[GROOVY-5418] Compilation error with covariant return types (incompatible types)

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.8.6
• Fix Version/s: 2.0.4, 1.8.9
• Component/s: Compiler
• Environment: Linux, jdk 1.6.0u31 (also reproducible with 1.7)
• Assignee: Cédric Champeau
• Reporter: Raffael Herzog
• Created: 25/Apr/12 05:11
• Updated: 21/Sep/12 16:58
• Resolved: 17/Sep/12 07:48

Description

Given the following files:

pkg/Base.java

package pkg;
public interface Base {
    Base doSomething();
}

pkg/Child.java

package pkg;
public interface Child extends Base {
    Child doSomething();
}

pkg/GChild.groovy

package pkg;
class GChild implements Child {
    Child doSomething() {
        return this
    }
}

When I try to compile this, groovyc complains about incompatible return types:

$ javac pkg/*.java
$ groovyc pkg/*.groovy
org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
pkg/GChild.groovy: 3: The return type of pkg.Child doSomething() in pkg.GChild is incompatible with pkg.Base doSomething() in pkg.Base
. At [3:2]  @ line 3, column 2.
        Child doSomething() {
    ^

1 error

$ javac -version
javac 1.6.0_31
$ groovyc -version
Groovy compiler version 1.8.6
Copyright 2003-2011 The Codehaus. http://groovy.codehaus.org/

$

A very similar (almost identical) issue has already been reported here: https://jira.codehaus.org/browse/GROOVY-2829 (marked as fixed in 1.5.7 and 1.6-beta2)