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.

5 files changed, 32 insertions, 0 deletions

diff --git a/test/files/neg/abstract-class-2.check b/test/files/neg/abstract-class-2.check
new file mode 100644
index 0000000000..ca79dd8293
--- /dev/null
+++ b/test/files/neg/abstract-class-2.check
@@ -0,0 +1,5 @@
+abstract-class-2.scala:11: error: object creation impossible, since method f in trait S2 of type (x: P2.this.p.S1)Int is not defined
+(Note that P.this.p.S1 does not match P2.this.S1: their prefixes (i.e. enclosing instances) differ)
+  object O2 extends S2 {
+         ^
+one error found
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
+  }
+}
diff --git a/test/files/neg/abstract-class-error.check b/test/files/neg/abstract-class-error.check
new file mode 100644
index 0000000000..b8a0c6e70b
--- /dev/null
+++ b/test/files/neg/abstract-class-error.check
@@ -0,0 +1,5 @@
+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
diff --git a/test/files/neg/abstract-class-error/J.java b/test/files/neg/abstract-class-error/J.java
new file mode 100644
index 0000000000..5877f5cc5b
--- /dev/null
+++ b/test/files/neg/abstract-class-error/J.java
@@ -0,0 +1,4 @@
+public abstract class J {
+  public abstract int f();
+  public abstract int g(int y, java.util.List z);
+}
\ No newline at end of file
diff --git a/test/files/neg/abstract-class-error/S.scala b/test/files/neg/abstract-class-error/S.scala
new file mode 100644
index 0000000000..67f6d8593e
--- /dev/null
+++ b/test/files/neg/abstract-class-error/S.scala
@@ -0,0 +1,4 @@
+class S extends J {
+  def f() = 55
+  def g(y: Int, z: java.util.List[String]) = 11
+}