Fix constraining against HKTypeLambda arguments

Author: dwijnand

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
             }

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