minor #16699 [Doctrine] Adding caution box on dependecy injection (ThomasLandauer)

This PR was merged into the 4.4 branch.

Discussion
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[Doctrine] Adding caution box on dependecy injection

I guessed this (based on trial and error), so please double-check!

Maybe add a second sentence like:
The reason is that the class is instantiated by Doctrine and not wired through Symfony's DI container.

Commits
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806310a Adding caution box on dependecy injection

Author: javiereguiluz

doctrine/custom_dql_functions.rst

@@ -146,4 +146,8 @@ In Symfony, you can register your custom DQL functions as follows:
                 ],
             ]);
 
+.. caution::
+
+    It is not possible to inject Symfony services or parameters into a custom DQL function.
+
 .. _`DQL User Defined Functions`: https://www.doctrine-project.org/projects/doctrine-orm/en/current/cookbook/dql-user-defined-functions.html