SI-5900 Fix pattern inference regression

This commit does not close SI-5900. It only addresses a regression
in 2.11 prereleases caused by SI-7886.

The fix for SI-7886 was incomplete (as shown by the last commit)
and incorrect (as shown by the regression in pos/t5900a.scala and
the fact it ended up inferring type parameters.)

I believe that the key to fixing this problem will be unifying
the inference of case class constructor patterns and extractor
patterns.

I've explored that idea:

  https://gist.github.com/retronym/7704153
  https://github.com/retronym/scala/compare/ticket/5900

But didn't quite get there.

1 files changed, 22 insertions, 0 deletions

diff --git a/test/pending/neg/t7886.scala b/test/pending/neg/t7886.scala
new file mode 100644
index 0000000000..55d80a0a43
--- /dev/null
+++ b/test/pending/neg/t7886.scala
@@ -0,0 +1,22 @@
+trait Covariant[+A]
+trait Contra[-A] { def accept(p: A): Unit }
+trait Invariant[A] extends Covariant[A] with Contra[A]
+
+case class Unravel[A](m: Contra[A], msg: A)
+
+object Test extends Covariant[Any] {
+  def g(m: Contra[Any]): Unit = m accept 5
+  def f(x: Any): Unit = x match {
+    case Unravel(m, msg) => g(m)
+    case _               =>
+  }
+  def main(args: Array[String]) {
+    f(Unravel[String](new Contra[String] { def accept(x: String) = x.length }, ""))
+  }
+}
+// java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String
+//   at Test$$anon$1.accept(a.scala:18)
+//   at Test$.g(a.scala:13)
+//   at Test$.f(a.scala:15)
+//   at Test$.main(a.scala:18)
+//   at Test.main(a.scala)