IllegalAccessError when calling a public method on a field whose type is declared to be a package-private implementation one

This seems somewhat similar to GROOVY-7549.

Consider the following interface:

package test18;

public interface Iface {
	String getBar();
}

and a package-private implementation:

package test18;

class IfaceImpl implements Iface {

	@Override
	public String getBar() {
		return "bar";
	}
}

Now the following base class:

package test18;

public class Base {

	private IfaceImpl foo = new IfaceImpl(); 
	
	public Iface getFoo() {
		return foo;
	}
}

Please note: the field is declared with the implementation type, the getter is public, but the getter declared return type is the public interface.

Then this Groovy class:

package test18.sub

import groovy.transform.CompileDynamic
import groovy.transform.CompileStatic
import test18.Base

class Test18 extends Base {
	
	@CompileStatic
	void foobar() {
		println foo.bar
	}
	
	static main(args) {
		Test18 t = new Test18()
		println t.foo.bar
		t.foobar()
	}
}

Please note the package is different.

If you run this code, the first bar is written correctly, the second invocation fails with: java.lang.IllegalAccessError: tried to access class test18.IfaceImpl from class test18.sub.Test18.

Workarounds:

• remove @CompileStatic from Test18.foobar() (or declare it with @CompileDynamic if the whole class is statically compiled)
• change the declaration of Base.foo to be of type Iface rather than IfaceImpl