JShell: sealed and final types in jshell

[Jan Lahoda]

It would be good to have an explicit approval from Robert. I can send a 
formal RFR here for the JShell part of the patch.

As a note, the most recent patch to add support for sealed types in 
JShell is here:
https://openjdk.github.io/cr/amber/21/webrev.01/

Besides the JShell tweaks, it also suppresses the "no supertype is 
sealed" error when the non-sealed modifier is used and there are 
erroneous/unresolvable supertypes. This is both to make things (much) 
easier in JShell, and also seems like a good thing to do. If a supertype 
is unresolvable, we don't know if it is sealed or not.

Jan

On 26. 05. 20 19:44, Vicente Romero wrote:
> well actually if we are OK with the patch it doesn't need another review 
> in compiler-dev
> 
> Vicente
> 
> On 5/26/20 8:29 AM, Vicente Romero wrote:
>> I'm OK with the change, thanks Jan, I will push it into the sealed 
>> types code, for it to be part of the current review.
>>
>> Thanks,
>> Vicente
>>
>> On 5/20/20 8:00 PM, Robert Field wrote:
>>> [adding kulla-dev]
>>>
>>> "final" is ignored/warning in jshell to allow maximal 
>>> experimentation.  But, in retrospect I think that is probably overly 
>>> heavy handed.
>>>
>>> I agree with removing the restriction on "final".
>>>
>>> Allowing people to explore new language features is one of explicit 
>>> goals of jshell -- so supporting sealed types is essential.
>>>
>>> Side-effect classes which could not be pasted into jshell would be 
>>> able to.
>>>
>>> Variables/methods still should probably not be final.
>>>
>>> Thoughts?
>>>
>>> -Robert
>>>
>>>
>>> On 2020-05-20 10:16, Jan Lahoda wrote:
>>>> So, I was looking at this today. So far, there are two problems, one 
>>>> simple (permitted classes need to be declaration references). The 
>>>> second problem is more difficult - if we would like this to work:
>>>> sealed class B permits I {}
>>>> final class I extends B {}
>>>>
>>>> we need to allow the "final" modifier, as having:
>>>> sealed class B permits I {}
>>>> class I extends B {}
>>>>
>>>> will not work (the class I must either final or non-sealed). Robert, 
>>>> what do you think?
>>>> ...
>>>
>>>> I'll continue looking into this tomorrow.
>>>>
>>>> Jan
>>>>
>>>> On 19. 05. 20 21:27, Robert Field wrote:
>>>>> Absolutely! Absolutely!
>>>>>
>>>>> Thanks,
>>>>> Robert
>>>>>
>>>>> On 2020-05-19 06:09, Jan Lahoda wrote:
>>>>>> Vicente, Robert,
>>>>>>
>>>>>> Looking at the sealed types, it does not seem support for sealed 
>>>>>> has been added to JShell - should that be added? Should I take a 
>>>>>> look?
>>>>>>
>>>>>> Jan
>>
>