Fix patching in stateful disks1

.changelog/7254.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+compute: added possibility to remove `stateful_disks` in `compute_instance_group_manager` and `compute_region_instance_group_manager`.
+```

google/resource_compute_instance_group_manager.go

@@ -877,23 +877,57 @@ func expandAutoHealingPolicies(configured []interface{}) []*compute.InstanceGrou
 }
 
 func expandStatefulPolicy(d *schema.ResourceData) *compute.StatefulPolicy {
+
 	preservedState := &compute.StatefulPolicyPreservedState{}
-	stateful_disks := d.Get("stateful_disk").(*schema.Set).List()
-	disks := make(map[string]compute.StatefulPolicyPreservedStateDiskDevice)
-	for _, raw := range stateful_disks {
-		data := raw.(map[string]interface{})
-		disk := compute.StatefulPolicyPreservedStateDiskDevice{
-			AutoDelete: data["delete_rule"].(string),
+
+	isRemovingAStatefulDisk := false
+	if d.HasChange("stateful_disk") {
+		oldDisks, newDisks := d.GetChange("stateful_disk")
+		preservedState.Disks = expandStatefulDisks(newDisks.(*schema.Set).List())
+		// Remove Disks
+		for _, raw := range oldDisks.(*schema.Set).List() {
+			data := raw.(map[string]interface{})
+			deviceName := data["device_name"].(string)
+			if _, exist := preservedState.Disks[deviceName]; !exist {
+				isRemovingAStatefulDisk = true
+				preservedState.NullFields = append(preservedState.NullFields, "Disks."+deviceName)
+			}
 		}
-		disks[data["device_name"].(string)] = disk
+		preservedState.ForceSendFields = append(preservedState.ForceSendFields, "Disks")
 	}
-	preservedState.Disks = disks
+	if !isRemovingAStatefulDisk {
+		preservedState := &compute.StatefulPolicyPreservedState{}
+		stateful_disks := d.Get("stateful_disk").(*schema.Set).List()
+		disks := make(map[string]compute.StatefulPolicyPreservedStateDiskDevice)
+		for _, raw := range stateful_disks {
+			data := raw.(map[string]interface{})
+			disk := compute.StatefulPolicyPreservedStateDiskDevice{
+				AutoDelete: data["delete_rule"].(string),
+			}
+			disks[data["device_name"].(string)] = disk
+		}
+		preservedState.Disks = disks
+	}
+
 	statefulPolicy := &compute.StatefulPolicy{PreservedState: preservedState}
 	statefulPolicy.ForceSendFields = append(statefulPolicy.ForceSendFields, "PreservedState")
 
 	return statefulPolicy
 }
 
+func expandStatefulDisks(statefulDisk []interface{}) map[string]compute.StatefulPolicyPreservedStateDiskDevice {
+	statefulDisksMap := make(map[string]compute.StatefulPolicyPreservedStateDiskDevice)
+
+	for _, raw := range statefulDisk {
+		data := raw.(map[string]interface{})
+		deviceName := compute.StatefulPolicyPreservedStateDiskDevice{
+			AutoDelete: data["delete_rule"].(string),
+		}
+		statefulDisksMap[data["device_name"].(string)] = deviceName
+	}
+	return statefulDisksMap
+}
+
 func expandVersions(configured []interface{}) []*compute.InstanceGroupManagerVersion {
 	versions := make([]*compute.InstanceGroupManagerVersion, 0, len(configured))
 	for _, raw := range configured {

google/resource_compute_instance_group_manager_test.go

@@ -1493,6 +1493,10 @@ resource "google_compute_instance_group_manager" "igm-basic" {
     device_name = "my-stateful-disk"
     delete_rule = "NEVER"
   }
+  stateful_disk {
+    device_name = "my-stateful-disk2"
+    delete_rule = "ON_PERMANENT_INSTANCE_DELETION"
+  }
 
 }
 
@@ -1570,10 +1574,6 @@ resource "google_compute_instance_group_manager" "igm-basic" {
   base_instance_name = "tf-test-igm-basic"
   zone               = "us-central1-c"
   target_size        = 2
-  stateful_disk {
-    device_name = "my-stateful-disk"
-    delete_rule = "NEVER"
-  }
 }
 `, network, template, target, igm)
 }

google/resource_compute_region_instance_group_manager_test.go

@@ -1507,14 +1507,6 @@ resource "google_compute_region_instance_group_manager" "igm-basic" {
     max_surge_fixed              = 0
     max_unavailable_fixed        = 6
   }
-  stateful_disk {
-    device_name = "stateful-disk"
-    delete_rule = "NEVER"
-  }
-  stateful_disk {
-    device_name = "stateful-disk2"
-    delete_rule = "ON_PERMANENT_INSTANCE_DELETION"
-  }
 }
 `, network, template, igm)
 }