[GROOVY-10324] STC is unable to infer type variable when combining parameterized types and the diamond operator

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.0-beta-2, 3.0.11
• Assignee: Eric Milles
• Reporter: Thodoris Sotiropoulos
• Created: 21/Oct/21 12:03
• Updated: 18/May/22 17:17
• Resolved: 01/Nov/21 19:03

Description

I have the following program

class A {
  <T> T foo(C<T> t) { return null; }
}


class C<T> {}

class B {

  void test() {
    C<String> x = (new A()).foo(new C<>());
  }
}

Actual behaviour

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
test.groovy: 12: [Static type checking] - Cannot assign value of type java.lang.Object to variable of type C<java.lang.String>
 @ line 12, column 19.
       C<String> x = (new A()).foo(new C<>());
                     ^

1 error

Expected behaviour

Compile successfully

Note that compilation fails only if the expected return type is parameterized (i.e., `D<String>`). If I replace the declared type of `x` with a regular type (i.e., `String`), the code compiles fine.

Tested against master.

Issue Links

• relates to: GROOVY-10342 STC is unable to infer type parameter of parameterized method call