[GROOVY-9074] CompileStatic does not throw expected exception

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.5.5
• Fix Version/s: 5.0.0-alpha-12
• Component/s: Static Type Checker
• Labels: breaking

Language

groovy

• Assignee: Eric Milles
• Reporter: Robert Stagner
• Created: 10/Apr/19 17:29
• Updated: 18/Nov/24 21:05
• Resolved: 13/Nov/24 13:36

Description

While reading about Java Generics and wildcards (see https://docs.oracle.com/javase/tutorial/extra/generics/wildcards.html), I came across the following code in the referenced oracle document

Collection<?> c = new ArrayList<String>();
 c.add(new Object()); // Compile time error

Now, I decided to wrap this in a class and try it out in Java and then in Groovy.

Here is the Java code

 

import java.util.*;
public class TestCollection {
 static Collection<?> c = new ArrayList<String>();
 public static void main(String[] args) {
   c.add(new Object()); // Compile time error
 }
}

 

  

and here is the groovy code

 

import java.util.*;
import groovy.transform.CompileStatic;

@CompileStatic
public class TestCollection {
 static Collection<?> c = new ArrayList<String>();
 public static void main(String[] args) {
   c.add(new Object()); // Compile time error
   println c.first();
 }
}

 

When I attempt to compile the Java code I get the following expected error

$ javac TestCollection.java
 TestCollection.java:7: error: incompatible types: Object cannot be converted to CAP#1
 c.add(new Object()); // Compile time error
 ^
 where CAP#1 is a fresh type-variable:
 CAP#1 extends Object from capture of ?

But, when I run the code through Groovy, I do not get a compile-time error.  Instead, I get the following output

java.lang.Object@41a0aa7d

Issue Links

• relates to: GROOVY-10588 TypeChecked/CompileStatic wildcard problems
• relates to: GROOVY-10371 STC involves improper subtyping rules for parameterized types with wildcard types
• relates to: GROOVY-6835 flow typing activated by if statement doing an "instanceof" check doesn't work as expected with interface types
• relates to: GROOVY-8084 Captured types doesn't work in @CompileStatic
• links to: GitHub Pull Request #945