Drop NotNull class and associated code.

Author: odersky

src/dotty/tools/dotc/TypeErasure.scala

@@ -374,7 +374,7 @@ class TypeErasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wild
 
   private def normalizeClass(cls: ClassSymbol)(implicit ctx: Context): ClassSymbol = {
     if (cls.owner == defn.ScalaPackageClass) {
-      if (cls == defn.AnyClass || cls == defn.AnyValClass || cls == defn.SingletonClass || cls == defn.NotNullClass)
+      if (cls == defn.AnyClass || cls == defn.AnyValClass || cls == defn.SingletonClass)
         return defn.ObjectClass
       if (cls == defn.UnitClass)
         return defn.BoxedUnitClass

src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -140,7 +140,6 @@ class ScalaSettings extends Settings.SettingGroup {
   val Ybuilderdebug = ChoiceSetting("-Ybuilder-debug", "manager", "Compile using the specified build manager.", List("none", "refined", "simple"), "none")
   val Yreifycopypaste = BooleanSetting("-Yreify-copypaste", "Dump the reified trees in copypasteable representation.")
   val Yreplsync = BooleanSetting("-Yrepl-sync", "Do not use asynchronous code for repl startup")
-  val Ynotnull = BooleanSetting("-Ynotnull", "Enable (experimental and incomplete) scala.NotNull.")
   val YmethodInfer = BooleanSetting("-Yinfer-argument-types", "Infer types for arguments of overriden methods.")
   val etaExpandKeepsStar = BooleanSetting("-Yeta-expand-keeps-star", "Eta-expand varargs methods to T* rather than Seq[T].  This is a temporary option to ease transition.")
   val Yinvalidate = StringSetting("-Yinvalidate", "classpath-entry", "Invalidate classpath entry before run", "")

src/dotty/tools/dotc/core/Definitions.scala

@@ -177,8 +177,6 @@ class Definitions {
       RootClass, nme.dummyApply, 1,
       pt => MethodType(List(FunctionType(Nil, PolyParam(pt, 0))), PolyParam(pt, 0)))
 
-  lazy val NotNullClass = ctx.requiredClass("scala.NotNull")
-
   lazy val NothingClass: ClassSymbol = newCompleteClassSymbol(
     ScalaPackageClass, tpnme.Nothing, AbstractFinal, List(AnyClass.typeRef))
   lazy val NullClass: ClassSymbol = newCompleteClassSymbol(
@@ -348,7 +346,6 @@ class Definitions {
   def AnyValType: Type = AnyValClass.typeRef
   def ObjectType: Type = ObjectClass.typeRef
   def AnyRefType: Type = AnyRefAlias.typeRef
-  def NotNullType: Type = NotNullClass.typeRef
   def NothingType: Type = NothingClass.typeRef
   def NullType: Type = NullClass.typeRef
   def SeqType: Type = SeqClass.typeRef

src/dotty/tools/dotc/core/TypeComparer.scala

@@ -648,8 +648,7 @@ class TypeComparer(initctx: Context) extends DotClass {
           if (cls2.isClass) {
             val base = tp1.baseTypeRef(cls2)
             if (base.exists && (base ne tp1)) return isSubType(base, tp2)
-            if ( cls2 == defn.SingletonClass && tp1.isStable
-               || cls2 == defn.NotNullClass && tp1.isNotNull) return true
+            if (cls2 == defn.SingletonClass && tp1.isStable) return true
           }
           tryRebase3rd
       }