Remove ContextDeriver and related functions (#430)

This was added as a way to create a detatched context for async
schedulers that still had some of the values of the original. Starting
in Go 1.21, the standard library now provides the WithoutCancel function
to make a copy of the values in a context but with a different lifetime.

Custom implementations of ContextDervier are likely very rare (if they
exist at all) and their main purpose would be to copy context values
other than the logger. Since WithoutCancel now copies all values, I
don't see any reason to keep supporting custom functions.

While we could deprecate the existing functions, their rare usage
combined with the fact that we frequently release breaking changes for
go-github upgrades makes me believe this is safe.

Author: bluekeyes

githubapp/scheduler.go

@@ -77,22 +77,6 @@ func MetricsAsyncErrorCallback(reg metrics.Registry) AsyncErrorCallback {
 	}
 }
 
-// ContextDeriver creates a new independent context from a request's context.
-// The new context must be based on context.Background(), not the input.
-type ContextDeriver func(context.Context) context.Context
-
-// DefaultContextDeriver copies the logger from the request's context to a new
-// context.
-func DefaultContextDeriver(ctx context.Context) context.Context {
-	newCtx := context.Background()
-
-	// this value is always unused by async schedulers, but is set for
-	// compatibility with existing handlers that call SetResponder
-	newCtx = InitializeResponder(newCtx)
-
-	return zerolog.Ctx(ctx).WithContext(newCtx)
-}
-
 // Scheduler is a strategy for executing event handlers.
 //
 // The Schedule method takes a Dispatch and executes it by calling the handler
@@ -120,16 +104,6 @@ func WithAsyncErrorCallback(onError AsyncErrorCallback) SchedulerOption {
 	}
 }
 
-// WithContextDeriver sets the context deriver for an asynchronous scheduler.
-// If not set, the scheduler uses DefaultContextDeriver.
-func WithContextDeriver(deriver ContextDeriver) SchedulerOption {
-	return func(s *scheduler) {
-		if deriver != nil {
-			s.deriver = deriver
-		}
-	}
-}
-
 // WithSchedulingMetrics enables metrics reporting for schedulers.
 func WithSchedulingMetrics(r metrics.Registry) SchedulerOption {
 	return func(s *scheduler) {
@@ -155,7 +129,6 @@ type queueDispatch struct {
 // core functionality and options for (async) schedulers
 type scheduler struct {
 	onError AsyncErrorCallback
-	deriver ContextDeriver
 
 	activeWorkers int64
 	queue         chan queueDispatch
@@ -183,13 +156,6 @@ func (s *scheduler) safeExecute(ctx context.Context, d Dispatch) {
 	err = d.Execute(ctx)
 }
 
-func (s *scheduler) derive(ctx context.Context) context.Context {
-	if s.deriver == nil {
-		return ctx
-	}
-	return s.deriver(ctx)
-}
-
 // DefaultScheduler returns a scheduler that executes handlers in the go
 // routine of the caller and returns any error.
 func DefaultScheduler() Scheduler {
@@ -207,7 +173,6 @@ func (s *defaultScheduler) Schedule(ctx context.Context, d Dispatch) error {
 func AsyncScheduler(opts ...SchedulerOption) Scheduler {
 	s := &asyncScheduler{
 		scheduler: scheduler{
-			deriver: DefaultContextDeriver,
 			onError: DefaultAsyncErrorCallback,
 		},
 	}
@@ -222,7 +187,7 @@ type asyncScheduler struct {
 }
 
 func (s *asyncScheduler) Schedule(ctx context.Context, d Dispatch) error {
-	go s.safeExecute(s.derive(ctx), d)
+	go s.safeExecute(context.WithoutCancel(ctx), d)
 	return nil
 }
 
@@ -239,7 +204,6 @@ func QueueAsyncScheduler(queueSize int, workers int, opts ...SchedulerOption) Sc
 
 	s := &queueScheduler{
 		scheduler: scheduler{
-			deriver: DefaultContextDeriver,
 			onError: DefaultAsyncErrorCallback,
 			queue:   make(chan queueDispatch, queueSize),
 		},
@@ -268,7 +232,7 @@ type queueScheduler struct {
 
 func (s *queueScheduler) Schedule(ctx context.Context, d Dispatch) error {
 	select {
-	case s.queue <- queueDispatch{ctx: s.derive(ctx), t: time.Now(), d: d}:
+	case s.queue <- queueDispatch{ctx: context.WithoutCancel(ctx), t: time.Now(), d: d}:
 	default:
 		if s.dropped != nil {
 			s.dropped.Inc(1)