[GROOVY-10306] STC rejects program when assigning a closure that returns a class field

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.0-beta-2
• Component/s: Static Type Checker
• Assignee: Eric Milles
• Reporter: Thodoris Sotiropoulos
• Created: 14/Oct/21 14:52
• Updated: 03/Feb/22 22:32
• Resolved: 30/Oct/21 15:15

Description

I have the following program

import java.util.function.Supplier;

class Main {
    byte x = 1;

    void foo() {
        Supplier<Number> y =  () -> x;
        
    }
}

Actual behaviour

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
Main.java: 8: [Static type checking] - Incompatible generic argument types. Cannot assign java.util.function.Supplier<java.lang.Byte> to: java.util.function.Supplier<java.lang.Number>
 @ line 8, column 31.
           Supplier<Number> y =  () -> x;
                                 ^

1 error

Expected behaviour

Compile successfully

Note that if `x` is a local variabled defined in function `foo`, groovyc compiles the program successfully.

Tested against master