feature #3597 Document how to create a custom type guesser (WouterJ)

This PR was merged into the 2.3 branch.

Discussion
----------

Document how to create a custom type guesser

| Q   | A
| --- | ---
| Doc fix? | no
| New docs? | yes
| Applies to | all
| Fixed tickets | #481

Commits
-------

0d37a3b Applied comments
3b3cd6f Added references
f36fdb7 Documented FormTypeGuesserInterface

Author: weaverryan

components/form/index.rst

@@ -5,3 +5,4 @@
     :maxdepth: 2
 
     introduction
+    type_guesser

components/form/type_guesser.rst

@@ -0,0 +1,191 @@
+.. index::
+    single: Forms; Custom Type Guesser
+
+Creating a Custom Type Guesser
+==============================
+
+The Form component can guess the type and some options of a form field by
+using type guessers. The component already includes a type guesser using the
+assertions of the Validation component, but you can also add your own custom
+type guessers.
+
+.. sidebar:: Form Type Guessers in the Bridges
+
+    Symfony also provides some form type guessers in the bridges:
+
+    * :class:`Symfony\\Bridge\\Propel1\\Form\\PropelTypeGuesser` provided by
+      the Propel1 bridge;
+    * :class:`Symfony\\Bridge\\Doctrine\\Form\\DoctrineOrmTypeGuesser`
+      provided by the Doctrine bridge.
+
+Create a PHPDoc Type Guesser
+----------------------------
+
+In this section, you are going to build a guesser that reads information about
+fields from the PHPDoc of the properties. At first, you need to create a class
+which implements :class:`Symfony\\Component\\Form\\FormTypeGuesserInterface`.
+This interface requires 4 methods:
+
+* :method:`Symfony\\Component\\Form\\FormTypeGuesserInterface::guessType` -
+  tries to guess the type of a field;
+* :method:`Symfony\\Component\\Form\\FormTypeGuesserInterface::guessRequired` -
+  tries to guess the value of the :ref:`required <reference-form-option-required>`
+  option;
+* :method:`Symfony\\Component\\Form\\FormTypeGuesserInterface::guessMaxLength` -
+  tries to guess the value of the :ref:`max_length <reference-form-option-max_length>`
+  option;
+* :method:`Symfony\\Component\\Form\\FormTypeGuesserInterface::guessPattern` -
+  tries to guess the value of the :ref:`pattern <reference-form-option-pattern>`
+  option.
+
+Start by creating the class and these methods. Next, you'll learn how to fill each on.
+
+.. code-block:: php
+
+    namespace Acme\Form;
+
+    use Symfony\Component\Form\FormTypeGuesserInterface;
+
+    class PhpdocTypeGuesser implements FormTypeGuesserInterface
+    {
+        public function guessType($class, $property)
+        {
+        }
+
+        public function guessRequired($class, $property)
+        {
+        }
+
+        public function guessMaxLength($class, $property)
+        {
+        }
+
+        public function guessPattern($class, $property)
+        {
+        }
+    }
+
+Guessing the Type
+~~~~~~~~~~~~~~~~~
+
+When guessing a type, the method returns either an instance of
+:class:`Symfony\\Component\\Form\\Guess\\TypeGuess` or nothing, to determine
+that the type guesser cannot guess the type.
+
+The ``TypeGuess`` constructor requires 3 options:
+
+* The type name (one of the :doc:`form types </reference/forms/types`);
+* Additional options (for instance, when the type is ``entity``, you also
+  want to set the ``class`` option). If no types are guessed, this should be
+  set to an empty array;
+* The confidence that the guessed type is correct. This can be one of the
+  constants of the :class:`Symfony\\Component\\Form\\Guess\Guess` class:
+  ``LOW_CONFIDENCE``, ``MEDIUM_CONFIDENCE``, ``HIGH_CONFIDENCE``,
+  ``VERY_HIGH_CONFIDENCE``. After all type guessers have been executed, the
+  type with the highest confidence is used.
+
+With this knowledge, you can easily implement the ``guessType`` method of the
+``PHPDocTypeGuesser``::
+
+    namespace Acme\Form;
+
+    use Symfony\Component\Form\Guess\Guess;
+    use Symfony\Component\Form\Guess\TypeGuess;
+
+    class PhpdocTypeGuesser implements FormTypeGuesserInterface
+    {
+        public function guessType($class, $property)
+        {
+            $annotations = $this->readPhpDocAnnotations($class, $property);
+
+            if (!isset($annotations['var'])) {
+                return; // guess nothing if the @var annotation is not available
+            }
+
+            // otherwise, base the type on the @var annotation
+            switch ($annotations['var']) {
+                case 'string':
+                    // there is a high confidence that the type is a string when
+                    // @var string is used
+                    return new TypeGuess('text', array(), Guess::HIGH_CONFIDENCE);
+
+                case 'int':
+                case 'integer':
+                    // integers can also be the id of an entity or a checkbox (0 or 1)
+                    return new TypeGuess('integer', array(), Guess::MEDIUM_CONFIDENCE);
+
+                case 'float':
+                case 'double':
+                case 'real':
+                    return new TypeGuess('number', array(), Guess::MEDIUM_CONFIDENCE);
+
+                case 'boolean':
+                case 'bool':
+                    return new TypeGuess('checkbox', array(), Guess::HIGH_CONFIDENCE);
+
+                default:
+                    // there is a very low confidence that this one is correct
+                    return new TypeGuess('text', array(), Guess::LOW_CONFIDENCE);
+            }
+        }
+
+        protected function readPhpDocAnnotations($class, $property)
+        {
+            $reflectionProperty = new \ReflectionProperty($class, $property);
+            $phpdoc = $reflectionProperty->getDocComment();
+
+            // parse the $phpdoc into an array like:
+            // array('type' => 'string', 'since' => '1.0')
+            $phpdocTags = ...;
+
+            return $phpdocTags;
+        }
+    }
+
+This type guesser can now guess the field type for a property if it has
+PHPdoc!
+
+Guessing Field Options
+~~~~~~~~~~~~~~~~~~~~~~
+
+The other 3 methods (``guessMaxLength``, ``guessRequired`` and
+``guessPattern``) return a :class:`Symfony\\Component\\Form\\Guess\\ValueGuess`
+instance with the value of the option. This constructor has 2 arguments:
+
+* The value of the option;
+* The confidence that the guessed value is correct (using the constants of the
+  ``Guess`` class).
+
+``null`` is guessed when you believe the value of the option should not be
+set.
+
+.. caution::
+
+    You should be very careful using the ``guessPattern`` method. When the
+    type is a float, you cannot use it to determine a min or max value of the
+    float (e.g. you want a float to be greater than ``5``, ``4.512313`` is not valid
+    but ``length(4.512314) > length(5)`` is, so the pattern will succeed). In
+    this case, the value should be set to ``null`` with a ``MEDIUM_CONFIDENCE``.
+
+Registering a Type Guesser
+--------------------------
+
+The last thing you need to do is registering your custom type guesser by using
+:method:`Symfony\\Component\\Form\\FormFactoryBuilder::addTypeGuesser` or
+:method:`Symfony\\Component\\Form\\FormFactoryBuilder::addTypeGuessers`::
+
+    use Symfony\Component\Form\Forms;
+    use Acme\Form\PHPDocTypeGuesser;
+
+    $formFactory = Forms::createFormFactoryBuilder()
+        // ...
+        ->addTypeGuesser(new PHPDocTypeGuesser())
+        ->getFormFactory();
+
+    // ...
+
+.. note::
+
+    When you use the Symfony framework, you need to register your type guesser
+    and tag it with ``form.type_guesser``. For more information see
+    :ref:`the tag reference <reference-dic-type_guesser>`.

components/map.rst.inc

@@ -68,6 +68,7 @@
 * :doc:`/components/form/index`
 
   * :doc:`/components/form/introduction`
+  * :doc:`/components/form/type_guesser`
 
 * :doc:`/components/http_foundation/index`
 

reference/dic_tags.rst

@@ -332,21 +332,22 @@ The ``alias`` key of the tag is the type of field that this extension should
 be applied to. For example, to apply the extension to any form/field, use the
 "form" value.
 
+.. _reference-dic-type_guesser:
+
 form.type_guesser
 -----------------
 
 **Purpose**: Add your own logic for "form type guessing"
 
 This tag allows you to add your own logic to the :ref:`Form Guessing <book-forms-field-guessing>`
 process. By default, form guessing is done by "guessers" based on the validation
-metadata and Doctrine metadata (if you're using Doctrine).
+metadata and Doctrine metadata (if you're using Doctrine) or Propel metadata
+(if you're using Propel).
 
-To add your own form type guesser, create a class that implements the
-:class:`Symfony\\Component\\Form\\FormTypeGuesserInterface` interface. Next,
-tag its service definition with ``form.type_guesser`` (it has no options).
+.. seelalso::
 
-To see an example of how this class might look, see the ``ValidatorTypeGuesser``
-class in the Form component.
+    For information on how to create your own type guesser, see
+    :doc:`/components/form/type_guesser`.
 
 kernel.cache_clearer
 --------------------

reference/forms/types/form.rst

@@ -17,6 +17,8 @@ on all fields.
 
 .. include:: /reference/forms/types/options/empty_data.rst.inc
 
+.. _reference-form-option-required:
+
 .. include:: /reference/forms/types/options/required.rst.inc
 
 .. include:: /reference/forms/types/options/label.rst.inc
@@ -43,6 +45,8 @@ on all fields.
 
 .. include:: /reference/forms/types/options/block_name.rst.inc
 
+.. _reference-form-option-max_length:
+
 .. include:: /reference/forms/types/options/max_length.rst.inc
 
 .. include:: /reference/forms/types/options/by_reference.rst.inc
@@ -61,6 +65,8 @@ on all fields.
 
 .. include:: /reference/forms/types/options/post_max_size_message.rst.inc
 
+.. _reference-form-option-pattern:
+
 .. include:: /reference/forms/types/options/pattern.rst.inc
 
 .. include:: /reference/forms/types/options/action.rst.inc