Anonymous class instance creation expression with diamond compatibility constraint is reduced to anonymous class type?

[Srikanth]

https://bugs.openjdk.java.net/browse/JDK-8133936 seems to have some 
wordings that explains the
rationale.

Srikanth


On Monday 13 March 2017 12:35 PM, Remi Forax wrote:
> Hi Maurizio,
>
> ----- Mail original -----
>> De: "Maurizio Cimadamore" <maurizio.cimadamore at oracle.com>
>> À: "B. Blaser" <bsrbnd at gmail.com>
>> Cc: compiler-dev at openjdk.java.net
>> Envoyé: Samedi 11 Mars 2017 22:49:34
>> Objet: Re: Anonymous class instance creation expression with diamond compatibility constraint is reduced to anonymous
>> class type?
>> On 11/03/17 15:05, B. Blaser wrote:
>>> Hi,
>>>
>>> On 10 March 2017 at 22:46, Maurizio Cimadamore
>>> <maurizio.cimadamore at oracle.com> wrote:
>>>> Hi Georgiy - thanks for the report. Just so that I understand - is this a
>>>> regression or is it a new test and that's the behavior you are seeing with
>>>> the latest build? I'm asking because I don't recall recent changes in this
>>>> area.
>>>>
>>>> That said, I think your analysis looks correct - the spec draft calls for
>>>> the anonymous inner class non-denotable type to be 'normalized'.
>>>>
>>>> Maurizio
>>> The problem seems to be present since build 82, 136, 152 and rev
>>> a21e5b9dc5c3 (1.5 month ago).
>> Uhm - I looked at  a21e5b9dc5c3, and all I found is this:
>>
>> http://hg.openjdk.java.net/jdk9/dev/langtools/rev/a21e5b9dc5c3
>>
>> Which seems unlikely to cause inference issues?
>>> Next is a patch that corrects this specific case upon rev a21e5b9dc5c3
>>> (needs to be well tested).
>>> It 'normalizes' T when checking for same type (Types.isSameType(),
>>> Types.SameTypeVisitor.visitClassType() and
>>> Types.SameTypeVisitor.visitUndetVar()).
>> I believe the issue should be addressed in a more direct way - as per
>> Georgiy's evaluation, the spec draft says that the type of
>>
>> new Foo<>() { ... }
>>
>> is simply Foo, not an anonymous type. So normalization should never be
>> needed during type-checking.
> You can not do that !
>
> new Object() {  } is typed as the anonymous inner class, not Object,
> the goal of the inference, at least for the average guy, is to fill the blank,
> the resulting type has to be either the anonymous inner class or we should remove this feature.
>
>> Maurizio
> Rémi
>
>>> Bernard
>>>
>>> diff --git a/src/jdk.compiler/share/classes/com/sun/tools/javac/code/Types.java
>>> b/src/jdk.compiler/share/classes/com/sun/tools/javac/code/Types.java
>>> --- a/src/jdk.compiler/share/classes/com/sun/tools/javac/code/Types.java
>>> +++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/code/Types.java
>>> @@ -1022,6 +1022,20 @@
>>>                    isSameTypeStrict.visit(t, s) :
>>>                    isSameTypeLoose.visit(t, s);
>>>        }
>>> +    private Type normalize(Type t) {
>>> +        if (t.tsym.name.isEmpty()) {
>>> +            // Anonymous class
>>> +            ClassType norm = (ClassType) t.tsym.type;
>>> +            if (norm == null)
>>> +                return null;
>>> +            else if (norm.interfaces_field != null &&
>>> norm.interfaces_field.nonEmpty())
>>> +                return norm.interfaces_field.head;
>>> +            else
>>> +                return norm.supertype_field;
>>> +        }
>>> +        else
>>> +            return t;
>>> +    }
>>>        // where
>>>            abstract class SameTypeVisitor extends TypeRelation {
>>>
>>> @@ -1070,7 +1084,7 @@
>>>
>>>                @Override
>>>                public Boolean visitClassType(ClassType t, Type s) {
>>> -                if (t == s)
>>> +                if (normalize(t) == normalize(s))
>>>                        return true;
>>>
>>>                    if (s.isPartial())
>>> @@ -1152,7 +1166,7 @@
>>>                        return true;
>>>                    }
>>>
>>> -                t.addBound(InferenceBound.EQ, s, Types.this);
>>> +                t.addBound(InferenceBound.EQ, normalize(s), Types.this);
>>>
>>>                    return true;
>>>                }
>>>
>>>> On 10/03/17 20:02, Georgiy Rakov wrote:
>>>>> class MyType<T> {}
>>>>>
>>>>> class MyList<T> {
>>>>>       MyList<T> copyThis() { return null; }
>>>>> }
>>>>>
>>>>> class Foo<T> {
>>>>>       Foo(MyType<String> a){ }
>>>>> }
>>>>>
>>>>> public class Test26  {
>>>>>       public static void main(String argv[]) {
>>>>>           MyList<Foo> l1 = new MyList<>();
>>>>>           m2(l1, m1(
>>>>>                      new Foo<>(new MyType()){ }
>>>>>                    ).copyThis());
>>>>>       }
>>>>>       public static <T> MyList<T> m2(MyList<T> l1, MyList<T> l2) { return
>>>>> null; }
>>>>>       public static <U> MyList<U> m1(U item) { return null; }
>>>>> }