REPL bells and whistles: -Dscala.repl.vids=<Boolean>

Displays identity hashcodes next to `res` values printed by REPL.
This proved quite useful in detecting reflection artifacts that look the same,
but are, in fact, different.

src/compiler/scala/tools/nsc/interpreter/MemberHandlers.scala

@@ -115,7 +115,11 @@ trait MemberHandlers {
           if (mods.isLazy) codegenln(false, "<lazy>")
           else any2stringOf(req fullPath name, maxStringElements)
 
-        """ + "%s: %s = " + %s""".format(prettyName, string2code(req typeOf name), resultString)
+        val vidString =
+          if (replProps.vids) """" + " @ " + "%%8x".format(System.identityHashCode(%s)) + " """.trim.format(req fullPath name)
+          else ""
+
+        """ + "%s%s: %s = " + %s""".format(prettyName, vidString, string2code(req typeOf name), resultString)
       }
     }
   }

src/compiler/scala/tools/nsc/interpreter/ReplProps.scala

@@ -23,4 +23,6 @@ class ReplProps {
   val replAutorunCode = Prop[JFile]("scala.repl.autoruncode")
   val powerInitCode   = Prop[JFile]("scala.repl.power.initcode")
   val powerBanner     = Prop[JFile]("scala.repl.power.banner")
+
+  val vids = bool("scala.repl.vids")
 }