feature #28812 [Form] add a convenience method to get the parent form in Twig templates (xabbuh)

This PR was merged into the 4.3-dev branch.

Discussion
----------

[Form] add a convenience method to get the parent form in Twig templates

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #28686
| License       | MIT
| Doc PR        |

Commits
-------

cb60642d15 add a convenience method to get the parent form in Twig templates

src/Symfony/Bridge/Twig/CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+4.3.0
+-----
+
+ * added the `parent_form()` function that allows to reliably retrieve the parent form in Twig templates
+
 4.2.0
 -----
 

src/Symfony/Bridge/Twig/Extension/FormExtension.php

@@ -54,6 +54,7 @@ class FormExtension extends AbstractExtension
             new TwigFunction('form_start', null, ['node_class' => 'Symfony\Bridge\Twig\Node\RenderBlockNode', 'is_safe' => ['html']]),
             new TwigFunction('form_end', null, ['node_class' => 'Symfony\Bridge\Twig\Node\RenderBlockNode', 'is_safe' => ['html']]),
             new TwigFunction('csrf_token', ['Symfony\Component\Form\FormRenderer', 'renderCsrfToken']),
+            new TwigFunction('parent_form', 'Symfony\Bridge\Twig\Extension\twig_get_parent_form'),
         ];
     }
 
@@ -115,3 +116,11 @@ function twig_is_root_form(FormView $formView)
 {
     return null === $formView->parent;
 }
+
+/**
+ * @internal
+ */
+function twig_get_parent_form(FormView $formView): ?FormView
+{
+    return $formView->parent;
+}