Parse 'case _' as 'Ident(_)'

Author: OlivierBlanvillain

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

@@ -4740,14 +4740,6 @@ object Types {
   object MatchType {
     def apply(bound: Type, scrutinee: Type, cases: List[Type])(using Context): MatchType =
       unique(new CachedMatchType(bound, scrutinee, cases))
-
-    /** Extractor for `case _ =>` match type patterns */
-    object WildcardPattern {
-      def unapply(tp: Type)(using Context): Option[Type] = tp match {
-        case HKTypeLambda(LambdaParam(tl1, 0) :: Nil, defn.MatchCase(TypeParamRef(tl2, 0), bodyTp)) => Some(bodyTp)
-        case _ => None
-      }
-    }
   }
 
   // ------ ClassInfo, Type Bounds --------------------------------------------------

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

@@ -2615,8 +2615,7 @@ object Parsers {
         in.token match {
           case USCORE if in.lookahead.isArrow =>
             val start = in.skipToken()
-            typeBounds().withSpan(Span(start, in.lastOffset, start))
-
+            Ident(tpnme.WILDCARD).withSpan(Span(start, in.lastOffset, start))
           case _ =>
             infixType()
         }

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -466,6 +466,8 @@ class Typer extends Namer
     if ctx.mode.is(Mode.Pattern) then
       if name == nme.WILDCARD then
         return tree.withType(pt)
+      if name == tpnme.WILDCARD then
+        return tree.withType(defn.AnyType)
       if untpd.isVarPattern(tree) && name.isTermName then
         return typed(desugar.patternVar(tree), pt)
     else if ctx.mode.is(Mode.QuotedPattern) then
@@ -1519,13 +1521,11 @@ class Typer extends Namer
                 val Typed(_, tpt) = tpd.unbind(tpd.unsplice(pat1))
                 instantiateMatchTypeProto(pat1, pt) match {
                   case defn.MatchCase(patternTp, _) => tpt.tpe frozen_=:= patternTp
-                  case MatchType.WildcardPattern(_) => tpt.tpe frozen_=:= defn.AnyType
                   case _ => false
                 }
               case (id @ Ident(nme.WILDCARD), pt) =>
                 pt match {
                   case defn.MatchCase(patternTp, _) => defn.AnyType frozen_=:= patternTp
-                  case MatchType.WildcardPattern(_) => true
                   case _ => false
                 }
               case _ => false
@@ -1637,7 +1637,6 @@ class Typer extends Namer
     def caseRest(pat: Tree)(using Context) = {
       val pt1 = instantiateMatchTypeProto(pat, pt) match {
         case defn.MatchCase(_, bodyPt) => bodyPt
-        case MatchType.WildcardPattern(bodyPt) => bodyPt
         case pt => pt
       }
       val pat1 = indexPattern(tree).transform(pat)