[sealed] Module & package constraints

[Gavin Bierman]

> On 24 Apr 2020, at 22:24, Dan Smith <daniel.smith at oracle.com> wrote:
> 
> Sounds like the conclusion is:
> 
>> On Apr 24, 2020, at 1:16 PM, Dan Smith <daniel.smith at oracle.com> wrote:
>> 
>> I presented this as an outline of our choices, but to put a stake in the ground, here are my preferences.
>> 
>>> On Apr 23, 2020, at 12:27 PM, Dan Smith <daniel.smith at oracle.com> wrote:
>>> 
>>> 1) Is it legal to have a permitted subclass/subinterface that does not actually extend the permitting class or interface?
>> 
>> At compile time, no. Let's prohibit that.
>> 
>> At run time, delay any validation until a particular subclass is loaded.
> 
> Agreement on both of these. (Requires a new rule in the language spec.)

Apologies. That rule was in the Feb spec, but got left out by mistake in the last draft. Now reinstated. 

Gavin