ClassInfo can appear as result of memberType in macros

[scf37]

Compiler version

3.0.1

Minimized code

import scala.quoted._
object Macro:
  inline def apply[A]: Unit = ${impl[A]}

  private def impl[A: Type](using Quotes): Expr[String] =
    import quotes.reflect._
    val t = TypeRepr.of[A]
    Expr.ofList(t.baseClasses.drop(1).filter(_.flags.is(Flags.Trait)).map { baseSymbol =>
        t.memberType(baseSymbol).asType  match { case '[t] => 42}
        Expr("")
    })
    Expr("")

Macro[Option[String]]

Output (click arrow to expand)

[info] compiling 2 Scala sources to /tmp/1/target/scala-3.0.1/classes ...
[info] assertion failure for trait Serializable in package java.io <:< t, frozen = false
[error] -- Error: /tmp/1/Main.scala:6:9 ------------------------------------------------
[error] 6 |    Macro[Option[String]]
[error]   |    ^^^^^^^^^^^^^^^^^^^^^
[error]   |Exception occurred while executing macro expansion.
[error]   |java.lang.AssertionError: assertion failed: ClassInfo(ThisType(TypeRef(NoPrefix,module class io)), trait Serializable, List(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any)))
[error]   |	at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
[error]   |	at dotty.tools.dotc.core.Types$TypeBounds.<init>(Types.scala:4791)
[error]   |	at dotty.tools.dotc.core.Types$RealTypeBounds.<init>(Types.scala:4852)
[error]   |	at dotty.tools.dotc.core.Types$TypeBounds$.apply(Types.scala:4896)
[error]   |	at dotty.tools.dotc.core.Types$TypeBounds.derivedTypeBounds(Types.scala:4799)
[error]   |	at dotty.tools.dotc.core.ConstraintHandling.addOneBound(ConstraintHandling.scala:108)
[error]   |	at dotty.tools.dotc.core.ConstraintHandling.addOneBound$(ConstraintHandling.scala:26)
[error]   |	at dotty.tools.dotc.core.ProperGadtConstraint.addOneBound(GadtConstraint.scala:60)
[error]   |	at dotty.tools.dotc.core.ConstraintHandling.addBoundTransitively(ConstraintHandling.scala:162)
[error]   |	at dotty.tools.dotc.core.ConstraintHandling.addBoundTransitively$(ConstraintHandling.scala:26)
[error]   |	at dotty.tools.dotc.core.ProperGadtConstraint.addBoundTransitively(GadtConstraint.scala:60)
[error]   |	at dotty.tools.dotc.core.ProperGadtConstraint.addBound(GadtConstraint.scala:159)
[error]   |	at dotty.tools.dotc.core.TypeComparer.gadtAddLowerBound(TypeComparer.scala:118)
[error]   |	at dotty.tools.dotc.core.TypeComparer.narrowGADTBounds(TypeComparer.scala:1870)
[error]   |	at dotty.tools.dotc.core.TypeComparer.compareGADT$1(TypeComparer.scala:505)
[error]   |	at dotty.tools.dotc.core.TypeComparer.thirdTryNamed$1(TypeComparer.scala:508)
[error]   |	at dotty.tools.dotc.core.TypeComparer.thirdTry$1(TypeComparer.scala:557)
[error]   |	at dotty.tools.dotc.core.TypeComparer.secondTry$1(TypeComparer.scala:488)
[error]   |	at dotty.tools.dotc.core.TypeComparer.compareNamed$1(TypeComparer.scala:297)
[error]   |	at dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:303)
[error]   |	at dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1282)
[error]   |	at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:185)
[error]   |	at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:195)
[error]   |	at dotty.tools.dotc.core.TypeComparer.topLevelSubType(TypeComparer.scala:128)
[error]   |	at dotty.tools.dotc.core.TypeComparer$.topLevelSubType(TypeComparer.scala:2673)
[error]   |	at dotty.tools.dotc.core.Types$Type.$less$colon$less(Types.scala:1032)
[error]   |	at scala.quoted.runtime.impl.QuoteMatcher$.$eq$qmark$eq(QuoteMatcher.scala:336)
[error]   |	at scala.quoted.runtime.impl.QuoteMatcher$.treeMatch(QuoteMatcher.scala:129)
[error]   |	at scala.quoted.runtime.impl.QuotesImpl.scala$quoted$runtime$impl$QuotesImpl$$treeMatch(QuotesImpl.scala:2961)
[error]   |	at scala.quoted.runtime.impl.QuotesImpl$TypeMatch$.unapply(QuotesImpl.scala:2931)
[error]   |	at Macro$.impl$$anonfun$2(Macro.scala:9)
[error]   |	at scala.collection.immutable.List.map(List.scala:246)
[error]   |	at Macro$.impl(Macro.scala:10)
[error]   |	at Macro$.inline$impl(Macro.scala:5)
[error]   |
[error]   | This location contains code that was inlined from Main.scala:6
[error] one error found
[error] one error found

[scf37]

It seems to fail on non-Scala interfaces as well:
assertion failed: ClassInfo(ThisType(TypeRef(NoPrefix,module class io)), trait Serializable, List(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any)))

[dwijnand]

The assert is:

https://github.com/lampepfl/dotty/blob/f27c250e4b25d592dce00bb36b6305f90a7e9152/compiler/src/dotty/tools/dotc/core/Types.scala#L4896-L4898

[dwijnand]

It seems to fail on non-Scala interfaces as well:
assertion failed: ClassInfo(ThisType(TypeRef(NoPrefix,module class io)), trait Serializable, List(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any)))

That's the same as in the original report. Did you see another one too?

[scf37]

@dwijnand I was confident I saw it for scala.Matchable as well

[scf37]

t.memberType(baseSymbol).show throws MatchError.
Is this a bug or some kind of "wrong type"? Because I need to process superclass and traits of given type.

[error]   |Exception occurred while executing macro expansion.
[error]   |scala.MatchError: ClassInfo(ThisType(TypeRef(NoPrefix,module class io)), trait Serializable, List(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any))) (of class dotty.tools.dotc.core.Types$CachedClassInfo)
[error]   |	at scala.quoted.runtime.impl.printers.Extractors$ExtractorsPrinter.visitType(Extractors.scala:233)
[error]   |	at scala.quoted.runtime.impl.printers.Extractors$.showType(Extractors.scala:12)
[error]   |	at scala.quoted.runtime.impl.QuotesImpl$$anon$17.show(QuotesImpl.scala:2898)
[error]   |	at scala.quoted.runtime.impl.QuotesImpl$$anon$17.show(QuotesImpl.scala:2897)
[error]   |	at scala.quoted.runtime.impl.QuotesImpl$reflect$TypeReprMethods$.show(QuotesImpl.scala:1660)
[error]   |	at scala.quoted.runtime.impl.QuotesImpl$reflect$TypeReprMethods$.show(QuotesImpl.scala:1660)
[error]   |	at scala.quoted.runtime.impl.printers.SourceCode$SourceCodePrinter.printType(SourceCode.scala:1228)
[error]   |	at scala.quoted.runtime.impl.printers.SourceCode$.showType(SourceCode.scala:13)
[error]   |	at scala.quoted.runtime.impl.QuotesImpl$$anon$14.show(QuotesImpl.scala:2886)
[error]   |	at scala.quoted.runtime.impl.QuotesImpl$$anon$14.show(QuotesImpl.scala:2885)
[error]   |	at scala.quoted.runtime.impl.QuotesImpl$reflect$TypeReprMethods$.show(QuotesImpl.scala:1660)
[error]   |	at scala.quoted.runtime.impl.QuotesImpl$reflect$TypeReprMethods$.show(QuotesImpl.scala:1660)
[error]   |	at Macro$.impl$$anonfun$2(Macro.scala:11)
[error]   |	at scala.collection.immutable.List.map(List.scala:246)
[error]   |	at Macro$.impl(Macro.scala:13)
[error]   |	at Macro$.inline$impl(Macro.scala:5)

[bishabosha]

I came across a similar issue with matching on the result of memberType when answering #14154:

package mcr

import scala.quoted.*

trait CaseClass[Companion <: AnyRef]:
  type CC <: Product

object CaseClass:
  transparent inline given mkCaseClass[Comp <: AnyRef]: CaseClass[Comp] = ${
    macroImpl[Comp]
  }
  def macroImpl[Comp <: AnyRef](using Quotes, Type[Comp]): Expr[CaseClass[Comp]] =
    import quotes.reflect.*

    val compObjTpe = TypeRepr.of[Comp]
    val clsSym = compObjTpe.typeSymbol.companionClass
    if !clsSym.paramSymss.forall(_.headOption.forall(_.isTerm)) then
      report.throwError("Case class with type parameters are not supported")

    val compPrefix = compObjTpe match
      case TermRef(pre, _) => pre
      case _ => report.throwError("Case class companion must be a term ref")
    val clsTpe = compPrefix.memberType(clsSym) // memberType returns ClassInfo here
    report.info(s"Case class type: ${clsTpe}")
    // clsTpe.asType match // uncomment causes match error when calling macro
      // case '[t] =>
        '{
          new CaseClass[Comp]:
            type CC = Nothing
        }
end CaseClass