MethodHandles.publicLookup().in() returns Lookup with no permissions?

[Mandy Chung]

On 11/24/20 10:21 AM, Simone Bordet wrote:
> Hi,
>
> testing the Jetty MethodHandle usages we encountered this situation:
>
> .class org.openjdk.mh.Main
> ----
> Class<?> klass = Main.class;
> MethodHandles.Lookup lookup = MethodHandles.publicLookup().in(klass);
> MethodHandle handle = lookup.findVirtual(klass, "test",
> MethodType.methodType(String.class));
> ----
>
> .module-info.java
> ----
> module org.openjdk.mh {
>      exports org.openjdk.mh to com.acme;
> }
> ----
>
> findVirtual() throws:
> java.lang.IllegalAccessException: symbolic reference class is not
> accessible: class org.openjdk.mh.Main, from
> org.openjdk.mh.Main/noaccess (module org.openjdk.mh)
>
> Removing the "to" clause from the exports in module-info.java fixes the issue.
>
> Seems that a class cannot get a MethodHandle on itself, the reason
> being that org.openjdk.mh is selectively exported in module-info.java.

You use MethodHandles::publicLookup which has access to unconditionally 
exported classes only.  It can't be used to teleport to a 
qualified-exported class.  You  can use MethodHandles.lookup().in(klass) 
instead.


> Is this intended behavior?

Yes, it's intended behavior.

Mandy

> I would have expected that a class could always get a MethodHandle on itself.
> I tested this with 11, 15, and 16+25, all fail.
>
> I have a simple reproducer, and I can open an OpenJDK bug.
>
> Thanks!
>