Default codecs shadowed by magnolia, if they are not explicitly imported in scope

[vpavkin]

At the moment, for default codecs (for example, Encoder[List]) to be picked up, they have to be imported explicitly.
Otherwise, deriver uses Magnolia to derive codecs for any types which are either case classes or sealed traits. These derived codecs then override the default ones.

There's a way to properly prioritize magnolia macro, but to make this possible, major changes to magnolia are required. See softwaremill/magnolia#107

If you want to switch from circe-generic's auto to circe-magnolia's auto today, you would have to add additional imports to every place where derivation takes place:

// import all default codecs, defined in circe
import io.circe.Encoder._
import io.circe.Decoder._
// also import all codecs, defined in the companion objects of your own data definitions
import Foo._, Bar._