Draft JEP: Incubating Language and VM Features

[Alex Buckley]

On 1/24/2018 1:30 AM, Volker Simonis wrote:
>>> Finally, the JEP doesn’t specify if version N may (silently or
>>> explicitly) support version N+1’s incubating features. This may be
>>> attractive for LTS releases.
>>
>> If Java SE N had no notion of feature X, and Java SE N+1 introduced X as an
>> incubating feature, then there is no realistic possibility of doing a
>> Maintenance Release of SE N to add an incubating feature X.
>
> I don't meant to do this in a "Maintenance Release of SE N". The
> question was if a Java vendor can do that in his implementation of
> "Java N" if that implementation still passes the "Java N TCK".

The JEP was careful to avoid vendor issues, and the above is a 
vendor-specific question, so I am unable to answer it here.

I think most people would agree that taking a final-and-permanent 
feature in Java SE $N+1 (say, LVTI in Java SE 10) and adding it behind 
an --incubating flag in an implementation of Java SE $N is very weird. 
After all, the feature was not listed as incubating in the relevant 
appendix of the Java SE $N Platform specification. And "Nothing in this 
JEP should be interpreted as encouraging or allowing fragmentation of 
the Java SE Platform."

Alex