undefined error when transforming a Tasty tree and getting a type wrong

[anatoliykmetyuk]

minimized code

Macro:

package playground

import scala.quoted._, scala.quoted.matching._
import delegate scala.quoted._
import scala.tasty._

delegate for Toolbox = Toolbox.make(getClass.getClassLoader)

inline def mcr(x: => Any): Any = ${mcrImpl('x)}

def mcrImpl(body: Expr[Any]) given (ctx: QuoteContext): Expr[Any] = {
  import ctx.tasty._

  def transformQualifier(qual: Term): Term =
    '{
      val tmp = ${qual.seal}//.cast[Boolean]}
      tmp
    }.unseal

  val res = body.unseal.underlyingArgument match {
    case app@Apply(sel@Select(qualifier, name), args) =>
      Apply.copy(app)(
        Select.copy(sel)(transformQualifier(qualifier), name)
      , args)
  }
  res.seal
}

Main:

package playground

val a = true
@main def main = println(mcr { a && false })

Error:

[error] -- Error: /Users/anatolii/Projects/dotty/playground/core/src/main/scala/playground/Main.scala:4:31
[error] 4 |@main def main = println(mcr { a && false })
[error]   |                               ^^^^^^^^^^
[error]   |undefined: {
[error]   |  {
[error]   |    val tmp: Any =
[error]   |      {
[error]   |        playground.a
[error]   |      }
[error]   |    (tmp:Any)
[error]   |  }
[error]   |}.&& # 95367: TermRef(TypeRef(TermRef(ThisType(TypeRef(NoPrefix,module class <root>)),module scala),Any),&&) at frontend
[error]   | This location is in code that was inlined at Main.scala:4
[error] one error found

It works as expected if you define the tmp variable in the macro as follows:

val tmp = ${qual.seal.cast[Boolean]}

expectation

A more user-friendly message saying what exactly is wrong.