[GROOVY-10254] STC: cannot return closure from method without casting

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.0.0-beta-1
• Fix Version/s: 4.0.0-beta-2, 2.5.19, 3.0.13
• Component/s: Static compilation, Static Type Checker
• Assignee: Eric Milles
• Reporter: Stefanos Chaliasos
• Created: 23/Sep/21 03:30
• Updated: 10/Sep/22 23:20
• Resolved: 26/Sep/21 21:53

Description

I have the following Groovy program.

import java.util.function.Supplier;

@groovy.transform.TypeChecked
public class Main {
    public static Supplier<Integer> foo() {
        { -> 10} as Supplier<Integer> // works
    }
    public static Supplier<Integer> bar() {
        { -> 10} //fails
    }
    public static void main(String[] args) {
        Supplier<Integer> v1 = { -> 10} as Supplier<Integer> // works
        Supplier<Integer> v2 = { -> 10} // works
        Supplier<Integer> v3 = foo()
        Supplier<Integer> v4 = bar()
    }
}

Actual Behavior

The program does not compile, and I get the following error.

Main.groovy: 10: [Static type checking] - Cannot return value of type groovy.lang.Closure<java.lang.Integer> on method returning type java.util.function.Supplier<java.lang.Integer>
 @ line 10, column 9.
           { -> 10} //fails
           ^

1 error

Expected Behavior

Compile successfully.