Fix errors; update documents

Author: noti0na1

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

@@ -77,6 +77,7 @@ object Types extends TypeUtils {
    *        |              +- TypeVar
    *        |              +- HKTypeLambda
    *        |              +- MatchType
+   *        |              +- FlexibleType
    *        |
    *        +- GroundType -+- AndType
    *                       +- OrType
@@ -3468,7 +3469,7 @@ object Types extends TypeUtils {
    * `T | Null .. T`, so that `T | Null <: FlexibleType(T) <: T`.
    * A flexible type will be erased to its original type `T`.
    */
-  case class FlexibleType(lo: Type, hi: Type) extends CachedProxyType with ValueType {
+  case class FlexibleType protected(lo: Type, hi: Type) extends CachedProxyType with ValueType {
 
     override def underlying(using Context): Type = hi
 
@@ -3481,7 +3482,7 @@ object Types extends TypeUtils {
   }
 
   object FlexibleType {
-    def apply(tp: Type)(using Context): Type = tp match {
+    def apply(tp: Type)(using Context): FlexibleType = tp match {
       case ft: FlexibleType => ft
       case _ =>
         // val tp1 = tp.stripNull()

compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -2345,17 +2345,15 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
 
     type FlexibleType = dotc.core.Types.FlexibleType
 
-    object FlexibleTypeTest extends TypeTest[TypeRepr, FlexibleType]:
+    object FlexibleTypeTypeTest extends TypeTest[TypeRepr, FlexibleType]:
       def unapply(x: TypeRepr): Option[FlexibleType & x.type] = x match
         case x: (Types.FlexibleType & x.type) => Some(x)
         case _ => None
-    end FlexibleTypeTest
+    end FlexibleTypeTypeTest
 
     object FlexibleType extends FlexibleTypeModule:
-      def apply(tp: TypeRepr): FlexibleType =
-        // why object FlexibleType.apply(Type) is not found here?
-        Types.FlexibleType(tp, tp)
-      def unapply(x: FlexibleType): TypeRepr = x.hi
+      def apply(tp: TypeRepr): FlexibleType = Types.FlexibleType(tp)
+      def unapply(x: FlexibleType): Some[TypeRepr] = Some(x.hi)
     end FlexibleType
 
     type Constant = dotc.core.Constants.Constant

library/src/scala/quoted/Quotes.scala

@@ -211,6 +211,7 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
    *               +- MatchCase
    *               +- TypeBounds
    *               +- NoPrefix
+   *               +- FlexibleType
    *
    *  +- MethodTypeKind -+- Contextual
    *                     +- Implicit
@@ -3442,7 +3443,7 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
     /** Methods of the module object `val FlexibleType` */
     trait FlexibleTypeModule { this: FlexibleType.type =>
       def apply(tp: TypeRepr): FlexibleType
-      def unapply(x: FlexibleType): TypeRepr
+      def unapply(x: FlexibleType): Option[TypeRepr]
     }
 
     ///////////////