cleanly error adding queue to client w/out workers

CHANGELOG.md

@@ -12,6 +12,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Set minimum Go version to Go 1.23. [PR #811](https://github.com/riverqueue/river/pull/811).
 - Deprecate `river.JobInsertMiddlewareDefaults` and `river.WorkerMiddlewareDefaults` in favor of the more general `river.MiddlewareDefaults` embeddable struct. The two former structs will be removed in a future version. [PR #815](https://github.com/riverqueue/river/pull/815).
 
+### Fixed
+
+- Cleanly error when attempting to add a queue at runtime to a `Client` which was not configured to run jobs (no `Workers`). [PR #826](https://github.com/riverqueue/river/pull/826).
+
 ## [0.19.0] - 2025-03-16
 
 ⚠️ Version 0.19.0 has minor breaking changes for the `Worker.Middleware`, introduced fairly recently in 0.17.0 that has a worker's `Middleware` function now taking a non-generic `JobRow` parameter instead of a generic `Job[T]`. We tried not to make this change, but found the existing middleware interface insufficient to provide the necessary range of functionality we wanted, and this is a secondary middleware facility that won't be in use for many users, so it seemed worthwhile.

client.go

@@ -606,7 +606,7 @@ func NewClient[TTx any](driver riverdriver.Driver[TTx], config *Config) (*Client
 		testSignals:          clientTestSignals{},
 		workCancel:           func(cause error) {}, // replaced on start, but here in case StopAndCancel is called before start up
 	}
-	client.queues = &QueueBundle{addProducer: client.addProducer}
+	client.queues = &QueueBundle{addProducer: client.addProducer, clientWillExecuteJobs: config.willExecuteJobs()}
 
 	baseservice.Init(archetype, &client.baseService)
 	client.baseService.Name = "Client" // Have to correct the name because base service isn't embedded like it usually is
@@ -2160,6 +2160,8 @@ type QueueBundle struct {
 	// Function that adds a producer to the associated client.
 	addProducer func(queueName string, queueConfig QueueConfig) *producer
 
+	clientWillExecuteJobs bool
+
 	fetchCtx context.Context //nolint:containedctx
 
 	// Mutex that's acquired when client is starting and stopping and when a
@@ -2174,6 +2176,10 @@ type QueueBundle struct {
 // producer for the queue is started. Context is inherited from the one given to
 // Client.Start.
 func (b *QueueBundle) Add(queueName string, queueConfig QueueConfig) error {
+	if !b.clientWillExecuteJobs {
+		return errors.New("client is not configured to execute jobs, cannot add queue")
+	}
+
 	if err := queueConfig.validate(queueName); err != nil {
 		return err
 	}

client_test.go

@@ -246,6 +246,19 @@ func Test_Client(t *testing.T) {
 		riversharedtest.WaitOrTimeout(t, workedChan)
 	})
 
+	t.Run("Queues_Add_WhenClientWontExecuteJobs", func(t *testing.T) {
+		t.Parallel()
+
+		config, bundle := setupConfig(t)
+		config.Queues = nil
+		config.Workers = nil
+		client := newTestClient(t, bundle.dbPool, config)
+
+		err := client.Queues().Add("new_queue", QueueConfig{MaxWorkers: 2})
+		require.Error(t, err)
+		require.Contains(t, err.Error(), "client is not configured to execute jobs, cannot add queue")
+	})
+
 	t.Run("Queues_Add_BeforeStart", func(t *testing.T) {
 		t.Parallel()