Compile shows weird message: `assertion failed: asTerm called on not-a-Term val <none>`

[lenguyenthanh]

Compiler version

I tested on 3.2.2, 3.3.0-RC6 and 3.nightly

Minimized code

//> using scala 3.2.2

trait FromString[A]:
  def parse(s: String): Either[String, A]

sealed trait Uci:

  case class Move(from: String, to: String) extends Uci

object Uci extends FromString[Uci]:
	def parse(s: String): Either[String, Uci] = ???

or in scastie

Output (click arrow to expand)

Compiling project (Scala 3.2.2, JVM) exception occurred while compiling /Users/tle/git/lichess/scripts/DottyBroke.scala Error compiling project (Scala 3.2.2, JVM) Error: Unexpected error when compiling project_ed944f97cf-10493a1c22: 'assertion failed: asTerm called on not-a-Term val ' Compilation failed

Expect

I expect a better error message.

[s5bug]

Further minimized:

// must be sealed
// must be trait (not class)
sealed trait A {
  // must be `object` or `case class`
  case class X() extends A
}

// companion object must exist
object A

Note that the above should not throw an error, as the following does not:

sealed trait A {
  case class X() extends A
}

val a = new A {}

a.X()
a.X().X()
a.X().X().X()

[szymon-rd]

stack trace:

        at dotty.tools.dotc.core.Symbols$Symbol.asTerm(Symbols.scala:170)
        at dotty.tools.dotc.transform.ExplicitOuter$.dotty$tools$dotc$transform$ExplicitOuter$$$outerParamAccessor(ExplicitOuter.scala:229)
        at dotty.tools.dotc.transform.ExplicitOuter$OuterOps$.loop$1(ExplicitOuter.scala:465)
        at dotty.tools.dotc.transform.ExplicitOuter$OuterOps$.path$extension(ExplicitOuter.scala:474)
        at dotty.tools.dotc.transform.Erasure$Typer.typedThis(Erasure.scala:802)
        at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2992)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3054)
        at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:126)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3126)
        at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3130)
        at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3242)
        at dotty.tools.dotc.transform.Erasure$Typer.$anonfun$7(Erasure.scala:849)
        at dotty.tools.dotc.core.Decorators$.zipWithConserve(Decorators.scala:155)
        at dotty.tools.dotc.transform.Erasure$Typer.typedApply(Erasure.scala:849)
        at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2991)
        at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3054)
        at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:126)
        [...]