Advice checks fail when subclass tries to access protected field of superclass

[yrodiere]

Description of the problem

Assuming I have a class with a protected field, and that class is extended by another in a different package:

package org.hibernate.bytebuddy.playground.differentpackage;

public class MySuperClass {

	protected int myField;

	public void setMyField(int myField) {
		this.myField = myField;
	}
}

package org.hibernate.bytebuddy.playground;

import org.hibernate.bytebuddy.playground.differentpackage.MySuperClass;

public class MyClass extends MySuperClass {

	public int myMethod() {
		return 0;
	}

}

If I create an advice that reads myField, and apply it to the subclass MyClass:

public class MyAdvice {
	@Retention(RetentionPolicy.RUNTIME)
	@interface FieldValue {

	}

	@Advice.OnMethodExit
	public static void exit(@FieldValue Object fieldValue,
			@Advice.Return(readOnly = false, typing = Assigner.Typing.DYNAMIC) Object returned)
			throws Throwable {
		returned = fieldValue;
	}
}

		DynamicType.Unloaded<MyClass> unloadedTypeWithAdvice = new ByteBuddy()
				.subclass( MyClass.class )
				.name( MyClass.class.getName() + "_withAdvice" )
				.method( named( "myMethod" ) )
				.intercept( Advice.withCustomMapping()
						.bind( MyAdvice.FieldValue.class, MySuperClass.class.getDeclaredField( "myField" ) )
						.to( MyAdvice.class ) )
				.make();

Then applying the advice will fail with the following error:

java.lang.IllegalStateException: Cannot access protected int org.hibernate.bytebuddy.playground.differentpackage.MySuperClass.myField from class org.hibernate.bytebuddy.playground.MyClass_withAdvice

	at net.bytebuddy.asm.Advice$OffsetMapping$ForField$Resolved.resolve(Advice.java:2558)
	at net.bytebuddy.asm.Advice$OffsetMapping$ForField.resolve(Advice.java:2305)
	at net.bytebuddy.asm.Advice$Dispatcher$Inlining$Resolved$ForMethodExit.doApply(Advice.java:8932)
	at net.bytebuddy.asm.Advice$Dispatcher$Inlining$Resolved$ForMethodExit.apply(Advice.java:8890)
	at net.bytebuddy.asm.Advice$Dispatcher$Inlining$Resolved$AdviceMethodInliner.visitMethod(Advice.java:8312)
	at net.bytebuddy.jar.asm.ClassReader.readMethod(ClassReader.java:1353)
	at net.bytebuddy.jar.asm.ClassReader.accept(ClassReader.java:744)
	at net.bytebuddy.jar.asm.ClassReader.accept(ClassReader.java:424)
	at net.bytebuddy.asm.Advice$Dispatcher$Inlining$Resolved$AdviceMethodInliner.apply(Advice.java:8306)
	at net.bytebuddy.asm.Advice$AdviceVisitor$WithExitAdvice.onUserEnd(Advice.java:10797)
	at net.bytebuddy.asm.Advice$AdviceVisitor.visitMaxs(Advice.java:10576)
	at net.bytebuddy.asm.Advice$Appender$EmulatingMethodVisitor.resolve(Advice.java:11148)
	at net.bytebuddy.asm.Advice$Appender.apply(Advice.java:11100)
	at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod$WithBody.applyCode(TypeWriter.java:709)
	at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod$WithBody.applyBody(TypeWriter.java:694)
	at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod.apply(TypeWriter.java:601)
	at net.bytebuddy.dynamic.scaffold.TypeWriter$Default$ForCreation.create(TypeWriter.java:5857)
	at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:2192)
	at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:232)
	at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:204)
	at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase.make(DynamicType.java:3659)
	at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$Delegator.make(DynamicType.java:3897)
	at org.hibernate.bytebuddy.playground.MyTest.test(MyTest.java:31)

Expected behavior

I would expect this advice to work fine. The error message is wrong: class org.hibernate.bytebuddy.playground.MyClass_withAdvice definitely can access protected int org.hibernate.bytebuddy.playground.differentpackage.MySuperClass.myField, because MyClass_withAdvice extends MySuperClass, the field has protected access, and we know we're accessing a field of the same instance.

Reproducer

See https://github.com/yrodiere/bytebuddy-playground/tree/protected-field . Just run with ./mvnw clean test.

Possible cause

I think net.bytebuddy.asm.Advice$OffsetMapping$ForField$Resolved.resolve should probably call isVisibleTo rather than isAccessibleTo, because we know we're accessing a field of the same instance.

Unless net.bytebuddy.asm.Advice$OffsetMapping$ForField$Resolved.resolve can be used in cases where the field being accessed is located on another instance, in which case... I really don't know what is going on :)

See also

Downstream reports:

• https://hibernate.atlassian.net/browse/HHH-15141
• Hibernate throws EnhancementException for embedded field in MappedSuperclass quarkusio/quarkus#24494

May be related to #976.

[raphw]

Yes, you are completely right about this. I fixed this on master. I am planning a release in the next week which comes with some additional Graal support. It will include this fix.

[yrodiere]

That's great, thanks a lot for the (very) quick fix @raphw!

[Sanne]

It seems this issue was fixed? We'll check... thanks @raphw !

[yrodiere]

I confirm this issue was fixed in 1.12.9 and can be closed. Thanks @raphw!

EDIT: Relevant commit: 994f4f0