[jira] [Assigned] (GROOVY-12247) NPE "Cannot invoke MetaMethod.isAbstract() because method is null" on super call to inherited generic method with default parameter

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

     [ https://issues.apache.org/jira/browse/GROOVY-12247?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Paul King reassigned GROOVY-12247:
----------------------------------

    Assignee: Paul King

> NPE "Cannot invoke MetaMethod.isAbstract() because method is null" on super call to inherited generic method with default parameter
> -----------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: GROOVY-12247
>                 URL: https://issues.apache.org/jira/browse/GROOVY-12247
>             Project: Groovy
>          Issue Type: Bug
>          Components: groovy-runtime
>    Affects Versions: 5.0.8, 6.0.0-beta-1
>            Reporter: Sean Fitts
>            Assignee: Paul King
>            Priority: Major
>
> A dynamic super. call throws:
> {quote}java.lang.NullPointerException: Cannot invoke "groovy.lang.MetaMethod.isAbstract()" because "method" is null
> at groovy.lang.MetaClassImpl.getSuperMethodWithCaching(MetaClassImpl.java:1423)
> at groovy.lang.MetaClassImpl.getMethodWithCaching(MetaClassImpl.java:1368)
> at groovy.lang.MetaClassImpl.getMetaMethod(MetaClassImpl.java:1263)
> at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1117)
> at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:143)
> {quote}
> when all of the following hold:
>  # The super method is declared in a generic class, uses the type variable as a parameter type, and has a default parameter value (which generates a short-form overload). Declaring two explicit overloads instead of using a default parameter fails the same way.
>  # An intermediate class binds the type parameter, so the overriding class sits two levels below the generic declaration. (If the overriding class extends the generic class directly, it works.)
>  # A subclass overrides the short-form overload with the concrete type argument (producing a bridge method) and invokes it via super. with the optional argument omitted.
> Reproducer (tried attaching file, but that failed):
>  
> abstract class Base<T extends Number> {
> protected String process(T value, String extra = null) {
> return "base(${value}, ${extra})"
> }
> }
> abstract class Mid extends Base<Integer> {}
> class Sub extends Mid {
> @Override
> protected String process(Integer value) {
> return 'sub->' + super.process(value)
> }
> }
> // Expected (Groovy 3/4): sub->base(42, null)
> // Groovy 5.0.8 / 6.0.0-beta-1: NPE "Cannot invoke groovy.lang.MetaMethod.isAbstract() because method is null"
> println new Sub().process(42)
>  
> Expected output sub->base(42, null), as produced by Groovy 3 and 4).
> Removing any one ingredient avoids the failure: dropping the default parameter (so the method is not overloaded), removing the intermediate class Mid, or calling the full-arity form explicitly (super.process(value, null)), which is a usable workaround.



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