[GROOVY-11457] STC does not properly handle try/catch in flow typing leading to type unsafety

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 5.0.0-alpha-10
• Component/s: Static Type Checker

Language

groovy

• Assignee: Eric Milles
• Reporter: Thodoris Sotiropoulos
• Created: 02/Sep/24 08:22
• Updated: 12/Nov/24 11:40
• Resolved: 04/Sep/24 19:33

Description

I have the following incorrect program

class Main {
  public static void main(String[] args) {
    var p1 = (java.lang.Appendable) null;
    if (false)  {
    } else {
      p1 = 51
    };
    //if (false) {} else {p1 = (java.lang.Appendable) null;}
    try {} catch(Exception e) { p1 = (java.lang.Appendable) null; }
    final java.lang.Appendable p2 = p1
  }
}

Actual behavior

The compiler accepts the program, but I get a ClassCastException

Exception in thread "main" org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object '51' with class 'java.lang.Integer' to class 'java.lang.Appendable'
        at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.continueCastOnSAM(DefaultTypeTransformation.java:416)
        at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.continueCastOnNumber(DefaultTypeTransformation.java:329)
        at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.castToType(DefaultTypeTransformation.java:248)
        at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:336)
        at Main.main(test.groovy:11)
 

Expected behavior

The code should have been rejected with

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
test.groovy: 11: [Static type checking] - Cannot assign value of type java.lang.Object to variable of type java.lang.Appendable
 @ line 11, column 37.
       final java.lang.Appendable p2 = p1
                                       ^1 error 

Notes

When replacing try/catch with another if/else like so:

class Main {
  public static void main(String[] args) {
    var p1 = (java.lang.Appendable) null;
    if (false)  {
    } else {
      p1 = 51
    };
    if (false) {} else {p1 = (java.lang.Appendable) null;}
    //try {} catch(Exception e) { p1 = (java.lang.Appendable) null; }
    final java.lang.Appendable p2 = p1
  }
} 

the compiler rejected the code as expected.