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package com.avsystem.commons
package misc

object Implicits {
  /**
    * Similar to `implicitly` from standard library but implemented as a macro which materializes directly into
    * the implicit value (without being wrapped as implicit parameter of a dummy method like `implicitly`).
    * Also, using `infer` lets you have more detailed control over implicit-not-found compilation error messages
    * through [[ImplicitNotFound]].
    */
  def infer[T]: T = macro macros.misc.MiscMacros.infer[T]
  def infer[T](clue: String): T = macro macros.misc.MiscMacros.clueInfer[T]
  def inferNonMacro[T](clue: String): T = macro macros.misc.MiscMacros.inferNonMacro[T]
}

/**
  * 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()
  * }}}
  */
sealed trait ImplicitNotFound[T]
object ImplicitNotFound {
  def apply[T](): ImplicitNotFound[T] = throw new NotImplementedError("ImplicitNotFound.apply")

  implicit def dummy[T]: ImplicitNotFound[T] = apply()
}