Fix regression in exhausitivity of HK types

Author: dwijnand

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -347,6 +347,9 @@ object SpaceEngine {
     case pat: Ident if isBackquoted(pat) =>
       Typ(pat.tpe, decomposed = false)
 
+    case pat: Ident if pat.name == nme.WILDCARD =>
+      Typ(erase(pat.tpe.stripAnnots.widenSkolem), decomposed = false)
+
     case Ident(_) | Select(_, _) =>
       Typ(erase(pat.tpe.stripAnnots.widenSkolem, isValue = true), decomposed = false)
 

tests/pos/i17230.min1.scala

@@ -0,0 +1,15 @@
+// scalac: -Werror
+trait Foo:
+  type Bar[_]
+
+object Foo:
+  type Aux[B[_]] = Foo { type Bar[A] = B[A] }
+
+class Test:
+  def t1[B[_]](self: Option[Foo.Aux[B]]) = self match
+    case Some(_) => 1
+    case None    => 2
+
+  def t2[B[_]](self: Option[Foo.Aux[B]]) = self match
+    case Some(f) => 1
+    case None    => 2

tests/pos/i17230.orig.scala

@@ -0,0 +1,20 @@
+// scalac: -Werror
+import scala.util.*
+
+trait Transaction {
+  type State[_]
+}
+object Transaction {
+  type of[S[_]] = Transaction { type State[A] = S[A] }
+}
+trait DynamicScope[State[_]]
+
+case class ScopeSearch[State[_]](self: Either[Transaction.of[State], DynamicScope[State]]) {
+
+  def embedTransaction[T](f: Transaction.of[State] => T): T =
+    self match {
+      case Left(integrated) => ???
+      case Right(ds)        => ???
+    }
+}
+