Fix #5495: Reject invalid modifiers on enums

Fixes #5034

Author: allanrenucci

compiler/src/dotty/tools/dotc/ast/DesugarEnums.scala

@@ -69,8 +69,8 @@ object DesugarEnums {
 
   /** Add implied flags to an enum class or an enum case */
   def addEnumFlags(cdef: TypeDef)(implicit ctx: Context): TypeDef =
-    if (cdef.mods.isEnumClass) cdef.withMods(cdef.mods.withFlags(cdef.mods.flags | Abstract | Sealed))
-    else if (isEnumCase(cdef)) cdef.withMods(cdef.mods.withFlags(cdef.mods.flags | Final))
+    if (cdef.mods.isEnumClass) cdef.withMods(cdef.mods.toTypeFlags | Abstract | Sealed)
+    else if (isEnumCase(cdef)) cdef.withMods(cdef.mods | Final)
     else cdef
 
   private def valuesDot(name: String) = Select(Ident(nme.DOLLAR_VALUES), name.toTermName)

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2388,17 +2388,25 @@ object Parsers {
     /**  EnumDef ::=  id ClassConstr [`extends' [ConstrApps]] EnumBody
      */
     def enumDef(start: Offset, mods: Modifiers, enumMod: Mod): TypeDef = atPos(start, nameStart) {
+      val InvalidEnumClassModifiers = ModifierFlags &~ (Private | Protected)
+      if (mods.is(InvalidEnumClassModifiers))
+        syntaxError("Only access modifiers are allowed on enum definitions", mods.pos)
+
+      val mods1 = addMod(mods, enumMod) &~ InvalidEnumClassModifiers
       val modName = ident()
       val clsName = modName.toTypeName
       val constr = classConstr(clsName)
       val impl = templateOpt(constr, isEnum = true)
-      TypeDef(clsName, impl).withMods(addMod(mods, enumMod)).setComment(in.getDocComment(start))
+      TypeDef(clsName, impl).withMods(mods1).setComment(in.getDocComment(start))
     }
 
     /** EnumCase = `case' (id ClassConstr [`extends' ConstrApps] | ids)
      */
     def enumCase(start: Offset, mods: Modifiers): DefTree = {
-      val mods1 = addMod(mods, atPos(in.offset)(Mod.Enum())) | Case
+      if (mods.is(ModifierFlags))
+        syntaxError("No modifier are allowed on enum cases", mods.pos)
+
+      val mods1 = addMod(mods, atPos(in.offset)(Mod.Enum())) &~ ModifierFlags | Case
       accept(CASE)
 
       in.adjustSepRegions(ARROW)

tests/neg/i5495.scala

@@ -0,0 +1,31 @@
+abstract enum Foo1 {} // error: only access modifiers allowed
+final    enum Foo2 {} // error: only access modifiers allowed
+sealed   enum Foo3 {} // error: only access modifiers allowed
+implicit enum Foo4 {} // error: only access modifiers allowed
+lazy     enum Foo5 {} // error: only access modifiers allowed
+erased   enum Foo6 {} // error: only access modifiers allowed
+override enum Foo7 {} // error: only access modifiers allowed
+
+enum Foo7 {
+  abstract  case C1() // error: no modifier allowed
+  final     case C2() // error: no modifier allowed
+  sealed    case C3() // error: no modifier allowed
+  implicit  case C4() // error: no modifier allowed
+  lazy      case C5() // error: no modifier allowed
+  erased    case C6() // error: no modifier allowed
+  override  case C7() // error: no modifier allowed
+  private   case C8() // error: no modifier allowed
+  protected case C9() // error: no modifier allowed
+}
+
+enum Foo8 {
+  abstract  case C1 // error: no modifier allowed
+  final     case C2 // error: no modifier allowed
+  sealed    case C3 // error: no modifier allowed
+  implicit  case C4 // error: no modifier allowed
+  lazy      case C5 // error: no modifier allowed
+  erased    case C6 // error: no modifier allowed
+  override  case C7 // error: no modifier allowed
+  private   case C8 // error: no modifier allowed
+  protected case C9 // error: no modifier allowed
+}

tests/pos/i2906.scala

@@ -1,6 +1,5 @@
 enum Foo {
   case A
-  private case B
-  @deprecated("Will be removed") case C
-  @deprecated("Will be removed") private case D
+  @deprecated("Will be removed") case B
+  @deprecated("Will be removed") @volatile case C
 }