added option -Xwarndeadcode

3 files changed, 17 insertions, 6 deletions

diff --git a/src/compiler/scala/tools/nsc/CompilationUnits.scala b/src/compiler/scala/tools/nsc/CompilationUnits.scala
index ad49327574..e76f95d207 100644
--- a/src/compiler/scala/tools/nsc/CompilationUnits.scala
+++ b/src/compiler/scala/tools/nsc/CompilationUnits.scala
@@ -40,14 +40,18 @@ trait CompilationUnits requires Global {
         reporter.error(position(pos), msg)
       }
 
-    def warning(pos: int, msg: String) = reporter.warning(position(pos), msg)
+    def warning(pos: int, msg: String) =
+      if (!(errorPositions contains pos)) {
+        errorPositions += pos
+        reporter.warning(position(pos), msg)
+      }
 
     def deprecationWarning(pos: int, msg: String) =
-      if (settings.deprecation.value) reporter.warning(position(pos), msg)
+      if (settings.deprecation.value) warning(pos, msg)
       else currentRun.deprecationWarnings = true
 
     def uncheckedWarning(pos: int, msg: String) =
-      if (settings.unchecked.value) reporter.warning(position(pos), msg)
+      if (settings.unchecked.value) warning(pos, msg)
       else currentRun.uncheckedWarnings = true
 
     def incompleteInputError(pos:int, msg:String) =
diff --git a/src/compiler/scala/tools/nsc/Settings.scala b/src/compiler/scala/tools/nsc/Settings.scala
index ade73ab2bc..ee02445fc6 100644
--- a/src/compiler/scala/tools/nsc/Settings.scala
+++ b/src/compiler/scala/tools/nsc/Settings.scala
@@ -122,6 +122,7 @@ class Settings(error: String => unit) {
   val inline        = BooleanSetting("-Xinline", "Perform inlining when possible")
   val Xcloselim     = BooleanSetting("-Xcloselim", "Perform closure elimination")
   val Xdce          = BooleanSetting("-Xdce", "Perform dead code elimination")
+  val Xwarndeadcode = BooleanSetting("-Xwarndeadcode", "Emit warnings for dead code")
   val XbytecodeRead = BooleanSetting("-XbytecodeRead", "Enable bytecode reader.")
   val Xdetach       = BooleanSetting("-Xdetach", "Perform detaching of remote closures")
   val Xshowcls      = StringSetting ("-Xshowcls", "class", "Show class info", "")
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 5962ef7d99..28431bf328 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -625,6 +625,9 @@ trait Typers requires Analyzer {
         } else if (!context.undetparams.isEmpty && (mode & POLYmode) == 0) { // (9)
           instantiate(tree, mode, pt)
         } else if (tree.tpe <:< pt) {
+          if (settings.Xwarndeadcode.value &&
+              tree.tpe.symbol == AllClass && pt != WildcardType && pt.symbol != AllClass)
+            context.unit.warning (tree.pos, "dead code")
           tree
         } else {
           if ((mode & PATTERNmode) != 0) {
@@ -652,8 +655,8 @@ trait Typers requires Analyzer {
                 // (13); the condition prevents chains of views
                 if (settings.debug.value) log("inferring view from "+tree.tpe+" to "+pt)
                 val coercion = inferView(tree.pos, tree.tpe, pt, true)
-               // convert forward views of delegate types into closures wrapped around
-               // the delegate's apply method (the "Invoke" method, which was translated into apply)
+                // convert forward views of delegate types into closures wrapped around
+                // the delegate's apply method (the "Invoke" method, which was translated into apply)
                 if (forMSIL && coercion != null && isCorrespondingDelegate(tree.tpe, pt)) {
                   val meth: Symbol = tree.tpe.member(nme.apply)
                   if(settings.debug.value)
@@ -1336,7 +1339,10 @@ trait Typers requires Analyzer {
           case _ =>
             val localTyper = if (inBlock || (stat.isDef && !stat.isInstanceOf[LabelDef])) this
                              else newTyper(context.make(stat, exprOwner))
-            localTyper.typed(stat)
+            val stat1 = localTyper.typed(stat)
+            if (settings.Xwarndeadcode.value && stat1.tpe.symbol == AllClass)
+              context.unit.warning(stat1.pos, "dead code")
+            stat1
         }
       }
       def accesses(accessor: Symbol, accessed: Symbol) =