fix(github): recover fork PR re-runs when GitHub omits PR metadata

When someone clicks Re-run on a Pipelines as Code check for a pull
request coming from a fork, GitHub can leave out the usual pull request
details in the webhook payload. That left PAC with no obvious way to
tell which pull request the check belonged to, so the re-run stopped
with an error instead of starting again.

This change teaches PAC to keep looking in a more practical way. If the
first GitHub API says it cannot find the pull request for the commit,
PAC now lists open pull requests in the repository and matches the one
whose head commit SHA is the same. In simple terms: when GitHub does not
hand us the answer directly, we now look through the open pull requests
and find the one built from that exact commit.

The change also checks pull request data attached directly to the
check_run event before falling back to SHA-based lookup, and the tests
now cover both the new fork pull request path and the empty-result error
cases.

Signed-off-by: Chmouel Boudjnah <chmouel@redhat.com>

Author: chmouel

pkg/provider/github/parse_payload.go

@@ -314,13 +314,55 @@ func selectSingleOpenPullRequest(prs []*github.PullRequest) (*github.PullRequest
 	}
 }
 
+func (v *Provider) findOpenPullRequestBySHA(ctx context.Context, org, repo, sha string) (*github.PullRequest, error) {
+	const maxPages = 10
+	opts := &github.PullRequestListOptions{
+		State:       "open",
+		Sort:        "updated",
+		ListOptions: github.ListOptions{PerPage: 100},
+	}
+	var matches []*github.PullRequest
+
+	for page := 0; page < maxPages; page++ {
+		prs, resp, err := wrapAPI(v, "list_pull_requests", func() ([]*github.PullRequest, *github.Response, error) {
+			return v.Client().PullRequests.List(ctx, org, repo, opts)
+		})
+		if err != nil {
+			return nil, fmt.Errorf("failed to list open pull requests in %s/%s: %w", org, repo, err)
+		}
+
+		for _, pr := range prs {
+			if pr.GetHead().GetSHA() == sha {
+				matches = append(matches, pr)
+			}
+		}
+
+		if resp.NextPage == 0 {
+			break
+		}
+		opts.Page = resp.NextPage
+	}
+
+	return selectSingleOpenPullRequest(matches)
+}
+
 func (v *Provider) resolveReRequestPullRequest(ctx context.Context, runevent *info.Event) (*github.PullRequest, error) {
 	prs, err := v.getPullRequestsWithCommit(ctx, runevent.SHA, runevent.Organization, runevent.Repository, false)
 	if err != nil {
 		return nil, err
 	}
 
-	return selectSingleOpenPullRequest(prs)
+	pr, err := selectSingleOpenPullRequest(prs)
+	if err != nil {
+		return nil, err
+	}
+	if pr != nil {
+		return pr, nil
+	}
+
+	// ListPullRequestsWithCommit may return no matches for fork PR commits.
+	v.Logger.Infof("No PR found via commits API for SHA %s, falling back to open PR listing", runevent.SHA)
+	return v.findOpenPullRequestBySHA(ctx, runevent.Organization, runevent.Repository, runevent.SHA)
 }
 
 func (v *Provider) processEvent(ctx context.Context, event *info.Event, eventInt any) (*info.Event, error) {
@@ -491,44 +533,58 @@ func (v *Provider) handleReRequestEvent(ctx context.Context, event *github.Check
 	if event.GetRepo() == nil {
 		return nil, errors.New("error parsing payload the repository should not be nil")
 	}
+	checkRun := event.GetCheckRun()
+	checkSuite := checkRun.GetCheckSuite()
+
 	runevent.Organization = event.GetRepo().GetOwner().GetLogin()
 	runevent.Repository = event.GetRepo().GetName()
 	runevent.URL = event.GetRepo().GetHTMLURL()
 	runevent.DefaultBranch = event.GetRepo().GetDefaultBranch()
-	runevent.SHA = event.GetCheckRun().GetCheckSuite().GetHeadSHA()
-	runevent.HeadBranch = event.GetCheckRun().GetCheckSuite().GetHeadBranch()
-	runevent.HeadURL = event.GetCheckRun().GetCheckSuite().GetRepository().GetHTMLURL()
-	// If we don't have a pull_request in this it probably mean a push
-	if len(event.GetCheckRun().GetCheckSuite().PullRequests) == 0 {
-		// If head_branch is null, try to find a PR by SHA before assuming push
-		if runevent.HeadBranch == "" && runevent.SHA != "" {
-			pr, err := v.resolveReRequestPullRequest(ctx, runevent)
-			if err != nil {
-				return nil, fmt.Errorf("cannot determine pull request for check_run rerequest and SHA %s: %w", runevent.SHA, err)
-			}
-			if pr != nil {
-				runevent.PullRequestNumber = pr.GetNumber()
-				runevent.TriggerTarget = triggertype.PullRequest
-				v.Logger.Infof("Recheck of PR %s/%s#%d has been requested (resolved from SHA)", runevent.Organization, runevent.Repository, runevent.PullRequestNumber)
-				return v.populateRunEventFromPullRequest(runevent, pr), nil
-			}
+	runevent.SHA = checkSuite.GetHeadSHA()
+	runevent.HeadBranch = checkSuite.GetHeadBranch()
+	runevent.HeadURL = checkSuite.GetRepository().GetHTMLURL()
+
+	if len(checkSuite.PullRequests) > 0 {
+		runevent.PullRequestNumber = checkSuite.PullRequests[0].GetNumber()
+		runevent.TriggerTarget = triggertype.PullRequest
+		v.Logger.Infof("Recheck of PR %s/%s#%d has been requested", runevent.Organization, runevent.Repository, runevent.PullRequestNumber)
+		return v.getPullRequest(ctx, runevent)
+	}
+
+	if len(checkRun.PullRequests) > 1 {
+		return nil, fmt.Errorf("cannot determine pull request for check_run rerequest: found %d associated pull requests in webhook payload", len(checkRun.PullRequests))
+	}
+	if len(checkRun.PullRequests) == 1 {
+		runevent.PullRequestNumber = checkRun.PullRequests[0].GetNumber()
+		runevent.TriggerTarget = triggertype.PullRequest
+		v.Logger.Infof("Recheck of PR %s/%s#%d has been requested (from check_run)", runevent.Organization, runevent.Repository, runevent.PullRequestNumber)
+		return v.getPullRequest(ctx, runevent)
+	}
+
+	// If head_branch is null, try to find a PR by SHA before assuming push.
+	if runevent.HeadBranch == "" && runevent.SHA != "" {
+		pr, err := v.resolveReRequestPullRequest(ctx, runevent)
+		if err != nil {
+			return nil, fmt.Errorf("cannot determine pull request for check_run rerequest and SHA %s: %w", runevent.SHA, err)
 		}
-		if runevent.HeadBranch == "" {
-			return nil, fmt.Errorf("cannot determine branch for check_run rerequest: head_branch is null and no associated PR found for SHA %s", runevent.SHA)
+		if pr != nil {
+			runevent.PullRequestNumber = pr.GetNumber()
+			runevent.TriggerTarget = triggertype.PullRequest
+			v.Logger.Infof("Recheck of PR %s/%s#%d has been requested (resolved from SHA)", runevent.Organization, runevent.Repository, runevent.PullRequestNumber)
+			return v.populateRunEventFromPullRequest(runevent, pr), nil
 		}
-		runevent.BaseBranch = runevent.HeadBranch
-		runevent.BaseURL = runevent.HeadURL
-		runevent.EventType = "push"
-		// we allow the rerequest user here, not the push user, i guess it's
-		// fine because you can't do a rereq without being a github owner?
-		runevent.Sender = event.GetSender().GetLogin()
-		v.userType = event.GetSender().GetType()
-		return runevent, nil
 	}
-	runevent.PullRequestNumber = event.GetCheckRun().GetCheckSuite().PullRequests[0].GetNumber()
-	runevent.TriggerTarget = triggertype.PullRequest
-	v.Logger.Infof("Recheck of PR %s/%s#%d has been requested", runevent.Organization, runevent.Repository, runevent.PullRequestNumber)
-	return v.getPullRequest(ctx, runevent)
+	if runevent.HeadBranch == "" {
+		return nil, fmt.Errorf("cannot determine branch for check_run rerequest: head_branch is null and no associated PR found for SHA %s", runevent.SHA)
+	}
+	runevent.BaseBranch = runevent.HeadBranch
+	runevent.BaseURL = runevent.HeadURL
+	runevent.EventType = "push"
+	// we allow the rerequest user here, not the push user, i guess it's
+	// fine because you can't do a rereq without being a github owner?
+	runevent.Sender = event.GetSender().GetLogin()
+	v.userType = event.GetSender().GetType()
+	return runevent, nil
 }
 
 func (v *Provider) handleCheckSuites(ctx context.Context, event *github.CheckSuiteEvent) (*info.Event, error) {