[Form] minor fixes in ChoiceType options

reference/forms/types/choice.rst

@@ -74,8 +74,8 @@ This will create a ``select`` drop-down like this:
 
 If the user selects ``No``, the form will return ``false`` for this field. Similarly,
 if the starting data for this field is ``true``, then ``Yes`` will be auto-selected.
-In other words, the **value** of each item is the value you want to get/set in PHP
-code, while the **key** is what will be shown to the user.
+In other words, the **choice** of each item is the value you want to get/set in PHP
+code, while the **key** is the **label** that will be shown to the user.
 
 Advanced Example (with Objects!)
 --------------------------------
@@ -95,23 +95,40 @@ method::
             new Category('Cat3'),
             new Category('Cat4'),
         ],
-        'choice_label' => function(Category $category, $key, $value) {
-            return strtoupper($category->getName());
+        // "name" is a property path, meaning Symfony will look for a public
+        // property or a public method like "getName()" to define the input
+        // string value that will be submitted by the form
+        'choice_value' => 'name',
+        // a callback to return the label for a given choice
+        // if a placeholder is used, its empty value (null) may be passed but
+        // its label is defined by its own "placeholder" option
+        'choice_label' => function(?Category $category) {
+            return $category ? strtoupper($category->getName()) : '';
         },
-        'choice_attr' => function(Category $category, $key, $value) {
-            return ['class' => 'category_'.strtolower($category->getName())];
+        // returns the html attributes for each option input (may be radio/checkbox)
+        'choice_attr' => function(?Category $category) {
+            return $category ? ['class' => 'category_'.strtolower($category->getName())] : [];
         },
-        'group_by' => function(Category $category, $key, $value) {
+        // every option can use a string property path or any callable that get
+        // passed each choice as argument, but it may not be needed
+        'group_by' => function() {
             // randomly assign things into 2 groups
             return rand(0, 1) == 1 ? 'Group A' : 'Group B';
         },
-        'preferred_choices' => function(Category $category, $key, $value) {
-            return $category->getName() == 'Cat2' || $category->getName() == 'Cat3';
+        // a callback to return whether a category is preferred
+        'preferred_choices' => function(?Category $category) {
+            return $category && 100 < $category->getArticleCounts();
         },
     ]);
 
-You can also customize the `choice_name`_ and `choice_value`_ of each choice if
-you need further HTML customization.
+You can also customize the `choice_name`_ of each choice. You can learn more
+about all of these options in the sections below.
+
+.. caution::
+
+    The *placeholder* is a specific field, when the choices are optional the
+    first item in the list must be empty, so the user can unselect.
+    Be sure to always handle the empty choice ``null`` when using callbacks.
 
 .. _forms-reference-choice-tags:
 
@@ -151,7 +168,7 @@ by passing a multi-dimensional ``choices`` array::
 .. image:: /_images/reference/form/choice-example4.png
    :align: center
 
-To get fancier, use the `group_by`_ option.
+To get fancier, use the `group_by`_ option instead.
 
 Field Options
 -------------
@@ -169,7 +186,10 @@ is the item's label and the array value is the item's value::
     // ...
 
     $builder->add('inStock', ChoiceType::class, [
-        'choices' => ['In Stock' => true, 'Out of Stock' => false],
+        'choices' => [
+            'In Stock' => true,
+            'Out of Stock' => false,
+        ],
     ]);
 
 If there are choice values that are not scalar or the stringified

reference/forms/types/options/choice_attr.rst.inc

@@ -1,7 +1,7 @@
 ``choice_attr``
 ~~~~~~~~~~~~~~~
 
-**type**: ``array``, ``callable`` or ``string`` **default**: ``[]``
+**type**: ``array``, ``callable``, ``string`` or :class:`Symfony\\Component\\PropertyAccess\\PropertyPath` **default**: ``[]``
 
 Use this to add additional HTML attributes to each choice. This can be
 an associative array where the keys match the choice keys and the values

reference/forms/types/options/choice_label.rst.inc

@@ -1,9 +1,9 @@
 ``choice_label``
 ~~~~~~~~~~~~~~~~
 
-**type**: ``string``, ``callable`` or ``false`` **default**: ``null``
+**type**: ``string``, ``callable``, ``false`` or :class:`Symfony\\Component\\PropertyAccess\\PropertyPath` **default**: ``null``
 
-Normally, the array key of each item in the ``choices`` option is used as the
+By default, the array key of each item in the ``choices`` option is used as the
 text that's shown to the user. The ``choice_label`` option allows you to take
 more control::
 

reference/forms/types/options/choice_name.rst.inc

@@ -1,14 +1,15 @@
 ``choice_name``
 ~~~~~~~~~~~~~~~
 
-**type**: ``callable`` or ``string`` **default**: ``null``
+**type**: ``callable``, ``string`` or :class:`Symfony\\Component\\PropertyAccess\\PropertyPath` **default**: ``null``
 
 Controls the internal field name of the choice. You normally don't care about this,
 but in some advanced cases, you might. For example, this "name" becomes the index
-of the choice views in the template.
+of the choice views in the template and is used as part o the field name
+attribute.
 
 This can be a callable or a property path. See `choice_label`_ for similar usage.
-If ``null`` is used, an incrementing integer is used as the name.
+By default, the choice key or an incrementing integer may be used (starting at ``0``).
 
 .. caution::
 

reference/forms/types/options/choice_value.rst.inc

@@ -1,28 +1,20 @@
 ``choice_value``
 ~~~~~~~~~~~~~~~~
 
-**type**: ``callable`` or ``string`` **default**: ``null``
+**type**: ``callable``, ``string`` or :class:`Symfony\\Component\\PropertyAccess\\PropertyPath` **default**: ``null``
 
 Returns the string "value" for each choice, which must be unique across all choices.
 This is used in the ``value`` attribute in HTML and submitted in the POST/PUT requests.
 You don't normally need to worry about this, but it might be handy when processing
 an API request (since you can configure the value that will be sent in the API request).
 
-This can be a callable or a property path. If ``null`` is given, an incrementing
-integer is used as the value.
+This can be a callable or a property path. By default, the choices are used if they
+can be casted to strings. Otherwise an incrementing integer is used (starting at ``0``).
 
 If you pass a callable, it will receive one argument: the choice itself. When using
 the :doc:`/reference/forms/types/entity`, the argument will be the entity object
-for each choice or ``null`` in some cases, which you need to handle::
+for each choice or ``null`` in a placeholder is used, which you need to handle::
 
-    'choice_value' => function (MyOptionEntity $entity = null) {
+    'choice_value' => function (?MyOptionEntity $entity) {
         return $entity ? $entity->getId() : '';
     },
-
-.. caution::
-
-    In Symfony 2.7, there was a small backwards-compatibility break with how the
-    ``value`` attribute of options is generated. This is not a problem unless you
-    rely on the option values in JavaScript. See `issue #14825`_ for details.
-
-.. _`issue #14825`: https://github.com/symfony/symfony/pull/14825

reference/forms/types/options/group_by.rst.inc

@@ -1,7 +1,7 @@
 ``group_by``
 ~~~~~~~~~~~~
 
-**type**: ``string`` or ``callable`` **default**: ``null``
+**type**: ``string``, ``callable`` or :class:`Symfony\\Component\\PropertyAccess\\PropertyPath` **default**: ``null``
 
 You can group the ``<option>`` elements of a ``<select>`` into ``<optgroup>``
 by passing a multi-dimensional array to ``choices``. See the
@@ -25,9 +25,9 @@ Take the following example::
         'group_by' => function($choice, $key, $value) {
             if ($choice <= new \DateTime('+3 days')) {
                 return 'Soon';
-            } else {
-                return 'Later';
             }
+
+            return 'Later';
         },
     ]);
 

reference/forms/types/options/preferred_choices.rst.inc

@@ -1,11 +1,11 @@
 ``preferred_choices``
 ~~~~~~~~~~~~~~~~~~~~~
 
-**type**: ``array``, ``callable`` or ``string`` **default**: ``[]``
+**type**: ``array``, ``callable``, ``string`` or :class:`Symfony\\Component\\PropertyAccess\\PropertyPath` **default**: ``[]``
 
 This option allows you to move certain choices to the top of your list with a visual
 separator between them and the rest of the options. If you have a form of languages,
-you can list the most popular on top, like Bork Bork and Pirate::
+you can list the most popular on top, like Bork and Pirate::
 
     use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
     // ...
@@ -14,7 +14,7 @@ you can list the most popular on top, like Bork Bork and Pirate::
         'choices' => [
             'English' => 'en',
             'Spanish' => 'es',
-            'Bork'   => 'muppets',
+            'Bork' => 'muppets',
             'Pirate' => 'arr',
         ],
         'preferred_choices' => ['muppets', 'arr'],