SI-6258 Reject partial funs with undefined param types

This regressed with virtpatmat.

With -Xoldpatmat, pattern matching anonymous functions with
an expected type of PartialFunction[A, B] are translated to
a Function tree, and typed by typedFunction, which issues an
error of the parameter types are not fully defined.

This commit adds the same check to MatchFunTyper.

It doesn't plug the hole in RefChecks#validateVariance (which is
reminiscent of SI-3577.) Seems to me that in general one should handle:
  a) both BoundedWildcardType and WildcardType
     when in a place that can be called during inference, or
  b) neither otherwise

1 files changed, 16 insertions, 0 deletions

diff --git a/test/files/neg/t6258.check b/test/files/neg/t6258.check
new file mode 100644
index 0000000000..73363d8280
--- /dev/null
+++ b/test/files/neg/t6258.check
@@ -0,0 +1,16 @@
+t6258.scala:2: error: missing parameter type for expanded function
+The argument types of an anonymous function must be fully known. (SLS 8.5)
+Expected type was: PartialFunction[?, Int]
+	val f : PartialFunction[_, Int] = { case a : Int => a } // undefined param
+                                          ^
+t6258.scala:5: error: missing parameter type for expanded function
+The argument types of an anonymous function must be fully known. (SLS 8.5)
+Expected type was: PartialFunction[?,Int]
+	foo { case a : Int => a } // undefined param
+            ^
+t6258.scala:22: error: missing parameter type for expanded function
+The argument types of an anonymous function must be fully known. (SLS 8.5)
+Expected type was: PartialFunction[?,Any]
+  bar[M[Any]] (foo { // undefined param
+                   ^
+three errors found