chore: prlinter not triggered when "Codebuild PR Build" completes

[pahud]

Added steps to save and upload pull request information.

Issue # (if applicable)

Closes #36055

Reason for this change

THE PROBLEM:

PR Linter can't determine which PR to validate because:

1. No pr_info artifact exists
2. pull_requests array is empty (GitHub limitation)

THE SOLUTION:

Add these steps to codebuild-pr-build.yml:

  - name: Save PR info for PR Linter
    if: github.event_name == 'pull_request'
    run: |
      mkdir -p ./pr
      echo "${{ github.event.pull_request.number }}" > ./pr/pr_number
      echo "${{ github.event.pull_request.head.sha }}" > ./pr/pr_sha

  - name: Upload PR info artifact
    if: github.event_name == 'pull_request'
    uses: actions/upload-artifact@v5
    with:
      name: pr_info
      path: pr/

WHY IT WORKS:

BEFORE (BROKEN):
┌─────────────────────────────────────────────────────────┐
│ Codebuild PR Build                                      │
│   Context: github.event.pull_request.number = 36049 ✓   │
│   Context: github.event.pull_request.head.sha = fc4... ✓│
│                                                          │
│   ✗ Does NOT save this info                             │
│   ✗ Does NOT upload artifact                            │
└─────────────────────────────────────────────────────────┘
                    │
                    │ workflow_run event
                    ▼
┌─────────────────────────────────────────────────────────┐
│ PR Linter (workflow_run context)                        │
│   Context: github.event.workflow_run.pull_requests = [] │
│   Context: No PR info available ✗                       │
│                                                          │
│   Tries to download pr_info artifact ──► ✗ Not found   │
│   Tries pull_requests[0].number ──────► ✗ Empty array  │
│                                                          │
│   Result: ✗ CANNOT DETERMINE PR NUMBER                  │
└─────────────────────────────────────────────────────────┘


AFTER (FIXED):
┌─────────────────────────────────────────────────────────┐
│ Codebuild PR Build                                      │
│   Context: github.event.pull_request.number = 36049 ✓   │
│   Context: github.event.pull_request.head.sha = fc4... ✓│
│                                                          │
│   ✓ Saves PR number to file: pr/pr_number               │
│   ✓ Saves PR SHA to file: pr/pr_sha                     │
│   ✓ Uploads pr_info artifact                            │
│      └─ Contains: pr_number=36049, pr_sha=fc4...        │
└─────────────────────────────────────────────────────────┘
                    │
                    │ workflow_run event
                    │ (artifact travels with event)
                    ▼
┌─────────────────────────────────────────────────────────┐
│ PR Linter (workflow_run context)                        │
│   Context: github.event.workflow_run.pull_requests = [] │
│                                                          │
│   Downloads pr_info artifact ─────────► ✓ Found!       │
│     └─ Extracts pr/pr_number ────────► ✓ 36049         │
│     └─ Extracts pr/pr_sha ───────────► ✓ fc4...        │
│                                                          │
│   Result: ✓ PR NUMBER DETERMINED = 36049                │
│           ✓ Can now validate the correct PR             │
└─────────────────────────────────────────────────────────┘

KEY INSIGHT:

┌──────────────────────────────────────────────────────────┐
│  The PR context EXISTS in Codebuild PR Build             │
│  (triggered by pull_request event)                       │
│                                                           │
│  But it DISAPPEARS in PR Linter                          │
│  (triggered by workflow_run event)                       │
│                                                           │
│  Solution: PERSIST the context via artifact              │
│            (artifacts survive the context switch)        │
└──────────────────────────────────────────────────────────┘

CONTEXT AVAILABILITY:

Codebuild PR Build (pull_request trigger):
✓ github.event.pull_request.number
✓ github.event.pull_request.head.sha
✓ github.event.pull_request.* (all PR data)

PR Linter (workflow_run trigger):
✗ github.event.pull_request (doesn't exist)
✗ github.event.workflow_run.pull_requests (empty array)
✓ github.event.workflow_run.id (can download artifacts)

ARTIFACT AS BRIDGE:

  Codebuild Context          Artifact           PR Linter Context
  ─────────────────          ────────           ─────────────────

  PR #36049                                     workflow_run event
  pull_request event                            (no PR context)
       │                                              │
       │ Has PR data                                  │ No PR data
       │                                              │
       ▼                                              ▼
  Save to files          ──────────►            Download files
  - pr_number: 36049        Upload               - pr_number: 36049
  - pr_sha: fc4...          artifact             - pr_sha: fc4...
                            pr_info
                                                 ✓ PR context restored!

EXECUTION FLOW WITH FIX:

1. PR opened ──► Codebuild PR Build starts
                 │
                 ├─ github.event.pull_request.number = 36049 ✓
                 ├─ github.event.pull_request.head.sha = fc4... ✓
                 │
                 ├─ echo 36049 > pr/pr_number
                 ├─ echo fc4... > pr/pr_sha
                 └─ upload-artifact: pr_info
                    └─ Artifact ID: 12345

2. Codebuild completes ──► workflow_run event fires
                            │
                            └─ github.event.workflow_run.id = 19342493369

3. PR Linter triggered ──► download-if-workflow-run job
                            │
                            ├─ Download artifact from run 19342493369
                            │  └─ Finds pr_info artifact (ID: 12345) ✓
                            │
                            ├─ Extract files:
                            │  ├─ pr/pr_number = 36049 ✓
                            │  └─ pr/pr_sha = fc4... ✓
                            │
                            └─ Pass to validate-pr job:
                               └─ PR_NUMBER=36049 ✓
                               └─ PR_SHA=fc4... ✓

4. validate-pr job ──► Validates PR #36049 ✓

SUMMARY:

The solution works because it:

1. Captures PR context when it's available (Codebuild)
2. Persists it in an artifact (survives context switch)
3. Restores it when needed (PR Linter)
4. Bypasses GitHub's pull_requests array limitation

See #36055 for details

How do I validate

Test Environment

Validated on fork repository: pahud#16

Validation Steps

1. Applied the fix to fork's codebuild-pr-build.yml (artifact upload steps)
2. Created test PR to trigger workflows
3. Verified Codebuild workflow uploaded pr_info artifact successfully
4. Verified PR Linter workflow downloaded artifact and applied label

Results

✅ Codebuild PR Build: Successfully uploaded pr_info artifact containing:

• pr_number: 16
• pr_sha: ebeaa4c...

✅ PR Linter: Successfully validated PR and applied label

• Workflow run: https://github.com/pahud/aws-cdk/actions/runs/19380492593
• Label applied: pr/needs-community-review
• Status: ✅ Success

Evidence

Before fix:

• PR Linter failed with "Cannot determine PR number"
• No pr_info artifact available
• workflow_run.pull_requests array was empty

After fix:

• PR Linter successfully downloaded pr_info artifact
• Correctly identified PR number and SHA
• Applied appropriate review label

Note on Fork Testing

For fork testing only, I added a pull_request_target fallback to pr-linter.yml since workflow_run events don't trigger from fork workflows. This fallback is not needed for aws/aws-cdk as workflows run in the base repository context where workflow_run works correctly.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[aws-cdk-automation]

(This review is outdated)

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[mergify]

This pull request has been removed from the queue for the following reason: pull request dequeued.

Pull request #36057 has been dequeued. The pull request rule doesn't match anymore. The following conditions don't match anymore:

• -label~=(blocked|do-not-merge|no-squash|two-approvers|priority-pr)
• check-success=build
• check-success=validate-pr
• any of: [🔀 queue conditions]
  • all of: [📌 queue conditions of queue default-squash]
    • -label~=(blocked|do-not-merge|no-squash|priority-pr)
    • check-success=build
    • check-success=validate-pr
    • any of: [🛡 GitHub branch protection]
      • check-neutral = validate-pr
      • check-skipped = validate-pr
      • check-success = validate-pr
    • any of: [🛡 GitHub branch protection]
      • check-neutral = build
      • check-skipped = build
      • check-success = build.

You should look at the reason for the failure and decide if the pull request needs to be fixed or if you want to requeue it.
If you do update this pull request, it will automatically be requeued once the queue conditions match again.
If you think this was a flaky issue instead, you can requeue the pull request, without updating it, by posting a @mergifyio requeue comment.

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[github-actions]

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