Fix #6281: Add full regression test

tests/run-with-compiler/i6281.scala

@@ -0,0 +1,51 @@
+import scala.quoted._
+
+object Test extends App {
+
+  sealed trait HList
+  sealed trait HNil extends HList
+  sealed trait ::[E, T <: HList] extends HList
+
+  type STM[A, L <: HList] = L match {
+    case HNil => Expr[A]
+    case e :: rs => (Expr[A] => STM[e, rs]) => STM[e, rs]
+  }
+
+  type Stm[A, L <: HList] = L match {
+    case HNil => A
+    case e :: rs => (A => Stm[e, rs]) => Stm[e, rs]
+  }
+
+  trait Effects[L <: HList] {
+    def reify[A] given Type[A]: STM[A, L] => Expr[Stm[A, L]]
+    def reflect[A] given Type[A]: Expr[Stm[A, L]] => STM[A, L]
+  }
+  delegate empty for Effects[HNil] {
+    def reify[A] given Type[A] = m => m
+    def reflect[A] given Type[A] = m => m
+  }
+  // for reify, we need type tags for E and also strangely for L.
+  implicit def cons [E, L <: HList] given Effects[L] given Type[E] given Type[L] given QuoteContext: Effects[E :: L] =  new Effects[E :: L] {
+    def reify[A] given Type[A]   = m => '{ k => ${ Effects[L].reify[E] {   m(   a =>    Effects[L].reflect[E]('k(a))) } }}
+    def reflect[A] given Type[A] = m =>    k =>    Effects[L].reflect[E] { m('{ a => ${ Effects[L].reify[E](   k('a)) } })}
+  }
+  def Effects[L <: HList] given Effects[L]: Effects[L] = the[Effects[L]]
+
+  type RS = Boolean :: RS2
+  type RS2 = Int :: String :: HNil
+
+  def m given QuoteContext: STM[Int, RS] = k => k('{42})
+
+  implicit val toolbox: scala.quoted.Toolbox = scala.quoted.Toolbox.make(getClass.getClassLoader)
+
+  withQuoteContext {
+     println(Effects[RS].reify[Int] { m }.show)
+
+     val effects = cons[Boolean, RS2] given (cons[Int, String :: HNil] given (cons[String, HNil] given empty))
+     println(effects.reify[Int] { m }.show)
+
+     val res : Expr[Stm[Int, RS]] = '{ k => ${ Effects[RS2].reify[Boolean] { m(a => Effects[RS2].reflect[Boolean]('k(a))) }}}
+     println(res.show)
+  }
+
+}