IAE: Cannot attach undefined variable TLeft under 16b30

Caused by this test: https://github.com/ReactiveX/RxJava/blob/3.x/src/test/java/io/reactivex/rxjava3/internal/operators/flowable/FlowableGroupJoinTest.java#L701-L718

io.reactivex.rxjava3.internal.operators.flowable.FlowableGroupJoinTest > leftRightState FAILED
org.mockito.exceptions.base.MockitoException: 
Mockito cannot mock this class: interface io.reactivex.rxjava3.internal.operators.flowable.FlowableGroupJoin$JoinSupport.

Mockito can only mock non-private & non-final classes.
If you're not sure why you're getting this error, please report to the mailing list.


Java               : 16
JVM vendor name    : Oracle Corporation
JVM vendor version : 16-ea+30-2130
JVM name           : OpenJDK 64-Bit Server VM
JVM version        : 16-ea+30-2130
JVM info           : mixed mode, sharing
OS name            : Linux
OS version         : 5.4.0-1032-azure


Underlying exception : java.lang.IllegalArgumentException: Cannot attach undefined variable: TLeft
    at io.reactivex.rxjava3.internal.operators.flowable.FlowableGroupJoinTest.leftRightState(FlowableGroupJoinTest.java:703)

    Caused by:
    java.lang.IllegalArgumentException: Cannot attach undefined variable: TLeft
        at net.bytebuddy.dynamic.Transformer$ForMethod$TransformedMethod$AttachmentVisitor.onTypeVariable(Transformer.java:592)
        at net.bytebuddy.dynamic.Transformer$ForMethod$TransformedMethod$AttachmentVisitor.onTypeVariable(Transformer.java:580)
        at net.bytebuddy.description.type.TypeDescription$Generic$OfTypeVariable$Symbolic.accept(TypeDescription.java:5938)
        at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$Substitutor.onParameterizedType(TypeDescription.java:1850)
        at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$Substitutor$WithoutTypeSubstitution.onParameterizedType(TypeDescription.java:1894)
        at net.bytebuddy.description.type.TypeDescription$Generic$OfParameterizedType.accept(TypeDescription.java:5149)
        at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$Substitutor.onParameterizedType(TypeDescription.java:1855)
        at net.bytebuddy.description.type.TypeDescription$Generic$Visitor$Substitutor$WithoutTypeSubstitution.onParameterizedType(TypeDescription.java:1894)
        at net.bytebuddy.description.type.TypeDescription$Generic$OfParameterizedType.accept(TypeDescription.java:5149)
        at net.bytebuddy.dynamic.Transformer$ForMethod$TransformedMethod.getReceiverType(Transformer.java:458)
        at net.bytebuddy.implementation.attribute.MethodAttributeAppender$ForInstrumentedMethod$2.appendReceiver(MethodAttributeAppender.java:177)
        at net.bytebuddy.implementation.attribute.MethodAttributeAppender$ForInstrumentedMethod.apply(MethodAttributeAppender.java:215)
        at net.bytebuddy.implementation.attribute.MethodAttributeAppender$Compound.apply(MethodAttributeAppender.java:484)
        at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod$WithBody.applyAttributes(TypeWriter.java:701)
        at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod$WithBody.applyBody(TypeWriter.java:691)
        at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod.apply(TypeWriter.java:600)
        at net.bytebuddy.dynamic.scaffold.TypeWriter$Default$ForCreation.create(TypeWriter.java:5751)
        at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:2166)
        at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:232)
        at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:204)
        at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase.make(DynamicType.java:3659)
        at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$Delegator.make(DynamicType.java:3897)
        at org.mockito.internal.creation.bytebuddy.SubclassBytecodeGenerator.mockClass(SubclassBytecodeGenerator.java:199)
        at org.mockito.internal.creation.bytebuddy.TypeCachingBytecodeGenerator$1.call(TypeCachingBytecodeGenerator.java:46)
        at org.mockito.internal.creation.bytebuddy.TypeCachingBytecodeGenerator$1.call(TypeCachingBytecodeGenerator.java:43)
        at net.bytebuddy.TypeCache.findOrInsert(TypeCache.java:153)
        at net.bytebuddy.TypeCache$WithInlineExpunction.findOrInsert(TypeCache.java:366)
        at net.bytebuddy.TypeCache.findOrInsert(TypeCache.java:175)
        at net.bytebuddy.TypeCache$WithInlineExpunction.findOrInsert(TypeCache.java:377)
        at org.mockito.internal.creation.bytebuddy.TypeCachingBytecodeGenerator.mockClass(TypeCachingBytecodeGenerator.java:36)
        at org.mockito.internal.creation.bytebuddy.SubclassByteBuddyMockMaker.createMockType(SubclassByteBuddyMockMaker.java:77)
        at org.mockito.internal.creation.bytebuddy.SubclassByteBuddyMockMaker.createMock(SubclassByteBuddyMockMaker.java:43)
        at org.mockito.internal.creation.bytebuddy.ByteBuddyMockMaker.createMock(ByteBuddyMockMaker.java:29)
        at org.mockito.internal.util.MockUtil.createMock(MockUtil.java:53)
        at org.mockito.internal.MockitoCore.mock(MockitoCore.java:61)
        at org.mockito.Mockito.mock(Mockito.java:1949)
        at org.mockito.Mockito.mock(Mockito.java:1860)
        ... 1 more

Related: #983

[raphw]

This is the result of a recent change in OpenJDK. As a matter of fact, I am involved in the change but I am wondering if we overlooked another scenario. The reflection API considers the outer class of a static member (in your case an interface) to be parameterized. As a result, the variable TLeft suddenly exists in the scope of the interface which is does not. (javac also forbids to consider the outer class as parameterized as a receiver of a method of the static member.)

Personally, I believe that the changes behavior of the reflection API is incorrect here, but I will check back with the person at Oracle who implemented the change if this is an oversight. The receiver type feature is much more complicated then it seems at first sight, unfortunately, so thanks for getting this back to us!

[akarnokd]

Confirmed fixed in 16b34 and 17b7. Thank you!