testserver/.github/workflows/pr_comment.yml

# This workflow run on the completion of the
# build workflow but only does anything if the
# triggering workflow uploaded an artifact.
#
# Do note that it is then the trigger workflow that
# determines if this will update the PR text body. All
# this workflow does is check if an uploaded artifact
# exists and there is a PR tied to the previous workflow.

name: Comment on pull request
on:
  workflow_run:
    workflows: ['Build Paper']
    types: [completed]
jobs:
  pr_comment:
    if: github.event.workflow_run.conclusion == 'success'
    runs-on: ubuntu-latest
    steps:
      - uses: actions/github-script@v6
        with:
          # This snippet is public-domain, taken from
          # https://github.com/oprypin/nightly.link/blob/master/.github/workflows/pr-comment.yml
          # Modified extensively by Machine_Maker
          script: |
            async function updatePR(owner, repo, issue_number, purpose, body) {
              const { data } = await github.rest.issues.get({ owner, repo, issue_number });
              core.debug(JSON.stringify(data, null, 2));
            
              const marker = `<!-- bot: ${purpose} -->`;
            
              let new_body = data.body ? data.body.trim().split(marker)[0] : "";
              if (!new_body.trim()) {
                new_body += `${marker}\n${body}`
              } else {
                new_body += `${marker}\n---\n${body}`
              }
            
              core.info(`Updating the text body of PR #${issue_number} in ${owner}/${repo}`);
              await github.rest.issues.update({ owner, repo, issue_number, body: new_body });
            }

            const { owner, repo } = context.repo;
            const run_id = ${{ github.event.workflow_run.id }};
            const repo_id = ${{ github.event.repository.id }};
            
            let pulls = [];
            const event_type = "${{ github.event.workflow_run.event}}";
            if (event_type === "push") { // if push, it's from the same repo which means `pull_requests` is populated
              pulls = ${{ toJSON(github.event.workflow_run.pull_requests) }};
            } else {
              const pr_branch = "${{ github.event.workflow_run.head_branch }}";
              const pr_sha = "${{ github.event.workflow_run.head_sha }}";
              const pr_owner = "${{ github.event.workflow_run.head_repository.owner.login }}";
              const { data } = await github.rest.pulls.list({ owner, repo, head: `${pr_owner}:${pr_branch}`, state: "open" });
              core.debug(JSON.stringify(data, null, 2));
              pulls = data.filter((pr) => pr.head.sha === pr_sha && pr.labels.find((l) => l.name === "build-pr-jar"));
            }

            if (!pulls.length) {
              return core.notice("This workflow doesn't have any pull requests!");
            } else if (pulls.length > 1) {
              core.info(JSON.stringify(pulls, null, 2));
              return core.error("Found multiple matching PRs");
            }
            const pull_request = pulls[0];

            const artifacts = await github.paginate(github.rest.actions.listWorkflowRunArtifacts, { owner, repo, run_id });
            if (!artifacts.length) {
              return core.info("Skipping comment due to no artifact found");
            }
            const artifact = artifacts.find((art) => art.name === `paper-${pull_request.number}`);
            if (!artifact) {
              return core.info("Skipping comment to no matching artifact found");
            }
            
            const link = `https://nightly.link/${owner}/${repo}/actions/artifacts/${artifact.id}.zip`;
            const body = `Download the paperclip jar for this pull request: [${artifact.name}.zip](${link})`;
            core.info(`Adding a link to ${link}`);
            await updatePR(owner, repo, pull_request.number, "paperclip-pr-build", body);