type inference regression related to JDK-8157149

[Maurizio Cimadamore]

You are right - JDK-8157149 introduced a regression in the treatment of 
propagation of poly expressions to outer contexts. This is caused by the 
fact that the propagation logic doesn't take this bullet from 18.5.2 
into account:

"Otherwise, if R θ is an inference variable α, and one of the following 
is true:

     T is a reference type, but is not a wildcard-parameterized type, 
and either i) B2 contains a bound of one of the forms α = S or S <: α, 
where S is a wildcard-parameterized type, or ii) B2 contains two bounds 
of the forms S1 <: α and S2 <: α, where S1 and S2 have supertypes that 
are two different parameterizations of the same generic class or interface.

     T is a parameterization of a generic class or interface, G, and B2 
contains a bound of one of the forms α = S or S <: α, where there exists 
no type of the form G<...> that is a supertype of S, but the raw type 
|G<...>| is a supertype of S.

*    T is a primitive type, and one of the primitive wrapper classes 
mentioned in §5.1.7 is an instantiation, upper bound, or lower bound for 
α in B2.*

then α is resolved in B2, and where the capture of the resulting 
instantiation of α is U, the constraint formula ‹U → T› is reduced and 
incorporated with B2. "

And as a result, javac tries to propagate the nested constraint f(i) -> 
long into the outer context, which is incorrect, because the type of 
f(i) needs to be eagerly instantiated.

Filed https://bugs.openjdk.java.net/browse/JDK-8168134

Thanks again

Maurizio

On 17/10/16 18:36, Maurizio Cimadamore wrote:
>
> I'll take a look - thanks for the report.
>
> Maurizio
>
> On 17/10/16 17:14, Liam Miller-Cushon wrote:
>> javac started rejecting the following program between 9-ea+119 and 
>> 9-ea+120. The culprit appears to be JDK-8157149 [1][2]. Was this 
>> intentional?
>>
>> Thanks,
>>
>> [1] https://bugs.openjdk.java.net/browse/JDK-8157149 
>> <https://bugs.openjdk.java.net/browse/JDK-8157149>
>> [2] http://hg.openjdk.java.net/jdk9/dev/langtools/rev/a8b7c9938b74 
>> <http://hg.openjdk.java.net/jdk9/dev/langtools/rev/a8b7c9938b74>
>>
>> === Test.java
>> abstract class Test {
>>   interface W<A> {}
>>   abstract <B> B f(W<B> e);
>>   abstract <C> C g(C b, long i);
>>
>>   void h(W<Long> i) {
>>     g("", f(i));
>>   }
>> }
>> ===
>>
>> $ javac Test.java
>> ...
>> error: method g in class Test cannot be applied to given types;
>>     g("", f(i));
>>     ^
>>   required: C,long
>>   found: String,Long
>>   reason: cannot infer type-variable(s) C,B
>>     (argument mismatch; B cannot be converted to long)
>>   where C,B are type-variables:
>>     C extends Object declared in method <C>g(C,long)
>>     B extends Object declared in method <B>f(W<B>)
>> 1 error
>

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