB_TOKEN }}

Lastly, we need to create a configuration file .github/regression-sniffer.yml:

upstream: systemd/systemd

Action currently accepts the following options:

# ...

- uses: redhat-plumbers-in-action/regression-sniffer@v1
  with:
    check-follow-up:  <boolean>
    check-revert:     <boolean>
    pr-metadata:      <pr-metadata.json>
    config-path:      <path to config file>
    status-title:     <status title>
    token:            <GitHub token or PAT>

# ...

Check if Pull Request has some follow-up commit related to cherri-picked commits in upstream available.

• default value: true
• requirements: optional

Check if Pull Request has some cherri-picked commits from upstream that were later reverted.

• default value: true
• requirements: optional

Stringified JSON Pull Request metadata provided by GitHub Action redhat-plumbers-in-action/gather-pull-request-metadata.

Pull Request metadata has the following format: metadata format

• default value: undefined
• requirements: required

Path to configuration file. Configuration file format is described in: Config section.

• default value: .github/regression-sniffer.yml
• requirements: optional

Optional H3 title of status message.

• default value: Pull Request validation
• requirements: optional

GitHub token or PAT is used for creating labels on Pull Request.

# required permission
permissions:
  pull-requests: write

• default value: undefined
• requirements: required
• recomended value: secrets.GITHUB_TOKEN

Message with status of Pull Request validation.

Action is configured using special config file: .github/regression-sniffer.yml. The structure needs to be as follows:

upstream: systemd/systemd
labels:
  follow-up: pr/follow-up
  revert: pr/revert
  mention: pr/mention
  waive: follow-up-waived
filters:
  follow-up:
    - 'follow-?up *(|:|-|for|to) *(https:\\/\\/github\\.com\\/systemd\\/systemd\\/commit\\/)?(%{sha}%)'
  revert:
    - '(This)? *reverts? *(commit)? *(|:|-) *(https:\\/\\/github\\.com\\/systemd\\/systemd\\/commit\\/)?(%{sha}%)'
  mention:
    - '(https:\\/\\/github\\.com\\/systemd\\/systemd\\/commit\\/)?(%{sha}%)'

Name of the upstream repository in the format: owner/repo. Currently only one upstream repository is supported. Also it is currently limited to public GitHub repositories.

• default value: undefined
• requirements: required

Configuration of labels used for marking Pull Requests. Supported labels are:

• follow-up - label used for marking Pull Requests with follow-up commits detected
  • default value: pr/follow-up
• revert - label used for marking Pull Requests with reverted commits detected
  • default value: pr/revert
• mention - label used for marking Pull Requests with mentioned commits detected
  • default value: pr/mention
• waive - label used for waiving results reported by Regression Sniffer
  • default value: follow-up-waived

labels section is optional and if not provided, default values will be used.

Configuration of filters used for detecting commit mentions, follow-up and revert commits. Each filter is a list of regular expressions. Regular expressions can contain special placeholders:

• %{sha}% - placeholder for commit SHA, it will be replaced with actual commit SHA at action runtime

List of regular expressions used for detecting follow-up commits. Each regular expression is a string.

• default value: follow-?up *(|:|-|for|to) *(https:\\/\\/github\\.com\\/systemd\\/systemd\\/commit\\/)?(%{sha}%)
• requirements: optional

List of regular expressions used for detecting revert commits. Each regular expression is a string.

• default value: (This)? *reverts? *(commit)? *(|:|-) *(https:\\/\\/github\\.com\\/systemd\\/systemd\\/commit\\/)?(%{sha}%)
• requirements: optional

List of regular expressions used for detecting commit mentions. Each regular expression is a string.

• default value: (https:\\/\\/github\\.com\\/systemd\\/systemd\\/commit\\/)?(%{sha}%)
• requirements: optional