Fix #4350: Do not check prefix of class type parameters

compiler/src/dotty/tools/dotc/quoted/TreeCleaner.scala

@@ -17,12 +17,14 @@ class TreeCleaner extends tpd.TreeMap {
   /** List of symbols and their types for type aliases `type T = U` */
   private[this] var aliasesSyms: List[Symbol] = Nil
   private[this] var aliasesTypes: List[Type] = Nil
+  private[this] val aliases = newMutableSymbolMap[Tree]
 
   override def transform(tree: Tree)(implicit ctx: Context): Tree = {
     val tree0 = tree match {
       case TypeDef(_, TypeBoundsTree(lo, hi)) if lo == hi =>
         aliasesSyms = tree.symbol :: aliasesSyms
         aliasesTypes = lo.tpe :: aliasesTypes
+        aliases(tree.symbol) = ref(lo.tpe.typeSymbol)
         Literal(Constant(()))
       case _ => tree
     }
@@ -40,6 +42,7 @@ class TreeCleaner extends tpd.TreeMap {
           case expr3 => Block(flatStats, expr3)
         }
       case tree1: TypeTree => TypeTree(tree1.tpe.subst(aliasesSyms, aliasesTypes))
+      case tree1: Ident => aliases.get(tree1.symbol).getOrElse(tree1)
       case tree1 => tree1
     }
   }

compiler/src/dotty/tools/dotc/transform/ReifyQuotes.scala

@@ -210,7 +210,10 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
         explicitTags.clear()
 
         // Maps type splices to type references of tags e.g., ~t -> some type T$1
-        val map: Map[Type, Type] = tagsExplicitTypeDefsPairs.map(x => (x._1, x._2.symbol.typeRef)).toMap
+        val map: Map[Type, Type] = {
+          tagsExplicitTypeDefsPairs.map(x => (x._1, x._2.symbol.typeRef)) ++
+          (itags.map(_._1) zip typeDefs.map(_.symbol.typeRef))
+        }.toMap
         val tMap = new TypeMap() {
           override def apply(tp: Type): Type = map.getOrElse(tp, mapOver(tp))
         }
@@ -245,7 +248,7 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
         l == level ||
         sym.is(Inline) && sym.owner.is(Macro) && sym.info.isValueType && l - 1 == level
       case None =>
-        true
+        level == 0
     }
 
     /** Issue a "splice outside quote" error unless we ar in the body of an inline method */
@@ -289,12 +292,12 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
         if (!isThis) sym.show
         else if (sym.is(ModuleClass)) sym.sourceModule.show
         else i"${sym.name}.this"
-      if (!isThis && sym.maybeOwner.isType)
+      if (!isThis && sym.maybeOwner.isType && !sym.is(Param))
         check(sym.owner, sym.owner.thisType, pos)
       else if (sym.exists && !sym.isStaticOwner && !levelOK(sym))
         for (errMsg <- tryHeal(tp, pos))
           ctx.error(em"""access to $symStr from wrong staging level:
-                        | - the definition is at level ${levelOf(sym)},
+                        | - the definition is at level ${levelOf.getOrElse(sym, 0)},
                         | - but the access is at level $level.$errMsg""", pos)
     }
 
@@ -313,7 +316,8 @@ class ReifyQuotes extends MacroTransformWithImplicits with InfoTransformer {
             }
           case tp: NamedType =>
             check(tp.symbol, tp, pos)
-            foldOver(acc, tp)
+            if (!tp.symbol.is(Param))
+              foldOver(acc, tp)
           case tp: ThisType =>
             check(tp.cls, tp, pos)
             foldOver(acc, tp)

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

@@ -571,7 +571,7 @@ trait Implicits { self: Typer =>
     }
 
     def synthesizedTypeTag(formal: Type): Tree = formal.argInfos match {
-      case arg :: Nil =>
+      case arg :: Nil if !arg.typeSymbol.is(Param) =>
         object bindFreeVars extends TypeMap {
           var ok = true
           def apply(t: Type) = t match {

tests/neg/i4350.scala

@@ -0,0 +1,5 @@
+import scala.quoted.Type
+
+class Foo[T] {
+  '(null.asInstanceOf[T]) // error
+}

tests/pos/i4350.scala

@@ -0,0 +1,5 @@
+import scala.quoted.Type
+
+class Foo[T: Type] {
+  '(null.asInstanceOf[T])
+}

tests/run-with-compiler/i4350.check

@@ -0,0 +1,6 @@
+{
+  null.asInstanceOf[Object]
+}
+{
+  null.asInstanceOf[String]
+}

tests/run-with-compiler/i4350.scala

@@ -0,0 +1,14 @@
+import dotty.tools.dotc.quoted.Toolbox._
+
+import scala.quoted.Type
+
+class Foo[T: Type] {
+  def q = '(null.asInstanceOf[T])
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    println((new Foo[Object]).q.show)
+    println((new Foo[String]).q.show)
+  }
+}