Add flag to disable withFilter pattern desugaring

bincompat-forward.whitelist.conf

@@ -389,6 +389,10 @@ filter {
     {
         matchName="scala.collection.immutable.Stream.scala$collection$immutable$Stream$$loop$2"
         problemName=MissingMethodProblem
+    },
+    {
+        matchName="scala.reflect.runtime.Settings.ZirrefutableGeneratorPatterns"
+        problemName=MissingMethodProblem
     }
   ]
 }

src/compiler/scala/tools/nsc/CompilerCommand.scala

@@ -82,6 +82,7 @@ class CompilerCommand(arguments: List[String], val settings: Settings) {
   def usageMsg    = createUsageMsg("where possible standard", shouldExplain = false, _.isStandard)
   def xusageMsg   = createUsageMsg("Possible advanced", shouldExplain = true, _.isAdvanced)
   def yusageMsg   = createUsageMsg("Possible private", shouldExplain = true, _.isPrivate)
+  def zusageMsg   = createUsageMsg("Possible Typelevel", shouldExplain = true, _.isTypelevel)
 
   /** For info settings, compiler should just print a message and quit. */
   def shouldStopWithInfo = settings.isInfo
@@ -95,6 +96,7 @@ class CompilerCommand(arguments: List[String], val settings: Settings) {
     else if (help)          usageMsg + global.pluginOptionsHelp
     else if (Xhelp)         xusageMsg
     else if (Yhelp)         yusageMsg
+    else if (Zhelp)         zusageMsg
     else if (showPlugins)   global.pluginDescriptions
     else if (showPhases)    global.phaseDescriptions + (
       if (debug) "\n" + global.phaseFlagDescriptions else ""

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

@@ -109,6 +109,7 @@ trait AbsSettings extends scala.reflect.internal.settings.AbsSettings {
      */
     def isAdvanced   = name match { case "-Y" => true ; case "-X" => false ; case _  => name startsWith "-X" }
     def isPrivate    = name match { case "-Y" => false ; case _  => name startsWith "-Y" }
+    def isTypelevel  = name match { case "-Z" => false ; case _  => name startsWith "-Z" }
     def isStandard   = !isAdvanced && !isPrivate
     def isForDebug   = name endsWith "-debug" // by convention, i.e. -Ytyper-debug
     def isDeprecated = deprecationMessage.isDefined

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

@@ -42,7 +42,7 @@ trait ScalaSettings extends AbsScalaSettings
   def optimiseSettings = List[BooleanSetting](inline, inlineHandlers, Xcloselim, Xdce, YconstOptimization)
 
   /** If any of these settings is enabled, the compiler should print a message and exit.  */
-  def infoSettings = List[Setting](version, help, Xhelp, Yhelp, showPlugins, showPhases, genPhaseGraph)
+  def infoSettings = List[Setting](version, help, Xhelp, Yhelp, Zhelp, showPlugins, showPhases, genPhaseGraph)
 
   /** Any -multichoice:help? Nicer if any option could report that it had help to offer. */
   private def multihelp = allSettings exists { case s: MultiChoiceSetting[_] => s.isHelping case _ => false }
@@ -237,6 +237,12 @@ trait ScalaSettings extends AbsScalaSettings
 
   private def removalIn212 = "This flag is scheduled for removal in 2.12. If you have a case where you need this flag then please report a bug."
 
+  /**
+   * -Z Typelevel settings
+   */
+  val Zhelp                         = BooleanSetting("-Z", "Print a synopsis of Typelevel options.")
+  val ZirrefutableGeneratorPatterns = BooleanSetting("-Zirrefutable-generator-patterns", "Treat patterns in for comprehensions as irrefutable. Do not add filter or withFilter calls.")
+
   object YstatisticsPhases extends MultiChoiceEnumeration { val parser, typer, patmat, erasure, cleanup, jvm = Value }
   val Ystatistics = {
     val description = "Print compiler statistics for specific phases"

src/reflect/scala/reflect/internal/TreeGen.scala

@@ -622,7 +622,7 @@ abstract class TreeGen {
             body) setPos splitpos
         case None =>
           atPos(splitpos) {
-            mkVisitor(List(CaseDef(pat, EmptyTree, body)), checkExhaustive = false)
+            mkVisitor(List(CaseDef(pat, EmptyTree, body)), checkExhaustive = settings.ZirrefutableGeneratorPatterns)
           }
       }
     }
@@ -768,7 +768,7 @@ abstract class TreeGen {
   }
 
   def mkCheckIfRefutable(pat: Tree, rhs: Tree)(implicit fresh: FreshNameCreator) =
-    if (treeInfo.isVarPatternDeep(pat)) rhs
+    if (treeInfo.isVarPatternDeep(pat) || settings.ZirrefutableGeneratorPatterns) rhs
     else {
       val cases = List(
         CaseDef(pat.duplicate, EmptyTree, Literal(Constant(true))),

src/reflect/scala/reflect/internal/settings/MutableSettings.scala

@@ -55,6 +55,8 @@ abstract class MutableSettings extends AbsSettings {
   def maxClassfileName: IntSetting
 
   def isScala211: Boolean
+
+  def ZirrefutableGeneratorPatterns: BooleanSetting
 }
 
 object MutableSettings {

src/reflect/scala/reflect/runtime/Settings.scala

@@ -51,4 +51,6 @@ private[reflect] class Settings extends MutableSettings {
   val Yrecursion        = new IntSetting(0)
   val maxClassfileName  = new IntSetting(255)
   def isScala211        = true
+
+  def ZirrefutableGeneratorPatterns = new BooleanSetting(false)
 }

test/files/pos/Zirrefutable-generator-patterns.flags

@@ -0,0 +1 @@
+-Zirrefutable-generator-patterns

test/files/pos/Zirrefutable-generator-patterns.scala

@@ -0,0 +1,11 @@
+case class Foo[A](a: A) {
+  def map[B](f: A => B): Foo[B] = Foo(f(a))
+  def flatMap[B](f: A => Foo[B]): Foo[B] = Foo(f(a).a)
+}
+
+object Test {
+  for {
+    (a, b) <- Foo((1, 'd'))
+    (c, d, e) <- Foo((1, true, "three"))
+  } yield (a + c, e :+ b, !d)
+}