8 files changed, 69 insertions, 2 deletions

diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala
index fb493fabd8..546df8a207 100644
--- a/src/reflect/scala/reflect/internal/Types.scala
+++ b/src/reflect/scala/reflect/internal/Types.scala
@@ -391,8 +391,8 @@ trait Types extends api.Types { self: SymbolTable =>
      *  This is assessed to be the case if the class is final,
      *  and all type parameters (if any) are invariant.
      */
-    def isFinalType =
-      typeSymbol.isFinal && (typeSymbol.typeParams forall symbolIsNonVariant)
+    def isFinalType: Boolean =
+      typeSymbol.isFinal && (typeSymbol.typeParams forall symbolIsNonVariant) && prefix.isStable
 
     /** Is this type completed (i.e. not a lazy type)? */
     def isComplete: Boolean = true
diff --git a/test/files/neg/t7171.check b/test/files/neg/t7171.check
new file mode 100644
index 0000000000..8bdf08129b
--- /dev/null
+++ b/test/files/neg/t7171.check
@@ -0,0 +1,7 @@
+t7171.scala:2: error: The outer reference in this type test cannot be checked at run time.
+  final case class A()
+                   ^
+t7171.scala:9: error: The outer reference in this type test cannot be checked at run time.
+    case _: A => true; case _ => false
+          ^
+two errors found
diff --git a/test/files/neg/t7171.flags b/test/files/neg/t7171.flags
new file mode 100644
index 0000000000..464cc20ea6
--- /dev/null
+++ b/test/files/neg/t7171.flags
@@ -0,0 +1 @@
+-Xfatal-warnings -unchecked
\ No newline at end of file
diff --git a/test/files/neg/t7171.scala b/test/files/neg/t7171.scala
new file mode 100644
index 0000000000..534b2070a3
--- /dev/null
+++ b/test/files/neg/t7171.scala
@@ -0,0 +1,11 @@
+trait T {
+  final case class A()
+
+  // Was:
+  // error: scrutinee is incompatible with pattern type;
+  // found   : T.this.A
+  // required: T#A
+  def foo(a: T#A) = a match {
+    case _: A => true; case _ => false
+  }
+}
diff --git a/test/files/neg/t7171b.check b/test/files/neg/t7171b.check
new file mode 100644
index 0000000000..bd6b2bcfb4
--- /dev/null
+++ b/test/files/neg/t7171b.check
@@ -0,0 +1,10 @@
+t7171b.scala:2: error: The outer reference in this type test cannot be checked at run time.
+  final case class A()
+                   ^
+t7171b.scala:8: error: The outer reference in this type test cannot be checked at run time.
+    case _: A => true; case _ => false
+          ^
+t7171b.scala:13: error: The outer reference in this type test cannot be checked at run time.
+    case _: A => true; case _ => false
+          ^
+three errors found
diff --git a/test/files/neg/t7171b.flags b/test/files/neg/t7171b.flags
new file mode 100644
index 0000000000..464cc20ea6
--- /dev/null
+++ b/test/files/neg/t7171b.flags
@@ -0,0 +1 @@
+-Xfatal-warnings -unchecked
\ No newline at end of file
diff --git a/test/files/neg/t7171b.scala b/test/files/neg/t7171b.scala
new file mode 100644
index 0000000000..53c7787f8b
--- /dev/null
+++ b/test/files/neg/t7171b.scala
@@ -0,0 +1,15 @@
+trait T {
+  final case class A()
+}
+
+final class U extends T {
+  // this match should also not be deemed impossible
+  def foo(a: U#A) = a match {
+    case _: A => true; case _ => false
+  }
+
+  // this match should also not be deemed impossible
+  def bar(a: T#A) = a match {
+    case _: A => true; case _ => false
+  }
+}
diff --git a/test/files/run/t7171.scala b/test/files/run/t7171.scala
new file mode 100644
index 0000000000..97585b9860
--- /dev/null
+++ b/test/files/run/t7171.scala
@@ -0,0 +1,22 @@
+trait T {
+  final case class A()
+
+  // Was:
+  // error: scrutinee is incompatible with pattern type;
+  // found   : T.this.A
+  // required: T#A
+  def foo(a: T#A) = a match {
+    case _: A => true; case _ => false
+  }
+}
+
+object Test extends App {
+  val t1 = new T {}
+  val t2 = new T {}
+  val a1 = new t1.A()
+  val a2 = new t1.A()
+  assert(t1.foo(a1))
+  // as noted in the unchecked warning (tested in the corresponding neg test),
+  // the outer pointer isn't checked
+  assert(t1.foo(a2))
+}