Clarify component scanning of abstract classes with `@Lookup` methods

[cselagea]

According to https://docs.spring.io/spring-framework/reference/core/beans/dependencies/factory-method-injection.html,

Concrete methods are also necessary for component scanning, which requires concrete classes to pick up.

Note that you should typically declare such annotated lookup methods with a concrete stub implementation, in order for them to be compatible with Spring’s component scanning rules where abstract classes get ignored by default.

Abstract @Lookup methods are compatible with component scanning as of 4.3.6 thanks to #19118, so the documentation is incorrect/misleading.

[sbrannen]

Hi @cselagea,

Congratulations on submitting your first issue for the Spring Framework! 👍

And thanks for bringing this to our attention.

The documentation has been updated in 6.1.x, 6.2.x, and main. See commit 819a7c8.

Cheers

Sam