Check all members for `Visibility.Unknown`,
otherwise we miss them when they come
from supertypes. This is the reason why
the FP intellij build failed with a
cryptic stacktrace instead of a
human-readable diagnostic.
Also, do report the diagnostic at all
cases of `Visibilities.Unknown`. Turns
out, there are no "simple to reason
about" situations here :(
Also, an interesting detail:
`retrieveDirectOverriddenOf` returns an
empty list for intersection overrides.
But this doesn't seem to break anything...
Replacing `CANNOT_INFER_VISIBILITY`'s
type `KtDeclaration` with
`PsiNameIdentifierOwner` and the related
changes in `PositioningStrategies`
were needed to prevent an exception saying that
`PsiClassImpl` is not a subtype of
`KtDeclaration`.
- base class method wins against a (default) interface method,
so an abstract base class method should always be implemented
in a derived class;
- interface methods clash regardless of abstract/default
with possibly undefined behavior at run-time,
so a class or interface should always define its own method
for methods inherited from multiple interfaces and not from base class;
- meaningful diagnostics for class inheriting conflicting JVM signatures.
Since no override will happen under Java 8 rules,
ACCIDENTAL_OVERRIDE is misleading for this case;
- update testData.
Nikolay Lunyak