Fix bootstrapping

Author: liufengyun

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

@@ -1223,7 +1223,7 @@ object Types {
      *  then the top-level union isn't widened. This is needed so that type inference can infer nullable types.
      */
     def widenUnion(using Context): Type = widen match
-      case tp @ OrNull(tp1): OrType =>
+      case tp @ OrNull(tp1) =>
         // Don't widen `T|Null`, since otherwise we wouldn't be able to infer nullable unions.
         val tp1Widen = tp1.widenUnionWithoutNull
         if (tp1Widen.isRef(defn.AnyClass)) tp1Widen
@@ -3158,7 +3158,7 @@ object Types {
   object OrNull {
     def apply(tp: Type)(using Context) =
       OrType(tp, defn.NullType, soft = false)
-    def unapply(tp: Type)(using Context): Option[Type] =
+    def unapply(tp: OrType)(using Context): Option[Type] =
       if (ctx.explicitNulls) {
         val tp1 = tp.stripNull()
         if tp1 ne tp then Some(tp1) else None

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

@@ -425,13 +425,17 @@ class Typer extends Namer
    *  (x: T | Null) => x.$asInstanceOf$[x.type & T]
    */
   def toNotNullTermRef(tree: Tree, pt: Type)(using Context): Tree = tree.tpe match
-    case ref @ OrNull(tpnn) : TermRef
+    case ref: TermRef
     if pt != AssignProto && // Ensure it is not the lhs of Assign
     ctx.notNullInfos.impliesNotNull(ref) &&
     // If a reference is in the context, it is already trackable at the point we add it.
     // Hence, we don't use isTracked in the next line, because checking use out of order is enough.
     !ref.usedOutOfOrder =>
-      tree.select(defn.Any_typeCast).appliedToType(AndType(ref, tpnn))
+      ref.widenSingleton match
+      case OrNull(tpnn) =>
+        tree.select(defn.Any_typeCast).appliedToType(AndType(ref, tpnn))
+      case _ =>
+        tree
     case _ =>
       tree