Imperative Redis support auto-configured in WebFlux based applications

[vpavic]

A simple WebFlux based application consisting of spring-boot-starter-webflux and spring-boot-starter-data-redis-reactive dependencies will result in imperative Redis support (namely, RedisTemplate<Object, Object> and StringRedisTemplate beans) being auto-configured.

This is because beans auto-configured by RedisAutoConfiguration (the ones listed earlier) are conditional on presence of imperative RedisConnectionFactory which is always the case with Lettuce due to LettuceConnectionFactory implementing both RedisConnectionFactory and ReactiveRedisConnectionFactory. This potentially sets up users for failure by configuring components that really shouldn't be available on a non-blocking runtime.

I'm not sure if there are other places where something like this is possible, but similarly like with #15574, it feels like Spring Boot could offer conditions to determine whether the runtime is Servlet or WebFlux based.

[snicoll]

Thanks, we are aware and have been brainstorming about this already, see #22692