Fix network field in google_compute_region_backend_service to force new on change (#15136) (#10738)

[upstream:6158b93d13d6d5a6b4de3118b2f92a17f6118bf5]

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/15136.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+compute: The network field in 'google_compute_region_backend_service' is now correctly handled, forcing a new resource on change. This resolves the "Network field cannot be modified" error when trying to add, remove, or modify a network on an existing resource
+```

google-beta/services/compute/resource_compute_region_backend_service.go

@@ -947,9 +947,12 @@ The default value is 1.0.`,
 			"network": {
 				Type:             schema.TypeString,
 				Optional:         true,
+				ForceNew:         true,
 				DiffSuppressFunc: tpgresource.CompareSelfLinkOrResourceName,
 				Description: `The URL of the network to which this backend service belongs.
-This field can only be specified when the load balancing scheme is set to INTERNAL.`,
+This field must be set for Internal Passthrough Network Load Balancers when the haPolicy is enabled, and for External Passthrough Network Load Balancers when the haPolicy fastIpMove is enabled.
+This field can only be specified when the load balancing scheme is set to INTERNAL, or when the load balancing scheme is set to EXTERNAL and haPolicy fastIpMove is enabled.
+Changes to this field force recreation of the resource.`,
 			},
 			"outlier_detection": {
 				Type:     schema.TypeList,

website/docs/r/compute_region_backend_service.html.markdown

@@ -888,7 +888,9 @@ The following arguments are supported:
 * `network` -
   (Optional)
   The URL of the network to which this backend service belongs.
-  This field can only be specified when the load balancing scheme is set to INTERNAL.
+  This field must be set for Internal Passthrough Network Load Balancers when the haPolicy is enabled, and for External Passthrough Network Load Balancers when the haPolicy fastIpMove is enabled.
+  This field can only be specified when the load balancing scheme is set to INTERNAL, or when the load balancing scheme is set to EXTERNAL and haPolicy fastIpMove is enabled.
+  Changes to this field force recreation of the resource.
 
 * `subsetting` -
   (Optional, [Beta](https://terraform.io/docs/providers/google/guides/provider_versions.html))