hashing function added for natIps

.changelog/4537.txt

@@ -0,0 +1,4 @@
+```release-note:bug
+compute : fixed a perma-diff for `nat_ips` that were specified as short forms in `google_compute_router_nat`
+
+```

google-beta/resource_compute_router_nat.go

@@ -20,6 +20,7 @@ import (
 	"log"
 	"reflect"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
@@ -104,6 +105,15 @@ func computeRouterNatSubnetworkHash(v interface{}) int {
 	return schema.HashString(NameFromSelfLinkStateFunc(name)) + sourceIpRangesHash + secondaryIpRangeHash
 }
 
+func computeRouterNatIPsHash(v interface{}) int {
+	val := (v.(string))
+	newParts := strings.Split(val, "/")
+	if len(newParts) == 1 {
+		return schema.HashString(newParts[0])
+	}
+	return schema.HashString(GetResourceNameFromSelfLink(val))
+}
+
 func resourceComputeRouterNat() *schema.Resource {
 	return &schema.Resource{
 		Create: resourceComputeRouterNatCreate,
@@ -221,7 +231,7 @@ is set to MANUAL_ONLY.`,
 					Type:             schema.TypeString,
 					DiffSuppressFunc: compareSelfLinkOrResourceName,
 				},
-				// Default schema.HashSchema is used.
+				Set: computeRouterNatIPsHash,
 			},
 			"region": {
 				Type:             schema.TypeString,

google-beta/resource_compute_router_nat_test.go

@@ -86,6 +86,22 @@ func TestAccComputeRouterNat_update(t *testing.T) {
 				ImportState:       true,
 				ImportStateVerify: true,
 			},
+			{
+				Config: testAccComputeRouterNatUpdateToNatIPsId(routerName),
+			},
+			{
+				ResourceName:      "google_compute_router_nat.foobar",
+				ImportState:       true,
+				ImportStateVerify: true,
+			},
+			{
+				Config: testAccComputeRouterNatUpdateToNatIPsName(routerName),
+			},
+			{
+				ResourceName:      "google_compute_router_nat.foobar",
+				ImportState:       true,
+				ImportStateVerify: true,
+			},
 			{
 				Config: testAccComputeRouterNatBasicBeforeUpdate(routerName),
 			},
@@ -409,6 +425,108 @@ resource "google_compute_router_nat" "foobar" {
 `, routerName, routerName, routerName, routerName, routerName)
 }
 
+func testAccComputeRouterNatUpdateToNatIPsId(routerName string) string {
+	return fmt.Sprintf(`
+resource "google_compute_router" "foobar" {
+name    = "%s"
+region  = google_compute_subnetwork.foobar.region
+network = google_compute_network.foobar.self_link
+}
+
+resource "google_compute_network" "foobar" {
+name = "%s-net"
+}
+resource "google_compute_subnetwork" "foobar" {
+name          = "%s-subnet"
+network       = google_compute_network.foobar.self_link
+ip_cidr_range = "10.0.0.0/16"
+region        = "us-central1"
+}
+
+resource "google_compute_address" "foobar" {
+name   = "%s-addr"
+region = google_compute_subnetwork.foobar.region
+}
+
+resource "google_compute_router_nat" "foobar" {
+  name   = "%s"
+  router = google_compute_router.foobar.name
+  region = google_compute_router.foobar.region
+
+  nat_ip_allocate_option = "MANUAL_ONLY"
+  nat_ips                = [google_compute_address.foobar.id]
+
+  source_subnetwork_ip_ranges_to_nat = "LIST_OF_SUBNETWORKS"
+
+  subnetwork {
+    name                    = google_compute_subnetwork.foobar.self_link
+    source_ip_ranges_to_nat = ["ALL_IP_RANGES"]
+  }
+
+  udp_idle_timeout_sec             = 60
+  icmp_idle_timeout_sec            = 60
+  tcp_established_idle_timeout_sec = 1600
+  tcp_transitory_idle_timeout_sec  = 60
+
+  log_config {
+    enable = true
+    filter = "TRANSLATIONS_ONLY"
+  }
+}
+`, routerName, routerName, routerName, routerName, routerName)
+}
+
+func testAccComputeRouterNatUpdateToNatIPsName(routerName string) string {
+	return fmt.Sprintf(`
+resource "google_compute_router" "foobar" {
+name    = "%s"
+region  = google_compute_subnetwork.foobar.region
+network = google_compute_network.foobar.self_link
+}
+
+resource "google_compute_network" "foobar" {
+name = "%s-net"
+}
+resource "google_compute_subnetwork" "foobar" {
+name          = "%s-subnet"
+network       = google_compute_network.foobar.self_link
+ip_cidr_range = "10.0.0.0/16"
+region        = "us-central1"
+}
+
+resource "google_compute_address" "foobar" {
+name   = "%s-addr"
+region = google_compute_subnetwork.foobar.region
+}
+
+resource "google_compute_router_nat" "foobar" {
+  name   = "%s"
+  router = google_compute_router.foobar.name
+  region = google_compute_router.foobar.region
+
+  nat_ip_allocate_option = "MANUAL_ONLY"
+  nat_ips                = [google_compute_address.foobar.name]
+
+  source_subnetwork_ip_ranges_to_nat = "LIST_OF_SUBNETWORKS"
+
+  subnetwork {
+    name                    = google_compute_subnetwork.foobar.self_link
+    source_ip_ranges_to_nat = ["ALL_IP_RANGES"]
+  }
+
+  udp_idle_timeout_sec             = 60
+  icmp_idle_timeout_sec            = 60
+  tcp_established_idle_timeout_sec = 1600
+  tcp_transitory_idle_timeout_sec  = 60
+
+  log_config {
+    enable = true
+    filter = "TRANSLATIONS_ONLY"
+  }
+}
+`, routerName, routerName, routerName, routerName, routerName)
+}
+
 func testAccComputeRouterNatWithManualIpAndSubnetConfiguration(routerName string) string {
 	return fmt.Sprintf(`
 resource "google_compute_network" "foobar" {