Improve unchecked warnings a lot.

Don't warn on "uncheckable" type patterns if they can be
statically guaranteed, regardless of their runtime checkability.
This covers patterns like Seq[Any] and lots more.

Review by @adriaanm.

2 files changed, 16 insertions, 0 deletions

diff --git a/test/files/pos/unchecked-a.flags b/test/files/pos/unchecked-a.flags
new file mode 100644
index 0000000000..779916d58f
--- /dev/null
+++ b/test/files/pos/unchecked-a.flags
@@ -0,0 +1 @@
+-unchecked -Xfatal-warnings
\ No newline at end of file
diff --git a/test/files/pos/unchecked-a.scala b/test/files/pos/unchecked-a.scala
new file mode 100644
index 0000000000..deceb91c36
--- /dev/null
+++ b/test/files/pos/unchecked-a.scala
@@ -0,0 +1,15 @@
+trait Y
+trait Z extends Y
+class X[+A <: Y]
+
+object Test {
+  def f1(x: X[_ <: Y]) = x match {
+    case _: X[Any] => // looks a little funny; `Any` is outside the bounds for `A`
+  }
+  def f2(x: X[_ <: Y]) = x match {
+    case _: X[Y]   => // looks better, let's allow this (too)
+  }
+
+  // NonLocalReturnControl[_] warnings
+  def foo: Int = List(0).foldLeft(0){case _ => return 0}
+}