In K1 .isFun is always false for Java classes, so extra check
is added for that. This is not needed for K2, because .isFun is
true for all Java classes. Here it is not necessary to check
that interface has only one method, because such check will be
done in the place where interface implementation is created.
^KT-39362 Fixed
For each platform declaration, there must be at least one impl declaration in
the module with the compatible signature; similarly, for each impl declaration,
there must be at least one platform declaration with the compatible signature.
Note that currently the presence of the 'impl' modifier is not checked yet.
Also, the sad fact is that if you have platform and impl declarations which are
not compatible, you get two errors: on the platform delcaration and on the impl
declaration. This needs to be addressed as well
Roman Efremov