sealed trait ImplicitNotFound[T] extends AnyRef

Extends the functionality of scala.annotation.implicitNotFound so that implicit-not-found error message is itself resolved using implicit search. This mechanism is used by Implicits.infer[T]:T* and macro engines that use it.

Example: we have a wrapper class Box[T] and we want a custom error message when GenCodec[Box[T]] for some type T is not found:

trait Box[T]
object Box {
  implicit def boxCodec[T: GenCodec]: GenCodec[Box[T]] = ...

  @implicitNotFound("GenCodec for Box[$${T}] not found. This is most likely caused by lack of GenCodec[$${T}]")
  implicit def boxCodecNotFound[T]: ImplicitNotFound[GenCodec[Box[T]]] = ImplicitNotFound()
}

It is also possible to compose error message for one type from error messages for other types. The example above could reuse the implicit-not-found message for GenCodec[T] when building the message for GenCodec[Box[T]]:

@implicitNotFound("GenCodec for Box[$${T}] not found, because:\n#{forUnboxed}")
implicit def boxCodecNotFound[T](
  implicit forUnboxed: ImplicitNotFound[GenCodec[T]]
): ImplicitNotFound[GenCodec[Box[T]]] = ImplicitNotFound()
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