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

["Eric Milles (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/GROOVY-9998?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Eric Milles resolved GROOVY-9998.
---------------------------------
    Fix Version/s: 4.0.0-alpha-3
       Resolution: Fixed

> 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
>            Assignee: Eric Milles
>            Priority: Major
>             Fix For: 4.0.0-alpha-3
>
>
> 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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