[jira] [Created] (GROOVY-10148) Groovy should not allow classes to extend sealed Java classes

["Paul King (Jira)" <ji...@apache.org>]

Paul King created GROOVY-10148:
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             Summary: Groovy should not allow classes to extend sealed Java classes
                 Key: GROOVY-10148
                 URL: https://issues.apache.org/jira/browse/GROOVY-10148
             Project: Groovy
          Issue Type: Improvement
          Components: Compiler
            Reporter: Paul King


For Java 15/16 under preview and targeted for 17+, sealed classes and interfaces can be created. Creating Groovy classes which extend such sealed Java classes or implement sealed interfaces, results in classes which will give a runtime error when loaded:
{noformat}
java.lang.RuntimeException: java.lang.IncompatibleClassChangeError: class MyGroovyChildClass cannot inherit from sealed class MyJavaSealedClass
{noformat}
When creating sealed classes, Java currently requires all mentioned permitted children to be compiled in the source set. However, it does allow subsequent compilation steps to include just one of the children (and have the parent pre-compiled). This in theory allows scenarios where one could have mixed Java/Groovy hierarchies by using stubs initially.

So, Groovy should eventually support compilation where the name of the Groovy class being compiled matched one of the declared permitted subclasses (though there may be some module implications too). I propose that we just disallow all cases in the first instance. We should create a GEP which outlines what we want to do with respect to Groovy support for sealed hierarchies and discuss further there how we might relax the restriction if it turns out to be feasible.



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