virtualnetwork: allow address_prefix to be null

The azure subnet resource allows for multiple address prefixes using the
address_prefixes argument. The virtual network resource allows inline subnets,
but does not current support this argument. When the address_prefixes argument
is used, address_prefix will be null when terraform refreshes its state causing
terraform to panic. This code updates the virtual network resource to allow
address_prefixes to be used and for address_prefix to be null.

https://bugzilla.redhat.com/show_bug.cgi?id=1808973

azurerm/internal/services/network/resource_arm_virtual_network.go

@@ -106,9 +106,17 @@ func resourceArmVirtualNetwork() *schema.Resource {
 						},
 
 						"address_prefix": {
-							Type:         schema.TypeString,
-							Required:     true,
-							ValidateFunc: validate.NoEmptyStrings,
+							Type:          schema.TypeString,
+							Optional:      true,
+							Deprecated:    "Use the `address_prefixes` property instead.",
+							ConflictsWith: []string{"subnet.0.address_prefixes"},
+						},
+
+						"address_prefixes": {
+							Type:          schema.TypeList,
+							Optional:      true,
+							Elem:          &schema.Schema{Type: schema.TypeString},
+							ConflictsWith: []string{"subnet.0.address_prefix"},
 						},
 
 						"security_group": {
@@ -307,7 +315,29 @@ func expandVirtualNetworkProperties(ctx context.Context, d *schema.ResourceData,
 			}
 			log.Printf("[INFO] Completed GET of Subnet props ")
 
-			prefix := subnet["address_prefix"].(string)
+			var prefixSet bool
+			properties := network.SubnetPropertiesFormat{}
+			if value, ok := subnet["address_prefixes"]; ok {
+				var addressPrefixes []string
+				for _, item := range value.([]interface{}) {
+					addressPrefixes = append(addressPrefixes, item.(string))
+				}
+				properties.AddressPrefixes = &addressPrefixes
+				prefixSet = len(addressPrefixes) > 0
+			}
+			if value, ok := subnet["address_prefix"]; ok {
+				addressPrefix := value.(string)
+				properties.AddressPrefix = &addressPrefix
+				prefixSet = len(addressPrefix) > 0
+			}
+			if properties.AddressPrefixes != nil && len(*properties.AddressPrefixes) == 1 {
+				properties.AddressPrefix = &(*properties.AddressPrefixes)[0]
+				properties.AddressPrefixes = nil
+			}
+			if !prefixSet {
+				return nil, fmt.Errorf("[ERROR] either address_prefix or address_prefixes is required")
+			}
+
 			secGroup := subnet["security_group"].(string)
 
 			//set the props from config and leave the rest intact
@@ -316,7 +346,8 @@ func expandVirtualNetworkProperties(ctx context.Context, d *schema.ResourceData,
 				subnetObj.SubnetPropertiesFormat = &network.SubnetPropertiesFormat{}
 			}
 
-			subnetObj.SubnetPropertiesFormat.AddressPrefix = &prefix
+			subnetObj.SubnetPropertiesFormat.AddressPrefixes = properties.AddressPrefixes
+			subnetObj.SubnetPropertiesFormat.AddressPrefix = properties.AddressPrefix
 
 			if secGroup != "" {
 				subnetObj.SubnetPropertiesFormat.NetworkSecurityGroup = &network.SecurityGroup{
@@ -399,6 +430,14 @@ func flattenVirtualNetworkSubnets(input *[]network.Subnet) *schema.Set {
 			}
 
 			if props := subnet.SubnetPropertiesFormat; props != nil {
+				if prefixes := props.AddressPrefixes; prefixes != nil {
+					var addressPrefixes []string
+					for _, prefix := range *prefixes {
+						addressPrefixes = append(addressPrefixes, prefix)
+					}
+					output["address_prefixes"] = addressPrefixes
+				}
+
 				if prefix := props.AddressPrefix; prefix != nil {
 					output["address_prefix"] = *prefix
 				}
@@ -434,8 +473,21 @@ func resourceAzureSubnetHash(v interface{}) int {
 
 	if m, ok := v.(map[string]interface{}); ok {
 		buf.WriteString(m["name"].(string))
-		buf.WriteString(m["address_prefix"].(string))
-
+		if v, ok := m["address_prefixes"]; ok {
+			switch v.(type) {
+			case []string:
+				for _, a := range v.([]string) {
+					buf.WriteString(a)
+				}
+			case []interface{}:
+				for _, a := range v.([]interface{}) {
+					buf.WriteString(a.(string))
+				}
+			}
+		}
+		if v, ok := m["address_prefix"]; ok {
+			buf.WriteString(v.(string))
+		}
 		if v, ok := m["security_group"]; ok {
 			buf.WriteString(v.(string))
 		}