[GROOVY-9984] Wrong type inference when passing null

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.0-alpha-3, 3.0.9
• Component/s: Static compilation, Static Type Checker
• Assignee: Eric Milles
• Reporter: Stefanos Chaliasos
• Created: 15/Mar/21 09:50
• Updated: 18/Aug/21 15:42
• Resolved: 21/Mar/21 15:09

Description

I have the following Groovy program.

@groovy.transform.CompileStatic
public class Main {
  public static void main(String[] args) {
    final A<Integer> x = new A<>(null);
    baz(x);
  }

  public static void baz(A<Integer> x) {}

}

class A<T> {
  T f;
  public A(T f) {
    this.f = f;
  }
}

Actual Behavior

The program does not compile, and I get the following error.

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
Test.groovy: 4: [Static type checking] - Incompatible generic argument types. Cannot assign A <java.lang.Object> to: A <Integer>
 @ line 4, column 26.
       final A<Integer> x = new A<>(null);
                            ^

Test.groovy: 5: [Static type checking] - Cannot call Main#baz(A <java.lang.Integer>) with arguments [A <java.lang.Object>]
 @ line 5, column 5.
       baz(x);
       ^

2 errors

Expected Behavior

Compile successfully.

Comment

This should be a regression bug because it compiles with the 4.0.0-alpha-2 compiler.

Affected Version

This programs fails when compiled with the compiler from the master (commit: f0eea862549529ef4e93fafe337f86dd4ac98751).