[GROOVY-8342] Static compilation error with a method returning an array in a type parameter

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.0.0-alpha-4, 2.5.3
• Component/s: Static compilation
• Assignee: Paul King
• Reporter: M. Justin
• Created: 05/Oct/17 15:09
• Updated: 13/Dec/18 10:05
• Resolved: 11/Oct/18 02:17

Description

A compilation error occurs when using static compilation and attempting to assign the result of a method that returns a parameterized argument that contains an array in the type parameter. The equivalent Java code has no issues.

Here is a specific example:

@CompileStatic
class ArrayGenericsIssue {
  static void main(String[] args) {
    Optional<Integer[]> value = testArrayMethod(1) //This fails to compile
  }

  static <E> Optional<E[]> testArrayMethod(E ignored) {
    return Optional.empty()
  }
}

The error returned is:

Error:(11, 33) Groovyc: [Static type checking] - Incompatible generic argument types. Cannot assign java.util.Optional <E[]> to: java.util.Optional <Integer[]>

The expected behavior is that this code would compile and run successfully with @CompileStatic enabled.

Note that equivalent code with a non-array generic parameter works just fine:

  static void main(String[] args) {
    Optional<List<Integer>> value = testListMethod(1)
  }

  static <E> Optional<List<E>> testListMethod(E ignored) {
    return Optional.empty()
  }

Additionally, there is no compilation issue if the value is cast:

Optional<Integer[]> value = (Optional<Integer[]>) testArrayMethod(1)

For some context, I'm running into this issue when working with jOOQ, as some of its API involves working with array type parameters.