Twig View Model

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Twig integration for async view models - provides the view() function for accessing resolved data in templates. This package bridges the toppy/async-view-model core with Twig's template engine through compile-time AST scanning and runtime data access.

Installation

composer require toppy/twig-view-model

Requirements

• PHP 8.4+
• Twig 3.23+
• toppy/async-view-model (automatically installed as dependency)

Quick Start

{# Template declares which data it needs, then accesses resolved results #}
{% set [product, error] = view('App\\ViewModel\\ProductViewModel') %}

{% if error %}
    <div class="error">{{ error.message }}</div>
{% elseif product %}
    <h1>{{ product.name }}</h1>
    <p>{{ product.description }}</p>
{% endif %}

Register the extension with Twig:

use Toppy\TwigViewModel\Twig\ViewExtension;
use Toppy\TwigViewModel\Twig\Runtime\ViewModelRuntime;

$twig->addExtension(new ViewExtension($twig->getLoader()));
$twig->addRuntimeLoader(new class implements RuntimeLoaderInterface {
    public function load(string $class): ?object {
        if ($class === ViewModelRuntime::class) {
            return new ViewModelRuntime($viewModelManager);
        }
        return null;
    }
});

Architecture

Key Classes

Class	Purpose
ViewExtension	Twig extension that registers the view() function and AST visitor
ViewDiscoveryVisitor	Node visitor that scans templates at compile-time to discover all view() calls
ViewModelRuntime	Runtime handler for the view() function, interfaces with ViewModelManagerInterface
DoPreloadMethodNode	Twig node that generates a doPreload() method in compiled templates
ViewModelError	Template-facing error representation with structured codes for error handling

Directory Structure

TwigViewModel/
├── Twig/
│   ├── ViewExtension.php           # Twig extension registration
│   ├── Runtime/
│   │   └── ViewModelRuntime.php    # view() function implementation
│   ├── NodeVisitor/
│   │   └── ViewDiscoveryVisitor.php # Compile-time AST scanning
│   └── Node/
│       └── DoPreloadMethodNode.php  # Generates doPreload() method
├── ViewModelError.php               # Error representation for templates
├── Tests/
│   └── Unit/                        # PHPUnit test suite
├── composer.json
└── phpunit.xml

Usage

The view() Function

The view() function retrieves resolved data from a preloaded view model. It returns an indexed array for sequence destructuring:

{% set [data, error] = view('App\\ViewModel\\StockViewModel') %}

The return value is always a 2-element array:

• data - The resolved data object (or null if unavailable)
• error - A ViewModelError object (or null if successful)

Handling Different States

{% set [stock, error] = view('App\\ViewModel\\StockViewModel') %}

{# Error state - resolution failed #}
{% if error %}
    {% if error.code == 'TIMEOUT' %}
        <span>Stock information temporarily unavailable</span>
    {% elseif error.code == 'NOT_FOUND' %}
        <span>Product not found</span>
    {% else %}
        <span>Error: {{ error.message }}</span>
    {% endif %}

{# Success state - data available #}
{% elseif stock %}
    <span>{{ stock.quantity }} in stock</span>

{# No data state - view model returned nothing #}
{% else %}
    <span>Stock information not available</span>
{% endif %}

Error Codes

The ViewModelError maps exceptions to semantic codes:

Code	Exception Type	Description
NOT_FOUND	NotFoundHttpException	Resource doesn't exist
FORBIDDEN	AccessDeniedHttpException	Access denied
UNAUTHORIZED	UnauthorizedHttpException	Authentication required
SERVICE_UNAVAILABLE	ServiceUnavailableHttpException	Backend service down
RATE_LIMITED	TooManyRequestsHttpException	Rate limit exceeded
TIMEOUT	TimeoutException	Request timed out
RESOLUTION_FAILED	ViewModelResolutionException	Generic resolution failure
UNKNOWN	Any other exception	Unexpected error

AST Discovery

The ViewDiscoveryVisitor performs compile-time scanning of Twig templates to discover all view model dependencies. This enables the preloading system to know which view models a template needs before rendering begins.

How It Works

1. Template Compilation: When Twig compiles a template, the visitor scans the AST
2. view() Detection: Finds all view('ClassName') function calls
3. Validation: Verifies each class exists and implements AsyncViewModel
4. Include Scanning: Recursively scans static {% include %} directives
5. Method Injection: Generates a doPreload() method in the compiled template class

Generated doPreload() Method

Each compiled template with view() calls gets a doPreload() method:

// Auto-generated in compiled template
public function doPreload(): array
{
    $classes = [
        'App\\ViewModel\\ProductViewModel',
        'App\\ViewModel\\StockViewModel',
    ];

    // Chain to parent template if exists
    $parentName = $this->doGetParent([]);
    if ($parentName !== false) {
        $parent = $this->load($parentName, 0)->unwrap();
        if (method_exists($parent, 'doPreload')) {
            $classes = array_merge($parent->doPreload(), $classes);
        }
    }

    return array_values(array_unique($classes));
}

This method:

• Returns all view model classes discovered in the template
• Chains to parent templates (for {% extends %} hierarchies)
• Deduplicates results across the inheritance chain

Compile-Time Validation

The visitor validates at compile time:

{# Error: Class does not exist #}
{% set [data, error] = view('App\\NonExistent\\ViewModel') %}
{# Throws: View model class "App\NonExistent\ViewModel" does not exist. #}

{# Error: Class doesn't implement AsyncViewModel #}
{% set [data, error] = view('App\\Entity\\Product') %}
{# Throws: Class "App\Entity\Product" must implement AsyncViewModel. #}

Include Scanning

Static includes are recursively scanned:

{# main.html.twig #}
{% set [product, error] = view('App\\ViewModel\\ProductViewModel') %}
{% include 'partials/stock.html.twig' %}

{# partials/stock.html.twig #}
{% set [stock, error] = view('App\\ViewModel\\StockViewModel') %}

The doPreload() method for main.html.twig will include both ProductViewModel and StockViewModel.

Note: Dynamic includes ({% include variable %}) cannot be scanned at compile-time.

Integration

This package is Layer 1 in the Toppy Stack architecture:

┌─────────────────────────────────────┐
│  symfony-async-twig-bundle (L3)     │  Symfony integration
└──────────────────┬──────────────────┘
                   │
      ┌────────────┴────────────┐
      ▼                         ▼
┌─────────────┐      ┌──────────────────┐
│ twig-prerender (L2)│  twig-streaming   │
└─────────────┘      └──────────────────┘
                   │
         ┌─────────┴─────────┐
         ▼                   ▼
┌─────────────────┐  ┌────────────────────┐
│ twig-view-model │  │                    │
│      (L1)       │  │                    │
└────────┬────────┘  │                    │
         │           │                    │
         └─────┬─────┘                    │
               ▼                          │
┌─────────────────────────────────────────┘
│        async-view-model (L0)
│     Framework-agnostic core
└─────────────────────────────────────────

Dependency on async-view-model

This package depends on toppy/async-view-model for:

• AsyncViewModel interface - Contract for async data fetching
• ViewModelManagerInterface - Orchestrates view model resolution
• NoDataException - Signals no data available (not an error)
• ViewModelNotPreloadedException - Developer error: view model wasn't preloaded
• ViewModelResolutionException - Resolution failed with error details

Testing

Run the test suite:

cd src/Toppy/Component/TwigViewModel
./vendor/bin/phpunit

Or from the monorepo root:

make demo-shell
cd /app/src/Toppy/Component/TwigViewModel && ./vendor/bin/phpunit

Test Coverage

• ViewModelRuntimeTest - Tests the view() function behavior
• ViewModelErrorTest - Tests error code mapping and serialization

License

Proprietary - See LICENSE file for details.