Deriving logic prefers derived case class mapper over custom provided

[alosich]

In case if case class contains case class, inner case class correctly interpreted as RECORD however, if custom mapper provided (as in example in documentation), schema generator treats it as field of custom type, but ToMappable derived in still treats it as RECORD.

This test (as per documentation) succeeds:

import shapeless.datatype.bigquery._
import java.net.URI

implicit val uriBigQueryType = BigQueryType.at[URI]("STRING")(v => URI.create(v.toString), _.toString)

case class Page(uri: URI, rank: Int)

val t = BigQueryType[Page]
val r = t.toTableRow(Page(URI.create("www.google.com"), 42))

// this is as expected
r.get("uri") ==== "www.google.com"

while this fails:

import shapeless.datatype.bigquery._

case class Yuri(ss: String)
implicit val uriBigQueryType = BigQueryType.at[Yuri]("STRING")(v => new Yuri(v.toString), _.ss)

case class Page(uri: Yuri, rank: Int)

val t = BigQueryType[Page]
val r = t.toTableRow(Page(new Yuri("www.google.com"), 42))

// this FAILS, instead of string, it contains linked hash map.
r.get("uri") ==== "www.google.com"

Note that the only difference here is that instead of system non-case URI class, custom case class Yuri is used (and if I switch it from being case class to normal class, the problem is gone).

I think that reason is that ToMappable.hconsToMappable0 (which constructs basing on internal structure of case class) implicit has bigger priority than ToMappable.hconsToMappable1 (which uses externally provided mapper).