RequireMsg compile-time error message escaping code context

This is a short code snippet that demonstrates the problem:

import singleton.ops.RequireMsg

object RequireMsgSpike {

  trait HasM {

    type M = Int
  }

  trait Foo {

    trait FF[T]
  }

  object Foo3 extends Foo {

    implicit def ev3[T <: HasM](
        implicit
        r: RequireMsg[false, "Just Bad Type"]
    ): Set[FF[T]] = ???
  }

  object Foo4 extends Foo {

    implicit def ev4[T <: HasM](
        implicit
        r: Int
    ): Set[FF[T]] = ???
  }

  implicitly[Set[Foo3.FF[HasM]]]
  implicitly[Set[Foo4.FF[HasM]]]
}

error message:

[Error] /***/RequireMsgSpike.scala:34:13: Just Bad Type
[Error] /***/RequireMsgSpike.scala:35:13: Just Bad Type

The second implicit error message got corrupted by the first.

if you delete the first implicit line implicitly[Set[Foo3.FF[HasM]]], the error message goes back to normal:

[Error] /home/peng/git/shapesafe/core/src/test/scala/shapesafe/core/debugging/RequireMsgSpike.scala:35:13: could not find implicit value for parameter e: Set[shapesafe.core.debugging.RequireMsgSpike.Foo4.FF[shapesafe.core.debugging.RequireMsgSpike.HasM]] (No implicit view available from shapesafe.core.debugging.RequireMsgSpike.Foo4.FF[shapesafe.core.debugging.RequireMsgSpike.HasM] => Boolean.)

I vaguely remember that RequireMsg macro overwrites @ImplicitNotFound annotation to achieve its purpose, and this implementation is derived from shapeless. So I guess the easiest way for me is to try the following solution:

• try to reproduce it in shapeless
  • if succeed, forward-port it to singleton-ops
  • otherwise, file the same issue for shapeless, and try to write an original fix or circumvention

[soronpo]

Actually this kind of looks like a Scalac bug, but maybe as a result of that tampering with @implicitNotFound via macros.

[tribbloid]

… Sorry the last option is out of context & doesn’t apply to your case. The implicit error will always write over the previous error