[GROOVY-10565] JDK 17: Sealed classes inside a package cause Exception in thread "main" java.lang.ClassFormatError: Illegal class name

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 4.0.0, 4.0.1
• Fix Version/s: 4.0.2
• Labels: ClassFormatError

Language

groovy

• Assignee: Paul King
• Reporter: Szymon Stępniak
• Created: 04/Apr/22 11:26
• Updated: 23/Jul/22 16:26
• Resolved: 05/Apr/22 15:42

Description

I have found an issue with using sealed types that are inside a package. I took the example from the Groovy 4 release notes and I run it successfully - all classes in this example use the default package. However, when I took the same code and I put it in any package (e.g. `example` package), the execution started failing with:

Exception in thread "main" java.lang.ClassFormatError: Illegal class name "example.Empty" in class file example/Tree
        at java.base/java.lang.ClassLoader.defineClass1(Native Method)
        at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1012)
        at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
        at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:862)
        at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:760)
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681)
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
        at java.base/java.lang.ClassLoader.defineClass1(Native Method)
        at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1012)
        at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
        at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:862)
        at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:760)
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681)
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
        at example.notworking.run(notworking.groovy:20)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:568)
        at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:343)
        at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:328)
        at groovy.lang.MetaClassImpl.doInvokeMethod(MetaClassImpl.java:1369)
        at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1103)
        at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1009)
        at org.codehaus.groovy.runtime.InvokerHelper.invokePogoMethod(InvokerHelper.java:610)
        at org.codehaus.groovy.runtime.InvokerHelper.invokeMethod(InvokerHelper.java:593)
        at org.codehaus.groovy.runtime.InvokerHelper.runScript(InvokerHelper.java:413)
        at org.codehaus.groovy.runtime.InvokerHelper$runScript.callStatic(Unknown Source)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallStatic(CallSiteArray.java:54)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callStatic(AbstractCallSite.java:217)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callStatic(AbstractCallSite.java:240)
        at example.notworking.main(notworking.groovy)

Here is the code that produces this error:

package example

import groovy.transform.Canonical

sealed interface Tree<T> {}

@Singleton final class Empty implements Tree {
    String toString() { 'Empty' }
}

@Canonical final class Node<T> implements Tree<T> {
    T value
    Tree<T> left, right

    String toString() {
        "Node($value, $left, $right)"
    }
}

Tree<Integer> tree = new Node<Integer>(42, new Node<>(0, Empty.instance, Empty.instance), Empty.instance)
assert tree.toString() == 'Node(42, Node(0, Empty, Empty), Empty)'

println "IT WORKS!"

One important note: this error shows up when I use Java 17. If I run the same code with Java 8 or Java 11, all works fine.

Also one thing: this problem does not occur in plain Java (I attached such an example in the repository below).

I created an exemplary Gradle project that reproduces this issue - https://github.com/wololock/groovy-4-sealed-issue