Returning a more helpful error message if the function app already ex…

…ists

azurerm/resource_arm_function_app.go

@@ -163,10 +163,25 @@ func resourceArmFunctionApp() *schema.Resource {
 
 func resourceArmFunctionAppCreate(d *schema.ResourceData, meta interface{}) error {
 	client := meta.(*ArmClient).appServicesClient
+	ctx := meta.(*ArmClient).StopContext
 
 	log.Printf("[INFO] preparing arguments for AzureRM Function App creation.")
 
 	name := d.Get("name").(string)
+
+	availabilityRequest := web.ResourceNameAvailabilityRequest{
+		Name: utils.String(name),
+		Type: web.CheckNameResourceTypesMicrosoftWebsites,
+	}
+	available, err := client.CheckNameAvailability(ctx, availabilityRequest)
+	if err != nil {
+		return fmt.Errorf("Error checking if the name %q was available: %+v", name, err)
+	}
+
+	if !*available.NameAvailable {
+		return fmt.Errorf("The name %q used for the Function App needs to be globally unique and isn't available: %s", name, *available.Message)
+	}
+
 	resGroup := d.Get("resource_group_name").(string)
 	location := d.Get("location").(string)
 	kind := "functionapp"
@@ -194,7 +209,6 @@ func resourceArmFunctionAppCreate(d *schema.ResourceData, meta interface{}) erro
 	forceDNSRegistration := false
 	skipCustomDomainVerification := true
 	ttlInSeconds := "60"
-	ctx := meta.(*ArmClient).StopContext
 	createFuture, err := client.CreateOrUpdate(ctx, resGroup, name, siteEnvelope, &skipDNSRegistration, &skipCustomDomainVerification, &forceDNSRegistration, ttlInSeconds)
 	if err != nil {
 		return err