do not enable validator auto mapping by default

src/Symfony/Bridge/Doctrine/Tests/Validator/DoctrineLoaderTest.php

@@ -36,7 +36,7 @@ class DoctrineLoaderTest extends TestCase
 
         $validator = Validation::createValidatorBuilder()
             ->enableAnnotationMapping()
-            ->addLoader(new DoctrineLoader(DoctrineTestHelper::createTestEntityManager()))
+            ->addLoader(new DoctrineLoader(DoctrineTestHelper::createTestEntityManager(), '{^Symfony\\\\Bridge\\\\Doctrine\\\\Tests\\\\Fixtures\\\\DoctrineLoaderEntity$}'))
             ->getValidator()
         ;
 
@@ -111,7 +111,7 @@ class DoctrineLoaderTest extends TestCase
     public function regexpProvider()
     {
         return [
-            [true, null],
+            [false, null],
             [true, '{^'.preg_quote(DoctrineLoaderEntity::class).'$|^'.preg_quote(Entity::class).'$}'],
             [false, '{^'.preg_quote(Entity::class).'$}'],
         ];

src/Symfony/Bridge/Doctrine/Validator/DoctrineLoader.php

@@ -42,7 +42,7 @@ final class DoctrineLoader implements LoaderInterface
     public function loadClassMetadata(ClassMetadata $metadata): bool
     {
         $className = $metadata->getClassName();
-        if (null !== $this->classValidatorRegexp && !preg_match($this->classValidatorRegexp, $className)) {
+        if (null === $this->classValidatorRegexp || !preg_match($this->classValidatorRegexp, $className)) {
             return false;
         }
 

src/Symfony/Component/Validator/DependencyInjection/AddAutoMappingConfigurationPass.php

@@ -70,8 +70,12 @@ class AddAutoMappingConfigurationPass implements CompilerPassInterface
     /**
      * Builds a regexp to check if a class is auto-mapped.
      */
-    private function getRegexp(array $patterns): string
+    private function getRegexp(array $patterns): ?string
     {
+        if (!$patterns) {
+            return null;
+        }
+
         $regexps = [];
         foreach ($patterns as $pattern) {
             // Escape namespace

src/Symfony/Component/Validator/Tests/DependencyInjection/AddAutoMappingConfigurationPassTest.php

@@ -70,4 +70,17 @@ class AddAutoMappingConfigurationPassTest extends TestCase
             ['Symfony\Component\Validator\Tests\Fixtures\\**', ['trailing_double_star'], '{^App\\\\|^Symfony\\\\Component\\\\Validator\\\\Tests\\\\Fixtures\\\\.*?$}'],
         ];
     }
+
+    public function testDoNotMapAllClassesWhenConfigIsEmpty()
+    {
+        $container = new ContainerBuilder();
+        $container->setParameter('validator.auto_mapping', []);
+
+        $container->register('validator.builder', ValidatorBuilder::class);
+        $container->register('loader')->addTag('validator.auto_mapper');
+
+        (new AddAutoMappingConfigurationPass())->process($container);
+
+        $this->assertNull($container->getDefinition('loader')->getArgument('$classValidatorRegexp'));
+    }
 }