[jira] [Created] (MCOMPILER-424) Annotation processor fails with AnnotationTypeMismatchException on Java 11 which targets Java 8

["Marian Macik (Jira)" <ji...@apache.org>]

Marian Macik created MCOMPILER-424:
--------------------------------------

             Summary: Annotation processor fails with AnnotationTypeMismatchException on Java 11 which targets Java 8
                 Key: MCOMPILER-424
                 URL: https://issues.apache.org/jira/browse/MCOMPILER-424
             Project: Maven Compiler Plugin
          Issue Type: Bug
    Affects Versions: 3.8.1
         Environment: Apache Maven 3.6.3
Java 11.0.7
            Reporter: Marian Macik


When I configure the Maven Compiler Plugin running on Java 11 to target Java 8:
{code:xml}
<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-compiler-plugin</artifactId>
  <version>3.8.1</version>
  <configuration>
    <source>1.8</source>
    <target>1.8</target>
  </configuration>
 </plugin>
{code}
My compilation will fail with {{java.lang.annotation.AnnotationTypeMismatchException}} when I use an annotation processor.

I investigated it a little bit and found out that this happens only in a very specific case which has to fulfil these criteria:

1. One annotation which has the second annotation as a parameter.
 2. The second annotation has a parameter of type {{String[]}}.
 3. Java 11 has the compilation target set to Java 8.

The same scenario works without any issues when I configure the Maven Compiler Plugin with {{<release>11</release>}}.

I debugged the code and when I set the Maven Compiler Plugin to source/target 1.8, I noticed changes in the *AnnotationProxyMaker$ValueVisitor#getValue()* method. In this case, on the line in the *getValue()* method
{code:java}
attr.accept(this);
{code}
the *attr* variable holds a *ClassReader$ArrayAttributeProxy* object (so the second annotation's String[] parameter is being handled) and then I can see a *ClassCastException* thrown inside the *ClassReader$ArrayAttributeProxy#accept()* method:
{code:java}
public void accept(Visitor v) { ((ProxyVisitor)v).visitArrayAttributeProxy(this); }
{code}
which says
{noformat}
class com.sun.tools.javac.model.AnnotationProxyMaker$ValueVisitor cannot be cast to class com.sun.tools.javac.jvm.ClassReader$ProxyVisitor (com.sun.tools.javac.model.AnnotationProxyMaker$ValueVisitor and com.sun.tools.javac.jvm.ClassReader$ProxyVisitor are in module jdk.compiler of loader 'app')
{noformat}
so the *Visitor v* (of type *AnnotationProxyMaker$ValueVisitor*) cannot be cast to *ClassReader$ProxyVisitor*, which is correct by looking at the source code, and then the exception is caught at the *{{AnnotationProxyMaker$ValueVisitor#visitCompound()}}* method which handles the whole second annotation (which the String[] parameter is a part of). After that, it fails with the *AnnotationTypeMismatchException*.

Now, when I execute this with {{<release>11</release>}}, the *attr* variable holds an *Attribute$Array* object and its *accept()* method looks different:
{code:java}
public void accept(Visitor v) { v.visitArray(this); }
{code}
and the code executes perfectly fine.

There is a workaround for this and it is pretty simple. You just need to add an import of the second annotation on the annotated class being processed by the processor, even if just the default value is used. Or, in case the annotated class is in the same package as the annotation itself, you just need to provide the default value explicitly, see:
{code:java}
package org.example;
/*
 * Uncomment one of these lines and the annotation processor starts working.
 */
//import org.example.MySecondAnnotation;
@MyFirstAnnotation(
        //secondAnnotation = @MySecondAnnotation
)
public class AnnotatedClass {
}
{code}
Now I don't know if the issue is with the Java compiler or the Maven Compiler Plugin, but if it is with the former, you can at least help me to contact the Java compiler developers or forward me to the correct Java compiler issue tracking system.

I have also prepared a reproducer which shows this issue. It is available on GitHub [1] and includes a short README file with instructions on how to run it.

Thanks for help!

[1] [https://github.com/MarianMacik/JDK11-annotation-processor-reproducer]



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