Add regression that demonstrates a type class derived method with macros

Author: biboudis

tests/run-macros/i8007.check

@@ -1 +1,3 @@
-List("name", "age")
+List("name", "age")
+
+Test 23 

tests/run-macros/i8007/Macro_1.scala

@@ -3,7 +3,7 @@ import scala.quoted._
 import scala.quoted.matching._
 import scala.compiletime.{erasedValue, summonFrom, constValue}
 
-object Macro {
+object Macro1 {
   case class Person(name: String, age: Int)
 
   def mirrorFields[T](t: Type[T])(given qctx: QuoteContext): List[String] =
@@ -12,23 +12,21 @@ object Macro {
       case '[Unit] => Nil
     }
 
-  inline def usingSummonFrom[T](value: =>T): List[String] =
-    ${ usingSummonFromImpl('value) }
+  // Macro method 1
+  //   Demonstrates the use of quoted pattern matching
+  //   over a refined type, extracting the tuple type
+  //   for e.g., MirroredElemLabels
+  inline def test1[T](value: =>T): List[String] =
+    ${ test1Impl('value) }
 
-  def usingSummonFromImpl[T: Type](value: Expr[T])(given qctx: QuoteContext): Expr[List[String]] = {
+  def test1Impl[T: Type](value: Expr[T])(given qctx: QuoteContext): Expr[List[String]] = {
     import qctx.tasty.{_, given}
 
-
     val mirrorTpe = '[Mirror.Of[T]]
 
     summonExpr(given mirrorTpe).get match {
-      case '{ $m: Mirror.ProductOf[T] } => {
-        val typeMember = TypeSelect(m.unseal, "MirroredElemLabels")
-
-        type TT
-        implicit val TT: quoted.Type[TT] = typeMember.tpe.seal.asInstanceOf[quoted.Type[TT]]
-
-        Expr(mirrorFields('[TT]))
+      case '{ $m: Mirror.ProductOf[T]{ type MirroredElemLabels = $t } } => {
+        Expr(mirrorFields(t))
       }
     }
   }

tests/run-macros/i8007/Macro_2.scala

@@ -0,0 +1,58 @@
+import scala.deriving._
+import scala.quoted._
+import scala.quoted.matching._
+import scala.compiletime.{erasedValue, summonFrom, constValue}
+
+object Macro2 {
+
+  def mirrorFields[T](t: Type[T])(given qctx: QuoteContext): List[String] =
+    t match {
+      case '[$field *: $fields] => field.show.substring(1, field.show.length-1) :: mirrorFields(fields)
+      case '[Unit] => Nil
+    }
+
+  trait JsonEncoder[T] {
+    def encode(elem: T): String
+  }
+
+  object JsonEncoder {
+    def emitJsonEncoder[T](body: T => String): JsonEncoder[T]=
+      new JsonEncoder[T] {
+          def encode(elem: T): String = body(elem)
+        }
+
+    def derived[T: Type](ev: Expr[Mirror.Of[T]])(given qctx: QuoteContext): Expr[JsonEncoder[T]] = {
+      import qctx.tasty.{_, given}
+
+      val fields = ev match {
+        case '{ $m: Mirror.ProductOf[T] { type MirroredElemLabels = $t } } =>
+          mirrorFields(t)
+      }
+
+      val body: Expr[T] => Expr[String] = elem =>
+        fields.reverse.foldLeft(Expr("")){ (acc, field) =>
+          val res = Select.unique(elem.unseal, field).seal
+          '{ $res.toString + " " + $acc }
+        }
+
+      '{
+        emitJsonEncoder((x: T) => ${body('x)})
+      }
+    }
+  }
+
+  inline def test2[T](value: =>T): Unit = ${ test2Impl('value) }
+
+  def test2Impl[T: Type](value: Expr[T])(given qctx: QuoteContext): Expr[Unit] = {
+    import qctx.tasty.{_, given}
+
+    val mirrorTpe = '[Mirror.Of[T]]
+    val mirrorExpr = summonExpr(given mirrorTpe).get
+    val derivedInstance = JsonEncoder.derived(mirrorExpr)
+
+    '{
+      val res = $derivedInstance.encode($value)
+      println(res)
+    }
+  }
+}

tests/run-macros/i8007/Test_2.scala

@@ -0,0 +1,10 @@
+import Macro1._
+import Macro2._
+
+@main def Test() = {
+  val list = test1(Person("Test", 23))
+  println(list)
+  println
+
+  test2(Person("Test", 23))
+}