[Form] Add "form_attr" FormType option

src/Symfony/Component/Form/Extension/Core/Type/FormType.php

@@ -96,6 +96,16 @@ class FormType extends BaseType
             }
 
             $helpTranslationParameters = array_merge($view->parent->vars['help_translation_parameters'], $helpTranslationParameters);
+
+            $rootFormAttrOption = $form->getRoot()->getConfig()->getOption('form_attr');
+            if ($options['form_attr'] || $rootFormAttrOption) {
+                $view->vars['attr']['form'] = \is_string($rootFormAttrOption) ? $rootFormAttrOption : $form->getRoot()->getName();
+                if (empty($view->vars['attr']['form'])) {
+                    throw new LogicException('"form_attr" option must be a string identifier on root form when it has no id.');
+                }
+            }
+        } elseif (\is_string($options['form_attr'])) {
+            $view->vars['id'] = $options['form_attr'];
         }
 
         $formConfig = $form->getConfig();
@@ -210,6 +220,7 @@ class FormType extends BaseType
             'is_empty_callback' => null,
             'getter' => null,
             'setter' => null,
+            'form_attr' => false,
         ]);
 
         $resolver->setAllowedTypes('label_attr', 'array');
@@ -221,6 +232,7 @@ class FormType extends BaseType
         $resolver->setAllowedTypes('is_empty_callback', ['null', 'callable']);
         $resolver->setAllowedTypes('getter', ['null', 'callable']);
         $resolver->setAllowedTypes('setter', ['null', 'callable']);
+        $resolver->setAllowedTypes('form_attr', ['bool', 'string']);
 
         $resolver->setInfo('getter', 'A callable that accepts two arguments (the view data and the current form field) and must return a value.');
         $resolver->setInfo('setter', 'A callable that accepts three arguments (a reference to the view data, the submitted value and the current form field).');

src/Symfony/Component/Form/Tests/Extension/Core/Type/FormTypeTest.php

@@ -14,6 +14,7 @@ namespace Symfony\Component\Form\Tests\Extension\Core\Type;
 use Symfony\Component\Form\CallbackTransformer;
 use Symfony\Component\Form\DataMapperInterface;
 use Symfony\Component\Form\Exception\InvalidArgumentException;
+use Symfony\Component\Form\Exception\LogicException;
 use Symfony\Component\Form\Exception\TransformationFailedException;
 use Symfony\Component\Form\Extension\Core\Type\CurrencyType;
 use Symfony\Component\Form\Extension\Core\Type\FormType;
@@ -774,6 +775,67 @@ class FormTypeTest extends BaseTypeTest
         $this->assertSame($error, $form->get('inherit_data_type')->getErrors()[0]);
         $this->assertCount(0, $form->get('inherit_data_type')->get('child')->getErrors());
     }
+
+    public function testFormAttrOnRoot()
+    {
+        $view = $this->factory
+            ->createNamedBuilder('parent', self::TESTED_TYPE, null, [
+                'form_attr' => true,
+            ])
+            ->add('child1', $this->getTestedType())
+            ->add('child2', $this->getTestedType())
+            ->getForm()
+            ->createView();
+        $this->assertArrayNotHasKey('form', $view->vars['attr']);
+        $this->assertSame($view->vars['id'], $view['child1']->vars['attr']['form']);
+        $this->assertSame($view->vars['id'], $view['child2']->vars['attr']['form']);
+    }
+
+    public function testFormAttrOnChild()
+    {
+        $view = $this->factory
+            ->createNamedBuilder('parent', self::TESTED_TYPE)
+            ->add('child1', $this->getTestedType(), [
+                'form_attr' => true,
+            ])
+            ->add('child2', $this->getTestedType())
+            ->getForm()
+            ->createView();
+        $this->assertArrayNotHasKey('form', $view->vars['attr']);
+        $this->assertSame($view->vars['id'], $view['child1']->vars['attr']['form']);
+        $this->assertArrayNotHasKey('form', $view['child2']->vars['attr']);
+    }
+
+    public function testFormAttrAsBoolWithNoId()
+    {
+        $this->expectException(LogicException::class);
+        $this->expectErrorMessage('form_attr');
+        $this->factory
+            ->createNamedBuilder('', self::TESTED_TYPE, null, [
+                'form_attr' => true,
+            ])
+            ->add('child1', $this->getTestedType())
+            ->add('child2', $this->getTestedType())
+            ->getForm()
+            ->createView();
+    }
+
+    public function testFormAttrAsStringWithNoId()
+    {
+        $stringId = 'custom-identifier';
+        $view = $this->factory
+            ->createNamedBuilder('', self::TESTED_TYPE, null, [
+                'form_attr' => $stringId,
+            ])
+            ->add('child1', $this->getTestedType())
+            ->add('child2', $this->getTestedType())
+            ->getForm()
+            ->createView();
+        $this->assertArrayNotHasKey('form', $view->vars['attr']);
+        $this->assertSame($stringId, $view->vars['id']);
+        $this->assertSame($view->vars['id'], $view['child1']->vars['attr']['form']);
+        $this->assertSame($view->vars['id'], $view['child2']->vars['attr']['form']);
+    }
 }
 
 class Money

src/Symfony/Component/Form/Tests/Fixtures/Descriptor/resolved_form_type_1.json

@@ -40,6 +40,7 @@
                 "by_reference",
                 "data",
                 "disabled",
+                "form_attr",
                 "getter",
                 "help",
                 "help_attr",

src/Symfony/Component/Form/Tests/Fixtures/Descriptor/resolved_form_type_1.txt

@@ -17,8 +17,9 @@ Symfony\Component\Form\Extension\Core\Type\ChoiceType (Block prefix: "choice")
   expanded                                             by_reference                                          
   group_by                                             data                                                  
   multiple                                             disabled                                              
-  placeholder                                          getter                                                
+  placeholder                                          form_attr                                             
-  preferred_choices                                    help                                                  
+  preferred_choices                                    getter                                                
+                                                       help                                                  
                                                        help_attr                                             
                                                        help_html                                             
                                                        help_translation_parameters                           

src/Symfony/Component/Form/Tests/Fixtures/Descriptor/resolved_form_type_2.json

@@ -17,6 +17,7 @@
             "disabled",
             "empty_data",
             "error_bubbling",
+            "form_attr",
             "getter",
             "help",
             "help_attr",

src/Symfony/Component/Form/Tests/Fixtures/Descriptor/resolved_form_type_2.txt

@@ -19,6 +19,7 @@ Symfony\Component\Form\Extension\Core\Type\FormType (Block prefix: "form")
   disabled                      
   empty_data                    
   error_bubbling                
+  form_attr                     
   getter                        
   help                          
   help_attr