Regression for pattern match over dependant sealed traits

[WojciechMazur]

Based on compilation failure found in OpenCB for sbt/sbt for version 2.0.0-M2

Compiler version

Introduced in 3.4.0
Backported to 3.3.4

Last good release: 3.4.0-RC1-bin-20231020-89a8fce-NIGHTLY
First bad release: 3.4.0-RC1-bin-20231023-44a537b-NIGHTLY

Bisect points to 2be1b41 however these changes were not backported to LTS.
Bisect on LTS commits only failed to build compiler, but issue could have been introduced in any of: c1dfcef
f87a634

Minimized code

//> using options -Werror
trait Init[ScopeType]:
  sealed trait Initialize[A1]
  final class Bind[S, A1](val f: S => Initialize[A1], val in: Initialize[S])
    extends Initialize[A1]
  final class Value[A1](val value: () => A1) extends Initialize[A1]
  final class ValidationCapture[A1](val key: ScopedKey[A1], val selfRefOk: Boolean)
        extends Initialize[ScopedKey[A1]]
  final class TransformCapture(val f: [x] => Initialize[x] => Initialize[x])
        extends Initialize[[x] => Initialize[x] => Initialize[x]]
  final class Optional[S, A1](val a: Option[Initialize[S]], val f: Option[S] => A1)
        extends Initialize[A1]
  object StaticScopes extends Initialize[Set[ScopeType]]

  sealed trait Keyed[S, A1] extends Initialize[A1]
  trait KeyedInitialize[A1] extends Keyed[A1, A1]
  sealed case class ScopedKey[A](scope: ScopeType, key: AttributeKey[A]) extends KeyedInitialize[A]
  sealed trait AttributeKey[A]

abstract class EvaluateSettings[ScopeType]:
    protected val init: Init[ScopeType]
    import init._

    val transform: [A] => Initialize[A] => Unit = [A] =>
        (fa: Initialize[A]) =>
          fa match
            case k: Keyed[s, A]          => ???
            case b: Bind[s, A]           => ???
            case v: Value[A]             => ???
            case v: ValidationCapture[a] => ??? // unrearchable warning
            case t: TransformCapture     => ??? // unrearchable warning
            case o: Optional[s, A]       => ??? // unrearchable warning
            case StaticScopes            => ??? // unrearchable warning 
        

Output

-- [E029] Pattern Match Exhaustivity Warning: /Users/wmazur/projects/sandbox/test.scala:26:10 --------------------------------------------------------------------------------------------------------------
26 |          fa match
   |          ^^
   |          match may not be exhaustive.
   |
   |          It would fail on pattern case: _: (Init[<?>] & (EvaluateSettings#init : Init[EvaluateSettings#ScopeType]))#TransformCapture
   |
   | longer explanation available when compiling with `-explain`
-- [E030] Match case Unreachable Warning: /Users/wmazur/projects/sandbox/test.scala:30:17 ------------------------------------------------------------------------------------------------------------------
30 |            case v: ValidationCapture[a] => ??? // warn
   |                 ^^^^^^^^^^^^^^^^^^^^^^^
   |                 Unreachable case
-- [E030] Match case Unreachable Warning: /Users/wmazur/projects/sandbox/test.scala:31:17 ------------------------------------------------------------------------------------------------------------------
31 |            case t: TransformCapture     => ??? // warn
   |                 ^^^^^^^^^^^^^^^^^^^
   |                 Unreachable case
-- [E030] Match case Unreachable Warning: /Users/wmazur/projects/sandbox/test.scala:32:17 ------------------------------------------------------------------------------------------------------------------
32 |            case o: Optional[s, A]       => ??? // warn
   |                 ^^^^^^^^^^^^^^^^^
   |                 Unreachable case
-- [E030] Match case Unreachable Warning: /Users/wmazur/projects/sandbox/test.scala:33:17 ------------------------------------------------------------------------------------------------------------------
33 |            case StaticScopes            => ??? // warn
   |                 ^^^^^^^^^^^^
   |                 Unreachable case
No warnings can be incurred under -Werror (or -Xfatal-warnings)

Expectation

Should not warn about unreachable cases or being non-exhaustive

[ivan-klass]

@dwijnand A much simpler example that I think is very relevant

https://scastie.scala-lang.org/7iPISGKwTfOBxOKWIRIiaw

trait Figure

sealed trait Corners {
  self: Figure =>
}


enum Shape extends Figure:
  case Triange extends Shape with Corners
  case Square extends Shape with Corners
  case Circle extends Shape
  case Ellipsis extends Shape


def hasCorners(s: Shape): Boolean = s match
  case hasCorners: Corners => true // unreachable warning
  case _ => false

println(hasCorners(Shape.Circle))

[dwijnand]

That seems to be a different issue.

[ivan-klass]

@dwijnand thanks, I'll create a new issue then

[ivan-klass]

@dwijnand thanks, I'll create a new issue then

Reported #21860