feat(ci): Add workflow_run workflow for posting CI failure comments on PRs

.github/workflows/ci-failure-comment.yml

@@ -0,0 +1,115 @@
+# Copyright (c) Facebook, Inc. and its affiliates.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: CI Failure Comment
+
+# This workflow runs in the context of the base repo (not the fork) and has
+# write access to post PR comments. It is triggered when the Linux Build
+# workflow completes and picks up failure artifacts uploaded by status jobs.
+#
+# Security: This workflow never checks out or executes PR code. It only reads
+# markdown artifacts generated by our own status jobs and posts them as
+# comments via the GitHub API. The artifact content is read as a string and
+# passed through the GitHub REST API (not interpolated into shell commands),
+# which prevents injection attacks.
+#
+# zizmor:disable:dangerous-triggers -- only reads artifacts and posts comments, no PR code execution.
+on:
+  workflow_run:
+    workflows: [Linux Build using GCC]
+    types:
+      - completed
+
+permissions:
+  pull-requests: write
+  issues: write
+  actions: read
+
+jobs:
+  post-failure-comment:
+    if: >
+      github.event.workflow_run.event == 'pull_request' &&
+      github.event.workflow_run.conclusion != 'success'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Get PR number
+        id: pr
+        env:
+          GH_TOKEN: ${{ github.token }}
+          REPO: ${{ github.repository }}
+          HEAD_OWNER: ${{ github.event.workflow_run.head_repository.owner.login }}
+          HEAD_BRANCH: ${{ github.event.workflow_run.head_branch }}
+        run: |
+          pr_number=$(gh api \
+            "/repos/${REPO}/pulls?head=${HEAD_OWNER}:${HEAD_BRANCH}&state=open" \
+            -q '.[0].number // empty')
+
+          if [ -z "$pr_number" ]; then
+            echo "No open PR found for branch ${HEAD_BRANCH}"
+            exit 0
+          fi
+          echo "number=$pr_number" >> "$GITHUB_OUTPUT"
+
+      - name: Download failure artifacts
+        if: steps.pr.outputs.number
+        uses: actions/download-artifact@v4
+        with:
+          github-token: ${{ github.token }}
+          run-id: ${{ github.event.workflow_run.id }}
+          pattern: ci-failure-*
+          path: /tmp/ci-failures
+          merge-multiple: false
+
+      - name: Post failure comments on PR
+        if: steps.pr.outputs.number
+        uses: actions/github-script@v7
+        env:
+          PR_NUMBER: ${{ steps.pr.outputs.number }}
+        with:
+          script: |
+            const fs = require('fs');
+            const path = require('path');
+            const prNumber = parseInt(process.env.PR_NUMBER, 10);
+            const failuresDir = '/tmp/ci-failures';
+
+            if (!fs.existsSync(failuresDir)) {
+              console.log('No failure artifacts found.');
+              return;
+            }
+
+            // Collect all comment.md files from artifact subdirectories
+            const comments = [];
+            for (const entry of fs.readdirSync(failuresDir)) {
+              const commentPath = path.join(failuresDir, entry, 'comment.md');
+              if (fs.existsSync(commentPath)) {
+                comments.push(fs.readFileSync(commentPath, 'utf8').trim());
+              }
+            }
+
+            if (comments.length === 0) {
+              console.log('No failure comment files found in artifacts.');
+              return;
+            }
+
+            // Combine all failure comments into a single PR comment
+            const body = comments.join('\n\n---\n\n');
+
+            await github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: prNumber,
+              body: body,
+            });
+
+            console.log(`Posted failure comment on PR #${prNumber}`);

.github/workflows/linux-build.yml

@@ -45,7 +45,6 @@ on:
 
 permissions:
   contents: read
-  pull-requests: write
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.repository }}-${{ github.head_ref || github.sha }}

.github/zizmor.yml

@@ -18,3 +18,4 @@ rules:
   dangerous-triggers:
     ignore:
       - build-impact-comment.yml
+      - ci-failure-comment.yml