[Nestmates] Add a core reflection API to get nestmate information

[Peter Levart]

Hi David,

On 11/20/2017 10:20 AM, Peter Levart wrote:
> Your comment in the issue:
>
> https://bugs.openjdk.java.net/browse/JDK-8187768?focusedCommentId=14123862&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14123862
>
> ...describes how access checking for private members behaves in VM and 
> what are the outcomes when class attributes are missing or not 
> consistent (access is denied - IllegalAccessError is thrown) vs. when 
> nest-host class can not be resolved (NoClassDefFoundError is thrown). 
> I think this is sound.

I found a wording in the spec update that maybe requires some 
explanation. This is the relevant part:

/A class or interface H grants nest membership to a class or interface D 
if H is declared in the same run-time package as D, H has a NestMembers 
attribute (4.7.29), and there is some value j in the classes array of 
the NestMembers attribute of H, such that item j of the run-time 
constant pool of H is a symbolic reference to D. //
////
//        Because H belongs to the same run-time package as D, it is not 
necessary to resolve a symbolic reference in H in order to determine 
whether it references D. It is only necessary to check the unresolved name./

What does it mean that "H belongs to the same run-time package as D"? 
Does it mean that package names of H and D are equal, or does it also 
imply that both H and D are loaded by the same class loader? While 
jigsaw makes the class loader check unnecessary (either H and D are in 
the same module and consequently loaded by same class loader or H is not 
resolvable from D when they share package name), java still has plain 
ClassLoader(s) and does not always guarantee the absence of split packages.

Regards, Peter