feature #5329 Adding a new entry about deprecation warnings (weaverryan)

This PR was merged into the 2.7 branch.

Discussion
----------

Adding a new entry about deprecation warnings

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.7+
| Fixed tickets | n/a

Hi guys!

In preparation for people seeing deprecated warning in Symfony 2.7, I thought we should have a clear document that people can find where we explain the issue and what to do properly.

If there's some important things that people should do or know, please let me know! There are others that know a lot more than I do about these deprecation warnings.

Thanks!

Commits
-------

1e8b75f Fix thanks to Wouter
060fe03 Added a section about the framework
702394e Tweaks thanks to Mr @javiereguiluz
e74bbc9 Adding a new entry about deprecation warnings

Author: weaverryan

cookbook/map.rst.inc

@@ -224,6 +224,7 @@
   * :doc:`/cookbook/upgrade/patch_version`
   * :doc:`/cookbook/upgrade/minor_version`
   * :doc:`/cookbook/upgrade/major_version`
+  * :doc:`/cookbook/upgrade/deprecation_warnings`
 
 * :doc:`/cookbook/validation/index`
 

cookbook/upgrade/deprecation_warnings.rst

@@ -0,0 +1,74 @@
+What do these "XXX is deprecated " E_USER_DEPRECATED Warnings mean?
+===================================================================
+
+Starting in Symfony 2.7, if you use a deprecated class, function or option,
+Symfony triggers an ``E_USER_DEPRECATED`` error. Internally, that looks something
+like this::
+
+    trigger_error(
+        'The fooABC method is deprecated since version 2.4 and will be removed in 3.0.',
+        E_USER_DEPRECATED
+    );
+
+This is great, because you can check your logs to know what needs to change
+before you upgrade. In the Symfony Framework, the number of deprecated calls
+shows up in the web debug toolbar. And if you install the `phpunit-bridge`_,
+you can get a report of deprecated calls after running your tests.
+
+How can I Silence the Warnings?
+-------------------------------
+
+As useful as these are, you don't want them to show up while developing and
+you may also want to silence them on production to avoid filling up your
+error logs.
+
+In the Symfony Framework
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+In the Symfony Framework, ``~E_USER_DEPRECATED`` is added to ``app/bootstrap.php.cache``
+automatically, but you need at least version 2.3.14 or 3.0.21 of the
+`SensioDistributionBundle`_. So, you may need to upgrade:
+
+.. code-block:: bash
+
+    $ composer update sensio/distribution-bundle
+
+Once you've updated, the ``bootstrap.php.cache`` file is rebuilt automatically.
+At the top, you should see a line adding ``~E_USER_DEPRECATED``.
+
+Outside of the Symfony Framework
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To do that, add ``~E_USER_DEPRECATED`` to your ``error_reporting``
+setting in ``php.ini``:
+
+.. code-block:: ini
+
+    ; before
+    error_reporting = E_ALL
+    ; after
+    error_reporting = E_ALL & ~E_USER_DEPRECATED
+
+Alternatively, you can set this directly in bootstrap of your project::
+
+    error_reporting(error_reporting() & ~E_USER_DEPRECATED);
+
+How can I Fix the Warnings?
+---------------------------
+
+Of course ultimately, you want to stop using the deprecated functionality.
+Sometimes, this is easy: the warning might tell you exactly what to change.
+
+But other times, the warning might be unclear: a setting somewhere might
+cause a class deeper to trigger the warning. In this case, Symfony does its
+best to give a clear message, but you may need to research that warning further.
+
+And sometimes, the warning may come from a third-party library or bundle
+that you're using. If that's true, there's a good chance that those deprecations
+have already been updated. In that case, upgrade the library to fix them.
+
+Once all the deprecation warnings are gone, you can upgrade with a lot
+more confidence.
+
+.. _`phpunit-bridge`: https://github.com/symfony/phpunit-bridge
+.. _`SensioDistributionBundle`: https://github.com/sensiolabs/SensioDistributionBundle

cookbook/upgrade/index.rst

@@ -16,3 +16,4 @@ There are three types of upgrades, all needing a little different preparation:
     /cookbook/upgrade/patch_version
     /cookbook/upgrade/minor_version
     /cookbook/upgrade/major_version
+    /cookbook/upgrade/deprecation_warnings