Fix updating NIC stack type for google compute instance

.changelog/9983.txt

@@ -0,0 +1,3 @@
+```release-note:enhancement
+compute: support updating `network_interface.stack_type` field on `google_compute_instance` resource.
+```

google/services/compute/resource_compute_instance.go

@@ -1927,6 +1927,23 @@ func resourceComputeInstanceUpdate(d *schema.ResourceData, meta interface{}) err
 			}
 		}
 
+		if !updateDuringStop && d.HasChange(prefix+".stack_type") {
+
+			networkInterfacePatchObj := &compute.NetworkInterface{
+				StackType:   d.Get(prefix + ".stack_type").(string),
+				Fingerprint: instNetworkInterface.Fingerprint,
+			}
+			updateCall := config.NewComputeClient(userAgent).Instances.UpdateNetworkInterface(project, zone, instance.Name, networkName, networkInterfacePatchObj).Do
+			op, err := updateCall()
+			if err != nil {
+				return errwrap.Wrapf("Error updating network interface: {{err}}", err)
+			}
+			opErr := ComputeOperationWaitTime(config, op, project, "network interface to update", userAgent, d.Timeout(schema.TimeoutUpdate))
+			if opErr != nil {
+				return opErr
+			}
+		}
+
 		if !updateDuringStop && d.HasChange(prefix+".ipv6_address") {
 
 			networkInterfacePatchObj := &compute.NetworkInterface{

google/services/compute/resource_compute_instance_test.go

@@ -2789,6 +2789,33 @@ func testAccCheckComputeInstanceUpdateMachineType(t *testing.T, n string) resour
 	}
 }
 
+func TestAccComputeInstance_NicStackTypeUpdate(t *testing.T) {
+	t.Parallel()
+	suffix := acctest.RandString(t, 10)
+	envRegion := envvar.GetTestRegionFromEnv()
+	instanceName := fmt.Sprintf("tf-test-compute-instance-%s", suffix)
+
+	acctest.VcrTest(t, resource.TestCase{
+		PreCheck:                 func() { acctest.AccTestPreCheck(t) },
+		ProtoV5ProviderFactories: acctest.ProtoV5ProviderFactories(t),
+		CheckDestroy:             testAccCheckComputeInstanceDestroyProducer(t),
+		Steps: []resource.TestStep{
+			{
+				Config: testAccComputeInstance_nicStackTypeUpdate(suffix, envRegion, "IPV4_ONLY", instanceName),
+			},
+			computeInstanceImportStep("us-central1-a", instanceName, []string{"allow_stopping_for_update"}),
+			{
+				Config: testAccComputeInstance_nicStackTypeUpdate(suffix, envRegion, "IPV4_IPV6", instanceName),
+			},
+			computeInstanceImportStep("us-central1-a", instanceName, []string{"allow_stopping_for_update"}),
+			{
+				Config: testAccComputeInstance_nicStackTypeUpdate(suffix, envRegion, "IPV4_ONLY", instanceName),
+			},
+			computeInstanceImportStep("us-central1-a", instanceName, []string{"allow_stopping_for_update"}),
+		},
+	})
+}
+
 func testAccCheckComputeInstanceDestroyProducer(t *testing.T) func(s *terraform.State) error {
 	return func(s *terraform.State) error {
 		config := acctest.GoogleProviderConfig(t)
@@ -7355,3 +7382,51 @@ resource "google_compute_disk" "debian" {
 }
 `, instance, diskName, suffix, suffix, suffix)
 }
+
+func testAccComputeInstance_nicStackTypeUpdate(suffix, region, stack_type, instance string) string {
+	return fmt.Sprintf(`
+data "google_compute_image" "my_image" {
+  family  = "debian-11"
+  project = "debian-cloud"
+}
+
+resource "google_compute_network" "net" {
+  name                    = "tf-test-network-%s"
+  enable_ula_internal_ipv6 = true
+  auto_create_subnetworks = false
+}
+
+resource "google_compute_subnetwork" "subnet-ipv6" {
+  region                     = "%s"
+  name                       = "tf-test-subnet-ip6-%s"
+  ip_cidr_range              = "10.0.0.0/22"
+  purpose                    = "PRIVATE"
+  stack_type                 = "IPV4_IPV6"
+  ipv6_access_type           = "INTERNAL"
+  network                    = google_compute_network.net.id
+}
+
+resource "google_compute_instance" "foobar" {
+  name         = "%s"
+  machine_type = "e2-medium"
+  zone         = "%s-a"
+  tags         = ["foo", "bar"]
+
+  boot_disk {
+    initialize_params {
+      image = data.google_compute_image.my_image.self_link
+    }
+  }
+
+  network_interface {
+    network = google_compute_network.net.self_link
+    subnetwork = google_compute_subnetwork.subnet-ipv6.self_link
+    stack_type = "%s"
+  }
+
+  metadata = {
+    foo = "bar"
+  }
+}
+`, suffix, region, suffix, instance, region, stack_type)
+}