Warn when Any or AnyVal is inferred.

For the very small price of annotating types as Any/AnyVal in those
cases where we wish to use them, we can obtain useful warnings.
I made trunk clean against this warning and found several bugs
or at least suboptimalities in the process.

I put the warning behind -Xlint for the moment, but I think this
belongs on by default, even for this alone:

  scala> List(1, 2, 3) contains "a"
  <console>:8: warning: a type was inferred to be `Any`; this may indicate a programming error.
                List(1, 2, 3) contains "a"
                                       ^
  res0: Boolean = false

Or this punishment meted out by SI-4042:

  scala> 1l to 5l contains 5
  <console>:8: warning: a type was inferred to be `AnyVal`; this may indicate a programming error.
                1l to 5l contains 5
                                  ^
  res0: Boolean = false

A different situation where this arises, which I have seen variations
of many times:

  scala> class A[T](default: T) {
    def get(x: => Option[T]) = x getOrElse Some(default)
  }
  <console>:7: warning: a type was inferred to be `Any`; this may indicate a programming error.
         class A[T](default: T) { def get(x: => Option[T]) = x getOrElse Some(default) }
                                                                             ^
  // Oops, this was what I meant
  scala> class A[T](default: T) {
    def get(x: => Option[T]) = x getOrElse default
  }
  defined class A

Harder to avoid spurious warnings when "Object" is inferred.

1 files changed, 3 insertions, 4 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/icode/ICodeCheckers.scala b/src/compiler/scala/tools/nsc/backend/icode/ICodeCheckers.scala
index 0d688d51f2..aa3f4dcb7e 100644
--- a/src/compiler/scala/tools/nsc/backend/icode/ICodeCheckers.scala
+++ b/src/compiler/scala/tools/nsc/backend/icode/ICodeCheckers.scala
@@ -381,10 +381,9 @@ abstract class ICodeCheckers {
       for (instr <- b) {
         this.instruction = instr
 
-        def checkLocal(local: Local): Unit = {
-          method lookupLocal local.sym.name getOrElse {
-            icodeError(" " + local + " is not defined in method " + method)
-          }
+        def checkLocal(local: Local) {
+          if ((method lookupLocal local.sym.name).isEmpty)
+            icodeError(s" $local is not defined in method $method")
         }
         def checkField(obj: TypeKind, field: Symbol): Unit = obj match {
           case REFERENCE(sym) =>