Bug in Generic with non-standard case class field names

[seanmcl]

The following program generates the output

List(abc, abc)

rather than the expected

List(abc, 5)

The cause seems to be the fact that the field 'foo' is a prefix of field foo-foo. E.g. when I rename the 'foo' field to 'foo1' I get the expected output.

import shapeless._

trait Const[A] {
  def const(v: A): String
}

object Const {
  def apply[A](implicit F: Const[A]): Const[A] = F
  def instance[A](g: A => String): Const[A] = v => g(v)
}

trait Consts[A] {
  def consts(v: A): List[String]
}

object Consts {
  def apply[A](implicit F: Consts[A]): Consts[A] = F
  def instance[A](g: A => List[String]): Consts[A] = v => g(v)

  implicit val hnil: Consts[HNil] = instance(_ => Nil)

  implicit def hlist[H, T <: HList](implicit F: Const[H], G: Consts[T]): Consts[H :: T] =
    instance({ case h :: t => F.const(h) +: G.consts(t) })

  implicit def generic[A, R](implicit F: Generic.Aux[A, R], G: Consts[R]): Consts[A] =
    instance(v => G.consts(F.to(v)))
}

case class Foo(s: String)

object Foo {
  implicit val const: Const[Foo] = Const.instance(_.s)
}

case class Bar(`foo-foo`: Foo, foo: Foo)

object Scratch extends App {
  println(Consts[Bar].consts(Bar(Foo("abc"), Foo("5"))))
}

The bug does not manifest when you swap the field order.

A smaller example, though that uses scalaz is

import scalaz._, Scalaz._
import shapeless._

trait Consts[A] {
  def consts(v: A): List[String]
}

object Consts {
  def apply[A](implicit F: Consts[A]): Consts[A] = F
  def instance[A](g: A => List[String]): Consts[A] = v => g(v)

  implicit val hnil: Consts[HNil] = instance(_ => Nil)

  implicit def hlist[H, T <: HList](implicit F: Show[H], G: Consts[T]): Consts[H :: T] =
    instance({ case h :: t => F.shows(h) +: G.consts(t) })

  implicit def generic[A, R](implicit F: Generic.Aux[A, R], G: Consts[R]): Consts[A] =
    instance(v => G.consts(F.to(v)))
}

case class Foo(s: String)

object Foo {
  implicit val show: Show[Foo] = Show.shows(_.s)
}

case class Bar(`foo-foo`: Foo, foo: Foo)

object Scratch extends App {
  println(Consts[Bar].consts(Bar(Foo("abc"), Foo("5"))))
}

[joroKr21]

Scala, go home you're drunk: scala/bug#8831

[milessabin]

@joroKr21 well spotted!

@seanmcl can you confirm that removing the identifier backticks resolves this issue?

[seanmcl]

Hi @milessabin. Yes, the bug requires the backticks.

[milessabin]

Thanks ... this is scala/bug#8831 then ... I'll close this now.