[jira] [Created] (GROOVY-9998) Wildcards with a lower bound fail static type checking

["Lyuben Atanasov (Jira)" <ji...@apache.org>]

Lyuben Atanasov created GROOVY-9998:
---------------------------------------

             Summary: Wildcards with a lower bound fail static type checking
                 Key: GROOVY-9998
                 URL: https://issues.apache.org/jira/browse/GROOVY-9998
             Project: Groovy
          Issue Type: Bug
          Components: Static compilation, Static Type Checker
    Affects Versions: 3.0.7
            Reporter: Lyuben Atanasov


The following code fails to compile when using {{@CompileStatic}}:
{code}
class A {
	public final int order;
	
	public A(int order) {
		this.order = order;
	}
}

class B extends A {
	public B(int order) {
		super(order);
	}
}

class Test {
	public void test() {
		Comparator<? super A> comparator = (a1, a2) -> Integer.compare(a1.order, a2.order);
		List<B> list = [new B(2), new B(3), new B(1), new B(0)];
		list.stream().sorted(comparator);
	}
}
{code}

The error is:
{noformat}
Exception in thread "main" org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
Script_49a5c0348548765c6a0257437aa3b031.groovy: 19: [Static type checking] - Cannot call java.util.stream.Stream <B>#sorted(java.util.Comparator <? super B>) with arguments [java.util.Comparator <A>] 
 @ line 19, column 3.
   		list.stream().sorted(comparator);
     ^
{noformat}

For some reason the type checker is confused when we have a method with a generic parameter that has a wildcard with a lower bound. The same code compiles with javac if I move the A and B classes to separate files and create the list java-style.

Curiously, if I change the comparator's type from {{Comparator<? super A>}} to {{Comparator<? extends A>}}, the code compiles successfully in Groovy (and it shouldn't!), but causes compilation failure in Java.



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