Scala 3 does not perform implicit conversion using <:<

[Swoorup]

Compiler version

3.0.2-RC1-bin-SNAPSHOT

Minimized code

import Tuple.Union

type Channel = "orders" | "trades"

def getChannelList[Channels <: NonEmptyTuple](c: Channels)(using Union[Channels] <:< Channel) = 
  val channels: List[Channel] = c.toList
  channels

Expectation

Compiles fine

Output

fails to compile with error:

[error] 6 |  val channels: List[Channel] = c.toList
[error]   |                                ^^^^^^^^
[error]   |Found:    List[Tuple.Union[(c : Channels)]]
[error]   |Required: List[Channel]
[error]   |
[error]   |where:    Channels is a type in method getChannelList with bounds <: NonEmptyTuple
[error]   |
[error]   |
[error]   |Note: a match type could not be fully reduced:
[error]   |
[error]   |  trying to reduce  Tuple.Union[(c : Channels)]
[error]   |  trying to reduce  scala.Tuple.Fold[(c : Channels), Nothing, [x, y] =>> x | y]
[error]   |  failed since selector  (c : Channels)
[error]   |  matches none of the cases
[error]   |
[error]   |    case EmptyTuple => Nothing
[error]   |    case h *: t => h | scala.Tuple.Fold[t, Nothing, [x, y] =>> x | y]

[nicolasstucki]

Might be related to #12721

[SethTisue]

@dwijnand I don't think you meant to assign me?

[dwijnand]

You were going to look if related PRs would fix this, and I was trying to get you hooked in enough to see if you could look into it further...

[SethTisue]

I have no recollection of that, and I don't have any special expertise here, so hopefully someone else would like to look into it.

[Swoorup]

I am surprised fixing this #10897 didn't fix this issue.

[SethTisue]

LOL, I just found a note I wrote to myself that says "I told Dale I would definitely follow up on this" 😅

But actually, it appears that all I was going to do was verify that it isn't actually fixed yet. And now @Swoorup has already checked that. (And I just double-checked it.)

[nicolasstucki]

Minimized

def test[A, B](using A <:< B) =
  val b: B = ??? : A