Initial JDK 11 RFR of JDK-8173382: Add -source 11 and -target 11 to javac - Java Bug System & JDK-8193291: Add SourceVersion.RELEASE_11

[Joseph D. Darcy]

Hello,

A follow-up on defining a final field RELEASE_CURRENT  as an alias for 
the latest SourceVersion constant to allow easier updating of 
annotations using SourceVersion constants. Somewht surprisingly, this is 
not legal Java code; an annotation must use an enum constant directly 
and not a constant expression which evaluates to an enum constant.

This rules is given in JLS 9.7.1 Normal Annotations:

> T [ the element type] is not an array type, and the type of V [the 
> element value] is assignment compatible (§5.2) with T, and:
>
>     If T is a primitive type or String, then V is a constant 
> expression (§15.28).
>     If T is Class or an invocation of Class (§4.5), then V is a class 
> literal (§15.8.2).
>     If T is an enum type (§8.9), then V is an enum constant (§8.9.1).
>     V is not null.
https://docs.oracle.com/javase/specs/jls/se9/html/jls-9.html#jls-9.7.1

The wording goes back to JLS 3rd edition which introduced enums and 
annotations.

Formally, the constant expression concept in JLS 15.28 only applies to 
primitive types and Strings. Presumably, it would not be too difficult 
to expand this concept to include class literals and enum constants.

In any case, in the mean time the suggested idiom will not work and the 
changes of RELEASE_9 => RELEASE_10 will need to stay.

Updated webrev with a minor merge:

     http://cr.openjdk.java.net/~darcy/8173382.3/

Cheers,

-Joe