minor #11297 Simplified some docs about getProjectDir (javiereguiluz)

This PR was merged into the 4.2 branch.

Discussion
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Simplified some docs about getProjectDir

Related to #11286, this simplifies things a bit and removes repeated contents.

Commits
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4ecda82 Simplified some docs about getProjectDir

Author: javiereguiluz

deployment.rst

@@ -217,28 +217,15 @@ Troubleshooting
 Deployments not Using the ``composer.json`` File
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Symfony applications provide a ``kernel.project_dir`` parameter and a related
-:method:`Symfony\\Component\\HttpKernel\\Kernel::getProjectDir` method.
-You can use this method to perform operations with file paths relative to your
-project's root directory. The logic to find that project root directory is based
-on the location of the main ``composer.json`` file.
-
-If your deployment method doesn't use Composer, you may have removed the
-``composer.json`` file and the application won't work on the production server.
-The solution is to override the ``getProjectDir()`` method in the application
-kernel and return your project's root directory::
-
-    // src/Kernel.php
-    // ...
-    class Kernel extends BaseKernel
-    {
-        // ...
-
-        public function getProjectDir()
-        {
-            return dirname(__DIR__);
-        }
-    }
+The :ref:`project root directory <configuration-kernel-project-directory>`
+(whose value is used via the ``kernel.project_dir`` parameter and the
+:method:`Symfony\\Component\\HttpKernel\\Kernel::getProjectDir` method) is
+calculated automatically by Symfony as the directory where the main
+``composer.json`` file is stored.
+
+In deployments not using the ``composer.json`` file, you'll need to override the
+:method:`Symfony\\Component\\HttpKernel\\Kernel::getProjectDir` method
+:ref:`as explained in this section <configuration-kernel-project-directory>`.
 
 Learn More
 ----------

reference/configuration/kernel.rst

@@ -61,17 +61,23 @@ The name of the kernel isn't usually directly important - it's used in the
 generation of cache files - and you probably will only change it when
 :doc:`using applications with multiple kernels </configuration/multiple_kernels>`.
 
+.. _configuration-kernel-project-directory:
+
 Project Directory
 ~~~~~~~~~~~~~~~~~
 
 **type**: ``string`` **default**: the directory of the project ``composer.json``
 
-This returns the root directory of your Symfony project. It's calculated as
-the directory where the main ``composer.json`` file is stored.
+This returns the root directory of your Symfony project, which is used by
+applications to perform operations with file paths relative to the project's
+root directory.
 
-If for some reason the ``composer.json`` file is not stored at the root of your
-project, you can override the :method:`Symfony\\Component\\HttpKernel\\Kernel::getProjectDir`
-method to return the right project directory::
+By default, its value is calculated automatically as the directory where the
+main ``composer.json`` file is stored. If you don't use Composer, or have moved
+the ``composer.json`` file location or have deleted it entirely (for example in
+the production servers), you can override the
+:method:`Symfony\\Component\\HttpKernel\\Kernel::getProjectDir` method to return
+the right project directory::
 
     // src/Kernel.php
     use Symfony\Component\HttpKernel\Kernel as BaseKernel;