From c3fc7dc6889aed9ff34ed0dfb1054220270d0b0b Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Thu, 13 Feb 2020 10:24:30 +0100
Subject: [PATCH] Add quoted Liftable derivation

---
 .../Derivation_1.scala                        | 63 +++++++++++++++++++
 .../Lib_2.scala                               | 24 +++++++
 .../Test_3.scala                              |  6 ++
 3 files changed, 93 insertions(+)
 create mode 100644 tests/run-macros/quoted-liftable-derivation-macro/Derivation_1.scala
 create mode 100644 tests/run-macros/quoted-liftable-derivation-macro/Lib_2.scala
 create mode 100644 tests/run-macros/quoted-liftable-derivation-macro/Test_3.scala

diff --git a/tests/run-macros/quoted-liftable-derivation-macro/Derivation_1.scala b/tests/run-macros/quoted-liftable-derivation-macro/Derivation_1.scala
new file mode 100644
index 000000000000..059ebc16e446
--- /dev/null
+++ b/tests/run-macros/quoted-liftable-derivation-macro/Derivation_1.scala
@@ -0,0 +1,63 @@
+import scala.compiletime.{erasedValue, summonFrom}
+import scala.deriving._
+import scala.quoted._
+
+trait Lft[T]:
+  def toExpr(x: T)(using Type[T], Quotes): Expr[T] // TODO remove `Type[T]`
+
+object Lft {
+  given Lft[Int] with
+    def toExpr(x: Int)(using Type[Int], Quotes) = Expr(x)
+
+  inline given derived[T](using inline m: Mirror.Of[T]): Lft[T] = ${ derivedExpr('m) }
+
+  private def derivedExpr[T](mirrorExpr: Expr[Mirror.Of[T]])(using qctx: Quotes, tpe: Type[T]): Expr[Lft[T]] = {
+    mirrorExpr match {
+      case '{ $mirrorExpr : Mirror.Sum { type MirroredElemTypes = mirroredElemTypes } } =>
+        val liftables = Expr.ofSeq(elemTypesLfts[mirroredElemTypes])
+        '{ new LiftableSum[T, mirroredElemTypes]($mirrorExpr, $liftables) }
+      case '{ $mirrorExpr : Mirror.Product { type MirroredElemTypes = mirroredElemTypes } } =>
+        val liftableExprs = Expr.ofSeq(elemTypesLfts[mirroredElemTypes])
+        '{ new LiftableProduct[T, mirroredElemTypes]($mirrorExpr, $liftableExprs) }
+    }
+  }
+
+  class LiftableSum[T, MElemTypes](
+    mirror: Mirror.Sum { type MirroredElemTypes = MElemTypes; type MirroredMonoType = T },
+    liftables: Seq[Lft[_]] // TODO make Lft creation lazy
+  ) extends Lft[T]:
+      def toExpr(x: T)(using Type[T], Quotes): Expr[T] =
+        val ordinal = mirror.ordinal(x)
+        val tp = Expr.summon[Mirror.SumOf[T]].get match
+          case '{ $mirrorExpr : Mirror.Sum { type MirroredElemTypes = mirroredElemTypes } } =>
+            elemType[mirroredElemTypes](ordinal)
+        val liftable = liftables.apply(ordinal).asInstanceOf[Lft[T]]
+        liftable.toExpr(x)(using tp.asInstanceOf[Type[T]], summon[Quotes])
+  end LiftableSum
+
+  class LiftableProduct[T, MElemTypes](
+    mirror: Mirror.Product { type MirroredElemTypes = MElemTypes; type MirroredMonoType = T },
+    liftables: Seq[Lft[_]]
+  ) extends Lft[T]:
+      def toExpr(x: T)(using Type[T], Quotes): Expr[T] =
+        val mirrorExpr = Expr.summon[Mirror.ProductOf[T]].get
+        val elemExprs =
+          x.asInstanceOf[Product].productIterator.zip(liftables.iterator).map { (elem, lift) =>
+            lift.asInstanceOf[Lft[Any]].toExpr(elem)
+          }.toSeq
+        val elemsTupleExpr = Expr.ofTupleFromSeq(elemExprs)
+        '{ $mirrorExpr.fromProduct($elemsTupleExpr) }
+  end LiftableProduct
+
+  private def elemTypesLfts[X: Type](using Quotes): List[Expr[Lft[_]]] =
+    Type.of[X] match
+      case '[ head *: tail ] =>
+        Expr.summon[Lft[head]].getOrElse(quotes.reflect.report.throwError(s"Could not find given Lft[${Type.show[head]}]")) :: elemTypesLfts[tail]
+      case '[ EmptyTuple ] => Nil
+
+  private def elemType[X: Type](ordinal: Int)(using Quotes): Type[_] =
+    Type.of[X] match
+      case '[ head *: tail ] =>
+        if ordinal == 0 then Type.of[head]
+        else elemType[tail](ordinal - 1)
+}
diff --git a/tests/run-macros/quoted-liftable-derivation-macro/Lib_2.scala b/tests/run-macros/quoted-liftable-derivation-macro/Lib_2.scala
new file mode 100644
index 000000000000..a5e3ea9d7cef
--- /dev/null
+++ b/tests/run-macros/quoted-liftable-derivation-macro/Lib_2.scala
@@ -0,0 +1,24 @@
+
+sealed trait Opt[+T] derives Lft
+case class Sm[T](t: T) extends Opt[T] derives Lft
+case object Nn extends Opt[Nothing] derives Lft
+
+object Lib {
+
+  import scala.quoted._
+  import Opt.*
+
+  inline def optTwo = ${optTwoExpr}
+  inline def smTwo = ${smTwoExpr}
+  inline def none = ${noneExpr}
+
+  private def optTwoExpr(using Quotes): Expr[Opt[Int]] =
+    summon[Lft[Opt[Int]]].toExpr(Sm(2))
+
+  private def smTwoExpr(using Quotes): Expr[Sm[Int]] =
+    summon[Lft[Sm[Int]]].toExpr(Sm(2))
+
+  private def noneExpr(using Quotes): Expr[Opt[Int]] =
+    summon[Lft[Nn.type]].toExpr(Nn)
+}
+
diff --git a/tests/run-macros/quoted-liftable-derivation-macro/Test_3.scala b/tests/run-macros/quoted-liftable-derivation-macro/Test_3.scala
new file mode 100644
index 000000000000..3ba5e8d2c3e7
--- /dev/null
+++ b/tests/run-macros/quoted-liftable-derivation-macro/Test_3.scala
@@ -0,0 +1,6 @@
+object Test extends App {
+  import Opt._
+  assert(Lib.optTwo == Sm(2))
+  assert(Lib.smTwo == Sm(2))
+  assert(Lib.none == Nn)
+}