Fix outer test in pattern matcher

Previous test did not reflect deeper paths for outer references. This caused
a -Ycheck:patMat failure for i1269.scala.

Author: odersky

src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -763,9 +763,8 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {thisTrans
 
         def outerTest(testedBinder: Symbol, expectedTp: Type): Tree = {
           val expectedOuter = expectedTp.normalizedPrefix match {
-            //case ThisType(clazz) => This(clazz)
             //case NoType          => Literal(Constant(true)) // fallback for SI-6183 todo?
-            case pre             => ref(pre.termSymbol)
+            case pre: SingletonType => singleton(pre)
           }
 
           // ExplicitOuter replaces `Select(q, outerSym) OBJ_EQ expectedPrefix` by `Select(q, outerAccessor(outerSym.owner)) OBJ_EQ expectedPrefix`

tests/pos/i1269.scala

@@ -0,0 +1,16 @@
+trait Module {
+  sealed abstract class Tree
+
+  case class LetL() extends Tree
+
+  object O {
+    case class LetR() extends Tree
+  }
+}
+
+class Patmat(val module: Module) {
+  def patmat(tree: module.Tree) = tree match {
+    case module.LetL() =>
+    case module.O.LetR() =>
+  }
+}