Add retaining unchanged alias ip ranges and handle permadiff caused by the change

.changelog/11321.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+compute: fixed maintaining unchanged `alias_ip_range` in `compute_instance` in between PATCH API calls and handled permadiff caused by the change
+```

go.mod

@@ -26,6 +26,7 @@ require (
 	github.com/mitchellh/go-homedir v1.1.0
 	github.com/mitchellh/hashstructure v1.1.0
 	github.com/sirupsen/logrus v1.8.1
+	github.com/stretchr/testify v1.9.0
 	go4.org/netipx v0.0.0-20231129151722-fdeea329fbba
 	golang.org/x/exp v0.0.0-20240409090435-93d18d7e34b8
 	golang.org/x/net v0.27.0
@@ -90,6 +91,7 @@ require (
 	github.com/mitchellh/mapstructure v1.5.0 // indirect
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/oklog/run v1.0.0 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/rogpeppe/go-internal v1.12.0 // indirect
 	github.com/vmihailenco/msgpack v4.0.4+incompatible // indirect
 	github.com/vmihailenco/msgpack/v5 v5.4.1 // indirect
@@ -114,4 +116,5 @@ require (
 	google.golang.org/genproto v0.0.0-20240730163845-b1a4ccb954bf // indirect
 	google.golang.org/genproto/googleapis/api v0.0.0-20240725223205-93522f1f2a9f // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

google/services/compute/compute_instance_helpers.go

@@ -51,15 +51,28 @@ func expandAliasIpRanges(ranges []interface{}) []*compute.AliasIpRange {
 	return ipRanges
 }
 
-func flattenAliasIpRange(ranges []*compute.AliasIpRange) []map[string]interface{} {
-	rangesSchema := make([]map[string]interface{}, 0, len(ranges))
+func flattenAliasIpRange(d *schema.ResourceData, ranges []*compute.AliasIpRange, i int) []map[string]interface{} {
+	prefix := fmt.Sprintf("network_interface.%d", i)
+
+	configData := []map[string]interface{}{}
+	for _, item := range d.Get(prefix + ".alias_ip_range").([]interface{}) {
+		configData = append(configData, item.(map[string]interface{}))
+	}
+
+	apiData := make([]map[string]interface{}, 0, len(ranges))
 	for _, ipRange := range ranges {
-		rangesSchema = append(rangesSchema, map[string]interface{}{
+		apiData = append(apiData, map[string]interface{}{
 			"ip_cidr_range":         ipRange.IpCidrRange,
 			"subnetwork_range_name": ipRange.SubnetworkRangeName,
 		})
 	}
-	return rangesSchema
+
+	//permadiff fix
+	sorted, err := tpgresource.SortMapsByConfigOrder(configData, apiData, "ip_cidr_range")
+	if err != nil {
+		return apiData
+	}
+	return sorted
 }
 
 func expandScheduling(v interface{}) (*compute.Scheduling, error) {
@@ -363,7 +376,7 @@ func flattenNetworkInterfaces(d *schema.ResourceData, config *transport_tpg.Conf
 			"subnetwork":         tpgresource.ConvertSelfLinkToV1(iface.Subnetwork),
 			"subnetwork_project": subnet.Project,
 			"access_config":      ac,
-			"alias_ip_range":     flattenAliasIpRange(iface.AliasIpRanges),
+			"alias_ip_range":     flattenAliasIpRange(d, iface.AliasIpRanges, i),
 			"nic_type":           iface.NicType,
 			"stack_type":         iface.StackType,
 			"ipv6_access_config": flattenIpv6AccessConfigs(iface.Ipv6AccessConfigs),

google/services/compute/resource_compute_instance.go

@@ -1988,6 +1988,9 @@ func resourceComputeInstanceUpdate(d *schema.ResourceData, meta interface{}) err
 					Fingerprint:     instNetworkInterface.Fingerprint,
 					ForceSendFields: []string{"AliasIpRanges"},
 				}
+				if commonAliasIpRanges := CheckForCommonAliasIp(instNetworkInterface, networkInterface); len(commonAliasIpRanges) > 0 {
+					ni.AliasIpRanges = commonAliasIpRanges
+				}
 				op, err := config.NewComputeClient(userAgent).Instances.UpdateNetworkInterface(project, zone, instance.Name, networkName, ni).Do()
 				if err != nil {
 					return errwrap.Wrapf("Error removing alias_ip_range: {{err}}", err)
@@ -3011,3 +3014,20 @@ func isEmptyServiceAccountBlock(d *schema.ResourceData) bool {
 	}
 	return false
 }
+
+// Alias ip ranges cannot be removed and created at the same time. This checks if there are any unchanged alias ip ranges
+// to be kept in between the PATCH operations on Network Interface
+func CheckForCommonAliasIp(old, new *compute.NetworkInterface) []*compute.AliasIpRange {
+	newAliasIpMap := make(map[string]bool)
+	for _, ipRange := range new.AliasIpRanges {
+		newAliasIpMap[ipRange.IpCidrRange] = true
+	}
+
+	resultAliasIpRanges := make([]*compute.AliasIpRange, 0)
+	for _, val := range old.AliasIpRanges {
+		if newAliasIpMap[val.IpCidrRange] {
+			resultAliasIpRanges = append(resultAliasIpRanges, val)
+		}
+	}
+	return resultAliasIpRanges
+}