[GROOVY-11082] Incompatible generic argument when mixing diamond operator and "super" wildcard

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: Static Type Checker
• Labels: diamond
• Assignee: Unassigned
• Reporter: Thodoris Sotiropoulos
• Created: 06/Jun/23 13:30
• Updated: 06/Jun/23 13:30

Description

Somewhat related to GROOVY-11254.

I have the following program

import java.util.function.*;

class Foo<T> {
  Foo(Supplier<? super T> x) {}
}

class Main {
  static final void test() {
    Supplier<CharSequence> func = null;
    Foo<StringBuffer> x = new Foo<>(func);

  }
}

Actual behaviour

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
test.groovy: 10: [Static type checking] - Incompatible generic argument types. Cannot assign Foo<java.lang.CharSequence> to: Foo<java.lang.StringBuffer>
 @ line 10, column 27.
       Foo<StringBuffer> x = new Foo<>(func);
                             ^

1 error

Expected behaviour

Compile successfully

Notes

Tested against master

Test case adapted from:

class Main {
  static final void test() {
    final org.apache.commons.collections4.functors.NotPredicate<CharSequence> x = null;
    final org.apache.commons.collections4.functors.PredicateDecorator<StringBuffer> y = new org.apache.commons.collections4.functors.NullIsTruePredicate<>(x);
  }
}