Fix scala#6997: Adapt quote type direct aliase to type splice

Author: nicolasstucki

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

@@ -112,6 +112,10 @@ class PCPCheckAndHeal(@constructorOnly ictx: Context) extends TreeMapWithStages(
           if (tp.isTerm)
             ctx.error(i"splice outside quotes", pos)
           tp
+        case tp: TypeRef if tp.prefix.derivesFrom(defn.QuotedTypeClass) && tp.name.toString == "T" =>
+          // Adapt direct references to the type of the type parameter T of a quoted.Type[T].
+          // Replace it with a properly encoded type splice. This is the normal for expected for type splices.
+          tp.prefix.select(tpnme.splice)
         case tp: NamedType =>
           checkSymLevel(tp.symbol, tp, pos) match {
             case Some(tpRef) => tpRef.tpe

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

@@ -63,6 +63,8 @@ class Staging extends MacroTransform {
       }
 
       tree.tpe match {
+        case tp: TypeRef if tp.prefix.derivesFrom(defn.QuotedTypeClass) =>
+          assert(tp.name.toString != "T", "unexpected reference t.T from t: quoted.Type[T]")
         case tpe @ TypeRef(prefix, _) if tpe.typeSymbol eq defn.QuotedType_splice =>
           // Type splices must have a know term ref, usually to an implicit argument
           // This is mostly intended to catch `quoted.Type[T]#splice` types which should just be `T`

tests/pos/i6997.scala

@@ -0,0 +1,8 @@
+
+import scala.quoted._
+class Foo {
+  def mcrImpl(body: Expr[Any]) given (t: Type[_ <: Any]) given (ctx: QuoteContext): Expr[Any] = '{
+    val tmp = ???.asInstanceOf[$t]
+    tmp
+  }
+}

tests/pos/i6997b.scala

@@ -0,0 +1,15 @@
+package playground
+
+import scala.quoted._, scala.quoted.matching._
+import delegate scala.quoted._
+
+inline def mcr(x: => Any): Any = ${mcrImpl('x)}
+
+def mcrImpl(body: Expr[Any]) given (ctx: QuoteContext): Expr[Any] = {
+  val '{$x: $t} = body
+  '{
+    val tmp: $t = $x.asInstanceOf[$t]
+    println(tmp)
+    tmp
+  }
+}