summonInline fails strangely

[soronpo]

Compiler version

v3.0.0-RC3

Minimized code

inline def convFail[Of, From](inline from : From) : Unit =
  val c = compiletime.summonInline[Conversion[from.type, Of]]

inline def convOK[Of, From](inline from : From)(using c : Conversion[from.type, Of]) : Unit = {}

class Bar[T](value : T) 
given [T <: Int] : Conversion[T, Bar[T]] = Bar(_)

@main def main : Unit = {
  convOK[Bar[1],1](1)
  convFail[Bar[1],1](1) //causes error
}

Output

Found:    Conversion[(1 : Int), Bar[(1 : Int)]]
Required: Conversion[From, Bar[(1 : Int)]]

Expectation

Both convOK and convFail should be equivalent

[soronpo]

Workaround:

  trait AlwaysGiven[T]:
    type Out = T
  object AlwaysGiven:
    given [T] : AlwaysGiven[T] = new AlwaysGiven[T]{}
  inline def convNoFail[Of, From](inline from : From)(using v : AlwaysGiven[from.type]) : Unit =
    val c = compiletime.summonInline[Conversion[v.Out, Of]]

[liufengyun]

The following code works:

inline def convFail[Of, From](inline from : From) : Unit =
  val c = compiletime.summonInline[Conversion[From, Of]]

inline def convOK[Of, From](inline from : From)(using c : Conversion[From, Of]) : Unit = {}

class Bar[T](value : T)
given [T <: Int] : Conversion[T, Bar[T]] = Bar(_)

@main def main : Unit = {
  convOK[Bar[1],1](1)
  convFail[Bar[1],1](1) //causes error
}

[soronpo]

The following code works:

inline def convFail[Of, From](inline from : From) : Unit =
  val c = compiletime.summonInline[Conversion[From, Of]]

inline def convOK[Of, From](inline from : From)(using c : Conversion[From, Of]) : Unit = {}

class Bar[T](value : T)
given [T <: Int] : Conversion[T, Bar[T]] = Bar(_)

@main def main : Unit = {
  convOK[Bar[1],1](1)
  convFail[Bar[1],1](1) //causes error
}

Yes, but from.type is important to get the actual type that is not widened.

[liufengyun]

I don't think it's widened. It can be checked with scalac -d out -Xprint:inlining tests/pos/i12379.scala:

    @main() def main: Unit =
      {
        {
          val c$proxy1: Conversion[(1 : Int), Bar[(1 : Int)]] =
            given_Conversion_T_Bar[(1 : Int)]
          {
            ()
          }:Unit
        }
        {
          val c: Conversion[(1 : Int), Bar[(1 : Int)]] =
            {
              given val t: Conversion[(1 : Int), Bar[(1 : Int)]] =
                given_Conversion_T_Bar[(1 : Int)]
              t:Conversion[(1 : Int), Bar[(1 : Int)]]
            }
          ()
        }:Unit
      }