Fixed various issues with -Ywarn-dead-code.

enjoy fewer spurious warnings. Closes #1681, no review.

4 files changed, 48 insertions, 3 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 8ce26c92a1..0f87d6ba33 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -1791,7 +1791,7 @@ trait Typers { self: Analyzer =>
       if (meth.isPrimaryConstructor && meth.isClassConstructor &&
           phase.id <= currentRun.typerPhase.id && !reporter.hasErrors)
         computeParamAliases(meth.owner, vparamss1, rhs1)
-      if (tpt1.tpe.typeSymbol != NothingClass && !context.returnsSeen) rhs1 = checkDead(rhs1)
+      if (tpt1.tpe.typeSymbol != NothingClass && !context.returnsSeen && rhs1.tpe.typeSymbol != NothingClass) rhs1 = checkDead(rhs1)
 
       if (phase.id <= currentRun.typerPhase.id && meth.owner.isClass &&
           meth.paramss.exists(ps => ps.exists(_.hasDefaultFlag) && isRepeatedParamType(ps.last.tpe)))
@@ -2205,8 +2205,11 @@ trait Typers { self: Analyzer =>
       else checkNoDoubleDefsAndAddSynthetics(result)
     }
 
-    def typedArg(arg: Tree, mode: Int, newmode: Int, pt: Type): Tree =
-      checkDead(constrTyperIf((mode & SCCmode) != 0).typed(arg, mode & stickyModes | newmode, pt))
+    def typedArg(arg: Tree, mode: Int, newmode: Int, pt: Type): Tree = {
+      val t = constrTyperIf((mode & SCCmode) != 0).typed(arg, mode & stickyModes | newmode, pt)
+      if ((newmode & BYVALmode) != 0) t
+      else checkDead(t)
+    }
 
     def typedArgs(args: List[Tree], mode: Int) =
       args mapConserve (arg => typedArg(arg, mode, 0, WildcardType))
diff --git a/test/files/neg/check-dead.check b/test/files/neg/check-dead.check
new file mode 100644
index 0000000000..be4de3060b
--- /dev/null
+++ b/test/files/neg/check-dead.check
@@ -0,0 +1,7 @@
+check-dead.scala:27: error: dead code following this construct
+    throw new Exception
+    ^
+check-dead.scala:31: error: dead code following this construct
+    throw new Exception
+    ^
+two errors found
diff --git a/test/files/neg/check-dead.flags b/test/files/neg/check-dead.flags
new file mode 100644
index 0000000000..c7d406c649
--- /dev/null
+++ b/test/files/neg/check-dead.flags
@@ -0,0 +1 @@
+-Ywarn-dead-code -Xfatal-warnings
\ No newline at end of file
diff --git a/test/files/neg/check-dead.scala b/test/files/neg/check-dead.scala
new file mode 100644
index 0000000000..851e81d886
--- /dev/null
+++ b/test/files/neg/check-dead.scala
@@ -0,0 +1,34 @@
+package dummy
+
+object Error {
+    def soSorry(msg: String = "sorry"): Nothing =
+        throw new Exception("we have a problem: "+msg)
+}
+
+class NoDeads {
+    def x = synchronized { throw new Exception }
+    def y[T](arg: T) = println("foo")
+    def z = this.y(throw new Exception)
+
+    def dummy1: Int = synchronized {
+        val i = 10 + 2
+        return i
+    }
+    def dummy1b: Int = synchronized {
+        val i = 10 + 2
+        i
+    }
+
+    def dummy2: String = Error.soSorry("we're dummies")
+}
+
+class Deads {
+  def x1 = synchronized {
+    throw new Exception
+    5 * 5
+  }
+  def x2: Int = synchronized {
+    throw new Exception
+    return 5
+  }
+}
\ No newline at end of file