JDK-8016196 : Inference: define supertype parameterization for wildcard-parameterized types
  • Type: Bug
  • Component: specification
  • Sub-Component: language
  • Affected Version: 5.0,7,8
  • Priority: P3
  • Status: Open
  • Resolution: Unresolved
  • Submitted: 2013-06-07
  • Updated: 2023-08-29
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tbd_majorUnresolved
Related Reports
Blocks :  
JDK-8206142 - type inference: javac is incorrectly applying capture conversion during incorporation
Blocks :  
JDK-8160244 - skip capture conversion before subtyping if types are parameterizations of the same class or interface
Relates :  
JDK-8030746 - 4.10: Define subtyping for inner classes of parameterized types
Relates :  
JDK-8164401 - Incorrect treatment of wildcards in subtyping
Relates :  
JDK-8170887 - 18.2.1: Capture variables should not escape lambda bodies
Relates :  
JDK-8160114 - Unexpected inferred type from wildcard subtyping constraint
Relates :  
JDK-8168760 - ClassCastException: Type$TypeMapping$3 cannot be cast to Type$WildcardType
Relates :  
JDK-8170885 - 18.4: Avoid inferring capture variables during resolution
Relates :  
JDK-8314380 - JLS 4. 10. 4. Least Upper Bound is a complete gibberish (full of bugs)
Relates :  
JDK-8251891 - Lower bound containing wildcard get lost during type inference
Relates :  
JDK-8155072 - Type inference regression
Relates :  
JDK-8177520 - Type inference "varargs mismatch; inference variable R has incompatible bounds"
Relates :  
JDK-8199234 - Code compiles in java8 but not in java9 : "incompatible types: java.lang.Object cannot be converted ..."
Relates :  
JDK-8039214 - Inference should not map capture variables to their upper bounds
Relates :  
JDK-8033709 - 4.5.1: Provable distinctness of intersection types
Description
Reduction of subtyping constraints (ArrayList<?> <: List<? super alpha>) invokes capture in javac, leading to incorrect constraints on ivars involving capture vars; these new types also foil the argument that incorporation will terminate.

The correct behavior is unspecified: what is the parameterization of List that is a supertype of ArrayList<?>?  How do we derive it?
Comments
Also a problem for interpreting inherited inner classes of wildcard-parameterized types (JDK-8030746): what are the type arguments of the enclosing class? class Parent<T> { class C {} } class Child<T> extends Parent<Foo<T>> {} Child<?>.C // means Parent<???>.C
07-02-2017
Inference also encounters the problem in incorporation (18.3.1): when it's necessary to find "a supertype of S of the form G<S1, ..., Sn>" and "a supertype of T of the form G<T1, ..., Tn>", we need to know whether "S1 = T1" is a valid new constraint -- which depends on whether S1 is a wildcard or not.
10-11-2015
This question is also relevant for lub (4.10.4).
26-08-2014