From 1ff7c3adaf6b3f28a04e509a5a7204689e24ca06 Mon Sep 17 00:00:00 2001
From: James Harris <contact@jamesharris.id.au>
Date: Wed, 26 Jun 2024 13:36:38 +1000
Subject: [PATCH] Panic if `EnableHandler()` option is passed an unrecognized
 handler name.

---
 engine/engine.go                 |  4 ++--
 engine/operationoption.go        | 25 +++++++++++++++----------
 internal/fixtures/protobuf.pb.go |  8 ++++----
 3 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/engine/engine.go b/engine/engine.go
index 9fd5b666..42ac91c0 100644
--- a/engine/engine.go
+++ b/engine/engine.go
@@ -89,7 +89,7 @@ func (e *Engine) Tick(
 	ctx context.Context,
 	options ...OperationOption,
 ) error {
-	oo := newOperationOptions(options)
+	oo := newOperationOptions(e, options)
 
 	oo.observers.Notify(
 		fact.TickCycleBegun{
@@ -198,7 +198,7 @@ func (e *Engine) Dispatch(
 		))
 	}
 
-	oo := newOperationOptions(options)
+	oo := newOperationOptions(e, options)
 	t := message.TypeOf(m)
 
 	if _, ok := e.routes[t]; !ok {
diff --git a/engine/operationoption.go b/engine/operationoption.go
index 0f5a4f9e..f446fb9e 100644
--- a/engine/operationoption.go
+++ b/engine/operationoption.go
@@ -1,6 +1,7 @@
 package engine
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/dogmatiq/configkit"
@@ -10,13 +11,13 @@ import (
 // OperationOption applies optional settings while dispatching a message or
 // performing a tick.
 type OperationOption interface {
-	applyOperationOption(*operationOptions)
+	applyOperationOption(*Engine, *operationOptions)
 }
 
-type operationOptionFunc func(*operationOptions)
+type operationOptionFunc func(*Engine, *operationOptions)
 
-func (f operationOptionFunc) applyOperationOption(opts *operationOptions) {
-	f(opts)
+func (f operationOptionFunc) applyOperationOption(e *Engine, opts *operationOptions) {
+	f(e, opts)
 }
 
 // WithObserver returns an option that registers the given observer for the
@@ -28,7 +29,7 @@ func WithObserver(o fact.Observer) OperationOption {
 		panic("observer must not be nil")
 	}
 
-	return operationOptionFunc(func(oo *operationOptions) {
+	return operationOptionFunc(func(_ *Engine, oo *operationOptions) {
 		oo.observers = append(oo.observers, o)
 	})
 }
@@ -70,7 +71,7 @@ func EnableProjections(enabled bool) OperationOption {
 func enableHandlerType(t configkit.HandlerType, enabled bool) OperationOption {
 	t.MustValidate()
 
-	return operationOptionFunc(func(oo *operationOptions) {
+	return operationOptionFunc(func(_ *Engine, oo *operationOptions) {
 		oo.enabledHandlerTypes[t] = enabled
 	})
 }
@@ -85,7 +86,11 @@ func EnableHandler(name string, enabled bool) OperationOption {
 		panic(err)
 	}
 
-	return operationOptionFunc(func(oo *operationOptions) {
+	return operationOptionFunc(func(e *Engine, oo *operationOptions) {
+		if _, ok := e.controllers[name]; !ok {
+			panic(fmt.Sprintf("the application does not have a handler named %q", name))
+		}
+
 		oo.enabledHandlers[name] = enabled
 	})
 }
@@ -93,7 +98,7 @@ func EnableHandler(name string, enabled bool) OperationOption {
 // WithCurrentTime returns an operation option that sets the engine's current
 // time.
 func WithCurrentTime(t time.Time) OperationOption {
-	return operationOptionFunc(func(oo *operationOptions) {
+	return operationOptionFunc(func(_ *Engine, oo *operationOptions) {
 		oo.now = t
 	})
 }
@@ -108,7 +113,7 @@ type operationOptions struct {
 }
 
 // newOperationOptions returns a new operationOptions with the given options.
-func newOperationOptions(options []OperationOption) *operationOptions {
+func newOperationOptions(e *Engine, options []OperationOption) *operationOptions {
 	oo := &operationOptions{
 		now: time.Now(),
 		enabledHandlerTypes: map[configkit.HandlerType]bool{
@@ -121,7 +126,7 @@ func newOperationOptions(options []OperationOption) *operationOptions {
 	}
 
 	for _, opt := range options {
-		opt.applyOperationOption(oo)
+		opt.applyOperationOption(e, oo)
 	}
 
 	return oo
diff --git a/internal/fixtures/protobuf.pb.go b/internal/fixtures/protobuf.pb.go
index ff19522e..93d0ea24 100644
--- a/internal/fixtures/protobuf.pb.go
+++ b/internal/fixtures/protobuf.pb.go
@@ -1,7 +1,7 @@
 // Code generated by protoc-gen-go. DO NOT EDIT.
 // versions:
-// 	protoc-gen-go v1.33.0
-// 	protoc        v4.23.4
+// 	protoc-gen-go v1.34.2
+// 	protoc        v5.27.2
 // source: github.com/dogmatiq/testkit/internal/fixtures/protobuf.proto
 
 package fixtures
@@ -98,7 +98,7 @@ func file_github_com_dogmatiq_testkit_internal_fixtures_protobuf_proto_rawDescGZ
 }
 
 var file_github_com_dogmatiq_testkit_internal_fixtures_protobuf_proto_msgTypes = make([]protoimpl.MessageInfo, 1)
-var file_github_com_dogmatiq_testkit_internal_fixtures_protobuf_proto_goTypes = []interface{}{
+var file_github_com_dogmatiq_testkit_internal_fixtures_protobuf_proto_goTypes = []any{
 	(*ProtoMessage)(nil), // 0: dogmatiq.testkit.fixtures.ProtoMessage
 }
 var file_github_com_dogmatiq_testkit_internal_fixtures_protobuf_proto_depIdxs = []int32{
@@ -115,7 +115,7 @@ func file_github_com_dogmatiq_testkit_internal_fixtures_protobuf_proto_init() {
 		return
 	}
 	if !protoimpl.UnsafeEnabled {
-		file_github_com_dogmatiq_testkit_internal_fixtures_protobuf_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+		file_github_com_dogmatiq_testkit_internal_fixtures_protobuf_proto_msgTypes[0].Exporter = func(v any, i int) any {
 			switch v := v.(*ProtoMessage); i {
 			case 0:
 				return &v.state