widen enum cases if not upper bound

Author: bishabosha

compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala

@@ -350,13 +350,24 @@ trait ConstraintHandling {
       val tpw = tp.widenSingletons
       if (tpw ne tp) && (tpw <:< bound) then tpw else tp
 
+    def widenEnum(tp: Type) =
+      val tpw = tp.widenEnumCase
+      if (tpw ne tp) && (tpw <:< bound) then tpw else tp
+
     def isSingleton(tp: Type): Boolean = tp match
       case WildcardType(optBounds) => optBounds.exists && isSingleton(optBounds.bounds.hi)
       case _ => isSubTypeWhenFrozen(tp, defn.SingletonType)
 
+    def isEnumCase(tp: Type): Boolean = tp match
+      case WildcardType(optBounds) => optBounds.exists && isEnumCase(optBounds.bounds.hi)
+      case _ => tp.classSymbol.isAllOf(EnumCase, butNot=JavaDefined)
+
     val wideInst =
       if isSingleton(bound) then inst
-      else dropSuperTraits(widenOr(widenSingle(inst)))
+      else
+        val lub   = widenOr(widenSingle(inst))
+        val asAdt = if isEnumCase(bound) then lub else widenEnum(lub)
+        dropSuperTraits(asAdt)
     wideInst match
       case wideInst: TypeRef if wideInst.symbol.is(Module) =>
         TermRef(wideInst.prefix, wideInst.symbol.sourceModule)

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1146,6 +1146,11 @@ object Types {
       case _ => this
     }
 
+    /** if this type is a reference to a class case of an enum, replace it by its first parent */
+    final def widenEnumCase(using Context): Type = this match
+      case tp: (TypeRef | AppliedType) if tp.classSymbol.isAllOf(EnumCase) => tp.parents.head
+      case _ => this
+
     /** Widen this type and if the result contains embedded union types, replace
      *  them by their joins.
      *  "Embedded" means: inside type lambdas, intersections or recursive types, or in prefixes of refined types.

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

@@ -1399,8 +1399,8 @@ object Scanners {
 
   object IndentWidth {
     private inline val MaxCached = 40
-    private val spaces = Array.tabulate(MaxCached + 1)(new Run(' ', _))
-    private val tabs = Array.tabulate(MaxCached + 1)(new Run('\t', _))
+    private val spaces = Array.tabulate[Run](MaxCached + 1)(new Run(' ', _)) // TODO: remove new after bootstrap
+    private val tabs = Array.tabulate[Run](MaxCached + 1)(new Run('\t', _)) // TODO: remove new after bootstrap
 
     def Run(ch: Char, n: Int): Run =
       if (n <= MaxCached && ch == ' ') spaces(n)