scope singly-implemented interfaces detection by file

Author: daniel-iwaniec

service_container/autowiring.rst

@@ -339,7 +339,7 @@ dealing with the ``TransformerInterface``.
 
     When using a `service definition prototype`_, if only one service is
     discovered that implements an interface, and that interface is also
-    discovered at the same time, configuring the alias is not mandatory
+    discovered in the same file, configuring the alias is not mandatory
     and Symfony will automatically create one.
 
 Dealing with Multiple Implementations of the Same Type