diff suppress the upgradeableTo field

Author: teowa

internal/services/redhatopenshift/redhat_openshift_cluster_resource.go

@@ -482,6 +482,11 @@ func (r RedHatOpenShiftCluster) Arguments() map[string]*pluginsdk.Schema {
 						Type:         pluginsdk.TypeString,
 						Optional:     true,
 						ValidateFunc: validate.ClusterVersion,
+						DiffSuppressFunc: func(_, old, new string, _ *pluginsdk.ResourceData) bool {
+							// The backend does not support clearing upgradeable_to via PATCH;
+							// suppress the diff so removing it from config is a no-op.
+							return old != "" && new == ""
+						},
 					},
 				},
 			},

website/docs/r/redhat_openshift_cluster.html.markdown

@@ -241,7 +241,7 @@ A `platform_workload_identity_profile` block supports the following:
 
 * `platform_workload_identity` - (Required) One or more `platform_workload_identity` blocks as defined above.
 
-* `upgradeable_to` - (Optional) The target OpenShift version (`x.y.z`) the platform workload identities should satisfy.
+* `upgradeable_to` - (Optional) The target OpenShift version (`x.y.z`) the platform workload identities should satisfy. Once set, this value cannot be cleared.
 
 ---