Divide incompatibility on two groups: strong and weak. Strong incompatibility means that if declaration with such incompatibility has no `actual` modifier then it's considered as usual overload and we'll not report any error on it.
#KT-20540 Fixed
#KT-20680 Fixed
Try to report most of the errors on the actual members of the impl
class. In many cases, there's a 1:1 mapping of header to impl class
members, so the error "some members are not implemented" on the class
declaration itself is redundant. Exceptions include functions/properties
from supertypes (there may be no other place to report a signature
mismatch error in this case), functions/properties not marked with
'impl' (the checker is only run for declarations explicitly marked with
'impl') and default constructors (the checker is not run for them)
#KT-18447 Fixed
Try to report most mismatch errors on the 'impl' declaration. Only
report a mismatch error on the 'header' declaration if no error would be
otherwise reported on any 'impl' declaration in the compilation unit.
Also render declaration kind in the message
#KT-18447 In Progress
Use "-Xno-check-impl" to suppress checking whether the platform declaration
implementation has the "impl" modifier.
Do not check presence of fake overrides from platform class in the impl class,
otherwise there would be a lot of errors about the fact that
equals/hashCode/toString are not marked with the "impl" modifier
When matching platform and impl classifiers, ensure that each declaration from
the platform class scope is present in the impl class scope.
Note that the presence of the 'impl' modifier is not checked yet
Alexander Udalov