是否可以匹配 sum 类型的带引号类型？

Question

我正在 Scala3 中进行类型类推导。 我的类型类是 BarOf[T] 扩展 Bar。 T 预计是一个 ADT。 Bar 有一个 children 方法，返回 T 的子类型的 BarOf[X]。

这里是 衍生 方法基于Quotes而不是Mirror。这是我的其余代码所必需的，已在此处删除。

找出 BarOf[X]（对于每个 X 子类型）的基本步骤是基于引用类型匹配。 （完整代码在文章末尾）

A.memberType(childSymbol).asType match {
        case '[f] => Expr.summon[BarOf[f]]
      }

这对于产品类型，特别是案例类来说效果很好。 但是，当应用于和类型时，编译器会触发一个断言：

assertion failure for class C1 <:< f, frozen = false
6 |sealed class Foo1 derives BarOf
  |                         ^
  |Exception occurred while executing macro expansion.
  |java.lang.AssertionError: assertion failed: ClassInfo(ThisType(TypeRef(NoPrefix,module class <empty>)), class C0, List(TypeRef(ThisType(TypeRef(NoPrefix,module class <empty>)),class Foo)))
  |     at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
  |     at dotty.tools.dotc.core.Types$TypeBounds.<init>(Types.scala:4918)
  |     at dotty.tools.dotc.core.Types$RealTypeBounds.<init>(Types.scala:4994)
  |     at dotty.tools.dotc.core.Types$TypeBounds$.apply(Types.scala:5038)
  |     at dotty.tools.dotc.core.Types$TypeBounds.derivedTypeBounds(Types.scala:4926)
  |     at dotty.tools.dotc.core.ConstraintHandling.addOneBound(ConstraintHandling.scala:116)
  |     at dotty.tools.dotc.core.ConstraintHandling.addOneBound$(ConstraintHandling.scala:27)
  |     at dotty.tools.dotc.core.ProperGadtConstraint.addOneBound(GadtConstraint.scala:60)
  |     at dotty.tools.dotc.core.ConstraintHandling.addBoundTransitively(ConstraintHandling.scala:170)
  |     at dotty.tools.dotc.core.ConstraintHandling.addBoundTransitively$(ConstraintHandling.scala:27)
  |     at dotty.tools.dotc.core.ProperGadtConstraint.addBoundTransitively(GadtConstraint.scala:60)
  |     at dotty.tools.dotc.core.ProperGadtConstraint.addBound(GadtConstraint.scala:159)
  |     at dotty.tools.dotc.core.TypeComparer.gadtAddLowerBound(TypeComparer.scala:118)
  |     at dotty.tools.dotc.core.TypeComparer.narrowGADTBounds(TypeComparer.scala:1913)
  |     at dotty.tools.dotc.core.TypeComparer.compareGADT$1(TypeComparer.scala:521)
  |     at dotty.tools.dotc.core.TypeComparer.thirdTryNamed$1(TypeComparer.scala:524)
  |     at dotty.tools.dotc.core.TypeComparer.thirdTry$1(TypeComparer.scala:573)
  |     at dotty.tools.dotc.core.TypeComparer.secondTry$1(TypeComparer.scala:504)
  |     at dotty.tools.dotc.core.TypeComparer.compareNamed$1(TypeComparer.scala:313)
  |     at dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:319)
  |     at dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1321)
  |     at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:201)
  |     at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:211)
  |     at dotty.tools.dotc.core.TypeComparer.topLevelSubType(TypeComparer.scala:128)
  |     at dotty.tools.dotc.core.TypeComparer$.topLevelSubType(TypeComparer.scala:2729)
  |     at dotty.tools.dotc.core.Types$Type.$less$colon$less(Types.scala:1035)
  |     at scala.quoted.runtime.impl.QuoteMatcher$.$eq$qmark$eq(QuoteMatcher.scala:336)
  |     at scala.quoted.runtime.impl.QuoteMatcher$.treeMatch(QuoteMatcher.scala:129)
  |     at scala.quoted.runtime.impl.QuotesImpl.scala$quoted$runtime$impl$QuotesImpl$$treeMatch(QuotesImpl.scala:3021)
  |     at scala.quoted.runtime.impl.QuotesImpl$TypeMatch$.unapply(QuotesImpl.scala:2991)
  |     at bar.BarOf$.childExpr$1(bar.scala:21)
  |     at bar.BarOf$.$anonfun$6(bar.scala:26)
  |     at scala.collection.immutable.List.map(List.scala:246)
  |     at bar.BarOf$.derivedImpl(bar.scala:26)

该断言由带引号的类型匹配触发：case '[f] =>。但我无法弄清楚我错过了什么。 我的代码合法吗？

• 如果不是：有什么替代方案？
• 如果是：是编译器错误吗？

完整的 bar 包源码：

package bar
import scala.quoted.*


trait Bar:
  def children : List[Bar]

trait BarOf[A] extends Bar

object BarOf :
  inline def derived[A]: BarOf[A] =  ${derivedImpl[A]}

  def derivedImpl[A:Type](using Quotes):Expr[BarOf[A]] =
    import quotes.reflect._
    val A           = TypeRepr.of[A]
    val mySymbol    = A.typeSymbol
    val terms       = mySymbol.children

    def childExpr(childSymbol:Symbol) =
      A.memberType(childSymbol).asType match {
        case '[f] => Expr.summon[BarOf[f]]
      } getOrElse {
        report.errorAndAbort(s"ChildType ${childSymbol} of ${mySymbol} does not derive BarOf")
      }

    val termsExpr =  Expr.ofList(terms.map(childExpr))
    '{  new BarOf[A]
        {   def children = ${termsExpr}
        }
     }

测试代码：

import bar.BarOf
  
// works
enum Foo0 derives BarOf :
  case C0

// does not work 
enum Foo1 derives BarOf :
  case C1(x:Int)

// does not work either :
sealed class Foo2 derives BarOf
class C2(x:Int) extends Foo2



@main def run:Unit =
  val x = summon[BarOf[Foo1]]
  println(x.children)

Answer 1

问题并不像我想象的那样出在类型模式匹配上，而是在匹配的符号上。

正确的查找是：

childSymbol.typeRef.asType match {
    case '[f] => Expr.summon[BarOf[f]]
}

而不是：

A.memberType(childSymbol).asType match {
    case '[f] => Expr.summon[BarOf[f]]
}

完整的功能代码：

package bar
import scala.quoted.*


trait Bar:
  def children : List[Bar]

trait BarOf[A] extends Bar

object BarOf :
  inline def derived[A]: BarOf[A] =  ${derivedImpl[A]}

  def derivedImpl[A:Type](using Quotes):Expr[BarOf[A]] =
    import quotes.reflect._
    val A           = TypeRepr.of[A]
    val mySymbol    = A.typeSymbol
    val terms       = mySymbol.children

    def childExpr(childSymbol:Symbol) =
      childSymbol.typeRef.asType match {
        case '[f] => Expr.summon[BarOf[f]]
      } getOrElse {
        report.errorAndAbort(s"ChildType ${childSymbol} of ${mySymbol} does not derive BarOf")
      }

    val termsExpr =  Expr.ofList(terms.map(childExpr))
    '{  new BarOf[A]
        {   def children = ${termsExpr}
            override def toString = ${Expr(s"BarOf[${mySymbol.fullName}]")}
        }
     }