[GROOVY-10356] STC changes the inferred type of variable in the presence of flow typing

• 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: 10/Nov/21 07:18
• Updated: 30/Nov/23 17:18
• Resolved: 15/May/22 18:45

Description

This may be related to GROOVY-10294.

I have the following program

interface A {
  void a();
}

class Test {

  void test_closure() {
    def a = (A) null;
    def x = { ->
      a = null;
    }

    a.a();
  }
}

Actual behaviour

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
test.groovy: 15: [Static type checking] - A closure shared variable [a] has been assigned with various types and the method [a()] 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 15, column 5.
       a.a();
       ^

1 error

Expected behaviour

Compile successfully

Tested against master (https://github.com/apache/groovy/commit/0ff632514f9e06b8cea96f2e70749b3da3bc6dbb).