bug #2491 [LiveComponent] Fix ComponentWithFormTrait::extractFormValues() with edge cases (smnandre)

This PR was squashed before being merged into the 2.x branch.

Discussion
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[LiveComponent] Fix `ComponentWithFormTrait::extractFormValues()` with edge cases

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Issues        | Fix #2487
| License       | MIT

#2403 fixed an old bug to simulate browser behaviour when a select field has no option selected,  no placeholder, and is required (it then uses the first option)
#2425 and #2426 fixed the way we handled empty strings as placeholders

In #2487 `@maciazek` explained us how a custom type with a "choices" option became unusable since the last changes.

Also.. while I was reading all this I realized we returned wrong values here when "option groups" were used.. leading to other problems.

I updated the code of `extractFormValues()` method to:
* check if most of the caracteristic keys added in `ChoiceType::buildView` were defined in the `$view->vars`, to ensure we are dealing with a `<select>` field built by a `ChoiceType`
* fetch recursively the value of the first displayed option (even with groups)

Commits
-------

b7f1ba437 [LiveComponent] Fix `ComponentWithFormTrait::extractFormValues()` with edge cases

Author: smnandre

src/ComponentWithFormTrait.php

@@ -11,6 +11,7 @@
 
 namespace Symfony\UX\LiveComponent;
 
+use Symfony\Component\Form\ChoiceList\View\ChoiceGroupView;
 use Symfony\Component\Form\ClearableErrorsInterface;
 use Symfony\Component\Form\FormInterface;
 use Symfony\Component\Form\FormView;
@@ -255,25 +256,39 @@ private function extractFormValues(FormView $formView): array
                 continue;
             }
 
+            // <input type="checkbox">
             if (\array_key_exists('checked', $child->vars)) {
-                // special handling for check boxes
                 $values[$name] = $child->vars['checked'] ? $child->vars['value'] : null;
                 continue;
             }
 
-            if (\array_key_exists('choices', $child->vars)
-                && $child->vars['required']
-                && !$child->vars['disabled']
-                && !$child->vars['value']
-                && (false === $child->vars['placeholder'] || null === $child->vars['placeholder'])
-                && !$child->vars['multiple']
-                && !$child->vars['expanded']
-                && $child->vars['choices']
+            // <select> - Simulate browser behavior
+            // When no option is selected, browsers send the value of the first
+            // option, when the following conditions are met:
+            if (
+                \array_key_exists('choices', $child->vars)
+                && $child->vars['choices']                  // has defined choices
+                && $child->vars['required']                 // is required
+                && !$child->vars['disabled']                // is not disabled
+                && '' === $child->vars['value']             // has no value set  ("0" can be a value)
+                && !array_diff_key(
+                    /* @see \Symfony\Component\Form\Extension\Core\Type\ChoiceType::buildView() */
+                    array_flip(['choices', 'expanded', 'multiple', 'placeholder', 'placeholder_in_choices', 'preferred_choices']),
+                    $child->vars,
+                )
+                && !$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)
             ) {
-                if (null !== $firstKey = array_key_first($child->vars['choices'])) {
-                    $values[$name] = $child->vars['choices'][$firstKey]->value ?? null;
-                }
-
+                $choices = $child->vars['choices'];
+                do {
+                    $choice = $choices[array_key_first($choices)];
+                    if (!$choice instanceof ChoiceGroupView) {
+                        break;
+                    }
+                } while ($choices = $choice->choices);
+
+                $values[$name] = $choice?->value;
                 continue;
             }
 

tests/Fixtures/Form/FormWithManyDifferentFieldsType.php

@@ -65,6 +65,15 @@ public function buildForm(FormBuilderInterface $builder, array $options)
                     'foo' => 1,
                 ],
             ])
+            ->add('choice_required_without_placeholder_and_choice_group', ChoiceType::class, [
+                'choices' => [
+                    'Bar Group' => [
+                        'Bar Label' => 'ok',
+                        'Foo Label' => 'foo_value',
+                    ],
+                    'foo' => 1,
+                ],
+            ])
             ->add('choice_expanded', ChoiceType::class, [
                 'choices' => [
                     'foo' => 1,

tests/Functional/Form/ComponentWithFormTest.php

@@ -181,6 +181,7 @@ public function testHandleCheckboxChanges(): void
             'choice_required_with_placeholder' => '',
             'choice_required_with_empty_placeholder' => '',
             'choice_required_without_placeholder' => '2',
+            'choice_required_without_placeholder_and_choice_group' => 'ok',
             'choice_expanded' => '',
             'choice_multiple' => ['2'],
             'select_multiple' => ['2'],

tests/Unit/Form/ComponentWithFormTest.php

@@ -46,6 +46,7 @@ public function testFormValues(): void
                 'choice_required_with_placeholder' => '',
                 'choice_required_with_empty_placeholder' => '',
                 'choice_required_without_placeholder' => '2',
+                'choice_required_without_placeholder_and_choice_group' => 'ok',
                 'choice_expanded' => '',
                 'choice_multiple' => ['2'],
                 'select_multiple' => ['2'],