From b6987cccbd84ddb53de4b7616be8bbec31d187ac Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Sat, 16 Jul 2022 16:38:19 +0100
Subject: [PATCH] Fix constraining against HKTypeLambda arguments

---
 .../dotty/tools/dotc/core/PatternTypeConstrainer.scala |  5 +++--
 tests/pos/i15677.scala                                 | 10 ++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)
 create mode 100644 tests/pos/i15677.scala

diff --git a/compiler/src/dotty/tools/dotc/core/PatternTypeConstrainer.scala b/compiler/src/dotty/tools/dotc/core/PatternTypeConstrainer.scala
index 5cd8d4f50eeb..c5f126580df5 100644
--- a/compiler/src/dotty/tools/dotc/core/PatternTypeConstrainer.scala
+++ b/compiler/src/dotty/tools/dotc/core/PatternTypeConstrainer.scala
@@ -275,9 +275,10 @@ trait PatternTypeConstrainer { self: TypeComparer =>
                 argP.typeSymbol.isPatternBound && patternTp.classSymbol == scrutineeTp.classSymbol
               then
                 val TypeBounds(loS, hiS) = argS.bounds
+                val TypeBounds(loP, hiP) = argP.bounds
                 var res = true
-                if variance <  1 then res &&= isSubType(loS, argP)
-                if variance > -1 then res &&= isSubType(argP, hiS)
+                if variance <  1 then res &&= isSubType(loS, hiP)
+                if variance > -1 then res &&= isSubType(loP, hiS)
                 res
               else true
             }
diff --git a/tests/pos/i15677.scala b/tests/pos/i15677.scala
new file mode 100644
index 000000000000..2ad2b5283057
--- /dev/null
+++ b/tests/pos/i15677.scala
@@ -0,0 +1,10 @@
+class Inv[A]
+
+class Foo[B, M[_]]
+
+class Bar[C, N[_]] extends Foo[C, N]:
+  def inv: Inv[C] = null
+
+def test(foo: Foo[Int, Option]): Inv[Int] = foo match
+  case bar: Bar[_, _] => bar.inv
+  case _              => null