Crash in summonExpr

[biboudis]

minimized code

import scala.quoted._
import scala.deriving._
import scala.quoted.matching._

object Macros {
  inline def m(): Unit = ${ macroImpl() }

  def macroImpl[T]()(given qctx: QuoteContext): Expr[Unit] = {
    summonExpr[Mirror.Of[Some[Int]]]
    '{()}
  }
}

@main def Test() = {
  println(Macros.m())
}

Stack trace

3 |  println(Helper.f(Some(0)))
  |          ^^^^^^^^^^^^^^^^^
  |Exception occurred while executing macro expansion.
  |java.lang.ClassCastException: dotty.tools.dotc.core.Symbols$NoSymbol$ cannot be cast to dotty.tools.dotc.core.Symbols$ClassSymbol
  |     at dotty.tools.dotc.core.Symbols$Symbol.asClass(Symbols.scala:539)
  |     at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2134)
  |     at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2201)
  |     at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:123)
  |     at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2240)
  |     at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2252)
  |     at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2274)
  |     at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2318)
  |     at dotty.tools.dotc.typer.Typer.typedBlockStats(Typer.scala:796)
  |     at dotty.tools.dotc.typer.Typer.typedBlock(Typer.scala:800)
  |     at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2152)
  |     at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2202)
  |     at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:123)
  |     at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2240)
  |     at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2252)
  |     at dotty.tools.dotc.typer.Typer.typedNew(Typer.scala:626)
  |     at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2148)
  |     at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2202)
  |     at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:123)
  |     at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2240)
  |     at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2252)
  |     at dotty.tools.dotc.typer.Implicits.anonymousMirror(Implicits.scala:892)
  |     at dotty.tools.dotc.typer.Implicits.mirrorFor$2(Implicits.scala:980)
  |     at dotty.tools.dotc.typer.Implicits.synthesizedProductMirror$$anonfun$1$$anonfun$1(Implicits.scala:991)
  |     at dotty.tools.dotc.typer.Implicits.synthesizedMirror$$anonfun$1$$anonfun$1(Implicits.scala:1080)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$1(Implicits.scala:1123)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$2$$anonfun$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.ast.Trees$Tree.orElse(Trees.scala:185)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$2$$anonfun$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.ast.Trees$Tree.orElse(Trees.scala:185)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$2$$anonfun$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.ast.Trees$Tree.orElse(Trees.scala:185)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$2$$anonfun$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.ast.Trees$Tree.orElse(Trees.scala:185)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$2$$anonfun$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.ast.Trees$Tree.orElse(Trees.scala:185)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$2$$anonfun$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.ast.Trees$Tree.orElse(Trees.scala:185)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$2$$anonfun$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.ast.Trees$Tree.orElse(Trees.scala:185)
  |     at dotty.tools.dotc.typer.Implicits.trySpecialCases$1(Implicits.scala:1125)
  |     at dotty.tools.dotc.typer.Implicits.inferImplicitArg(Implicits.scala:1130)
  |     at dotty.tools.dotc.typer.Typer.inferImplicitArg(Typer.scala:83)
  |     at dotty.tools.dotc.tastyreflect.ReflectionCompilerInterface.searchImplicit(ReflectionCompilerInterface.scala:1912)
  |     at dotty.tools.dotc.tastyreflect.ReflectionCompilerInterface.searchImplicit(ReflectionCompilerInterface.scala:1911)
  |     at scala.tasty.reflect.ImplicitsOps.searchImplicit(ImplicitsOps.scala:6)
  |     at scala.tasty.Reflection.searchImplicit(Reflection.scala:6)
  |     at scala.quoted.matching.package$.summonExpr(package.scala:15)
  |     at Helper$.macroImpl(Macro_1.scala:26)
  |
  | This location contains code that was inlined from Test_2.scala:3

inlined at Test_2.scala:3:

This resulted after further investigating this #7974

[biboudis]

It is related to the fact that Some is Scala2 and it gets through that mechanism of anonymousMirror and blows up when the following is going to be typed:

final class $anon extends Object {
  type MirroredMonoType = Some[Int]
}

but its symbol is None

[milessabin]

How come Some's symbol is None?

[biboudis]

So, the insight that the stacktrace gives is that after the anonymousMirror call we see instances of ReTyper. ReTyper has different assumptions with regard to completed symbols than Typer. We've tried to setTyper manually but ReTyper still is used. It needs a bit more investigation.

[milessabin]

Is this actually related to Mirror? Or would any type with a comparable refinement trip the same bug?

[biboudis]

Did you have in mind something like that?

given (Option[Int] { type TT }) = Some(2).asInstanceOf[Option[Int] { type TT = Float }]
summonExpr[Option[Int] { type TT = Float }]

^^ compiles ok btw

[milessabin]

Yeah, something like that.

compiles ok btw

In the body of a macro?

[biboudis]

Yeap

[nicolasstucki]

We were just using the wrong kind of typer.

[biboudis]

Ah. During macro expansion. The Type Assigner. Nice. 👍👍👍