summonFrom and using clause should act the same

[liewhite]

3.0.0-RC3

If a report.error in a given macro and use NotGiven to deal with it, It works with a summonFrom but compile error in a using clause.

Minimized code

MkGiven.scala:

import scala.compiletime.*
import scala.quoted.*

object MkGiven:
  inline def mkInt:Int = ${ mkIntMacro }

  inline given Int = mkInt

  def mkIntMacro(using q: Quotes): Expr[Int] = 
    import q.reflect._
    report.error("no int found") // this break using but  summonFrom works well
    Expr(1)

Main.scala:

import scala.compiletime.{summonFrom}
import scala.util.NotGiven
import MkGiven.given

trait OptionGiven[T]:
  def give: Option[T]

object OptionGiven:
  given exist[T](using NotGiven[T]): OptionGiven[T] with
    def give = None

  given notExist[T](using t: T): OptionGiven[T] with
    def give = Some(t)

inline def mySummon[T] = summonFrom {
  case t: T => t
}

def usingFailed(using i:Int) = i

@main def hello: Unit = {
  val ok = mySummon[OptionGiven[Int]].give
  val error = usingFailed
}

Output

no int found

Expectation

I think the using clause and summonFrom should act the same.

[odersky]

The purpose of summonFrom is that it is not equivalent to using since it gets elaborated at the call site not the definition site. So the argument "they should act the same" does not hold per se. Can we have a self-contained example? Without that it's hard to make progress here.

[liewhite]

@odersky update the code to reproduce the problem.

[som-snytt]

If MkGiven uses transparent inline, then implicit search continues as described at https://dotty.epfl.ch/docs/reference/metaprogramming/inline.html#transparent-inline-methods

The no implicit argument error message adds:

But given instance given_Int in object MkGiven does not match type Int.

which is potentially confusing.

There is a similar question of how Scala 2 macro error reporting ought to interact with implicit search at scala/bug#12388

[nicolasstucki]

The code seems to work as intended. What did you mean by this break using but summonFrom works well?

[liewhite]

@nicolasstucki Oh, I forgot to close this. using and summonFrom should act differently as design.