azure: reject bad configuration faster

builder/azure/arm/config.go

@@ -519,6 +519,10 @@ func assertRequiredParametersSet(c *Config, errs *packer.MultiError) {
 		}
 	}
 
+	if c.TempResourceGroupName != "" && c.BuildResourceGroupName != "" {
+		errs = packer.MultiErrorAppend(errs, fmt.Errorf("The settings temp_resource_group_name and build_resource_group_name cannot both be defined.  Please define one or neither."))
+	}
+
 	/////////////////////////////////////////////
 	// Compute
 	toInt := func(b bool) int {

builder/azure/arm/config_test.go

@@ -899,6 +899,31 @@ func TestConfigShouldAcceptManagedImageStorageAccountTypes(t *testing.T) {
 	}
 }
 
+func TestConfigShouldRejectTempAndBuildResourceGroupName(t *testing.T) {
+	config := map[string]interface{}{
+		"capture_name_prefix":    "ignore",
+		"capture_container_name": "ignore",
+		"image_offer":            "ignore",
+		"image_publisher":        "ignore",
+		"image_sku":              "ignore",
+		"location":               "ignore",
+		"storage_account":        "ignore",
+		"resource_group_name":    "ignore",
+		"subscription_id":        "ignore",
+		"communicator":           "none",
+
+		// custom may define one or the other, but not both
+		"temp_resource_group_name": "rgn00",
+		"build_resource_group_name": "rgn00",
+	}
+
+	_, _, err := newConfig(config, getPackerConfiguration())
+	if err == nil {
+		t.Fatal("expected config to reject the use of both temp_resource_group_name and build_resource_group_name")
+	}
+}
+
+
 func getArmBuilderConfiguration() map[string]string {
 	m := make(map[string]string)
 	for _, v := range requiredConfigValues {

website/source/docs/builders/azure.html.md

@@ -134,8 +134,9 @@ When creating a managed image the following two options are required.
     assigned.  Knowing the resource group and VM name allows one to execute commands to update the VM during a Packer
     build, e.g. attach a resource disk to the VM.
 
--   `temp_resource_group_name` (string) name assigned to the temporary resource group created during the build.  If this value is not set, a random
-    value will be assigned. Cannot be used together with `build_resource_group_name`.
+-   `temp_resource_group_name` (string) name assigned to the temporary resource group created during the build.  If this 
+    value is not set, a random value will be assigned. This resource group is deleted at the end of the build. Cannot be
+    used together with `build_resource_group_name`.
 
 -   `tenant_id` (string) The account identifier with which your `client_id` and `subscription_id` are associated. If not
     specified, `tenant_id` will be looked up using `subscription_id`.