[Agent] Allow translatable prompts in SystemPromptInputProcessor

Author: VincentLanglet

src/agent/composer.json

@@ -42,6 +42,7 @@
         "symfony/dom-crawler": "^7.3|^8.0",
         "symfony/event-dispatcher": "^7.3|^8.0",
         "symfony/http-foundation": "^7.3|^8.0",
+        "symfony/translation": "^7.3|^8.0",
         "symfony/translation-contracts": "^3.6"
     },
     "autoload": {

src/agent/src/InputProcessor/SystemPromptInputProcessor.php

@@ -19,6 +19,7 @@
 use Symfony\AI\Agent\Toolbox\ToolboxInterface;
 use Symfony\AI\Platform\Message\Message;
 use Symfony\AI\Platform\Tool\Tool;
+use Symfony\Contracts\Translation\TranslatableInterface;
 use Symfony\Contracts\Translation\TranslatorInterface;
 
 /**
@@ -27,19 +28,17 @@
 final readonly class SystemPromptInputProcessor implements InputProcessorInterface
 {
     /**
-     * @param \Stringable|string    $systemPrompt the system prompt to prepend to the input messages
-     * @param ToolboxInterface|null $toolbox      the tool box to be used to append the tool definitions to the system prompt
+     * @param \Stringable|TranslatableInterface|string $systemPrompt the system prompt to prepend to the input messages
+     * @param ToolboxInterface|null                    $toolbox      the tool box to be used to append the tool definitions to the system prompt
      */
     public function __construct(
-        private \Stringable|string $systemPrompt,
+        private \Stringable|TranslatableInterface|string $systemPrompt,
         private ?ToolboxInterface $toolbox = null,
         private ?TranslatorInterface $translator = null,
-        private bool $enableTranslation = false,
-        private ?string $translationDomain = null,
         private LoggerInterface $logger = new NullLogger(),
     ) {
-        if ($this->enableTranslation && !$this->translator) {
-            throw new RuntimeException('Prompt translation is enabled but no translator was provided.');
+        if ($this->systemPrompt instanceof TranslatableInterface && !$this->translator) {
+            throw new RuntimeException('Translatable system prompt is not supported when no translator is provided.');
         }
     }
 
@@ -53,8 +52,8 @@ public function processInput(Input $input): void
             return;
         }
 
-        $message = $this->enableTranslation
-            ? $this->translator->trans((string) $this->systemPrompt, [], $this->translationDomain)
+        $message = $this->systemPrompt instanceof TranslatableInterface
+            ? $this->systemPrompt->trans($this->translator)
             : (string) $this->systemPrompt;
 
         if ($this->toolbox instanceof ToolboxInterface

src/agent/tests/InputProcessor/SystemPromptInputProcessorTest.php

@@ -29,6 +29,7 @@
 use Symfony\AI\Platform\Result\ToolCall;
 use Symfony\AI\Platform\Tool\ExecutionReference;
 use Symfony\AI\Platform\Tool\Tool;
+use Symfony\Component\Translation\TranslatableMessage;
 use Symfony\Contracts\Translation\TranslatorInterface;
 
 #[CoversClass(SystemPromptInputProcessor::class)]
@@ -106,7 +107,7 @@ public function execute(ToolCall $toolCall): mixed
     public function testIncludeToolDefinitions()
     {
         $processor = new SystemPromptInputProcessor(
-            'This is a',
+            new TranslatableMessage('This is a'),
             new class implements ToolboxInterface {
                 public function getTools(): array
                 {
@@ -130,7 +131,6 @@ public function execute(ToolCall $toolCall): mixed
                 }
             },
             $this->getTranslator(),
-            true,
         );
 
         $input = new Input(new Gpt(), new MessageBag(Message::ofUser('This is a user message')));
@@ -196,7 +196,7 @@ public function execute(ToolCall $toolCall): mixed
 
     public function testWithTranslatedSystemPrompt()
     {
-        $processor = new SystemPromptInputProcessor('This is a', null, $this->getTranslator(), true);
+        $processor = new SystemPromptInputProcessor(new TranslatableMessage('This is a'), null, $this->getTranslator());
 
         $input = new Input(new Gpt(), new MessageBag(Message::ofUser('This is a user message')), []);
         $processor->processInput($input);
@@ -211,11 +211,9 @@ public function testWithTranslatedSystemPrompt()
     public function testWithTranslationDomainSystemPrompt()
     {
         $processor = new SystemPromptInputProcessor(
-            'This is a',
+            new TranslatableMessage('This is a', domain: 'prompts'),
             null,
             $this->getTranslator(),
-            true,
-            'prompts'
         );
 
         $input = new Input(new Gpt(), new MessageBag(), []);
@@ -229,13 +227,12 @@ public function testWithTranslationDomainSystemPrompt()
 
     public function testWithMissingTranslator()
     {
-        $this->expectExceptionMessage('Prompt translation is enabled but no translator was provided');
+        $this->expectExceptionMessage('Translatable system prompt is not supported when no translator is provided.');
 
         new SystemPromptInputProcessor(
-            'This is a',
+            new TranslatableMessage('This is a'),
             null,
             null,
-            true,
         );
     }
 

src/ai-bundle/composer.json

@@ -29,7 +29,8 @@
         "phpstan/phpstan": "^2.1",
         "phpunit/phpunit": "^11.5",
         "symfony/expression-language": "^7.3|^8.0",
-        "symfony/security-core": "^7.3|^8.0"
+        "symfony/security-core": "^7.3|^8.0",
+        "symfony/translation": "^7.3|^8.0"
     },
     "autoload": {
         "psr-4": {

src/ai-bundle/src/AiBundle.php

@@ -84,6 +84,7 @@
 use Symfony\Component\HttpClient\HttpClient;
 use Symfony\Component\HttpKernel\Bundle\AbstractBundle;
 use Symfony\Component\Security\Core\Authorization\AuthorizationCheckerInterface;
+use Symfony\Component\Translation\TranslatableMessage;
 use Symfony\Contracts\HttpClient\HttpClientInterface;
 
 use function Symfony\Component\String\u;
@@ -623,13 +624,21 @@ private function processAgentConfig(string $name, array $config, ContainerBuilde
         if (isset($config['prompt'])) {
             $includeTools = isset($config['prompt']['include_tools']) && $config['prompt']['include_tools'];
 
+            if ($config['prompt']['enable_translation']) {
+                if (!class_exists(TranslatableMessage::class)) {
+                    throw new RuntimeException('For using prompt translataion, symfony/translation package is required. Try running "composer require symfony/translation".');
+                }
+
+                $prompt = new TranslatableMessage($config['prompt']['text'], domain: $config['prompt']['translation_domain']);
+            } else {
+                $prompt = $config['prompt']['text'];
+            }
+
             $systemPromptInputProcessorDefinition = (new Definition(SystemPromptInputProcessor::class))
                 ->setArguments([
-                    $config['prompt']['text'],
+                    $prompt,
                     $includeTools ? new Reference('ai.toolbox.'.$name) : null,
                     new Reference('translator', ContainerInterface::NULL_ON_INVALID_REFERENCE),
-                    $config['prompt']['enable_translation'],
-                    $config['prompt']['translation_domain'],
                     new Reference('logger', ContainerInterface::IGNORE_ON_INVALID_REFERENCE),
                 ])
                 ->addTag('ai.agent.input_processor', ['agent' => $agentId, 'priority' => -30]);

src/ai-bundle/tests/DependencyInjection/AiBundleTest.php

@@ -34,6 +34,7 @@
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\DependencyInjection\Definition;
 use Symfony\Component\DependencyInjection\Reference;
+use Symfony\Component\Translation\TranslatableMessage;
 
 #[CoversClass(AiBundle::class)]
 #[UsesClass(ContainerBuilder::class)]
@@ -682,10 +683,8 @@ public function testSystemPromptWithArrayStructure()
         $definition = $container->getDefinition('ai.agent.test_agent.system_prompt_processor');
         $arguments = $definition->getArguments();
 
-        $this->assertSame('You are a helpful assistant.', $arguments[0]);
+        $this->assertEquals(new TranslatableMessage('You are a helpful assistant.', domain: 'prompts'), $arguments[0]);
         $this->assertNull($arguments[1]); // include_tools is false, so null reference
-        $this->assertTrue($arguments[3]);
-        $this->assertSame('prompts', $arguments[4]);
     }
 
     #[TestDox('System prompt with include_tools enabled works correctly')]