RFR: universal type variables: initial prototype [v3]

[Vicente Romero]

On Tue, 10 Aug 2021 21:22:04 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   second iteration of review comments
>
> src/jdk.compiler/share/classes/com/sun/tools/javac/code/Types.java line 3616:
> 
>> 3614:                         !t.isValueProjection() &&
>> 3615:                         from.head.hasTag(TYPEVAR) &&
>> 3616:                         ((TypeVar)from.head).projection != null &&
> 
> Shouldn't this test be `isUniversal()` ?

doing this change right now breaks the build, I think it is because we generate reference projections for universal type vars in a lazy way, so some universal type variables could have its projection field set to null

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PR: https://git.openjdk.java.net/valhalla/pull/521