Handle sealed prefixes in exh checking

[dwijnand]

No description provided.

[liufengyun]

In the example mentioned above, the code is as follows:

  def handle(schema: Schema[String]) =
    schema match // was: match may not be exhaustive
      case Y.Field() =>
      case Y.Thing   =>

[dwijnand]

So, in that case it still does the right thing, though the showType logic isn't handling it very well.

[liufengyun]

Sorry, I was not clear. If I run the following example with this PR:

// scalac: -Werror
sealed trait Schema[A]

sealed class Outer:
  sealed trait RecordInstances[B]:
    case class Field() extends Schema[B]
    case object Thing extends Schema[B]

object O1 extends Outer
object O2 extends Outer

object X extends O1.RecordInstances[Int]
object Y extends O2.RecordInstances[String]

// Match not exhaustive error! (with fatal warnings :P)
class Test:
  def handle(schema: Schema[String]) =
    schema match // was: match may not be exhaustive
      case Y.Field() =>
      case Y.Thing   =>

I get the following warning:

-- [E029] Pattern Match Exhaustivity Warning: tests/pos/i15029.more.scala:18:4 -
18 |    schema match // was: match may not be exhaustive
   |    ^^^^^^
   |    match may not be exhaustive.
   |
   |    It would fail on pattern case: X.Field(), Thing
   |
   | longer explanation available when compiling with `-explain`

I expect no warnings in this case.

[dwijnand]

Ah, my mistake, didn't see the Schema[String] either time.

[dwijnand]

Excellent, found a simplier way to do it, which makes your more complicated version work! ❤️

[liufengyun]

Elegant fix, LGTM 👍