RFR 8191802: Upward projection result is A<? extends Number> instead of A<? super Integer>
Maurizio Cimadamore
maurizio.cimadamore at oracle.com
Wed Nov 29 16:43:12 UTC 2017
Here's another update:
http://cr.openjdk.java.net/~mcimadamore/8191802-v3/
* fixed the comments in the test UpperBounds.java
* used explicit UPWARDS and DOWNWARDS instead of
pkind/pkind.complement() in TypeArgumentProjection::visitType
* moved the check for VOID/NULL in Check::checkLocalVarType
Maurizio
On 27/11/17 15:09, Maurizio Cimadamore wrote:
>
> This is an updated version of the webrev:
>
> http://cr.openjdk.java.net/~mcimadamore/8191802-v2/
>
> I realized that there were further discrepancies w.r.t. the spec text,
> so I handled them all at once:
>
> * the spec has different treatment for when a type argument is a
> wildcard and for when it's a regular type - the implementation was
> treating both wildcards and regular types in the same way, which led
> to inconsistencies (see JDK-8191893). I now defined separate visitors
> for the outer projection and type argument projection parts, so that
> the code should be easier to follow.
>
> * not all fresh types created during a projection overrode the
> 'needStripping' method, which could lead to issue with type annotation
> processing
>
> * the fact that TypeProjection extended from StructuralMapping had a
> subtle issue - on the one hand, StructuralMapping has the required
> logic to handle arrays (e.g. map component type and return new array
> if needed) - on the other hand, with projections we need to be careful
> - if the element type has no projection, then projection of the array
> is also undefined. The impl was returning an array of <null> which was
> then causing crashes inside the compiler. This is now called out
> explicitly.
>
> Maurizio
>
>
> On 24/11/17 17:39, Maurizio Cimadamore wrote:
>>
>> Hi,
>> please review the fix for JDK-8191802:
>>
>> http://cr.openjdk.java.net/~mcimadamore/8191802/
>>
>> This is a conformance issue with local variable type inference - the
>> specification text for upper projection says this (section 4.10.5):
>>
>> "The upward projection of a type T with respect to a set of
>> restricted type variables is defined as follows:
>>
>> [...]
>>
>> If T is a parameterized class type or a parameterized interface
>> type, G<A1, ..., An>, then the result is G<A1', ..., An'>, where, for
>> 1 ≤ i ≤ n, Ai' is derived from Ai as follows:
>>
>> [...]
>> If Ai is a type that mentions a restricted type variable,
>> then Ai' is a wildcard. Let U be the upward projection of Ai. There
>> are three cases:
>> *If U is not Object, and if either the declared bound of the ith
>> parameter of G, Bi, mentions a type parameter of G, or Bi is not a
>> subtype of U, then Ai' is an upper-bounded wildcard, ? extends U.*
>> Otherwise, if the downward projection of Ai is L, then
>> Ai' is a lower-bounded wildcard, ? super L.
>> Otherwise, the downward projection of Ai is undefined and
>> Ai' is an unbounded wildcard, ?."
>>
>> The text in bold is not implemented accurately by javac. What javac
>> used to do was simply to throw away the upper bound and favor the
>> lower bound if the upper was Object.
>>
>> The spec text is much more subtle and precise, allowing javac to
>> throw away upper bounds that do not add any extra information w.r.t.
>> declared bounds.
>>
>> As a result of this change, there are few places where the compiler
>> used to infer A<? extend B> (where B was same type as declared bound)
>> and now it infers A<?> as per spec - this caused few changes in the
>> jshell test TypeNameTest.
>>
>> I've added a lvti harness test to verify the assertions in the above
>> paragraph.
>>
>> Cheers
>> Maurizio
>>
>
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