[jira] [Resolved] (GROOVY-11341) @CompileStatic: Compilation fails due to a synthetic bridge method in the subclass

["Eric Milles (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/GROOVY-11341?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Eric Milles resolved GROOVY-11341.
----------------------------------
    Fix Version/s: 5.0.0-alpha-8
       Resolution: Fixed

https://github.com/apache/groovy/commit/d82ae1715efff292e48f712d71aee8f4b9d7ab77

> @CompileStatic: Compilation fails due to a synthetic bridge method in the subclass
> ----------------------------------------------------------------------------------
>
>                 Key: GROOVY-11341
>                 URL: https://issues.apache.org/jira/browse/GROOVY-11341
>             Project: Groovy
>          Issue Type: Bug
>          Components: Static compilation, Static Type Checker
>    Affects Versions: 2.4.x, 2.5.x, 3.0.21, 5.0.0-alpha-7, 4.0.20
>            Reporter: Peter Schmitz
>            Assignee: Eric Milles
>            Priority: Minor
>              Labels: CompileStatic, groovyc
>             Fix For: 5.0.0-alpha-8
>
>
> Given the following Java classes:
> {code:java}
> public interface InterfaceBase {
>     Object getValue();
> }
>  
> public class MyImplBase {
>     public Long getValue() {
>         return 42L;
>     }
> }
>  
> public class MyImpl extends MyImplBase implements InterfaceBase {
> } {code}
>  
> And the following SimpleCaller.groovy:
> {code:java}
> @groovy.transform.CompileStatic
> class SimpleCaller {
>    public static void main(String[] args) {
>       Long v = new MyImpl().getValue();
>       System.out.println(v); //42
>    }
> } {code}
> The compilation fails with:
>  
> {{SimpleCaller.groovy: 7: [Static type checking] - Cannot assign value of type java.lang.Object to variable of type java.lang.Long}}
> {{ @ line 7, column 16.}}
> {{         Long v = new MyImpl().getValue();}}
> {{                  ^}}
>  
> Compiling the equivalent {{SimpleCaller.java}} with _javac_ completes successfully.
>  
> This structure is a bit uncommon, because MyImplBase uses a covariant return type and doesn't implement the interface directly, only its subclass does.
>  
> I believe the problem is connected to the synthetic bridge method inserted into the bytecode of {_}MyImpl{_}, which is picked up and preferred by _groovyc_ over the non-synthetic method in {_}MyImplBase{_}.
>  
>  
> In case this is related: The synthetic bridge method is selected when using reflection as well, causing the inferred type by javac and reflection to diverge:
> {code:java}
> Method getValueMethod = MyImpl.class.getMethod("getValue");
> // public java.lang.Object MyImpl.getValue() {code}
>  
>  
> Workarounds: 
>  
>  * Disable static compilation
>  * An explicit cast to Long in SimpleCaller.
>  * Explicitly repeat the covariant method signature in MyImpl
>  * If possible, add/Move the implements to MyImplBase - then the synthetic method is in the same class as the real one, which _groovyc_ is able to detect.
> Using generics in the Interface doesn't work either (probably due to type erasure).
>  
> Seems to be a more generalized issue when compared to the similar GROOVY-5003



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