Here's the isolated example I have with freestyle migration.

Macro in SomeTrait.scala shows what type argument is passed to it.

Please note that if type lambda is passed (even without kind projector), we got a correct type (Option) so implicit derivation can proceed if it's depending on the structure of the type.

If just a typealias is passed, only type alias reaches the macro via WeakTypeTag so I don't have access to the real type and it's structure.

If instance derivation depends on type structure, we'll have abort inside macro and the implicit value will be silently not found (in case of whitebox macro)