Fix #7919: Make sure that quoted.Type does not have unexpected subclasses

Now that quoted.Type and quoted.Expr are not sealed we make them have
private constructors to make sure users do not exten them (possibly by mistake).

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/quoted/PickledQuotes.scala

@@ -19,7 +19,6 @@ import dotty.tools.dotc.tastyreflect.{ReflectionImpl, TastyTreeExpr, TreeType}
 
 import dotty.tools.tasty.TastyString
 
-import scala.internal.quoted._
 import scala.reflect.ClassTag
 
 import scala.runtime.quoted.Unpickler._

compiler/src/dotty/tools/dotc/tastyreflect/TastyTreeExpr.scala

@@ -9,7 +9,7 @@ import dotty.tools.dotc.ast.tpd.Tree
  *
  *  May contain references to code defined outside this TastyTreeExpr instance.
  */
-final class TastyTreeExpr(val tree: Tree, val scopeId: Int) extends scala.quoted.Expr[Any] {
+final class TastyTreeExpr(val tree: Tree, val scopeId: Int) extends scala.internal.quoted.Expr[Any] {
   override def equals(that: Any): Boolean = that match {
     case that: TastyTreeExpr =>
       // TastyTreeExpr are wrappers around trees, therfore they are equals if their trees are equal.

compiler/src/dotty/tools/dotc/tastyreflect/TreeType.scala

@@ -3,7 +3,7 @@ package dotty.tools.dotc.tastyreflect
 import dotty.tools.dotc.ast.tpd.Tree
 
 /** An Type backed by a tree */
-final class TreeType(val typeTree: Tree, val scopeId: Int) extends scala.quoted.Type[Any] {
+final class TreeType(val typeTree: Tree, val scopeId: Int) extends scala.internal.quoted.Type[Any] {
   override def equals(that: Any): Boolean = that match {
     case that: TreeType => typeTree ==
       // TastyTreeExpr are wrappers around trees, therfore they are equals if their trees are equal.

library/src/scala/internal/quoted/Expr.scala

@@ -2,6 +2,13 @@ package scala.internal.quoted
 
 import scala.quoted._
 
+/** Quoted expression of type `T`
+ *
+ *  Restriction: only the QuoteContext.tasty.internal implementation is allowed to extend this trait.
+ *  Any other implementation will result in an undefined behavior.
+ */
+class Expr[+T] extends scala.quoted.Expr[T]
+
 object Expr {
 
   /** Pattern matches an the scrutineeExpr against the patternExpr and returns a tuple
@@ -25,7 +32,7 @@ object Expr {
    *  @param qctx the current QuoteContext
    *  @return None if it did not match, `Some(tup)` if it matched where `tup` contains `Expr[Ti]``
    */
-  def unapply[TypeBindings <: Tuple, Tup <: Tuple](scrutineeExpr: Expr[_])(implicit patternExpr: Expr[_],
+  def unapply[TypeBindings <: Tuple, Tup <: Tuple](scrutineeExpr: scala.quoted.Expr[_])(implicit patternExpr: scala.quoted.Expr[_],
         hasTypeSplices: Boolean, qctx: QuoteContext): Option[Tup] = {
     import qctx.tasty.{_, given}
     new Matcher.QuoteMatcher[qctx.type].termMatch(scrutineeExpr.unseal, patternExpr.unseal, hasTypeSplices).asInstanceOf[Option[Tup]]

library/src/scala/internal/quoted/Type.scala

@@ -2,6 +2,13 @@ package scala.internal.quoted
 
 import scala.quoted._
 
+/** Quoted type (or kind) `T`
+ *
+ *  Restriction: only the QuoteContext.tasty.internal implementation is allowed to extend this trait.
+ *  Any other implementation will result in an undefined behavior.
+ */
+class Type[T <: AnyKind] extends scala.quoted.Type[T]
+
 object Type {
 
   /** Pattern matches an the scrutineeType against the patternType and returns a tuple
@@ -17,7 +24,7 @@ object Type {
    *  @param qctx the current QuoteContext
    *  @return None if it did not match, `Some(tup)` if it matched where `tup` contains `Type[Ti]``
    */
-  def unapply[TypeBindings <: Tuple, Tup <: Tuple](scrutineeType: Type[_])(implicit patternType: Type[_],
+  def unapply[TypeBindings <: Tuple, Tup <: Tuple](scrutineeType: scala.quoted.Type[_])(implicit patternType: scala.quoted.Type[_],
         hasTypeSplices: Boolean, qctx: QuoteContext): Option[Tup] = {
     import qctx.tasty.{_, given}
     new Matcher.QuoteMatcher[qctx.type].typeTreeMatch(scrutineeType.unseal, patternType.unseal, hasTypeSplices).asInstanceOf[Option[Tup]]

library/src/scala/quoted/Expr.scala

@@ -2,12 +2,8 @@ package scala.quoted
 
 import scala.quoted.show.SyntaxHighlight
 
-/** Quoted expression of type `T`
- *
- *  Restriction: only the QuoteContext.tasty.internal implementation is allowed to extend this trait.
- *  Any other implementation will result in an undefined behavior.
- */
-trait Expr[+T] {
+/** Quoted expression of type `T` */
+class Expr[+T] private[scala] {
 
   /** Show a source code like representation of this expression without syntax highlight */
   def show(implicit qctx: QuoteContext): String = qctx.show(this, SyntaxHighlight.plain)
@@ -57,8 +53,6 @@ trait Expr[+T] {
 
 object Expr {
 
-  import scala.internal.quoted._
-
   /** Converts a tuple `(T1, ..., Tn)` to `(Expr[T1], ..., Expr[Tn])` */
   type TupleOfExpr[Tup <: Tuple] = Tuple.Map[Tup, [X] =>> (given QuoteContext) => Expr[X]]
 

library/src/scala/quoted/Type.scala

@@ -2,12 +2,8 @@ package scala.quoted
 
 import scala.quoted.show.SyntaxHighlight
 
-/** Quoted type (or kind) `T`
- *
- *  Restriction: only the QuoteContext.tasty.internal implementation is allowed to extend this trait.
- *  Any other implementation will result in an undefined behavior.
- */
-trait Type[T <: AnyKind] {
+/** Quoted type (or kind) `T` */
+class Type[T <: AnyKind] private[scala] {
   type `$splice` = T
 
   /** Show a source code like representation of this type without syntax highlight */

tests/neg/i7919.scala

@@ -0,0 +1,20 @@
+import scala.quoted._
+
+object Test {
+  def staged[T](given qctx: QuoteContext) = {
+    import qctx.tasty.{_, given}
+    given typeT: quoted.Type[T] // error
+    val tTypeTree = typeT.unseal
+    val tt = typeOf[T]
+    '{ "in staged" }
+  }
+
+  given Expr[Int] // error
+  new Expr[Int] // error
+  class Expr2 extends Expr[Int] // error
+
+  given Type[Int] // error
+  new Type[Int] // error
+  class Type2 extends Type[Int] // error
+
+}