symfony/twig-bundle

The `symfony/twig-bundle` is the official integration of the Twig templating engine into the Symfony framework. It provides a robust and flexible way to render views in Symfony applications, leveraging all the powerful features of Twig while seamlessly integrating with Symfony's architecture.

Purpose and Functionality:
1. View Rendering: Its primary purpose is to allow developers to use Twig templates (`.html.twig` files) for generating HTML responses from Symfony controllers. It provides a `render()` method (accessible via `AbstractController` or the `Twig\Environment` service) that takes a template path and an array of variables.
2. Configuration: It registers and configures the Twig environment as a service (`twig.environment` or simply `twig`). Developers can customize Twig's behavior (e.g., template paths, caching, debug mode, global variables, extensions) through configuration files, typically `config/packages/twig.yaml`.
3. Dependency Injection Integration: The Twig environment and related services are available through Symfony's dependency injection container, making it easy to use Twig in any service or controller.
4. Symfony-Specific Extensions: It automatically registers several Symfony-specific Twig extensions that provide useful functions, filters, and global variables for common tasks:
* Asset Management: The `asset()` function helps manage static assets (CSS, JavaScript, images) with features like versioning and CDN integration.
* Routing: The `path()` and `url()` functions generate URLs based on Symfony routes.
* Translation: The `trans()` filter/function integrates with Symfony's translation component.
* Security: Provides functions for checking user roles (`is_granted()`) and retrieving user information.
* Forms: Offers dedicated functions and macros (`form_start()`, `form_row()`, etc.) for rendering Symfony forms, making it incredibly easy to display complex forms.
* WebLink: Provides functions to render `Link` HTTP headers for things like preloading assets.
5. Caching: Twig compiles templates into PHP classes for performance. The bundle manages the caching of these compiled templates.
6. Debugging: When Symfony is in debug mode, `twig-bundle` provides enhanced debugging tools for Twig templates, including error reporting with precise line numbers.

In essence, `symfony/twig-bundle` is crucial for any Symfony application that requires a view layer. It bridges the gap between the application's business logic (controllers) and its presentation (templates), providing a powerful, flexible, and well-integrated templating solution.

```php
<?php

namespace App\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Annotation\Route;

class ProductController extends AbstractController
{
    /
     * @Route("/products", name="product_list")
     * 
     * This method demonstrates rendering a Twig template using symfony/twig-bundle.
     * It fetches some dummy product data and passes it to the template.
     */
    public function listProducts(): Response
    {
        // In a real application, you would fetch data from a database or service
        $products = [
            ['id' => 1, 'name' => 'Laptop', 'price' => 1200.00],
            ['id' => 2, 'name' => 'Mouse', 'price' => 25.50],
            ['id' => 3, 'name' => 'Keyboard', 'price' => 75.99],
            ['id' => 4, 'name' => 'Monitor', 'price' => 300.00]
        ];

        // The `render` method is provided by AbstractController (which uses Twig internally).
        // It takes the template path (relative to `templates/`) and an array of variables.
        return $this->render('product/list.html.twig', [
            'page_title' => 'Our Product Catalog',
            'products' => $products,
            'currency_symbol' => '$'
        ]);
    }

    /
     * A corresponding Twig template (templates/product/list.html.twig) might look like this:
     * 
     * ```twig
     * {# templates/product/list.html.twig #}
     * {% extends 'base.html.twig' %}
     *
     * {% block title %}{{ page_title }}{% endblock %}
     *
     * {% block body %}
     *     <h1>{{ page_title }}</h1>
     *
     *     {% if products is not empty %}
     *         <table>
     *             <thead>
     *                 <tr>
     *                     <th>ID</th>
     *                     <th>Name</th>
     *                     <th>Price</th>
     *                 </tr>
     *             </thead>
     *             <tbody>
     *                 {% for product in products %}
     *                     <tr>
     *                         <td>{{ product.id }}</td>
     *                         <td>{{ product.name }}</td>
     *                         <td>{{ currency_symbol }}{{ product.price|number_format(2, '.', ',') }}</td>
     *                     </tr>
     *                 {% endfor %}
     *             </tbody>
     *         </table>
     *     {% else %}
     *         <p>No products available.</p>
     *     {% endif %}
     * {% endblock %}
     * ```
     */
}
```