This look like a duplicate of #22872

You're right, though #22872 does not correctly handle the KernelInterface, because the method must not necessarily be there…?

FrameworkBundle 3.3 has a lowest dep on HttpKernel 3.3, which always has the method, so the check is not required.
Closing as duplicate, thanks for the PR anyway.

FrameworkBundle 3.3 has a lowest dep on HttpKernel 3.3, which always has the method, so the check is not required.

Well but my kernel could implement the interface and not extend the Kernel class. I agree that is rather theoretical, but according to the current code the method should expect a Kernel instance and not a KernelInterface.

Hum, you're right. If you care enough about it, I invite you to open a PR against branch 3.3 with the corresponding patch :)

Which one would you prefer, the method check or expect the class?

method check to allow having the feature without extending the Kernel class I think

see #22921

@nicolas-grekas I also suggest deprecating having a kernel not implementing it, so that we can add the method in the interface in 4.0 (which will be fine as deprecation, as most people should be extending Kernel anyway, or should just be using HttpKernelInterface otherwise)