See doNotCaptureSupertype test for clarification:
When resolving b.collect(toList()) we're building a common system with
two variables T and R.
The problem was that when introducing the constraint
C<T, Inv<T>> <: C<in String, R> we then were seeing the constraint
T <= in String, and add the constaint T=Captured(in String)
That lead to R=Inv<T>=Inv<Captured(in String)>, and after approximation
R=Inv<in String>, that is not the desirable result (Inv<String> suits here)
But the root problem was that we add captured constaint when projection was from supertype,
that seems to be wrong, and for example Java doesn't do that in the similar situation.
#KT-11259 Fixed
1. Substitution variance (sv) is a substitution composition of type alias argument variance (av)
and corresponding expanding type argument variance (ev):
sv =
| av == ev -> av
| av == INVARIANT -> ev
| ev == INVARIANT -> av
| else -> (variance conflict error; av)
2. Resulting variance (rv) is a type argument composition of sv and type parameter variance (pv):
rv =
| sv == tv => INVARIANT
| sv == INVARIANT => INVARIANT
| tv == INVARIANT => sv
| else -> (variance conflict error; sv)
When resolving arguments on inner classifier, one can omit the arguments
for outer class 'Outer' if they are present implicitly in the scope:
- One of the supertypes of current class is Outer
- One of the outer classes or one of their supertypes is Outer
Relevant arguments are obtained from the first type found by
the algorithm above
Note that before this commit implicit arguments were only been searched
in containing classes
#KT-11123 Fixed
Mostly it's about detecting loops in supertypes
Test data changes:
- Loops are being disconnected in Java classes too
- functions.kt: loops disconnection mechanism runs supertypes calculation,
so when we start check T it forces F' supertypes calculation, that ends
with CYCLIC_GENERIC_UPPER_BOUND reported on F
#KT-11287 In Progress
Instead of erasing descriptors with conflicting substitution,
use invariant CapturedType(<projection>) as replacement for type parameter
within default member scope.
After substitution leave such types 'as is' everywhere except return types,
use common approximation for them.
#KT-9294 In Progress
#KT-5411 Fixed
#KT-8647 Fixed
#KT-9462 Fixed
#KT-9893 Fixed
#KT-7581 Fixed
#KT-7296 In Progress
Mikhail Zarechenskiy