Fail check on error, format message

.github/workflows/missing-ops.yml

@@ -24,6 +24,7 @@ jobs:
     continue-on-error: true
     outputs:
       should_notify: ${{ steps.check_status.outputs.result }}
+      job_id: ${{ job }}
     steps:
       - uses: actions/checkout@v4
       - uses: mozilla-actions/[email protected]
@@ -60,10 +61,23 @@ jobs:
     if: ${{ needs.missing-optypes.outputs.should_notify == 'true' }}
     with:
       channel-id: 'C04SHCL4FKP'
-      slack-message: '`tket-json-rs` is missing OpType definitions. See the failing check for more info.\nhttps://github.com/CQCL/tket-json-rs/actions/workflows/missing-ops.yml'
+      slack-message: |
+        `tket-json-rs` is missing OpType definitions.
+        See <https://github.com/CQCL/tket-json-rs/actions/runs/${{ github.run_id }}/job/${{ needs.missing-optypes.outputs.job_id }}|the failing check> for more info.
       # An unique identifier for the message type, to use in rate limiting.
       message-label: "missing-op"
       # Rate-limit the message to once per week
       timeout-minutes: 10080
     secrets:
-        SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}
+        SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}
+
+  # This is required since `missing-optypes` is set to continue-on-error,
+  # and we want to ultimately fail the check after notifying.
+  fail-on-missing-optypes:
+    name: Fail the build on missing op types
+    runs-on: ubuntu-latest
+    needs: missing-optypes
+    if: ${{ needs.missing-optypes.outputs.should_notify == 'true' }}
+    steps:
+      - name: Fail the build
+        run: exit 1