SelectBox: prompt key is always unique

Author: dg

src/Forms/Controls/SelectBox.php

@@ -90,14 +90,22 @@ public function setItems(array $items, bool $useKeys = true)
 
 	public function getControl(): Nette\Utils\Html
 	{
-		$items = $this->prompt === false ? [] : ['' => $this->translate($this->prompt)];
+		$items = [];
 		foreach ($this->options as $key => $value) {
 			$items[is_array($value) ? $this->translate($key) : $key] = $this->translate($value);
 		}
 
 		$attrs = $this->optionAttributes;
 		$attrs['disabled:'] = is_array($this->disabled) ? $this->disabled : null;
 
+		if ($this->prompt !== false) {
+			$promptKey = '';
+			while (isset($items[$promptKey])) {
+				$promptKey .= "\x1";
+			}
+			$items = [$promptKey => $this->translate($this->prompt)] + $items;
+		}
+
 		return Nette\Forms\Helpers::createSelectBox($items, $attrs, $this->value)
 			->addAttributes(parent::getControl()->attrs);
 	}

tests/Forms/Controls.SelectBox.render.phpt

@@ -61,6 +61,20 @@ test('selected 2x', function () {
 });
 
 
+test('unique prompt', function () {
+	$form = new Form;
+	$input = $form->addSelect('list', 'Label', [
+		'' => 'First',
+	])->setPrompt('prompt');
+
+	Assert::same('<select name="list" id="frm-list"><option value="' . "\x01" . '">prompt</option><option value="">First</option></select>', (string) $input->getControl());
+
+	$input->setValue('');
+
+	Assert::same('<select name="list" id="frm-list"><option value="' . "\x01" . '">prompt</option><option value="" selected>First</option></select>', (string) $input->getControl());
+});
+
+
 test('translator & groups', function () {
 	$form = new Form;
 	$input = $form->addSelect('list', 'Label', [