Credit for bug discovery, investigation and reproducer: Christian Beikov, https://github.com/beikov/

Quoting:

> [With the following code,] Javac gets confused when compiling `b.a()` in the constructor `pkg2.Impl(pkg2.AbstractBase)`.
> It emits `invokevirtual pkg2/AbstractBase.a:()Ljava/lang/String` instead of `invokeinterface pkg2/BaseInterface.a:()Ljava/lang/String`.
>
> This leads to a verifier error:
>
> ```
> java.lang.VerifyError: Bad access to protected data in invokevirtual
> Exception Details:
> Location:
> pkg2/Impl.<init>(Lpkg2/AbstractBase;)V @5: invokevirtual
> Reason:
> Type 'pkg2/AbstractBase' (current frame, stack[0]) is not assignable to > 'pkg2/Impl'
> Current Frame:
> bci: @5
> flags: { }
> locals: { 'pkg2/Impl', 'pkg2/AbstractBase' }
> stack: { 'pkg2/AbstractBase' }
> Bytecode:
> 0000000: 2ab7 0001 2bb6 0007 57b1
> ```

The problem can be reproduced at least with OpenJDK 11 through 23 GA (build 23+37-2369).

A reproducer is available at https://github.com/beikov/javac-visibility-verifier
Since the reproducer uses Maven, I believe it technically compiles using javax.tools, but using javac directly (passing `-Dmaven.compiler.forceJavacCompilerUse=true`) gives the same result.

To run the reproducer:

```
git clone https://github.com/beikov/javac-visibility-verifier.git
./mvnw clean package
java -jar target/javac-visibility-bug-1.0-SNAPSHOT.jar
```

Relevant code:

```
package pkg1;

public abstract class AbstractRootBase {
protected abstract String a();
}
```

```
package pkg2;

import pkg1.AbstractRootBase;

public abstract class AbstractBase extends AbstractRootBase implements BaseInterface {
}
```

```
package pkg2;

public interface BaseInterface {
String a();
}
```

```
package pkg2;

public class Impl extends AbstractBase {
Impl() {
}
Impl(AbstractBase b) {
b.a(); // This leads to bad access
}

@Override
public String a() {
return null;
}

public static void main(String[] args) {
Impl impl = new Impl();
new Impl(impl);
}
}
```