Support `@CircuitBreaker` on suspend functions (including `suspend fun` fallback methods) in Spring Boot 2

Resilience4j version: 1.7.1 Java version: 16 kotlin version: 1.5.30

@CircuitBreaker does not work with bean suspend functions even when it boasts Kotlin Coroutines support.

First, FallbackMethod.create(...) will always fail to find the fallback method because of how kotlin inserts a kotlin.coroutines.Continuation<T> as the last parameter of suspend functions. This is illustrated below.

@Service class MyBean {

  @CircuitBreaker("breakerName", fallbackMethod = "aFallbackMethod")
  suspend fun aMethod(aParam: String): String { ... }
  
  suspend fun aFallbackMethod(theParam: String, error: Throwable): String { ... }
}

For the above bean the runtime method signatures are

aMethod(String, Continuation): Object & aFallbackMethod(String, Throwable, Continuation): Object

which is why the fallback method cannot be determined, because the throwable is not the last parameter in the fallback function.

Also, being a suspend function, its inherently asynchronous and needs to be explicitly handled (or wrapped somehow) inside of CircuitBreakerAspect to function correctly

[efemoney]

@RobWin Sounds good. I will open a PR soon for this.

[RobWin]

No