Closed as not planned
Description
Based on OpenCB failures in jcouyang/dhall-generic - build logs
The compiler fails to search for implicit instances defined in companion of the typeclass. It requires explicit import at the place of usage
Compiler version
Last good release: 3.5.0-RC1-bin-20240406-521ce95-NIGHTLY
First bad release: 3.5.0-RC1-bin-20240408-1e8a653-NIGHTLY
The compilation errors when building compiler prevented gathering the exact commit that coused regression it can be any of:
d2a6392
1dc5b99
321d0d2
1e8a653
The project-wise bisect nominated 90c3fbd as the cause of the regression
Minimized code
Needs to be defined as 2 compilation units
I was able to reproducer Decoder[Empty] in single file, but the other cases required definitions and usage to be split in previous Scala versions.
// 1_defns.scala
import scala.compiletime.*
import scala.deriving.*
sealed trait Decoder[T]
object Decoder:
inline given summonEmptyTuple[H]: Tuple.Map[EmptyTuple.type, Decoder] = EmptyTuple
inline given summonTuple[H, T <: Tuple](using
hd: Decoder[H],
td: Tuple.Map[T, Decoder]
): Tuple.Map[H *: T, Decoder] = hd *: td
inline given derived[T](using
m: Mirror.Of[T],
d: Tuple.Map[m.MirroredElemTypes, Decoder]
): Decoder[T] = ???
given Decoder[Double] = ???// 2_usage.scala
case class Empty()
object Empty {
val fails = Decoder.derived[Empty]
}
enum Shape:
case Rectangle(width: Double, height: Double)
case Circle(radius: Double)
object Shape:
val fails1 = Decoder.derived[Rectangle]
val fails2 = Decoder.derived[Shape]Output
-- [E172] Type Error: /Users/wmazur/projects/sandbox/repro.test.scala:4:39 -----
4 | val instance = Decoder.derived[Empty]
| ^
|No given instance of type Tuple.Map[m.MirroredElemTypes, Decoder] was found for parameter d of given instance derived in object Decoder
|
|Note: a match type could not be fully reduced:
|
| trying to reduce Tuple.Map[m.MirroredElemTypes, Decoder]
| failed since selector m.MirroredElemTypes
| does not match case EmptyTuple => EmptyTuple
| and cannot be shown to be disjoint from it either.
| Therefore, reduction cannot advance to the remaining case
|
| case h *: t => Decoder[h] *: Tuple.Map[t, Decoder]
-- [E172] Type Error: /Users/wmazur/projects/sandbox/repro.test.scala:12:38 ----
12 | val rec = Decoder.derived[Rectangle]
| ^
|No given instance of type Tuple.Map[m.MirroredElemTypes, Decoder] was found for parameter d of given instance derived in object Decoder.
|I found:
|
| Decoder.summonTuple[Double, Double *: EmptyTuple.type](
| Decoder.given_Decoder_Double,
| Decoder.summonTuple[Double, EmptyTuple.type](Decoder.given_Decoder_Double,
| /* missing */summon[Tuple.Map[EmptyTuple.type, Decoder]])
| )
|
|But no implicit values were found that match type Tuple.Map[EmptyTuple.type, Decoder].
|
|Note: a match type could not be fully reduced:
|
| trying to reduce Tuple.Map[m.MirroredElemTypes, Decoder]
| failed since selector m.MirroredElemTypes
| does not match case EmptyTuple => EmptyTuple
| and cannot be shown to be disjoint from it either.
| Therefore, reduction cannot advance to the remaining case
|
| case h *: t => Decoder[h] *: Tuple.Map[t, Decoder]
3 errors foundExpectation
Should compile