FIX Make AJAX validation work on the front-end again

Author: GuySartorelli

_config/extensions.yml

@@ -4,7 +4,3 @@ Name: signify-composable-validators-extensions
 SilverStripe\Forms\Form:
   extensions:
     - Signify\ComposableValidators\Extensions\FormExtension
-
-SilverStripe\Admin\LeftAndMain:
-  extensions:
-    - Signify\ComposableValidators\Extensions\LeftAndMainAjaxValidationExtension

src/Extensions/LeftAndMainAjaxValidationExtension.php

@@ -7,6 +7,7 @@
 use SilverStripe\Control\HTTPRequest;
 use SilverStripe\Core\ArrayLib;
 use SilverStripe\Forms\Form;
+use SilverStripe\Forms\FormAction;
 use SilverStripe\Forms\Validation\CompositeValidator;
 use SilverStripe\Forms\Validation\Validator;
 use SilverStripe\View\Requirements;
@@ -51,6 +52,11 @@ class AjaxCompositeValidator extends CompositeValidator
     public function setForm(Form $form): static
     {
         if ($this->ajax) {
+            // We need to add a hidden validation-exempt action to prevent unexpected errors
+            $form->Actions()->add(
+                // Name matches the method in FormExtension that gets called to handle ajax validation.
+                FormAction::create('app_ajaxValidate')->setValidationExempt(true)->setTemplate('HiddenFormAction')
+            );
             Requirements::javascript(
                 'guysartorelli/silverstripe-composable-validators:client/dist/AjaxCompositeValidator.js',
                 ['defer' => true]