[GROOVY-9934] Bounded type parameter is not captured by closure

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.7
• Fix Version/s: 3.0.8, 4.0.0-alpha-3
• Component/s: Static compilation
• Assignee: Eric Milles
• Reporter: Thodoris Sotiropoulos
• Created: 09/Feb/21 10:18
• Updated: 02/May/21 09:16
• Resolved: 02/Mar/21 15:04

Description

I have the following Groovy program

class Bar {}

class Foo<T extends Bar> {
  public T method(T x) {
    def bar = {x}
    return bar()
  }
}

Actual Behavior

The compiler raise the following compile-time error 

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
Main.groovy: 6: [Static type checking] - Cannot return value of type java.lang.Object on method returning type T
 @ line 6, column 12.
       return bar()
              ^1 error

Expected Behavior

Compile successfully. Notably, when I remove the "extends" keyword from the type parameter, the code type checks as expected.