[GROOVY-10688] LUB does not work properly when mixing type parameter names and using wildcards

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.5, 3.0.20
• Component/s: Static Type Checker
• Assignee: Eric Milles
• Reporter: Thodoris Sotiropoulos
• Created: 15/Jul/22 13:40
• Updated: 11/Dec/23 19:15
• Resolved: 25/Jul/22 19:24

Description

This might be related to GROOVY-10662.

I have the following program

class A<T, X> {
}

class Test<T> {
  void test(A<Double, ? extends T> x) {
    A<Double, ? extends T> y = x;
    A<Double, ? extends T> z = (true) ? y : x;
  }
}

Actual behavior

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
test.groovy: 7: [Static type checking] - Incompatible generic argument types. Cannot assign A<java.lang.Double, java.lang.Object> to: A<java.lang.Double, ? extends T>
 @ line 7, column 32.
       A<Double, ? extends T> z = (true) ? y : x;
                                  ^

1 error

Expected behavior

Compile successfully

Notes: The bug is triggered when the following conditions hold:

• The name of the first type parameter of class A matches the type parameter of class Test.
• We the wildcard type "? extends T" for instantiating the type constructor A on lines 5, 6, 7.

Tested against master (commit: 1ea7b9619e7a3ec0da9a3e065f78e394206ea632)