Using Nette\Utils\Html as label with validation causes: rtrim() expects parameter 1 to be string, object given

[JanMikes]

Version: 3.0.1

Bug Description

When using Nette\Utils\Html as caption/label for input, it will fail on TypeError in validator. This code worked in 2.4

Steps To Reproduce

$label = \Nette\Utils\Html::el()->setHtml('<i>Demo</i>');
        
$form->addText('demo', $label)
    ->setRequired('Please fill in %label.');

Expected Behavior

To not throw exception and return (string) $html in %label placeholder.

Possible Solution

This fix worked for us:

+                   $caption = $rule->control->getCaption();
                    return $rule->control instanceof Controls\BaseControl
-                        ? rtrim($rule->control->translate($rule->control->getCaption()), ':')
+                        ? $caption instanceof Nette\Utils\Html ? $caption : rtrim($rule->control->translate($caption), ':')
                        : null;