Fix issue 2621

Author: stehled

src/LiveComponent/composer.json

@@ -31,6 +31,7 @@
         "symfony/property-access": "^5.4.5|^6.0|^7.0",
         "symfony/property-info": "^5.4|^6.0|^7.0",
         "symfony/stimulus-bundle": "^2.9",
+        "symfony/translation-contracts": "^2.5|^3.0",
         "symfony/ux-twig-component": "^2.8",
         "twig/twig": "^3.8.0"
     },

src/LiveComponent/src/ComponentWithFormTrait.php

@@ -16,6 +16,7 @@
 use Symfony\Component\Form\FormInterface;
 use Symfony\Component\Form\FormView;
 use Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException;
+use Symfony\Contracts\Translation\TranslatableInterface;
 use Symfony\UX\LiveComponent\Attribute\LiveProp;
 use Symfony\UX\LiveComponent\Attribute\PreReRender;
 use Symfony\UX\LiveComponent\Util\LiveFormUtility;
@@ -286,7 +287,10 @@ private function extractFormValues(FormView $formView): array
                 )
                 && !$child->vars['expanded']                // is a <select>     (not a radio/checkbox)
                 && !$child->vars['multiple']                // is not multiple
-                && !\is_string($child->vars['placeholder'])  // has no placeholder (empty string is valid)
+                && (
+                    !\is_string($child->vars['placeholder'])
+                    && !$child->vars['placeholder'] instanceof TranslatableInterface
+                )                                           // has no placeholder (empty string is valid, translatable interface is valid)
             ) {
                 $choices = $child->vars['preferred_choices'] ?: $child->vars['choices']; // preferred_choices has precedence, as they rendered before regular choices
                 do {