feature #20496 [Form] Allow pass filter callback to delete_empty option. (Koc)

This PR was merged into the 3.4 branch.

Discussion
----------

[Form] Allow pass filter callback to delete_empty option.

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #13601, #13940, #22008, #22014
| License       | MIT
| Doc PR        | coming soon

Commits
-------

8630abe27a [Form] Allow pass filter callback to delete_empty option.

src/Symfony/Component/Form/Extension/Core/EventListener/ResizeFormListener.php

@@ -48,7 +48,7 @@ class ResizeFormListener implements EventSubscriberInterface
     protected $allowDelete;
 
     /**
-     * @var bool
+     * @var bool|callable
      */
     private $deleteEmpty;
 
@@ -148,14 +148,15 @@ class ResizeFormListener implements EventSubscriberInterface
             throw new UnexpectedTypeException($data, 'array or (\Traversable and \ArrayAccess)');
         }
 
-        if ($this->deleteEmpty) {
-            $previousData = $event->getForm()->getData();
+        if ($entryFilter = $this->deleteEmpty) {
+            $previousData = $form->getData();
             foreach ($form as $name => $child) {
                 $isNew = !isset($previousData[$name]);
+                $isEmpty = is_callable($entryFilter) ? $entryFilter($child->getData()) : $child->isEmpty();
 
                 // $isNew can only be true if allowAdd is true, so we don't
                 // need to check allowAdd again
-                if ($child->isEmpty() && ($isNew || $this->allowDelete)) {
+                if ($isEmpty && ($isNew || $this->allowDelete)) {
                     unset($data[$name]);
                     $form->remove($name);
                 }

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

@@ -100,6 +100,7 @@ class CollectionType extends AbstractType
         ));
 
         $resolver->setNormalizer('entry_options', $entryOptionsNormalizer);
+        $resolver->setAllowedTypes('delete_empty', array('bool', 'callable'));
     }
 
     /**

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

@@ -12,6 +12,7 @@
 namespace Symfony\Component\Form\Tests\Extension\Core\Type;
 
 use Symfony\Component\Form\Tests\Fixtures\Author;
+use Symfony\Component\Form\Tests\Fixtures\AuthorType;
 
 class CollectionTypeTest extends BaseTypeTest
 {
@@ -110,6 +111,49 @@ class CollectionTypeTest extends BaseTypeTest
         $this->assertEquals(array('foo@foo.com'), $form->getData());
     }
 
+    public function testResizedDownWithDeleteEmptyCallable()
+    {
+        $form = $this->factory->create(static::TESTED_TYPE, null, array(
+            'entry_type' => AuthorType::class,
+            'allow_delete' => true,
+            'delete_empty' => function (Author $obj = null) {
+                return null === $obj || empty($obj->firstName);
+            },
+        ));
+
+        $form->setData(array(new Author('Bob'), new Author('Alice')));
+        $form->submit(array(array('firstName' => 'Bob'), array('firstName' => '')));
+
+        $this->assertTrue($form->has('0'));
+        $this->assertFalse($form->has('1'));
+        $this->assertEquals(new Author('Bob'), $form[0]->getData());
+        $this->assertEquals(array(new Author('Bob')), $form->getData());
+    }
+
+    public function testResizedDownIfSubmittedWithCompoundEmptyDataDeleteEmptyAndNoDataClass()
+    {
+        $form = $this->factory->create(static::TESTED_TYPE, null, array(
+            'entry_type' => AuthorType::class,
+            // If the field is not required, no new Author will be created if the
+            // form is completely empty
+            'entry_options' => array('data_class' => null),
+            'allow_add' => true,
+            'allow_delete' => true,
+            'delete_empty' => function ($author) {
+                return empty($author['firstName']);
+            },
+        ));
+        $form->setData(array(array('firstName' => 'first', 'lastName' => 'last')));
+        $form->submit(array(
+            array('firstName' => 's_first', 'lastName' => 's_last'),
+            array('firstName' => '', 'lastName' => ''),
+        ));
+        $this->assertTrue($form->has('0'));
+        $this->assertFalse($form->has('1'));
+        $this->assertEquals(array('firstName' => 's_first', 'lastName' => 's_last'), $form[0]->getData());
+        $this->assertEquals(array(array('firstName' => 's_first', 'lastName' => 's_last')), $form->getData());
+    }
+
     public function testDontAddEmptyDataIfDeleteEmpty()
     {
         $form = $this->factory->create(static::TESTED_TYPE, null, array(