minor #944 LiveComponents: nested dependent fields example (bendavies)

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

Discussion
----------

LiveComponents: nested dependent fields example

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Tickets       | instead -->
| License       | MIT

This PR update the LiveComponents dependant form fields example to include a 3rd dependent field which is dependent on the 2nd.

Here, we need to use `FormFactoryInterface::createNamedBuilder()` to get access to `addEventListener()`,
as that method is not available on `FormInterface`.

Some refactoring was done to introduce enums to make this a bit more managable.

![pizza-size](https://github.com/symfony/ux/assets/625392/20b1a2bd-8e25-4eed-9100-f800ae6f0e77)

Commits
-------

166500d LiveComponents: nested dependent fields example

Author: weaverryan

ux.symfony.com/composer.json

@@ -20,6 +20,7 @@
         "symfony/asset-mapper": "6.3.x-dev",
         "symfony/console": "6.3.*",
         "symfony/dotenv": "6.3.*",
+        "symfony/expression-language": "6.3.*",
         "symfony/flex": "^2",
         "symfony/form": "6.3.*",
         "symfony/framework-bundle": "6.3.x-dev",

ux.symfony.com/composer.lock

@@ -0,0 +1,47 @@
+<?php
+
+namespace App\Enum;
+
+enum Food: string
+{
+    case Eggs = 'eggs';
+    case Bacon = 'bacon';
+    case Strawberries = 'strawberries';
+    case Croissant = 'croissant';
+    case Bagel = 'bagel';
+    case Kiwi = 'kiwi';
+    case Avocado = 'avocado';
+    case Waffles = 'waffles';
+    case Pancakes = 'pancakes';
+    case Salad = 'salad';
+    case Tea = 'tea️';
+    case Sandwich = 'sandwich';
+    case Cheese = 'cheese';
+    case Sushi = 'sushi';
+    case Pizza = 'pizza';
+    case Pint = 'pint';
+    case Pasta = 'pasta';
+
+    public function getReadable(): string
+    {
+        return match ($this) {
+            self::Eggs => 'Eggs 🍳',
+            self::Bacon => 'Bacon 🥓',
+            self::Strawberries => 'Strawberries 🍓',
+            self::Croissant => 'Croissant 🥐',
+            self::Bagel => 'Bagel 🥯',
+            self::Kiwi => 'Kiwi 🥝',
+            self::Avocado => 'Avocado 🥑',
+            self::Waffles => 'Waffles 🧇',
+            self::Pancakes => 'Pancakes 🥞',
+            self::Salad => 'Salad 🥙',
+            self::Tea => 'Tea ☕️',
+            self::Sandwich => 'Sandwich 🥪',
+            self::Cheese => 'Cheese 🧀',
+            self::Sushi => 'Sushi 🍱',
+            self::Pizza => 'Pizza 🍕',
+            self::Pint => 'A Pint 🍺',
+            self::Pasta => 'Pasta 🍝',
+        };
+    }
+}

ux.symfony.com/src/Enum/Food.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace App\Enum;
+
+enum Meal: string
+{
+    case Breakfast = 'breakfast';
+    case SecondBreakfast = 'second_breakfast';
+    case Elevenses = 'elevenses';
+    case Lunch = 'lunch';
+    case Dinner = 'dinner';
+
+    public function getReadable(): string
+    {
+        return match ($this) {
+            self::Breakfast => 'Breakfast',
+            self::SecondBreakfast => 'Second Breakfast',
+            self::Elevenses => 'Elevenses',
+            self::Lunch => 'Lunch',
+            self::Dinner => 'Dinner',
+        };
+    }
+
+    /**
+     * @return list<Food>
+     */
+    public function getFoodChoices(): array
+    {
+        return match ($this) {
+            self::Breakfast => [Food::Eggs, Food::Bacon, Food::Strawberries, Food::Croissant],
+            self::SecondBreakfast => [Food::Bagel, Food::Kiwi, Food::Avocado, Food::Waffles],
+            self::Elevenses => [Food::Pancakes, Food::Strawberries, Food::Tea],
+            self::Lunch => [Food::Sandwich, Food::Cheese, Food::Sushi],
+            self::Dinner => [Food::Pizza, Food::Pint, Food::Pasta],
+        };
+    }
+}

ux.symfony.com/src/Enum/Meal.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace App\Enum;
+
+enum PizzaSize: int
+{
+    case Small = 12;
+    case Medium = 14;
+    case Large = 16;
+
+    public function getReadable(): string
+    {
+        return match ($this) {
+            self::Small => '12 inch',
+            self::Medium => '14 inch',
+            self::Large => '16 inch',
+        };
+    }
+}

ux.symfony.com/src/Enum/PizzaSize.php

@@ -2,94 +2,118 @@
 
 namespace App\Form;
 
+use App\Enum\Food;
+use App\Enum\Meal;
+use App\Enum\PizzaSize;
 use App\Model\MealPlan;
 use Symfony\Component\Form\AbstractType;
-use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
+use Symfony\Component\Form\Extension\Core\Type\EnumType;
 use Symfony\Component\Form\FormBuilderInterface;
 use Symfony\Component\Form\FormEvent;
 use Symfony\Component\Form\FormEvents;
+use Symfony\Component\Form\FormFactoryInterface;
 use Symfony\Component\Form\FormInterface;
 use Symfony\Component\OptionsResolver\OptionsResolver;
 
 class MealPlannerForm extends AbstractType
 {
-    public const MEAL_BREAKFAST = 'breakfast';
-    public const MEAL_SECOND_BREAKFAST = 'second breakfast';
-    public const MEAL_ELEVENSES = 'elevenses';
-    public const MEAL_LUNCH = 'lunch';
-    public const MEAL_DINNER = 'dinner';
+    private FormFactoryInterface $factory;
+
+    /**
+     * @var array<string, mixed>
+     */
+    private $dependencies = [];
 
     public function buildForm(FormBuilderInterface $builder, array $options)
     {
-        $choices = [
-            'Breakfast' => self::MEAL_BREAKFAST,
-            'Second Breakfast' => self::MEAL_SECOND_BREAKFAST,
-            'Elevenses' => self::MEAL_ELEVENSES,
-            'Lunch' => self::MEAL_LUNCH,
-            'Dinner' => self::MEAL_DINNER,
-        ];
-        $builder->add('meal', ChoiceType::class, [
-            'choices' => $choices,
+        $this->factory = $builder->getFormFactory();
+
+        $builder->add('meal', EnumType::class, [
+            'class' => Meal::class,
+            'choice_label' => fn (Meal $meal): string => $meal->getReadable(),
             'placeholder' => 'Which meal is it?',
             'autocomplete' => true,
         ]);
 
-        $builder->addEventListener(
-            FormEvents::PRE_SET_DATA,
-            function (FormEvent $event) {
-                // the object tied to your form
-                /** @var ?MealPlan $data */
-                $data = $event->getData();
-
-                $meal = $data?->getMeal();
-                $this->addFoodField($event->getForm(), $meal);
-            }
-        );
+        $builder->addEventListener(FormEvents::PRE_SET_DATA, [$this, 'onPreSetData']);
+        $builder->addEventListener(FormEvents::POST_SUBMIT, [$this, 'onPostSubmit']);
 
-        $builder->get('meal')->addEventListener(
-            FormEvents::POST_SUBMIT,
-            function (FormEvent $event) {
-                // It's important here to fetch $event->getForm()->getData(), as
-                // $event->getData() will get you the client data (that is, the ID)
-                $meal = $event->getForm()->getData();
-
-                // since we've added the listener to the child, we'll have to pass on
-                // the parent to the callback functions!
-                $this->addFoodField($event->getForm()->getParent(), $meal);
-            }
-        );
+        $builder->get('meal')->addEventListener(FormEvents::POST_SUBMIT, [$this, 'storeDependencies']);
+        $builder->get('meal')->addEventListener(FormEvents::POST_SUBMIT, [$this, 'onPostSubmitMeal']);
     }
 
-    public function configureOptions(OptionsResolver $resolver)
+    public function configureOptions(OptionsResolver $resolver): void
     {
         $resolver->setDefaults(['data_class' => MealPlan::class]);
     }
 
-    private function getAvailableFoodChoices(string $meal): array
+    public function onPreSetData(FormEvent $event): void
     {
-        $foods = match ($meal) {
-            self::MEAL_BREAKFAST => ['Eggs 🍳', 'Bacon 🥓', 'Strawberries 🍓', 'Croissant 🥐'],
-            self::MEAL_SECOND_BREAKFAST => ['Bagel 🥯', 'Kiwi 🥝', 'Avocado 🥑', 'Waffles 🧇'],
-            self::MEAL_ELEVENSES => ['Pancakes 🥞', 'Salad 🥙', 'Tea ☕️'],
-            self::MEAL_LUNCH => ['Sandwich 🥪', 'Cheese 🧀', 'Sushi 🍱'],
-            self::MEAL_DINNER => ['Pizza 🍕', 'A Pint 🍺', 'Pasta 🍝'],
-        };
+        // the object tied to your form
+        /** @var ?MealPlan $data */
+        $data = $event->getData();
+
+        $this->addFoodField($event->getForm(), $data?->getMeal());
+        $this->addPizzaSizeField($event->getForm(), $data?->getPizzaSize());
+    }
 
-        $foods = array_combine($foods, $foods);
+    public function onPostSubmit(FormEvent $event): void
+    {
+        $this->dependencies = [];
+    }
 
-        return $foods;
+    public function storeDependencies(FormEvent $event): void
+    {
+        $this->dependencies[$event->getForm()->getName()] = $event->getForm()->getData();
     }
 
-    public function addFoodField(FormInterface $form, ?string $meal)
+    public function onPostSubmitMeal(FormEvent $event): void
     {
-        $foodChoices = null === $meal ? [] : $this->getAvailableFoodChoices($meal);
-
-        $form->add('mainFood', ChoiceType::class, [
-            'placeholder' => null === $meal ? 'Select a meal first' : sprintf('What\'s for %s?', $meal),
-            'choices' => $foodChoices,
-            'disabled' => null === $meal,
-            // silence real-time "invalid" message when switching "meals"
-            'invalid_message' => false,
+        $this->addFoodField(
+            $event->getForm()->getParent(),
+            $this->dependencies['meal'],
+        );
+    }
+
+    public function onPostSubmitFood(FormEvent $event): void
+    {
+        $this->addPizzaSizeField(
+            $event->getForm()->getParent(),
+            $this->dependencies['mainFood'],
+        );
+    }
+
+    public function addFoodField(FormInterface $form, ?Meal $meal): void
+    {
+        $mainFood = $this->factory
+            ->createNamedBuilder('mainFood', EnumType::class, $meal, [
+                'class' => Food::class,
+                'placeholder' => null === $meal ? 'Select a meal first' : sprintf('What\'s for %s?', $meal->getReadable()),
+                'choices' => $meal?->getFoodChoices(),
+                'choice_label' => fn (Food $food): string => $food->getReadable(),
+                'disabled' => null === $meal,
+                // silence real-time "invalid" message when switching "meals"
+                'invalid_message' => false,
+                'autocomplete' => true,
+                'auto_initialize' => false,
+            ])
+            ->addEventListener(FormEvents::POST_SUBMIT, [$this, 'storeDependencies'])
+            ->addEventListener(FormEvents::POST_SUBMIT, [$this, 'onPostSubmitFood']);
+
+        $form->add($mainFood->getForm());
+    }
+
+    public function addPizzaSizeField(FormInterface $form, ?Food $food): void
+    {
+        if (Food::Pizza !== $food) {
+            return;
+        }
+
+        $form->add('pizzaSize', EnumType::class, [
+            'class' => PizzaSize::class,
+            'placeholder' => 'What size pizza?',
+            'choice_label' => fn (PizzaSize $pizzaSize): string => $pizzaSize->getReadable(),
+            'required' => true,
             'autocomplete' => true,
         ]);
     }