Files
2026-09-23 13:31:12 +01:00

688 lines
24 KiB
Go

package github
import (
"context"
"errors"
"fmt"
"strings"
"sync"
"time"
"go.uber.org/zap"
)
// SubmitReview submits a review on a pull request. For APPROVE events it
// first checks that the authenticated user is not the PR author, returning
// ErrSelfApprove instead of letting the request fail at GitHub with an opaque
// 422. Lookup failures here are non-fatal — we fall through to GitHub so a
// transient API hiccup doesn't block legitimate approvals.
func (s *Service) SubmitReview(ctx context.Context, owner, repo string, number int, event, body string) error {
if s.client == nil {
return fmt.Errorf("github client not configured")
}
return submitReview(ctx, s.client, owner, repo, number, event, body)
}
// SubmitReviewForWorkspace submits a user-triggered review with an explicitly
// resolved workspace principal. GitHub App fallback is allowed by the resolver
// and remains attributable to the App rather than impersonating the user.
func (s *Service) SubmitReviewForWorkspace(
ctx context.Context,
workspaceID string,
userID string,
owner string,
repo string,
number int,
event string,
body string,
) (AuthPrincipal, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return AuthPrincipal{}, err
}
resolved, err := s.resolvePersonalWriteClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
return AuthPrincipal{}, err
}
if err := requireGitHubCapability(resolved, CapabilityPullRequestWrite); err != nil {
return AuthPrincipal{}, err
}
return resolved.Principal, submitReview(ctx, resolved.Client, owner, repo, number, event, body)
}
func submitReview(ctx context.Context, client Client, owner, repo string, number int, event, body string) error {
if event == reviewEventApprove {
user, userErr := client.GetAuthenticatedUser(ctx)
if userErr == nil && user != "" {
pr, prErr := client.GetPR(ctx, owner, repo, number)
if prErr == nil && pr != nil &&
strings.EqualFold(strings.TrimSpace(pr.AuthorLogin), strings.TrimSpace(user)) {
return ErrSelfApprove
}
}
}
return client.SubmitReview(ctx, owner, repo, number, event, body)
}
// RequestReviewers requests reviews and evicts the affected PR caches so the
// next feedback/status fetch reflects GitHub's new requested reviewer state.
func (s *Service) RequestReviewers(ctx context.Context, owner, repo string, number int, reviewers []string) error {
if s.client == nil {
return ErrNoClient
}
return s.requestReviewersWithClient(ctx, s.client, "legacy", owner, repo, number, reviewers)
}
// RequestReviewersForWorkspace requests a review using the workspace's
// personal-write routing rules and returns the identity GitHub will attribute.
func (s *Service) RequestReviewersForWorkspace(
ctx context.Context,
workspaceID string,
userID string,
owner string,
repo string,
number int,
reviewers []string,
) (AuthPrincipal, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return AuthPrincipal{}, err
}
resolved, err := s.resolvePersonalWriteClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
return AuthPrincipal{}, err
}
if err := requireGitHubCapability(resolved, CapabilityPullRequestWrite); err != nil {
return AuthPrincipal{}, err
}
return resolved.Principal, s.requestReviewersWithClient(
ctx, resolved.Client, resolved.cacheScopeForPurpose(CredentialPurposePersonalRead), owner, repo, number, reviewers,
)
}
func (s *Service) requestReviewersWithClient(
ctx context.Context,
client Client,
cacheScope string,
owner string,
repo string,
number int,
reviewers []string,
) error {
if err := client.RequestReviewers(ctx, owner, repo, number, reviewers); err != nil {
return err
}
// The legacy API still stores its entries in the explicit legacy cache
// namespace. Keep invalidation in that same generation namespace so a
// successful request cannot leave stale feedback or status behind.
key := scopedCacheKey(cacheScope, prStatusCacheKey(owner, repo, number))
s.prFeedbackCache.invalidateKey(key)
s.prStatusCache.invalidateKey(key)
s.invalidateWorkflowAttentionForPR(cacheScope, owner, repo, number, "")
return nil
}
// MergePR merges a pull request. mergeMethod is one of "merge", "squash",
// "rebase"; an empty string asks the service to pick the first method the
// repo allows. The caller is expected to refresh PR feedback after a
// successful merge — the background poller will catch the merged state on
// its next pass.
func (s *Service) MergePR(ctx context.Context, owner, repo string, number int, mergeMethod string) (MergeOutcome, error) {
if s.client == nil {
return "", ErrNoClient
}
return s.mergePRWithClient(ctx, s.client, "legacy", owner, repo, number, MergePRRequest{MergeMethod: mergeMethod})
}
// MergePRForWorkspace performs a user-triggered merge using the workspace's
// personal-write routing rules and returns the actual attributed principal.
func (s *Service) MergePRForWorkspace(
ctx context.Context,
workspaceID string,
userID string,
owner string,
repo string,
number int,
mergeMethod string,
) (AuthPrincipal, MergeOutcome, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return AuthPrincipal{}, "", err
}
resolved, err := s.resolvePersonalWriteClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
return AuthPrincipal{}, "", err
}
if err := requireGitHubCapability(resolved, CapabilityPullRequestWrite); err != nil {
return AuthPrincipal{}, "", err
}
outcome, err := s.mergePRWithClient(
ctx, resolved.Client, resolved.CacheScope, owner, repo, number, MergePRRequest{MergeMethod: mergeMethod},
)
return resolved.Principal, outcome, err
}
func (s *Service) mergePRWithClient(
ctx context.Context,
client Client,
cacheScope string,
owner string,
repo string,
number int,
request MergePRRequest,
) (MergeOutcome, error) {
if request.MergeMethod == "" {
// Resolve to an allowed method up-front so we don't rely on GitHub's
// "default to merge" behavior, which 405s on repos that disallow
// merge commits (squash-only / rebase-only). Best-effort: if the
// lookup fails (or — degenerate config — reports no method allowed),
// fall back to GitHub's default and surface its error rather than
// blocking the merge attempt.
if methods, err := s.getRepoMergeMethods(ctx, client, cacheScope, owner, repo); err == nil {
if pick := pickDefaultMergeMethod(methods); pick != "" {
request.MergeMethod = pick
}
}
}
return client.MergePR(ctx, owner, repo, number, request)
}
// GetRepoMergeMethods returns the merge methods a repo allows, cached for
// a few minutes since repo settings rarely change.
func (s *Service) GetRepoMergeMethods(ctx context.Context, owner, repo string) (RepoMergeMethods, error) {
if s.client == nil {
return RepoMergeMethods{}, ErrNoClient
}
return s.getRepoMergeMethods(ctx, s.client, "legacy", owner, repo)
}
func (s *Service) GetRepoMergeMethodsForWorkspace(
ctx context.Context, workspaceID, userID, owner, repo string,
) (RepoMergeMethods, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return RepoMergeMethods{}, err
}
resolved, err := s.resolvePersonalReadClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
return RepoMergeMethods{}, err
}
return s.getRepoMergeMethods(ctx, resolved.Client, resolved.CacheScope, owner, repo)
}
func (s *Service) getRepoMergeMethods(
ctx context.Context,
client Client,
cacheScope string,
owner string,
repo string,
) (RepoMergeMethods, error) {
key := scopedCacheKey(cacheScope, owner+"/"+repo)
v, err := s.mergeMethodsCache.doOrFetch(key, func() (any, error) {
return client.GetRepoMergeMethods(ctx, owner, repo)
})
if err != nil {
return RepoMergeMethods{}, err
}
return v.(RepoMergeMethods), nil
}
// Merge method identifiers accepted by GitHub's pulls/{number}/merge endpoint
// and used throughout the merge resolution paths.
const (
mergeMethodMerge = "merge"
mergeMethodSquash = "squash"
mergeMethodRebase = "rebase"
)
// pickDefaultMergeMethod picks the merge method to use when the caller
// didn't pin one. Prefers squash (matches the convention most repos in
// this codebase follow) and falls back to merge, then rebase.
func pickDefaultMergeMethod(m RepoMergeMethods) string {
switch {
case m.Squash:
return mergeMethodSquash
case m.Merge:
return mergeMethodMerge
case m.Rebase:
return mergeMethodRebase
default:
return ""
}
}
// --- PR info and feedback (live) ---
// GetPR fetches basic PR details from GitHub.
func (s *Service) GetPR(ctx context.Context, owner, repo string, number int) (*PR, error) {
if s.client != nil {
pr, err := s.client.GetPR(ctx, owner, repo, number)
if !errors.Is(err, ErrNoClient) {
return pr, err
}
}
return getPRAnonymous(ctx, owner, repo, number)
}
func (s *Service) GetPRForWorkspace(
ctx context.Context, workspaceID, userID, owner, repo string, number int,
) (*PR, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return nil, err
}
resolved, err := s.resolvePersonalReadClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
if errors.Is(err, ErrGitHubNotConfigured) {
return getPRAnonymous(ctx, owner, repo, number)
}
return nil, err
}
return resolved.Client.GetPR(ctx, owner, repo, number)
}
// GetPRForAutomation fetches pull-request details through the workspace-owned
// automation credential. It is used by background launch paths that have a
// repository workspace but no interactive user identity.
func (s *Service) GetPRForAutomation(
ctx context.Context, workspaceID, owner, repo string, number int,
) (*PR, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return nil, err
}
resolved, err := s.resolveAutomationClient(ctx, workspaceID, owner, repo)
if err != nil {
return nil, err
}
return resolved.Client.GetPR(ctx, owner, repo, number)
}
// GetIssue fetches basic issue details from GitHub. The create-task dialog is
// currently the only caller and dedupes requests per URL on the frontend.
func (s *Service) GetIssue(ctx context.Context, owner, repo string, number int) (*Issue, error) {
if s.client != nil {
issue, err := s.client.GetIssue(ctx, owner, repo, number)
if !errors.Is(err, ErrNoClient) {
return issue, err
}
}
return getIssueAnonymous(ctx, owner, repo, number)
}
func (s *Service) GetIssueForWorkspace(
ctx context.Context, workspaceID, userID, owner, repo string, number int,
) (*Issue, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return nil, err
}
resolved, err := s.resolvePersonalReadClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
return nil, err
}
return resolved.Client.GetIssue(ctx, owner, repo, number)
}
// GetPRFeedback fetches live PR feedback from GitHub. Cached briefly with
// singleflight coalescing: the task page fires this for the same PR many times
// in quick succession (chat-bar CI chip, detail panel, hover popover — each on
// its own render/mount triggers), and each miss is 4 sequential GitHub REST
// calls. Without this, a burst fanned out into dozens of slow, rate-limited
// duplicate requests. The returned pointer is shared — callers must not mutate it.
func (s *Service) GetPRFeedback(ctx context.Context, owner, repo string, number int) (*PRFeedback, error) {
if s.client == nil {
return nil, fmt.Errorf("github client not available")
}
// No workspace to scope a persist to; this legacy entry point reads only.
return s.getPRFeedback(ctx, s.client, "legacy", "", owner, repo, number)
}
func (s *Service) GetPRFeedbackForWorkspace(
ctx context.Context, workspaceID, userID, owner, repo string, number int,
) (*PRFeedback, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return nil, err
}
resolved, err := s.resolvePersonalReadClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
return nil, err
}
return s.getPRFeedback(ctx, resolved.Client, resolved.CacheScope, workspaceID, owner, repo, number)
}
func (s *Service) getPRFeedback(
ctx context.Context, client Client, cacheScope, workspaceID, owner, repo string, number int,
) (*PRFeedback, error) {
// Detach the upstream call's context from the singleflight leader: a
// cancelled leader (user closes the tab) would otherwise return its
// context error to all co-waiters, cascading a single client disconnect
// into a burst of transient failures across concurrent callers.
// context.WithoutCancel strips the deadline too, so re-attach the
// parent deadline explicitly — without this, a still-active caller's
// timeout wouldn't bound the shared fetch and quota could keep being
// consumed past the deadline.
fetchCtx, cancelFetch := derivedFetchContext(ctx)
defer cancelFetch()
fetchCtx = withWorkflowAttentionCollector(fetchCtx, func(
collectorCtx context.Context, collectorClient Client, collectorOwner, collectorRepo string, pr *PR,
) (*WorkflowAttention, error) {
return s.collectWorkflowAttention(
collectorCtx, collectorClient, cacheScope, collectorOwner, collectorRepo, pr,
)
})
key := scopedCacheKey(cacheScope, prStatusCacheKey(owner, repo, number))
v, err := s.prFeedbackCache.doOrFetch(key, func() (any, error) {
feedback, fetchErr := client.GetPRFeedback(fetchCtx, owner, repo, number)
if fetchErr != nil {
return nil, fetchErr
}
// Persist inside the fetch closure, not around doOrFetch: this runs
// once per real upstream call (TTL miss, singleflight leader) rather
// than on every panel render served from cache, and it inherits
// fetchCtx so a client disconnecting mid-flight can't abort the write
// that its own fetch just earned.
s.persistPRFeedbackState(fetchCtx, workspaceID, feedback)
return feedback, nil
})
if err != nil {
return nil, err
}
return v.(*PRFeedback), nil
}
// GetPRStatus fetches lightweight PR status (review + checks + mergeable).
// Cached briefly so repeat loads of the same list (pagination, re-render,
// back-navigation) don't refetch. The returned pointer is shared — callers
// must not mutate it.
func (s *Service) GetPRStatus(ctx context.Context, owner, repo string, number int) (*PRStatus, error) {
if s.client == nil {
return nil, fmt.Errorf("github client not available")
}
return s.getPRStatus(ctx, s.client, "legacy", owner, repo, number)
}
func (s *Service) GetPRStatusForWorkspace(
ctx context.Context, workspaceID, userID, owner, repo string, number int,
) (*PRStatus, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return nil, err
}
resolved, err := s.resolvePersonalReadClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
return nil, err
}
return s.getPRStatus(ctx, resolved.Client, resolved.CacheScope, owner, repo, number)
}
func (s *Service) getPRStatus(
ctx context.Context, client Client, cacheScope, owner, repo string, number int,
) (*PRStatus, error) {
// Detach the upstream call from the singleflight leader's context; see
// GetPRFeedback for the cascading-cancel + deadline-preserve rationale.
fetchCtx, cancelFetch := derivedFetchContext(ctx)
defer cancelFetch()
fetchCtx = withWorkflowAttentionCollector(fetchCtx, func(
collectorCtx context.Context, collectorClient Client, collectorOwner, collectorRepo string, pr *PR,
) (*WorkflowAttention, error) {
return s.collectWorkflowAttention(
collectorCtx, collectorClient, cacheScope, collectorOwner, collectorRepo, pr,
)
})
key := scopedCacheKey(cacheScope, prStatusCacheKey(owner, repo, number))
v, err := s.prStatusCache.doOrFetch(key, func() (any, error) {
return client.GetPRStatus(fetchCtx, owner, repo, number)
})
if err != nil {
return nil, err
}
return v.(*PRStatus), nil
}
// derivedFetchContext builds the upstream-fetch context used by the
// singleflight-cached GetPRFeedback / GetPRStatus paths. It strips the
// caller's cancellation via context.WithoutCancel so a single client
// disconnect doesn't cascade the same error to all co-waiters, but
// preserves the caller's deadline (when present) so the fetch can't
// outlive the request budget and keep consuming GitHub quota past it.
// Returns the derived context and a cancel func the caller must defer
// to release resources promptly.
func derivedFetchContext(ctx context.Context) (context.Context, context.CancelFunc) {
fetchCtx := context.WithoutCancel(ctx)
if deadline, ok := ctx.Deadline(); ok {
return context.WithDeadline(fetchCtx, deadline)
}
return fetchCtx, func() {}
}
// PRRef identifies a pull request by owner/repo/number.
type PRRef struct {
Owner string `json:"owner"`
Repo string `json:"repo"`
Number int `json:"number"`
}
// prStatusBatchConcurrency bounds how many upstream GetPRStatus calls run in
// parallel. GitHub has per-hour quotas and per-endpoint concurrency limits;
// this is well under both while still collapsing a 25-PR page into a single
// short wait on the client.
const prStatusBatchConcurrency = 8
// GetPRStatusesBatch fetches statuses for multiple PRs concurrently, honoring
// the per-PR cache. The returned map is keyed by prStatusCacheKey; PRs that
// fail to fetch are logged and omitted from the result so one bad repo
// doesn't poison the page.
func (s *Service) GetPRStatusesBatch(ctx context.Context, refs []PRRef) (map[string]*PRStatus, error) {
if s.client == nil {
return nil, fmt.Errorf("github client not available")
}
return s.getPRStatusesBatchWithClient(ctx, s.client, "legacy", refs)
}
func (s *Service) GetPRStatusesBatchForWorkspace(
ctx context.Context, workspaceID, userID string, refs []PRRef,
) (map[string]*PRStatus, error) {
resolved, err := s.resolvePersonalReadClient(ctx, workspaceID, userID, "", "")
if err != nil {
return nil, err
}
settings, err := s.GetWorkspaceSettings(ctx, workspaceID)
if err != nil {
return nil, err
}
filtered := make([]PRRef, 0, len(refs))
for _, ref := range refs {
if repositoryInWorkspaceScope(settings, ref.Owner, ref.Repo) {
filtered = append(filtered, ref)
}
}
visibilityInput := make([]RepoFilter, 0, len(filtered))
for _, ref := range filtered {
visibilityInput = append(visibilityInput, RepoFilter{Owner: ref.Owner, Name: ref.Repo})
}
visible, err := s.automationRepositoryVisibility(ctx, workspaceID, visibilityInput)
if err != nil {
return nil, err
}
allowed := filtered[:0]
for _, ref := range filtered {
if visible[repositoryIdentityKey(ref.Owner, ref.Repo)] {
allowed = append(allowed, ref)
}
}
return s.getPRStatusesBatchWithClient(ctx, resolved.Client, resolved.CacheScope, allowed)
}
func (s *Service) getPRStatusesBatchWithClient(
ctx context.Context, client Client, cacheScope string, refs []PRRef,
) (map[string]*PRStatus, error) {
result := make(map[string]*PRStatus, len(refs))
var mu sync.Mutex
sem := make(chan struct{}, prStatusBatchConcurrency)
var wg sync.WaitGroup
for _, ref := range refs {
if ref.Owner == "" || ref.Repo == "" || ref.Number <= 0 {
continue
}
wg.Add(1)
go func(r PRRef) {
defer wg.Done()
// Release queued goroutines early when the caller disconnects —
// otherwise up to 200 refs queue up serially behind the semaphore
// and each still runs its full upstream fetch.
select {
case sem <- struct{}{}:
case <-ctx.Done():
return
}
defer func() { <-sem }()
status, err := s.getPRStatus(ctx, client, cacheScope, r.Owner, r.Repo, r.Number)
if err != nil {
s.logger.Debug("batch PR status fetch failed",
zap.String("owner", r.Owner),
zap.String("repo", r.Repo),
zap.Int("number", r.Number),
zap.Error(err))
return
}
mu.Lock()
result[prStatusCacheKey(r.Owner, r.Repo, r.Number)] = status
mu.Unlock()
}(ref)
}
wg.Wait()
return result, nil
}
// --- PR files and commits (live) ---
// GetPRFiles fetches files changed in a PR from GitHub.
func (s *Service) GetPRFiles(ctx context.Context, owner, repo string, number int) ([]PRFile, error) {
if s.client == nil {
return nil, fmt.Errorf("github client not available")
}
return s.client.ListPRFiles(ctx, owner, repo, number)
}
func (s *Service) GetPRFilesForWorkspace(
ctx context.Context, workspaceID, userID, owner, repo string, number int,
) ([]PRFile, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return nil, err
}
resolved, err := s.resolvePersonalReadClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
return nil, err
}
return resolved.Client.ListPRFiles(ctx, owner, repo, number)
}
// GetPRCommits fetches commits in a PR from GitHub.
func (s *Service) GetPRCommits(ctx context.Context, owner, repo string, number int) ([]PRCommitInfo, error) {
if s.client == nil {
return nil, fmt.Errorf("github client not available")
}
return s.client.ListPRCommits(ctx, owner, repo, number)
}
// GitHub's pull-request commit endpoint returns at most 250 commits, even
// when pagination has been requested. Treat a response at that limit as
// incomplete because the missing older ancestry can change a safe relation
// into an apparent divergence.
const githubPRCommitHistoryLimit = 250
func completePRCommitHistory(headSHA string, commits []PRCommitInfo) bool {
if headSHA == "" || len(commits) == 0 || len(commits) >= githubPRCommitHistoryLimit {
return false
}
for _, commit := range commits {
if commit.SHA == "" {
return false
}
}
return commits[len(commits)-1].SHA == headSHA
}
func (s *Service) GetPRCommitsForWorkspace(
ctx context.Context, workspaceID, userID, owner, repo string, number int,
) (PRCommitsResult, error) {
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return PRCommitsResult{}, err
}
resolved, err := s.resolvePersonalReadClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
return PRCommitsResult{}, err
}
pr, err := resolved.Client.GetPR(ctx, owner, repo, number)
if err != nil {
return PRCommitsResult{}, fmt.Errorf("get PR #%d for commit history: %w", number, err)
}
if pr == nil {
return PRCommitsResult{}, fmt.Errorf("get PR #%d for commit history: empty response", number)
}
commits, err := resolved.Client.ListPRCommits(ctx, owner, repo, number)
if err != nil {
return PRCommitsResult{}, fmt.Errorf("list PR #%d commits: %w", number, err)
}
return PRCommitsResult{
Commits: commits,
HeadSHA: pr.HeadSHA,
Complete: completePRCommitHistory(pr.HeadSHA, commits),
}, nil
}
// GetPRCommitDetailForWorkspace fetches one commit through the workspace's
// authorized personal read client. It never consults a task worktree.
func (s *Service) GetPRCommitDetailForWorkspace(
ctx context.Context, workspaceID, userID, owner, repo, sha string,
) (PRCommitDetail, error) {
if err := validateGitHubCommitSHA(sha); err != nil {
return PRCommitDetail{}, err
}
if err := s.ensureRepositoryInWorkspaceScope(ctx, workspaceID, owner, repo); err != nil {
return PRCommitDetail{}, err
}
resolved, err := s.resolvePersonalReadClient(ctx, workspaceID, userID, owner, repo)
if err != nil {
return PRCommitDetail{}, err
}
return resolved.Client.GetPRCommitDetail(ctx, owner, repo, sha)
}
// timeEqual compares two nullable time pointers for equality.
func timeEqual(a, b *time.Time) bool {
if a == nil && b == nil {
return true
}
if a == nil || b == nil {
return false
}
return a.Equal(*b)
}
// intPtrEqual compares two nullable int pointers for equality.
func intPtrEqual(a, b *int) bool {
if a == nil && b == nil {
return true
}
if a == nil || b == nil {
return false
}
return *a == *b
}
// boolPtrEqual compares two nullable bool pointers for equality.
func boolPtrEqual(a, b *bool) bool {
if a == nil && b == nil {
return true
}
if a == nil || b == nil {
return false
}
return *a == *b
}
// stringPtrEqual compares two nullable string pointers for equality.
func stringPtrEqual(a, b *string) bool {
if a == nil && b == nil {
return true
}
if a == nil || b == nil {
return false
}
return *a == *b
}