Fix problem in unapply typing.

GADT bound resetting may only be applied when comparing
<pattern type> <: <expected type>, not when comparing the
other way around.

The fix revealed an error in a test case (t1048) which looks like a real error.
Therefore the test got moved to neg.

Conflicts:
	src/dotty/tools/dotc/typer/Applications.scala
	test/dotc/tests.scala
	tests/disabled/t1048.scala

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/neg/t1048.scala b/tests/neg/t1048.scala
new file mode 100644
index 000000000..4b8e78b4c
--- /dev/null
+++ b/tests/neg/t1048.scala
@@ -0,0 +1,21 @@
+trait T[U] {
+  def x: T[_ <: U]
+}
+
+object T {
+  def unapply[U](t: T[U]): Option[T[_ <: U]] = Some(t.x)
+}
+
+object Test {
+  def f[W](t: T[W]) = t match {
+    case T(T(_)) => ()
+// Gives:
+// t1048.scala:11: error: There is no best instantiation of pattern type T[Any']
+// that makes it a subtype of selector type T[_ <: W].
+// Non-variant type variable U cannot be uniquely instantiated.
+//     case T(T(_)) => ()
+//             ^
+// one error found
+  }
+}
+