我正在使用类型类，并且在自动派生类型时遇到了问题，这些类型没有延迟地扩展了额外的（标记/指示符）特性。这很难解释，但这个小小的例子应该能让我明白我的意思：

// Base type we are working on
trait Food {}

// Marker trait - unrelated to Food's edibility
trait Plentiful {}

// Indicator type class we want to derive
trait IsHarmfulToEat[F<:Food] {}

object IsHarmfulToEat {
  // Rule that says that if some food is harmful to eat, 
  // an enormous amount is so as well
  implicit def ignoreSupply[F1<:Food,F2<:F1 with Plentiful]
                  (implicit isHarmful: IsHarmfulToEat[F1],
                   constraint: F2=:=F1 with Plentiful): IsHarmfulToEat[F2] = 
                         new IsHarmfulToEat[F2]{}
}

// Example of food
case class Cake() extends Food {}

object Cake {
  // Mark Cake as being bad for you
  implicit val isBad: IsHarmfulToEat[Cake] = new IsHarmfulToEat[Cake] {}
}

object FoodTest extends App {
  // Our main program
  val ignoreSupplyDoesWork: IsHarmfulToEat[Cake with Plentiful] = 
    IsHarmfulToEat.ignoreSupply[Cake,Cake with Plentiful] // compiles fine

  val badCake = implicitly[IsHarmfulToEat[Cake]] // compiles fine
  val manyBadCakes = implicitly[IsHarmfulToEat[Cake with Plentiful]] 
  // ^^^ does not compile - I do not understand why
}

（如果我做出同样的行为 Plentiful 通用和/或添加自身类型的 Food 对它来说。）
研究编译中的隐式日志，我发现：

Food.scala:33: util.this.IsHarmfulToEat.ignoreSupply is not a valid implicit value for IsHarmfulToEat[F1] because:
hasMatchingSymbol reported error: diverging implicit expansion for type IsHarmfulToEat[F1]
starting with method ignoreSupply in object IsHarmfulToEat
  val manyBadCakes = implicitly[IsHarmfulToEat[Cake with Plentiful]]
                               ^
Food.scala:33: util.this.IsHarmfulToEat.ignoreSupply is not a valid implicit value for IsHarmfulToEat[Cake with Plentiful] because:
hasMatchingSymbol reported error: diverging implicit expansion for type IsHarmfulToEat[F1]
starting with method ignoreSupply in object IsHarmfulToEat
  val manyBadCakes = implicitly[IsHarmfulToEat[Cake with Plentiful]]
                               ^
Food.scala:33: diverging implicit expansion for type IsHarmfulToEat[Cake with Plentiful]
starting with method ignoreSupply in object IsHarmfulToEat
  val manyBadCakes = implicitly[IsHarmfulToEat[Cake with Plentiful]]

在我看来，f1的类型推断正在崩溃，就像 ignoreSupply 只是在编译器查找 IsHarmfulToEat[Cake with Plentiful] . 有人能解释一下为什么吗？和/或如何引导编译器尝试正确的类型？和/或以另一种方式实现ignoresupply规则？