[Cookbook][Configuration] add configuration cookbook handlig parameters in Configurator class

cookbook/bundles/extension.rst

@@ -89,6 +89,8 @@ The second method has several specific advantages:
     supported configuration settings for which backward compatibility will
     be maintained.
 
+For other usages of the parameter ``%`` syntax see :doc:`Configuration </cookbook/configuration>`.
+
 .. index::
    single: Bundle; Extension
    single: DependencyInjection; Extension

cookbook/configuration.rst

@@ -0,0 +1,182 @@
+.. index::
+single: Configuration
+
+Configuration Usages
+====================
+
+Parameters are common in configuration such as ``%kernel.root_dir%``
+(which is used for passing a path) or ``%kernel.debug%`` (which is used for
+passing a boolean indicating if mode is debug). The syntax wrapping an
+alias string with ``%`` conveys that this is a value defined as a parameter
+and will be evaluated somewhere down the line and used. Within Symfony
+we can have parameters defined in a bundle and used only in that bundle and
+also parameters defined in a bundle and used in another. Usually they would
+have a namespace like ``demo_bundle.service_doer.local_parameter`` making
+explicit where this parameter comes from. If the parameter is global then
+it may not have a namespace, e.g. ``%some_global_option_here%``.
+
+We can have parameters being used inside ``parameters.yml``:
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        # app/config/parameters.yml
+        parameters:
+            payment_test_mode: %kernel.root_dir%
+
+Inside ``config.yml`` and other configuration files building larger
+strings:
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+
+        # app/config/config.yml
+        my_bundle:
+            local:
+                directory:  %kernel.root_dir%/../web/media/image
+
+We can also use parameters in service configuration files:
+
+.. configuration-block::
+
+    .. code-block:: xml
+
+        <parameters>
+            <parameter id="some_service.class" class="\Acme\DemoBundle\Service\Doer">
+        </parameters>
+
+        <services>
+            <service id="%some_service%" class="%some_service.class%" />
+        </services>
+
+For more information on how parameters are used in Symfony please see
+:ref:`parameters <book-service-container-parameters>`.
+
+Besides these usages above we can use this syntax in routing files and handle
+parameters in special cases as discussed below.
+
+If for instance, there is a use case in which we want to use the
+``%kernel.debug%`` debug mode parameter to make our bundle adapt its
+configuration depending on this. For this case we cannot use
+the syntax directly and expect this to work. The configuration handling
+will just tread this ``%kernel.debug%`` as a string. Let's consider
+this example with ``AcmeDemoBundle``:
+
+.. code-block:: php
+
+    // Inside Configuration class
+    ->booleanNode('logging')->defaultValue('%kernel.debug%')->end()
+
+    // Inside the Extension class
+    $config = $this->processConfiguration($configuration, $configs);
+    var_dump($config['logging']);
+
+Now let's examine the results to see this closely:
+
+.. configuration-block::
+
+    .. code-block:: xml
+
+        my_bundle:
+            logging: true
+            # true, as expected
+
+        my_bundle:
+            logging: %kernel.debug%
+            # true/false (depends on 2nd parameter of AppKernel),
+            # as expected, because %kernel.debug% inside configuration
+            # gets evaluated before being passed to the extension
+
+        my_bundle: ~
+        # passes the string ``%kernel.debug%``.
+        # Which is always considered as true.
+        # Configurator class does not know anything about the default
+        # string ``%kernel.debug%``.
+
+In order to support this use case ``Configuration`` class has to
+be injected with this parameter via the extension as follows:
+
+.. code-block:: php
+
+    <?php
+
+    namespace Acme\DemoBundle\DependencyInjection;
+
+    use Symfony\Component\Config\Definition\Builder\ArrayNodeDefinition;
+    use Symfony\Component\Config\Definition\Builder\TreeBuilder;
+    use Symfony\Component\Config\Definition\ConfigurationInterface;
+
+    class Configuration implements ConfigurationInterface
+    {
+        private $debug;
+
+        /**
+         * Constructor
+         *
+         * @param Boolean $debug Whether to use the debug mode
+         */
+        public function  __construct($debug)
+        {
+            $this->debug = (Boolean) $debug;
+        }
+
+         /**
+         * {@inheritDoc}
+         */
+        public function getConfigTreeBuilder()
+        {
+            $treeBuilder = new TreeBuilder();
+            $rootNode = $treeBuilder->root('acme_demo');
+
+            $rootNode
+                // ...
+                ->booleanNode('logging')->defaultValue($this->debug)->end()
+                // ...
+            ;
+
+            return $treeBuilder;
+        }
+    }
+
+And set it in the constructor of ``Configuration`` via the Extension class:
+
+.. code-block:: php
+
+    <?php
+
+    namespace Acme\DemoBundle\DependencyInjection;
+
+    use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;
+    use Symfony\Component\DependencyInjection\ContainerBuilder;
+    use Symfony\Component\DependencyInjection\Definition;
+    use Symfony\Component\Config\FileLocator;
+
+    class AcmeDemoExtension extends AbstractDoctrineExtension
+    {
+        // ...
+
+        /**
+         * {@inheritDoc}
+         */
+        public function getConfiguration(array $config, ContainerBuilder $container)
+        {
+            return new Configuration($container->getParameter('kernel.debug'));
+        }
+    }
+
+There are some instances of ``%kernel.debug%`` usage within a ``Configurator``
+class in ``TwigBundle`` and ``AsseticBundle``, however this is because they are
+setting the parameter value in the container via the Extension class. For
+example in ``AsseticBundle`` we have:
+
+.. code-block:: php
+
+    $container->setParameter('assetic.debug', $config['debug']);
+
+The string ``%kernel.debug%`` passed here as an argument handles the
+interpreting job to the container which in turn does the evaluation.
+Both ways accomplish similar goals. ``AsseticBundle`` will not use
+anymore ``%kernel.debug%`` but rather the new ``%assetic.debug%`` parameter.

cookbook/index.rst

@@ -7,6 +7,7 @@ The Cookbook
     assetic/index
     bundles/index
     cache/index
+    configuration
     configuration/index
     console/index
     controller/index

cookbook/routing/service_container_parameters.rst

@@ -120,3 +120,5 @@ path):
     However, as the ``%`` characters included in any URL are automatically encoded,
     the resulting URL of this example would be ``/score-50%25`` (``%25`` is the
     result of encoding the ``%`` character).
+
+For other usages of the parameter ``%`` syntax see :doc:`Configuration </cookbook/configuration>`.