Do I understand correctly that the intention here is that the interceptor will be added here when the WebClient wasn't created by spring. For example when there is something like

@Bean
WebClient webClient() {
  return WebClient.create();
}

I'd guess the WebClientCustomizer won't run then. What if there is

@Bean
WebClient.Builder webClientBuilder() {
  return WebClient.builder();
}

I'd guess the WebClientCustomizer won't run then either. Should we handle that? Should this be aligned with RestClientBeanPostProcessor (cc @zeitlinger, do you remember why you wrote RestClientBeanPostProcessor the way it is).
Assuming that the intent is to add the interceptor in post processor when the customizer didn't run do we have any tests for this?

My goal was to make sure that we add the interceptor in every possible way that you can do it - either by creating a builder or the client bean directly.

I did add unit and smoke tests - but maybe I missed a case: #11038

Sorry for not getting back here.

I'd guess the WebClientCustomizer won't run then either. Should we handle that? Should this be aligned with RestClientBeanPostProcessor

The existing behaviour was RestClient.Builder was not processed by a BPP but by WebClient.Builder was. The current state was that neither builder was handled in that case. I think this is an expected pattern in Spring Boot when a Builder bean is created; the choice to apply customizer beans lies with the creator, consistent with how other customizers would be treated in the Spring Boot world.

Open to discuss otherwise, too.