draft: feat: Unleash as env variable processor

README.md

@@ -341,6 +341,41 @@ have access to implicit `variant` variable.
 {% endfeature %}
 ```
 
+## Environment variable
+
+You can use it within a yaml/xml/php configuration as an environment variable and combine it with others [Environment Variable Processors](https://symfony.com/doc/current/configuration/env_var_processors.html)
+
+### YAML
+```yaml
+# config/services.yaml
+parameters:
+  # The next line in case you need a default value
+  %env(unleash:feature_name)%: false
+  feature_toggle: %env(unleash:feature_name)%
+```
+### XML
+```xml
+<!-- config/services.xml -->
+<?xml version="1.0" encoding="UTF-8" ?>
+<container xmlns="http://symfony.com/schema/dic/services"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns:framework="http://symfony.com/schema/dic/symfony"
+    xsi:schemaLocation="http://symfony.com/schema/dic/services
+        https://symfony.com/schema/dic/services/services-1.0.xsd
+        http://symfony.com/schema/dic/symfony
+        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">
+    <parameters>
+        <parameter key="feature_toggle">%env(unleash:feature_name)%</parameter>
+    </parameters>
+
+</container>
+```
+### PHP
+```php
+// config/services.php
+$container->setParameter('feature_toggle', '%env(unleash:feature_name)%');
+```
+
 ## Custom strategies
 
 Defining custom strategies is very easy because they get automatically injected, you just need to create a class

composer.json

@@ -7,6 +7,7 @@
         "symfony/event-dispatcher": "^5.0 | ^6.0 | ^7.0",
         "symfony/http-client": "^5.0 | ^6.0 | ^7.0",
         "symfony/cache": "^5.0 | ^6.0 | ^7.0",
+        "symfony/dependency-injection": "^5.0 | ^6.0 | ^7.0",
         "nyholm/psr7": "^1.0",
         "unleash/client": "^1.6 | ^2.0",
         "php": "^8.2"

src/DependencyInjection/UnleashEnvVarProcessor.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace Unleash\Client\Bundle\DependencyInjection;
+
+use Symfony\Component\DependencyInjection\EnvVarProcessorInterface;
+use Unleash\Client\Unleash;
+
+final class UnleashEnvVarProcessor implements EnvVarProcessorInterface
+{
+    private Unleash $client;
+
+    public function __construct(Unleash $client)
+    {
+        $this->client = $client;
+    }
+
+    public function getEnv(string $prefix, string $name, \Closure $getEnv): bool
+    {
+        $value = $this->client->isEnabled($name);
+
+        // Env vars declared from yaml/xml files have string type
+        // 1 : Use unleash value first
+        // 2 : Retrieve the value of declared/default env var of unleash value is false or not retrieved
+        return $value || filter_var($getEnv($name), FILTER_VALIDATE_BOOL);
+    }
+
+    /**
+     * @return string[]
+     */
+    public static function getProvidedTypes(): array
+    {
+        return [
+            'unleash' => 'string',
+        ];
+    }
+}

src/Resources/config/services.yaml

@@ -160,3 +160,8 @@ services:
       $cache: '@unleash.client.internal.cache'
     tags:
       - console.command
+
+  unleash.client.env_var_processor:
+    class: Unleash\Client\Bundle\DependencyInjection\UnleashEnvVarProcessor
+    arguments:
+      $client: '@unleash.client.unleash'

src/UnleashClientBundle.php

@@ -9,6 +9,7 @@
 use Unleash\Client\Bundle\DependencyInjection\Compiler\BootstrapResolver;
 use Unleash\Client\Bundle\DependencyInjection\Compiler\CacheServiceResolverCompilerPass;
 use Unleash\Client\Bundle\DependencyInjection\Compiler\HttpServicesResolverCompilerPass;
+use Unleash\Client\Bundle\DependencyInjection\UnleashEnvVarProcessor;
 use Unleash\Client\Strategy\StrategyHandler;
 
 final class UnleashClientBundle extends Bundle
@@ -19,6 +20,8 @@ public function build(ContainerBuilder $container): void
             ->addTag('unleash.client.strategy_handler');
         $container->registerForAutoconfiguration(BootstrapProvider::class)
             ->addTag('unleash.client.bootstrap_provider');
+        $container->registerForAutoconfiguration(UnleashEnvVarProcessor::class)
+            ->addTag('container.env_var_processor');
 
         $container->addCompilerPass(
             new HttpServicesResolverCompilerPass(),