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javadelegatesannotationsxtextxtend

Is extending the DelegateProcessor of the @Delegate active annotation possible?

I am currently working on an active annotation that is an adjusted version of the Xtend active annotation @Delegate. I already have an ugly version that is just an adapted copy of the class DelegateProcessor and its inner class Util. But this means I copied the whole class just do adapt a few lines of code in two methods.

I tried to extend the DelegateProcessor and Util to override the few methods I need to change. Even in a minimal setup (see code) this is not working. I recognize that the Javadoc tags suggest me not to do this, but I cannot believe that there is no other way than copying the whole 300 lines of code.

This is my minimal setup:

import com.google.common.annotations.Beta
import com.google.common.annotations.GwtCompatible
import java.lang.annotation.Documented
import java.lang.annotation.ElementType
import java.lang.annotation.Target
import java.util.List
import org.eclipse.xtend.lib.annotations.Delegate
import org.eclipse.xtend.lib.annotations.DelegateProcessor
import org.eclipse.xtend.lib.macro.Active
import org.eclipse.xtend.lib.macro.TransformationContext
import org.eclipse.xtend.lib.macro.TransformationParticipant
import org.eclipse.xtend.lib.macro.declaration.MutableMemberDeclaration

/**
 * Copy of the Xtend {@link Delegate} annotation.
 */
@Beta
@GwtCompatible
@Target(ElementType.FIELD, ElementType.METHOD)
@Active(DelegateDeclaredProcessor)
@Documented
annotation DelegateDeclared {
    /**
     * Optional list of interfaces that this delegate is restricted to.
     * Defaults to the common interfaces of the context type and the annotated
     * element.
     */
    Class<?>[] value = #[]
}

@Beta
class DelegateDeclaredProcessor extends DelegateProcessor implements TransformationParticipant<MutableMemberDeclaration> {

    override doTransform(List<? extends MutableMemberDeclaration> elements, extension TransformationContext context) {
        val extension util = new Util(context) // Overridden to use my own Util class, which i want to adapt later on.
        elements.forEach [
            if (validDelegate) {
                methodsToImplement.forEach[method|implementMethod(method)]
            }
        ]
    }

    @Beta
    static class Util extends DelegateProcessor.Util { // this is where I want to later override some methods.
        new(TransformationContext context) {
            super(context)
        }
    }
}

This code produces the following error when using the annotation:

    Error during annotation processing:
java.lang.NullPointerException
    at org.eclipse.xtend.lib.annotations.DelegateProcessor$Util.listedInterfaces(DelegateProcessor.java:258)
    at org.eclipse.xtend.lib.annotations.DelegateProcessor$Util.areListedInterfacesValid(DelegateProcessor.java:184)
    at org.eclipse.xtend.lib.annotations.DelegateProcessor$Util._isValidDelegate(DelegateProcessor.java:67)
    at org.eclipse.xtend.lib.annotations.DelegateProcessor$Util.isValidDelegate(DelegateProcessor.java:592)
    at jce.util.DelegateDeclaredProcessor.lambda$0(DelegateDeclaredProcessor.java:28)
    at jce.util.DelegateDeclaredProcessor$$Lambda$15311/667735929.accept(Unknown Source)
    at java.lang.Iterable.forEach(Iterable.java:75)
    at jce.util.DelegateDeclaredProcessor.doTransform(DelegateDeclaredProcessor.java:36)

What is the problem here? Am I doing anything wrong or is it just not possible to do that? Is there another way to create adapted versions of existing active annotations such as @Delegate?

Solution

  • looks like you miss some overrides

    @Beta
static class Util extends DelegateProcessor.Util { // this is where I want to later override some methods.

    extension TransformationContext context

    new(TransformationContext context) {
        super(context)
        this.context = context
    }

    override getDelegates(TypeDeclaration it) {
        declaredMembers.filter[findAnnotation(findTypeGlobally(DelegateDeclared)) !== null]
    }

    override listedInterfaces(MemberDeclaration it) {
        findAnnotation(findTypeGlobally(DelegateDeclared)).getClassArrayValue("value").toSet
    }

}