Locally defined implicit transformers are ignored

[jonathan-ostrander]

Chimney version: 0.6.1 (Latest)

This issue is best demonstrated with the following example:

import io.scalaland.chimney.dsl._
import io.scalaland.chimney.Transformer

case class Foo(a: Int, b: Int)
case class Bar(c: Int = 0)

case class FooWrapper(foo: Foo)
case class BarWrapper(bar: Option[Bar])

// warning below that localT is never used
implicit val t: Transformer[FooWrapper, BarWrapper] = {
  implicit val localT: Transformer[Foo, Bar] = foo => Bar(foo.a + foo.b)
  Transformer.define[FooWrapper, BarWrapper].withFieldRenamed(_.foo, _.baz).buildTransformer
}
// warning: local val localT in value t is never used
//         implicit val localT: Transformer[Foo, Bar] = foo => Bar(foo.a + foo.b)
//                      ^
// error: No warnings can be incurred under -Xfatal-warnings.

// no warning because Bar has a default value in its default constructor
implicit val t: Transformer[FooWrapper, BarWrapper] =
  Transformer.define[FooWrapper, BarWrapper].withFieldRenamed(_.foo, _.baz).buildTransformer

FooWrapper(Foo(1, 2)).transformInto[BarWrapper]
// BarWrapper(Bar(0))

// redefine wrapper transformer with a Transformer[Foo, Bar] outside of a local scope
implicit val fooBarT: Transformer[Foo, Bar] = foo => Bar(foo.a + foo.b)
implicit val newT: Transformer[FooWrapper, BarWrapper] =
  Transformer.define[FooWrapper, BarWrapper].withFieldRenamed(_.foo, _.baz).buildTransformer

FooWrapper(Foo(1, 2)).transformInto[BarWrapper]
// BarWrapper(Bar(3))

There are obvious workarounds. disableDefaultValues can be used when building the wrapper transformer, but this is annoying when defining transformers with code generated by ScalaPB because the unknownFields argument must have a default value specified. Transformers can always be defined outside of a local scope, but sometimes a local scope is desired if multiple transformers require different transformation behavior for a given type in the same package.

[MateuszKubuszok]

This issue can be solved adding a flag to scalapb:

option (scalapb.options) = {
  preserve_unknown_fields: false // true by default in Proto 3
}

Then your protobufs won't have unknownField generated in the first place.

This will also enable you to use

option (scalapb.options) = {
  no_default_values_in_constructor: true
}

[MateuszKubuszok]

From what I checked, this seem to be fixes on our scala-3 branch. I checked in console:

chimney-build(scala-3)> chimney/console
[info] Starting scala interpreter...
Welcome to Scala 2.13.11 (OpenJDK 64-Bit Server VM, Java 17.0.3).
Type in expressions for evaluation. Or try :help.
import io.scalaland.chimney._
import io.scalaland.chimney.dsl._

scala> case class Foo(a: Int, b: Int)
     | case class Bar(c: Int = 0)
     |
     | case class FooWrapper(foo: Foo)
     | case class BarWrapper(bar: Option[Bar])
class Foo
class Bar
class FooWrapper
class BarWrapper

scala> locally {
     |   implicit val localT: Transformer[Foo, Bar] = foo => Bar(foo.a + foo.b)
     |   implicit val t = Transformer.define[FooWrapper, BarWrapper].withFieldRenamed(_.foo, _.bar).buildTransformer
     |   FooWrapper(Foo(1, 2)).transformInto[BarWrapper]
     | }
val res3: BarWrapper = BarWrapper(Some(Bar(3)))

and I didn't feel the need to add a test case for it as there is already one. Once #325 is published if you still find that there is a bug, please reopen.