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.