In the following code example
fun test(f: Any.() -> Unit) = 42.f()
front-end resolves variable-as-function call for 'f' as 'invoke'
with signature 'Function1<Any, Unit>#Any.() -> Unit'.
However, Function1<Any, Unit> has a single 'invoke' method
with signature 'Function1<Any, Unit>#(Any) -> Unit'.
This didn't cause any problems with loosely typed JVM and JS back-ends.
However, in IR with symbols this means a reference to non-existing
declaration.
Jinseong Jeon