ci: auto-create issue on scheduled Stan check failure

Author: seabbs-bot

.github/workflows/check-cmdstan.yaml

@@ -103,3 +103,38 @@ jobs:
             all(message == "Stan program is syntactically correct")
           )
         shell: Rscript {0}
+
+      - name: Create issue on failure
+        if: failure() && github.event_name == 'schedule'
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const title = 'Stan syntax check failed on scheduled run';
+            const { data: issues } = await github.rest.issues.listForRepo({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              state: 'open',
+              labels: 'stan-check-failure'
+            });
+            if (issues.length === 0) {
+              await github.rest.issues.create({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                title: title,
+                body: [
+                  'The weekly `check-cmdstan` workflow failed.',
+                  '',
+                  'This likely means an upstream dependency ' +
+                  '(e.g. primarycensored) changed its Stan ' +
+                  'function signatures.',
+                  '',
+                  `Run: ${context.serverUrl}/${context.repo.owner}` +
+                  `/${context.repo.repo}/actions/runs` +
+                  `/${context.runId}`,
+                  '',
+                  'This was opened by a bot. Please ping ' +
+                  '@seabbs for any questions.'
+                ].join('\n'),
+                labels: ['stan-check-failure']
+              });
+            }