[GROOVY-10098] Unexpected behaviour when the return type of a closure is a type parameter

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.0-beta-1, 3.0.9, 2.5.19
• Component/s: Static Type Checker
• Assignee: Eric Milles
• Reporter: Thodoris Sotiropoulos
• Created: 19/May/21 18:44
• Updated: 06/Sep/22 13:08
• Resolved: 20/May/21 18:01

Description

This may be a recent regression.

I have the following program

class Foo<T extends Number> {
  T f  Foo(T f) {
    this.f = f
  }
  T foo() {
    Closure<T> clos = { -> f}
    clos()
  }
}

Actual behaviour

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
test.groovy: 10: [Static type checking] - Cannot return value of type java.lang.Object on method returning type T
 @ line 10, column 5.
       clos()
       ^1 error

Expected behaviour

Compile successfully

Comment

The code works as expected if I remove the bound from the type parameter of class `Foo`.

 

Tested against https://github.com/apache/groovy/commit/f3d030afaaae44eca567ead74e68efb932831b08