From 30731c12edc064da0e7980d775554d7caaaa685f Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Thu, 27 Jul 2023 13:13:38 +0100
Subject: [PATCH] Fix regression in exhausitivity of HK types

---
 .../tools/dotc/transform/patmat/Space.scala   |  3 +++
 tests/pos/i17230.min1.scala                   | 15 ++++++++++++++
 tests/pos/i17230.orig.scala                   | 20 +++++++++++++++++++
 3 files changed, 38 insertions(+)
 create mode 100644 tests/pos/i17230.min1.scala
 create mode 100644 tests/pos/i17230.orig.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
index 45c1444879db..1590bd77e991 100644
--- a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
+++ b/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)
 
diff --git a/tests/pos/i17230.min1.scala b/tests/pos/i17230.min1.scala
new file mode 100644
index 000000000000..e2df63e168c1
--- /dev/null
+++ b/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
diff --git a/tests/pos/i17230.orig.scala b/tests/pos/i17230.orig.scala
new file mode 100644
index 000000000000..d72a0082a116
--- /dev/null
+++ b/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)        => ???
+    }
+}
+