minor #7959 Added a caution note about services that must maintain the "class" parameter (javiereguiluz, HeahDude)

This PR was merged into the 3.3 branch.

Discussion
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Added a caution note about services that must maintain the "class" parameter

This fixes #7935.

Commits
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4219a5e minor fix
b857caf Added a caution note about services that must maintain the "class" parameter

Author: xabbuh

service_container/3.3-di-changes.rst

@@ -572,6 +572,14 @@ Start by updating the service ids to class names:
         app.api_client_sl_connect:
             # ...
 
+.. caution::
+
+    Services associated with global PHP classes (i.e. not using PHP namespaces)
+    must maintain the ``class`` parameter. For example, when using the old Twig
+    classes (e.g. ``Twig_Extensions_Extension_Intl`` instead of ``Twig\Extensions\IntlExtension``),
+    you can't redefine the service as ``Twig_Extensions_Extension_Intl: ~`` and
+    you must keep the original ``class`` parameter.
+
 But, this change will break our app! The old service ids (e.g. ``app.github_notifier``)
 no longer exist. The simplest way to fix this is to find all your old service ids
 and update them to the new class id: ``app.github_notifier`` to ``AppBundle\Service\GitHubNotifier``.