minor #18346 [DependencyInjection] Warns instanceof should be called before services registration (MatTheCat)

This PR was merged into the 5.4 branch.

Discussion
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[DependencyInjection] Warns `instanceof` should be called before services registration

Fixes symfony/symfony#49988 and symfony/symfony#50329

Order matters when configuring the service container using PHP.

Maybe we should warn about `defaults` too but I’m not sure where 🤔

Commits
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dc2d048 [DependencyInjection] Warns `instanceof` should be called before services registration

Author: javiereguiluz

service_container/tags.rst

@@ -113,6 +113,11 @@ If you want to apply tags automatically for your own services, use the
                     ->tag('app.custom_tag');
         };
 
+.. caution::
+
+    If you're using PHP, you need to call ``instanceof`` before any service
+    registration to make sure tags are correctly applied.
+
 It is also possible to use the ``#[AutoconfigureTag]`` attribute directly on the
 base class or interface::