It should have been WeakIncompatible from the beginning because it's not
possible to overload by return type in Kotlin
This commit is a step forward to fix KT-62591
Unfortunately, the test cannot demonstrate the problem because of
another bug in K2 KT-59887
^KT-62752 Fixed
Review: https://jetbrains.team/p/kt/reviews/12750/timeline
Motivation:
It makes expect-actual matching-checking model more consistent.
expect-actual "matching" is run before FirResolvePhase.BODY_RESOLVE. You
can't know return types, until you run BODY_RESOLVE. That's why the
return type can't be checked during expect-actual matching. But it's
cursed: you have something that have to match by, but, at the same time,
you can't do it.
expect-actual "checking" is run after FirResolvePhase.BODY_RESOLVE.
That's why if we convert ReturnType incompatibility to WeakIncompatible
(which should have been called CheckingIncompatible), then expect-actual
matching model becomes consistent.
We will also be able to get rid of unnecessary
FirActualCallableDeclarationChecker. Because it won't be necessary.
Return types will be checked by common logic of expect-actual "checker"
Nikita Bobko
bc5180656d