Better pattern matcher error message.

For the common case when someone hasn't quite grokked
the significance of lower case in a pattern match.  I'd
like to make all the unreachables errors, not warnings,
but there may be a bug or two to clear out first.

class A {
  def badEquals(x: Any, y: Any) = x match {
    case y => true
    case _ => false
  }
}

a.scala:3: warning: patterns after a variable pattern cannot match (SLS 8.1.1)
If you intended to match against parameter y of method badEquals, you must use backticks, like: case `y` =>
    case y => true
         ^
a.scala:4: warning: unreachable code due to variable pattern 'y' on line 3
    case _ => false
              ^
two warnings found

1 files changed, 7 insertions, 1 deletions

diff --git a/test/files/neg/pat_unreachable.scala b/test/files/neg/pat_unreachable.scala
index fc0fd41920..1f402e5212 100644
--- a/test/files/neg/pat_unreachable.scala
+++ b/test/files/neg/pat_unreachable.scala
@@ -8,7 +8,7 @@ object Test extends App {
     case Seq(x, y, _*) => x::y::Nil
     case Seq(x, y) => List(x, y)
   }
-  
+
   def not_unreachable(xs:Seq[Char]) = xs match {
     case Seq(x, y, _*) => x::y::Nil
     case Seq(x) => List(x)
@@ -17,4 +17,10 @@ object Test extends App {
     case Seq(x, y) => x::y::Nil
     case Seq(x, y, z, _*) => List(x,y)
   }
+
+  def contrivedExample[A, B, C](a: A, b: B, c: C): Unit = a match {
+    case b => println("matched b")
+    case c => println("matched c")
+    case _ => println("matched neither")
+  }
 }