fix crash in serviceAccountDiffSuppress

.changelog/4748.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+compute: fixed bug where terraform would crash if updating from no `service_account.scopes` to more.
+```

google/resource_compute_instance.go

@@ -2242,7 +2242,11 @@ func hash256(raw string) (string, error) {
 }
 
 func serviceAccountDiffSuppress(k, old, new string, d *schema.ResourceData) bool {
-	o, n := d.GetChange(strings.TrimSuffix(k, ".#"))
+	if k != "service_account.#" {
+		return false
+	}
+
+	o, n := d.GetChange("service_account")
 	var l []interface{}
 	if old == "0" && new == "1" {
 		l = n.([]interface{})

google/resource_compute_instance_test.go

@@ -851,6 +851,48 @@ func TestAccComputeInstance_serviceAccount_updated(t *testing.T) {
 	})
 }
 
+func TestAccComputeInstance_serviceAccount_updated0to1to0scopes(t *testing.T) {
+	t.Parallel()
+
+	var instance compute.Instance
+	var instanceName = fmt.Sprintf("tf-test-%s", randString(t, 10))
+
+	vcrTest(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckComputeInstanceDestroyProducer(t),
+		Steps: []resource.TestStep{
+			{
+				Config: testAccComputeInstance_serviceAccount_update01(instanceName),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckComputeInstanceExists(
+						t, "google_compute_instance.foobar", &instance),
+					testAccCheckComputeInstanceScopes(&instance, 0),
+				),
+			},
+			computeInstanceImportStep("us-central1-a", instanceName, []string{"allow_stopping_for_update"}),
+			{
+				Config: testAccComputeInstance_serviceAccount_update4(instanceName),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckComputeInstanceExists(
+						t, "google_compute_instance.foobar", &instance),
+					testAccCheckComputeInstanceScopes(&instance, 1),
+				),
+			},
+			computeInstanceImportStep("us-central1-a", instanceName, []string{"allow_stopping_for_update"}),
+			{
+				Config: testAccComputeInstance_serviceAccount_update01(instanceName),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckComputeInstanceExists(
+						t, "google_compute_instance.foobar", &instance),
+					testAccCheckComputeInstanceScopes(&instance, 0),
+				),
+			},
+			computeInstanceImportStep("us-central1-a", instanceName, []string{"allow_stopping_for_update"}),
+		},
+	})
+}
+
 func TestAccComputeInstance_scheduling(t *testing.T) {
 	t.Parallel()
 
@@ -4009,6 +4051,34 @@ resource "google_compute_instance" "foobar" {
 `, instance)
 }
 
+func testAccComputeInstance_serviceAccount_update4(instance string) string {
+	return fmt.Sprintf(`
+data "google_compute_image" "my_image" {
+  family  = "debian-9"
+  project = "debian-cloud"
+}
+resource "google_compute_instance" "foobar" {
+  name         = "%s"
+  machine_type = "e2-medium"
+  zone         = "us-central1-a"
+  boot_disk {
+    initialize_params {
+      image = data.google_compute_image.my_image.self_link
+    }
+  }
+  network_interface {
+    network = "default"
+  }
+  service_account {
+    scopes = [
+      "userinfo-email",
+    ]
+  }
+  allow_stopping_for_update = true
+}
+`, instance)
+}
+
 func testAccComputeInstance_scheduling(instance string) string {
 	return fmt.Sprintf(`
 data "google_compute_image" "my_image" {