RFR 8191802: Upward projection result is A<? extends Number> instead of A<? super Integer>

[Maurizio Cimadamore]

Thanks - pushed

Maurizio


On 29/11/17 17:20, Vicente Romero wrote:
> looks good,
>
> Thanks,
> Vicente
>
> On 11/29/2017 11:43 AM, Maurizio Cimadamore wrote:
>>
>> 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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