feat: add labels from comments (#2460)

.github/PULL_REQUEST_TEMPLATE.md

@@ -9,3 +9,6 @@
 
 * Please make sure the PR has excellent documentation and tests.
   If we label it `missing documentation` or `missing tests` then it needs fixing!
+
+* You can manage the `awaiting-review`, `awaiting-author`, and `WIP` labels
+  yourself, by writing a comment containing one of these labels on its own line.

.github/workflows/labels-from-comments.yml

@@ -0,0 +1,43 @@
+# This workflow allows any user to add one of the `awaiting-review`, `awaiting-author`, or `WIP` labels,
+# by commenting on the PR or issue.
+# Other labels from this set are removed automatically at the same time.
+
+name: Label PR based on Comment
+
+on:
+  issue_comment:
+    types: [created]
+
+jobs:
+  update-label:
+    if: github.event.issue.pull_request != null && (contains(github.event.comment.body, 'awaiting-review') || contains(github.event.comment.body, 'awaiting-author') || contains(github.event.comment.body, 'WIP'))
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Add label based on comment
+      uses: actions/github-script@v6
+      with:
+        github-token: ${{ secrets.GITHUB_TOKEN }}
+        script: |
+          const { owner, repo, number: issue_number  } = context.issue;
+          const commentLines = context.payload.comment.body.split('\r\n');
+
+          const awaitingReview = commentLines.includes('awaiting-review');
+          const awaitingAuthor = commentLines.includes('awaiting-author');
+          const wip = commentLines.includes('WIP');
+
+          if (awaitingReview || awaitingAuthor || wip) {
+            await github.rest.issues.removeLabel({ owner, repo, issue_number, name: 'awaiting-review' }).catch(() => {});
+            await github.rest.issues.removeLabel({ owner, repo, issue_number, name: 'awaiting-author' }).catch(() => {});
+            await github.rest.issues.removeLabel({ owner, repo, issue_number, name: 'WIP' }).catch(() => {});
+          }
+
+          if (awaitingReview) {
+            await github.rest.issues.addLabels({ owner, repo, issue_number, labels: ['awaiting-review'] });
+          }
+          if (awaitingAuthor) {
+            await github.rest.issues.addLabels({ owner, repo, issue_number, labels: ['awaiting-author'] });
+          }
+          if (wip) {
+            await github.rest.issues.addLabels({ owner, repo, issue_number, labels: ['WIP'] });
+          }