Fail Nexus Operation for incompatible input type (#1800)

internal/workflow.go

@@ -28,6 +28,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"reflect"
 	"strings"
 	"time"
 
@@ -2649,13 +2650,18 @@ func (wc *workflowEnvironmentInterceptor) prepareNexusOperationParams(ctx Contex
 	var ok bool
 	var operationName string
 	if operationName, ok = input.Operation.(string); ok {
-	} else if regOp, ok := input.Operation.(interface{ Name() string }); ok {
+	} else if regOp, ok := input.Operation.(interface {
+		Name() string
+		InputType() reflect.Type
+	}); ok {
 		operationName = regOp.Name()
+		inputType := reflect.TypeOf(input.Input)
+		if inputType != nil && !inputType.AssignableTo(regOp.InputType()) {
+			return executeNexusOperationParams{}, fmt.Errorf("cannot assign argument of type %s to type %s for operation %s", inputType.Name(), regOp.InputType().Name(), operationName)
+		}
 	} else {
 		return executeNexusOperationParams{}, fmt.Errorf("invalid 'operation' parameter, must be an OperationReference or a string")
 	}
-	// TODO(bergundy): Validate operation types against input once there's a good way to extract the generic types from
-	// OperationReference in the Nexus Go SDK.
 
 	payload, err := dc.ToPayload(input.Input)
 	if err != nil {

test/nexus_test.go

@@ -557,6 +557,25 @@ func TestSyncOperationFromWorkflow(t *testing.T) {
 	})
 }
 
+func TestInvalidOperationInput(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
+	defer cancel()
+	tc := newTestContext(t, ctx)
+
+	wf := func(ctx workflow.Context) error {
+		c := workflow.NewNexusClient(tc.endpoint, "test")
+		fut := c.ExecuteOperation(ctx, workflowOp, 3456, workflow.NexusOperationOptions{})
+		return fut.Get(ctx, nil)
+	}
+	w := worker.New(tc.client, tc.taskQueue, worker.Options{})
+	w.RegisterWorkflow(wf)
+	w.Start()
+	t.Cleanup(w.Stop)
+	run, err := tc.client.ExecuteWorkflow(ctx, client.StartWorkflowOptions{TaskQueue: tc.taskQueue}, wf)
+	require.NoError(t, err)
+	require.ErrorContains(t, run.Get(ctx, nil), `cannot assign argument of type int to type string for operation workflow-op`)
+}
+
 func TestSignalOperationFromWorkflow(t *testing.T) {
 	receiverID := "nexus-signal-receiver-" + uuid.NewString()