-Wperformance lints *Ref boxing and nonlocal return

-Xlint:nonlocal-return is supported for compatibility.

src/compiler/scala/tools/nsc/settings/Warnings.scala

@@ -98,7 +98,7 @@ trait Warnings {
          |to prevent the shell from expanding patterns.""".stripMargin),
     prepend = true)
 
-  // Non-lint warnings. -- TODO turn into MultiChoiceEnumeration
+  // Non-lint warnings.
   val warnMacros           = ChoiceSetting(
     name    = "-Wmacros",
     helpArg = "mode",
@@ -117,6 +117,20 @@ trait Warnings {
   val warnNumericWiden     = BooleanSetting("-Wnumeric-widen", "Warn when numerics are widened.") withAbbreviation "-Ywarn-numeric-widen"
   val warnOctalLiteral     = BooleanSetting("-Woctal-literal", "Warn on obsolete octal syntax.") withAbbreviation "-Ywarn-octal-literal"
 
+  object PerformanceWarnings extends MultiChoiceEnumeration {
+    val Captured       = Choice("captured",        "Modification of var in closure causes boxing.")
+    val NonlocalReturn = Choice("nonlocal-return", "A return statement used an exception for flow control.")
+  }
+  val warnPerformance = MultiChoiceSetting(
+    name    = "-Wperformance",
+    helpArg = "warning",
+    descr   = "Enable or disable specific lints for performance",
+    domain  = PerformanceWarnings,
+    default = Some(List("_"))
+  )
+  def warnCaptured       = warnPerformance.contains(PerformanceWarnings.Captured)
+  def warnNonlocalReturn = warnPerformance.contains(PerformanceWarnings.NonlocalReturn)
+
   object UnusedWarnings extends MultiChoiceEnumeration {
     val Imports   = Choice("imports",   "Warn if an import selector is not referenced.")
     val PatVars   = Choice("patvars",   "Warn if a variable bound in a pattern is unused.")
@@ -215,7 +229,6 @@ trait Warnings {
   def warnStarsAlign             = lint contains StarsAlign
   def warnConstant               = lint contains Constant
   def lintUnused                 = lint contains Unused
-  def warnNonlocalReturn         = lint contains NonlocalReturn
   def lintImplicitNotFound       = lint contains ImplicitNotFound
   def warnSerialization          = lint contains Serial
   def lintValPatterns            = lint contains ValPattern
@@ -239,6 +252,8 @@ trait Warnings {
     if (s contains Unused) warnUnused.enable(UnusedWarnings.Linted)
     else warnUnused.disable(UnusedWarnings.Linted)
     if (s.contains(Deprecation) && deprecation.isDefault) deprecation.value = true
+    if (s.contains(NonlocalReturn)) warnPerformance.enable(PerformanceWarnings.NonlocalReturn)
+    else warnPerformance.disable(PerformanceWarnings.NonlocalReturn)
   }
 
   // Backward compatibility.

src/compiler/scala/tools/nsc/transform/LambdaLift.scala

@@ -505,6 +505,9 @@ abstract class LambdaLift extends InfoTransform {
               }
             }
 
+            if (settings.warnCaptured)
+              reporter.warning(tree.pos, s"Modification of variable $name within a closure causes it to be boxed.")
+
             treeCopy.ValDef(tree, mods, name, tpt1, factoryCall)
           } else tree
         case Return(Block(stats, value)) =>

test/files/neg/t10820-warn.scala

@@ -1,4 +1,4 @@
-// scalac: -Xfatal-warnings -Xlint:nonlocal-return
+// scalac: -Werror -Wperformance
 //
 
 import util.Try

test/files/neg/xlint-captured.check

@@ -0,0 +1,9 @@
+xlint-captured.scala:10: warning: return statement uses an exception to pass control to the caller of the enclosing named method f
+  def f(): Unit = List(42).foreach(i => if (i > 27) return)
+                                                    ^
+xlint-captured.scala:5: warning: Modification of variable c within a closure causes it to be boxed.
+    var c = a // nok
+        ^
+error: No warnings can be incurred under -Werror.
+2 warnings
+1 error

test/files/neg/xlint-captured.scala

@@ -0,0 +1,11 @@
+// scalac: -Werror -Wperformance
+object Test {
+  var a, b = 0 // ok
+  def mkStrangeCounter(): Int => Int = {
+    var c = a // nok
+    object _d { var d = b }; import _d._ // ok
+    e => { c += a; d += b; a *= b; b -= c; c ^ d }
+  }
+
+  def f(): Unit = List(42).foreach(i => if (i > 27) return)
+}

test/files/run/nonlocalreturn.scala

@@ -6,9 +6,7 @@ object Test {
     wrap({ return Some(1) ; None })
   }
 
-  def main(args: Array[String]): Unit = {
-    println(f())
-  }
+  def main(args: Array[String]): Unit = assert(f() == Some(1))
 }
 // java.lang.ClassCastException: scala.Some cannot be cast to scala.None$
 //  at Test$$anonfun$f$1.apply(nonlocalreturn.scala:5)

test/files/run/retclosure.scala

@@ -17,7 +17,5 @@ object Test {
     }
   }
 
-  def main(args: Array[String]): Unit = {
-    Console.println(response)
-  }
+  def main(args: Array[String]): Unit = assert(response == "check failed: some problem")
 }

test/files/run/spec-nlreturn.scala

@@ -1,17 +1,13 @@
 //scalac: -Xlint:-nonlocal-return
 object Test {
   def f(): Int = {
-    try {
-      val g = (1 to 10 map { i => return 16 ; i }).sum
-      g
-    }
-    catch { case x: runtime.NonLocalReturnControl[_] =>
-      println(x.getClass.getName)
-      x.value.asInstanceOf[Int]
+    try (1 to 10).map { i => return 16 ; i }.sum
+    catch {
+      case x: runtime.NonLocalReturnControl[_] =>
+        assert(x.getClass.getName == "scala.runtime.NonLocalReturnControl$mcI$sp")
+        x.value.asInstanceOf[Int]
     }
   }
 
-  def main(args: Array[String]): Unit = {
-    println(f())
-  }
+  def main(args: Array[String]): Unit = assert(f() == 16)
 }