Xtend compilation issues with static nested interfaces

Question

I've been trying to solve this very strange bug for hours, and I simply can't figure it out.

I have the following code in its own Xtend source file in a project in Eclipse:

interface Apple {
    def void test() {}
    static interface Green extends Apple {
        override test() {
            Apple.super.test();
        }
    }
}

And for some reason I get a compiler error on the keyword "super" in the above code that says:

Java problem: No enclosing instance of the type Apple is accessible in scope

Upon inspecting the Java source code that Xtend produces, I see that it is creating the nested interface as non-static, as well as using the keyword "this" instead of "super", which would obviously cause this error.

Xtend output (reformatted):

public interface Apple {
    public default void test() {}
    public interface Green extends Apple {
        @Override
        public default void test() {
            Apple.this.test();
        }
    }
}

Why is the Xtend compiler doing this?

Perhaps the weirdest part is that the output of the compiler is inconsistent. When I rename the superinterface, the Java source code generated by Xtend changes semantically.

I'm using the Eclipse Xtend plugin for Xtend 2.9.0 with a source target of Java 8.

Edit: I should note, I am aware that the above code seems to be semantically pointless, and is obviously unnecessary given that the method is inherited. However, this is a simplified case of my actual, more practical, code.

I reported the issue: https://bugs.eclipse.org/bugs/show_bug.cgi?id=487861 — snorbi, Feb 16 '16 at 10:12

score 1 · Accepted Answer · answered Feb 16 '16 at 10:04

it is creating the nested interface as non-static

Nested interfaces are always static therefore the explicit static modifier you specified is redundant. (So the Xtend compiler is correct here.)

using the keyword "this" instead of "super"

I guess this is an Xtend compiler bug, the corresponding Java source is compiled and executed as expected:

interface AppleJava {
    default void test() {
        System.out.println("AppleJava.test()");
    }

    interface GreenJava extends AppleJava {
        @Override
        default void test() {
            AppleJava.super.test();
            System.out.println("GreenJava.test()");
        }
    }
}

class Test1 {
    public static void main(String[] args) {
        new AppleJava() {}.test();
        new AppleJava.GreenJava() {}.test();
    }
}

Result:

AppleJava.test()
AppleJava.test()
GreenJava.test()

Xtend compilation issues with static nested interfaces

1 Answers1