[GROOVY-5640] static type checking fails in for-each loops

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0.0, 2.0.1
• Fix Version/s: 2.0.2
• Component/s: Static Type Checker

Environment

$ uname -a
Linux studio 3.2.0-25-generic #40-Ubuntu SMP Wed May 23 20:30:51 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

$ java -version
java version "1.7.0_04"
Java(TM) SE Runtime Environment (build 1.7.0_04-b20)
Java HotSpot(TM) 64-Bit Server VM (build 23.0-b21, mixed mode)

• Assignee: Cédric Champeau
• Reporter: wujek srujek
• Created: 28/Jul/12 08:05
• Updated: 11/Sep/12 01:15
• Resolved: 27/Aug/12 09:38

Description

I have some code that fail to compile with type checking. The example is not contrived, it comes from a real-life project that uses neo4j. The Node_ class is called Node, and I changed it here so that we exclude the possibility that Groovy somehow treats it as its Node class (which it doesn't anyways). The following code:

package test

import groovy.transform.TypeChecked

@TypeChecked
class Test {

    public void traverse() {
        println new Node_().class.name
        for (/*Object*/Node_ node : new MyTraverser().nodes()) {
            println node.class.name
        }
    }
}

class Node_ {}

interface Traverser {

    Iterable<Node_> nodes();
}

class MyTraverser implements Traverser {

    @Override
    Iterable<Node_> nodes() {
        []
    }
}

does not compile with the following error:

$ groovyc Test.groovy 
org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
Test.groovy: 12: [Static type checking] - Cannot loop with element of type test.Node -> test.Node with collection of type java.util.List <java.lang.Object> -> java.util.List <E extends java.lang.Object -> java.lang.Object>
 @ line 12, column 9.
           for (/*Object*/Node node : new MyTraverser().nodes()) {

It compiles fine when the iteration uses Object instead of Node_, and when there is no type checking.