[GROOVY-10480] Closure that assigns null to object changes the type of variable

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Duplicate
• Component/s: Static Type Checker
• Assignee: Unassigned
• Reporter: Thodoris Sotiropoulos
• Created: 15/Feb/22 01:47
• Updated: 15/Feb/22 01:55
• Resolved: 15/Feb/22 01:55

Description

I have the following Groovy program

class Foo {
  void foo() {}
}


class Main  {

  static void bar() {
    def x = new Foo();
    if (false) {
      x = null;
    }
    x.foo(); // works
  }

  static void baz() {
    def x  = new Foo();
    def clos = { -> {
      x = null;
      
    }}
    x.foo(); // fails
  }

}

Actual behaviour

The assignment that takes inside closure changes the type of variable `x`, even though closure is never being called.
The compilerthen rejects the program by raising the following error message.

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
test.groovy: 22: [Static type checking] - A closure shared variable [x] has been assigned with various types and the method [foo()] does not exist in the lowest upper bound of those types: [java.lang.Object]. In general, this is a bad practice (variable reuse) because the compiler cannot determine safely what is the type of the variable at the moment of the call in a multithreaded context.
 @ line 22, column 5.
       x.foo();
       ^

1 error

Expected behaviour

Compile successfully

Tested against master (https://github.com/apache/groovy/commit/5601ea14304b67e71586b0196e38f90fa1a46f5b).