feat: Add action workflow for blocking merge via labels

[averikitsch]

Addresses #138

On each label/un-label event on a pull request will execute the workflow. The settings need to be updated to have this required status check.

Limitations of GitHub Actions:

• Each label add or removal, even if done as a batch, triggers a check in the checks tab though it should only show up once in the PR status checks.

Decisions made:

• This uses action actions/github-script@v4 to extract the event and PR context for more control and results in only 1 status check. This is compared to Adam's example using workflow expressions and functions to extract this information. There was minimal control over arrays of labels.

Future considerations:

• This similar pattern using actions/github-script@v4 can be used to add labels on PR creation

     - uses: actions/github-script@v3
        with:
          github-token: ${{secrets.GITHUB_TOKEN}}
          script: |
            github.issues.addLabels({
              issue_number: context.issue.number,
              owner: context.repo.owner,
              repo: context.repo.repo,
              labels: ['do not merge']
            })

• Similar add comments to the PR

github.issues.createComment({
  issue_number: context.issue.number,
  owner: context.repo.owner,
  repo: context.repo.repo,
  body: welcomeMessage
});

• Lastly, can read the PR body

      - uses: actions/github-script@v4
        with:
          script: |
            const body = context.payload.pull_request.body;
            if (body.includes("Decision Record")) {
         ...

[grayside]

Neat! I assume "core" is a basic Github Actions built-in I somehow hadn't understood yet.

[averikitsch]

Neat! I assume "core" is a basic Github Actions built-in I somehow hadn't understood yet.

The action exposes Github libraries and context available for building actions. The core library provides functions for setting results, logging, registering secrets and exporting variables across actions. Your example works, just not as flexible.

[grayside]

Thanks for making it work & look good.