bug symfony#37276 [Form] Fixed block prefixes hierarchy of the CollectionType (yceruto)

This PR was merged into the 5.1 branch.

Discussion
----------

[Form] Fixed block prefixes hierarchy of the CollectionType

| Q             | A
| ------------- | ---
| Branch?       | 5.1
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix symfony#37024
| License       | MIT
| Doc PR        | -

/cc @HeahDude

Commits
-------

a8f2c60 fixed block prefixes hierarchy of the CollectionType

Author: fabpot

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

@@ -72,7 +72,7 @@ public function buildView(FormView $view, FormInterface $form, array $options)
      */
     public function finishView(FormView $view, FormInterface $form, array $options)
     {
-        $prefixOffset = -1;
+        $prefixOffset = -2;
         // check if the entry type also defines a block prefix
         /** @var FormInterface $entry */
         foreach ($form as $entry) {

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

@@ -415,8 +415,8 @@ public function testEntriesBlockPrefixes()
 
         $expectedBlockPrefixes = [
             'form',
-            'text',
             'collection_entry',
+            'text',
             '_fields_entry',
         ];
 
@@ -436,8 +436,8 @@ public function testEntriesBlockPrefixesWithCustomBlockPrefix()
         $this->assertCount(1, $collectionView);
         $this->assertSame([
             'form',
-            'text',
             'collection_entry',
+            'text',
             'field',
             '_fields_entry',
         ], $collectionView[0]->vars['block_prefixes']);
@@ -454,8 +454,8 @@ public function testEntriesBlockPrefixesWithCustomBlockPrefixedType()
         $this->assertCount(1, $collectionView);
         $this->assertSame([
             'form',
-            'block_prefixed_foo_text',
             'collection_entry',
+            'block_prefixed_foo_text',
             'foo',
             '_fields_entry',
         ], $collectionView[0]->vars['block_prefixes']);