Cannot close over local variables

[atorstling]

Java8StepDefinition and more specifically ConstantPoolTypeIntrospector confuses closed variables with arguments to the accept function. This has the consequence that you are unable to close over local variables.

For example, if you define something like

class Steps implements En {
  Steps() {
      String prefix = "hello ";
      When("^blabla$", () -> prefix + "world" ); 
  }
}

, the lambda closes over the prefix variable. Subsequently, the ConstantPoolTypeIntrospector will read out a typeString not of the expected ()V, but of (Ljava/lang/String;)V. Java8StepDefinition will therefore get typeArguments of Type[]{ String.class }. It will then proceed looking for a method called accept with a single Object argument, which will fail (it treats all arguments as Object arguments, disregarding the specific type). In other words, it "thinks" that the lamda looks as follows:

class Steps implements En {
  Steps() {
      String prefix = "hello ";
      When("^blabla$", (prefix) -> prefix + "world" ); 
  }
}

, even though prefix is implicitly passed. I believe this could be solved by simply calling clazz.getDeclaredMethod("accept"), instead of looking in the constant pool, which evidently exposes implicit dependencies as well as explicit ones.

This problem is not present if you close over fields in the Steps class.

The exception you get when this happens is:

cucumber.runtime.CucumberException: java.lang.NoSuchMethodException:  com.example.Steps$$Lambda$3/358849801.accept(java.lang.Object)
    at cucumber.runtime.java.JavaBackend.addStepDefinition(JavaBackend.java:164)
    at cucumber.api.java8.En.When(En.java:370)
    at com.example.Steps.<init>(Steps.java:54)

I'm using cucumber 1.2.4

[aslakhellesoy]

Interesting. Would you be able to send a pull request with your proposed fix?

[atorstling]

Sure thing, please see above.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.