[ci skip] Rework workflows to support optional paperclip build (#8583)

.github/workflows/pr_comment.yml

@@ -0,0 +1,68 @@
+# 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.info(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 }};
+
+            const pull_requests = ${{ toJSON(github.event.workflow_run.pull_requests) }};
+            if (!pull_requests.length) {
+              return core.notice("This workflow doesn't have any pull requests!");
+            }
+            const pull_request = pull_requests.find((pr) => pr.base.repo.id === repo_id);
+            if (!pull_request) {
+              return core.notice("This workflow doesn't match any pull request!");
+            }
+
+            const artifacts = await github.paginate(github.rest.actions.listWorkflowRunArtifacts, {owner, repo, run_id});
+            if (!artifacts.length) {
+              return core.info("Skipping comment due to no artifact found");
+            }
+            const artifact = artifacts.find((art) => art.name === `paper-${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);