Improved the error message for another of the m...

Improved the error message for another of the most common situations
I hear about in newbieland. It could be taken further. If compilation
fails due to an unimplemented abstract method, and there is a concrete
method of the same name and arity, it will do a pairwise analysis of the
parameters and attempt to further explain where you went off the beam if
it feels it can do so sensibly. Such as in the test case:

  % scalac S.scala
  S.scala:1: error: class S needs to be abstract, since method g in class J of type (y: Int,z: java.util.List)Int is not defined
  (Note that java.util.List does not match java.util.List[String]. To implement a raw type, use java.util.List[_])
  class S extends J {
        ^
  one error found

No review.

1 files changed, 14 insertions, 0 deletions

diff --git a/test/files/neg/abstract-class-2.scala b/test/files/neg/abstract-class-2.scala
new file mode 100644
index 0000000000..19f74f3da6
--- /dev/null
+++ b/test/files/neg/abstract-class-2.scala
@@ -0,0 +1,14 @@
+class P {
+  trait S1
+  val p = new P
+
+  trait S2 {
+    def f(x: p.S1): Int
+  }
+}
+
+class P2 extends P {
+  object O2 extends S2 {
+    def f(x: S1) = 5
+  }
+}