Remove stale processing and reference to form_type_TYPE_value

Patch does exactly as per the @todo that it removes, the blocker is fixed and the tests are passing. LGTM.

I agree with @mstrelan, the blocker is done and so is the @todo, all are green there is nothing much left to say other than RTBC.

+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -1221,10 +1221,7 @@ protected function handleInputElement($form_id, &$element, FormStateInterface &$
+      $value_callable = $element['#value_callback'] ?? NULL;
       if (!is_callable($value_callable)) {
         $value_callable = '\Drupal\Core\Render\Element\FormElement::valueCallback';
       }

My first instinct is that the FormElement::valueCallback should be used instead of NULL. But currently this code protects against someone setting a non-callable as the #value_callback, and while that should be happening, it's probably not worth removing the protection.

So unless someone else disagrees, I think this is a great change.

1. What are the odds of someone having migrated from D7 to D8 with such procedural value callbacks still in place and working? (Without deprecation notice)
2. There are some references to form_type_checkboxes_value() in other files. I'm not sure if those are being tackled elsewhere or not. And if fixing those is in scope here or not.

There are some references to form_type_checkboxes_value() in other files. I'm not sure if those are being tackled elsewhere or not. And if fixing those is in scope here or not.

Currently, Drupal 9.4.1 ha only two references to form_type_checkboxes_value and they are inside comments:

Drupal\Core\Command\InstallCommand:

'enable_update_status_module' => TRUE,
// form_type_checkboxes_value() requires NULL instead of FALSE values   <---------
// for programmatic form submissions to disable a checkbox.
'enable_update_status_emails' => NULL,

Drupal\Core\Test\FunctionalTestSetupTrait:

// form_type_checkboxes_value() requires NULL instead of FALSE values   <---------
// for programmatic form submissions to disable a checkbox.
'enable_update_status_module' => NULL,
'enable_update_status_emails' => NULL,

So I guess that's not a concern anymore.

I think it would be nice to have a deprecation just in case someone has custom code. Better safe then sorry

I don't think we need to do a deprecation dance here - see http://grep.xnddx.ru/search?text=function+form_type_&filename= all the calls here would be broken due to the core functions no longer existing.

We do need to update the document in \Drupal\Core\Form\FormBuilderInterface::doBuildForm() though as this says:

   * - $element['#value_callback']: A callable that implements how user input is
   *   mapped to an element's #value property. This defaults to a function named
   *   'form_type_TYPE_value' where TYPE is $element['#type'].

Made changes as per comment #14.

Thanks @larowan. I fixed this before I saw your comment in the course of working on #value_callback in #2966711: Limit what can be called by a callback in form arrays and did it just as you did in your patch. My only difference is the stated default. The logic of the code sets the default to \Drupal\Core\Render\Element\FormElement::valueCallback. I'll leave a comment on the other issue and perhaps we can close them together?

Talking in slack wtih @FatherShawn and the two tickets do overlap but think we agreed this could probably land first (or has a better shot of it) while the larger task of #2966711: Limit what can be called by a callback in form arrays is worked on.

+++ b/core/lib/Drupal/Core/Form/FormBuilderInterface.php
@@ -257,8 +257,7 @@ public function prepareForm($form_id, &$form, FormStateInterface &$form_state);
    * - $element['#value_callback']: A callable that implements how user input is
+   *   mapped to an element's #value property. This defaults to a function is NULL.

Not sure what this sentence is trying to say. I think we can just say something like:

    * - $element['#value_callback']: A optional callable that implements how user
    *   input is mapped to an element's #value property.

Discussed with @longwave and the change from form_type_* functions to valueCallback is part of https://www.drupal.org/node/2320115 - a very old CR indeed!

Going fix the comment on commit (after discussing with @longwave).

Committed and pushed 5cbb5c9f46f to 11.x and 884929d80ba to 10.2.x. Thanks!