[GROOVY-5650] Groovy 2.0.1: Regression in generic type inference

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0.1
• Fix Version/s: 2.0.2
• Component/s: Static Type Checker
• Assignee: Cédric Champeau
• Reporter: Daniel Lichtenberger
• Created: 01/Aug/12 02:38
• Updated: 11/Sep/12 01:15
• Resolved: 22/Aug/12 07:43

Description

The following Groovy code compiles with @TypeChecked in 2.0.0, but not in 2.0.1:

JavaClass.java

import java.util.List;
import java.util.ArrayList;
import java.util.Collection;

public class JavaClass {

    public static class Container<T> {
    }

    public static class StringContainer extends Container<String> {
    }

    public static <T> List<T> unwrap(Collection<? extends Container<T>> list) {
        return null;
    }

    public static void main(String[] args) {
        final List<StringContainer> containers = new ArrayList<>();
        final List<String> strings = unwrap(containers);
    }
}

GroovyClass.groovy

import groovy.transform.TypeChecked;

@TypeChecked
class GroovyClass {

    public static void javaCall() {
        final List<JavaClass.StringContainer> containers = new ArrayList<>();
        containers.add(new JavaClass.StringContainer()); 
        final List<String> strings = JavaClass.unwrap(containers);
    }

    public static void main(String[] args) { 
        javaCall();
    }
}

Groovy 2.0.0 compiles the code without errors or warnings, but 2.0.1 gives the following error message:

/home/.../GroovyClass.groovy: 8: [Static type checking] - Incompatible generic argument types. Cannot assign java.util.List <JavaClass> to: java.util.List <String>
 @ line 8, column 38.
           final List<String> strings = JavaClass.unwrap(containers);
                                        ^

1 error

Somehow Groovy infers the type to the static method's class, instead of the container's type argument.