no need to TaskStateUpdated to return an error

also updated comments

client/allocrunnerv2/alloc_runner.go

@@ -233,14 +233,10 @@ func (ar *allocRunner) Restore() error {
 	})
 }
 
-// TaskStateUpdated is called when a task's state has been updated. This hook is
-// used to compute changes to the alloc's ClientStatus and to update the server
-// with the new state.
-func (ar *allocRunner) TaskStateUpdated(taskName string, state *structs.TaskState) error {
-	if state == nil {
-		return fmt.Errorf("nil state given to TaskStateUpdated")
-	}
-
+// TaskStateUpdated is called by TaskRunner when a task's state has been
+// updated. This hook is used to compute changes to the alloc's ClientStatus
+// and to update the server with the new state.
+func (ar *allocRunner) TaskStateUpdated(taskName string, state *structs.TaskState) {
 	// If a task is dead, we potentially want to kill other tasks in the group
 	if state.State == structs.TaskStateDead {
 		// Find all tasks that are not the one that is dead and check if the one
@@ -293,8 +289,6 @@ func (ar *allocRunner) TaskStateUpdated(taskName string, state *structs.TaskStat
 	if err := ar.stateUpdater.AllocStateUpdated(calloc); err != nil {
 		ar.logger.Error("failed to update remote allocation state", "error", err)
 	}
-
-	return nil
 }
 
 // clientAlloc takes in the task states and returns an Allocation populated

client/allocrunnerv2/interfaces/runner.go

@@ -23,5 +23,5 @@ type AllocRunner interface {
 // TaskStateHandler exposes a handler to be called when a task's state changes
 type TaskStateHandler interface {
 	// TaskStateUpdated is used to emit updated task state
-	TaskStateUpdated(task string, state *structs.TaskState) error
+	TaskStateUpdated(task string, state *structs.TaskState)
 }

client/allocrunnerv2/taskrunner/task_runner.go

@@ -519,10 +519,8 @@ func (tr *TaskRunner) SetState(state string, event *structs.TaskEvent) {
 	// Update the local state
 	stateCopy := tr.setStateLocal(state, event)
 
-	// Create a copy and notify the alloc runner of the transition
-	if err := tr.stateUpdater.TaskStateUpdated(tr.taskName, stateCopy); err != nil {
-		tr.logger.Error("failed to update remote state", "error", err)
-	}
+	// Notify the alloc runner of the transition
+	tr.stateUpdater.TaskStateUpdated(tr.taskName, stateCopy)
 }
 
 // setStateLocal updates the local in-memory state, persists a copy to disk and returns a