implicit parameters passed to macros can not be resolved

[rssh]

minimized code

package direct1
  
import org.junit.Test
import org.junit.Assert._

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


trait DM[F[_]] {

   def pure[T:Type](t:Expr[T]):(given ctx:QuoteContext) => Expr[F[T]]

}

sealed trait CB[T]
case class Done[T](value:T) extends CB[T]

implicit object dmCB extends DM[CB] {

  def pure[T:Type](t:Expr[T]):(given ctx:QuoteContext) => Expr[CB[T]] =
    '{ Done(${t}) }

}


object A {

  inline def transform[F[_],T](expr: =>T): F[T] =
    ${   A.transformImpl('expr)  }

  def transformImpl[F[_]:DM,T:Type](f: Expr[T])(given QuoteContext):Expr[F[T]] =
    f match
      case Const(t) => implicitly[DM[F]].pure(f)
      case _ => print(f)
         throw new IllegalStateException("language construction is not supported")

}

class TestBS2

  @Test def tConstant(): Unit = {
     val c = A.transform[CB,Int](3)
     assert(c == Done(3))
  }

During compiling we have:

[error] -- Error: /Users/rssh/work/oss/dotty-async/dotty-async/src/test/scala/direct/TestCBS2.scala:31:29 
[error] 31 |       A.transformImpl('expr)
[error]    |                             ^
[error]    |no implicit argument of type direct1.DM[F] was found for parameter evidence$2 of method transformImpl in object A

but dmCB was defined.

expectation

compilation without a problem.

[nicolasstucki]

dmCB is not a valid implicit for DM[F].

Passing it explicitly shows why

  inline def transform[F[_],T](expr: =>T): F[T] =
    ${   A.transformImpl('expr)(given dmCB)  }

30 |    ${   A.transformImpl('expr)(given dmCB)  }
   |                                      ^^^^
   |                     Found:    direct1.dmCB.type
   |                     Required: direct1.DM[F]
   |
   |                     where:    F is a type variable with constraint <: F

[rssh]

dbCB extends DM[CB]. When you insert dbCB explicitly in transform[F,T], you loose information about binding CB to F. (i.e. you insert the object explicitly too early). I guess you should insert one explicitly in transform[CB, T]

[rssh]

looking at original -- look's like event like we pass it direct:

package direct

import org.junit.{Test,Ignore}
import org.junit.Assert._

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


trait DM[F[_]] {

   def pure[T:Type](t:Expr[T]):(given ctx:QuoteContext) => Expr[F[T]]

}

sealed trait CB[T]
case class Done[T](value:T) extends CB[T]

implicit val dmCB: DM[CB] = new DM[CB] {

  def pure[T:Type](t:Expr[T]):(given ctx:QuoteContext) => Expr[CB[T]] =
    '{ Done(${t}) }

}


object A {

  inline def transform[F[_]:DM,T](expr: =>T): F[T] =
    ${
       A.transformImpl('expr)
     }

  def transformImpl[F[_]:DM,T:Type](f: Expr[T])(given QuoteContext):Expr[F[T]] =
    f match
      case Const(t) => implicitly[DM[F]].pure(f)
      case _ => print(f)
         throw new IllegalStateException("language construction is not supported")


}

class TestBS2

  @Test def tConstant(): Unit = {
     val c = A.transform[CB,Int](3)
     assert(c == Done(3))
  }

We still have a problem:

[error] -- Error: /Users/rssh/work/oss/dotty-cps/dotty-cps/src/test/scala/cps/cbs2/TestCBS2.scala:31:29 
[error] 31 |       A.transformImpl('expr)
[error]    |                             ^
[error]    |                             Malformed macro parameter
[error]    |
[error]    |                             Parameters may be:
[error]    |                              * Quoted parameters or fields
[error]    |                              * References to inline parameters
[error]    |                              * Literal values of primitive types

(but other, then first. Looks like I miss extra passing of '''given DM[F]''' during minimizing.)

[nicolasstucki]

The issue is clearer if we write the implcilits explicitly

  ...
  inline def transform[F[_],T](expr: =>T)(dm: DM[F]): F[T] =
    ${
       A.transformImpl('expr)(using dm)
     }

  def transformImpl[F[_],T:Type](f: Expr[T])(using dm: DM[F])(using QuoteContext): Expr[F[T]] =
  ...

29 |       A.transformImpl('expr)(using dm)
   |                                    ^^
   |                                    Malformed macro parameter
   |
   |                                    Parameters may be:
   |                                     * Quoted parameters or fields
   |                                     * References to inline parameters
   |                                     * Literal values of primitive types

[nicolasstucki]

The error message is correct. It should be improved when the argument is implicit.