[FEATURE] Allow custom default in getFormValue() conditions function

Resolves: #102077
Releases: main
Change-Id: I6c5428f97e35807dbb22db0e4d862b62ab7c84cf
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81307


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>

typo3/sysext/core/Documentation/Changelog/13.0/Feature-102077-AllowCustomDefaultValueInGetFormValueConditionsFunction.rst

+.. include:: /Includes.rst.txt
+
+.. _feature-102077-1696240251:
+
+===================================================================================
+Feature: #102077 - Allow custom default value in getFormValue() conditions function
+===================================================================================
+
+See :issue:`102077`
+
+Description
+===========
+
+The `getFormValue()` function can be used in conditions of form variants to
+safely retrieve form values. Before, `null` was returned as default value. This
+made it impossible to use this, for example, with the `in` operator to check
+values in multi-value form fields. An additional check was necessary to avoid
+type issues:
+
+..  code-block:: yaml
+
+    variants:
+      - identifier: variant-1
+        condition: 'getFormValue("multiCheckbox") && "foo" in getFormValue("multiCheckbox")'
+
+A second argument has been added to this function to set a custom default value.
+This allows shortening conditions accordingly:
+
+..  code-block:: yaml
+
+    variants:
+      - identifier: variant-1
+        condition: '"foo" in getFormValue("multiCheckbox", [])'
+
+
+Impact
+======
+
+Form variant conditions can be shortened.
+
+.. index:: YAML, ext:form

typo3/sysext/form/Classes/Domain/Condition/Functions/FormConditionFunctionsProvider.php

@@ -45,8 +45,8 @@ class FormConditionFunctionsProvider implements ExpressionFunctionProviderInterf
         return new ExpressionFunction(
             'getFormValue',
             static fn() => null, // Not implemented, we only use the evaluator
-            static function ($arguments, $field) {
-                return $arguments['formValues'][$field] ?? null;
+            static function ($arguments, $field, $default = null) {
+                return $arguments['formValues'][$field] ?? $default;
             }
         );
     }