From 31b7a658ec3e34ecd21281acbd374b65d0fcf422 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Mon, 25 May 2020 11:41:28 +0200
Subject: [PATCH] Make NonEmptyTuple a Product

---
 .../src/dotty/tools/dotc/typer/Applications.scala     |  2 +-
 compiler/src/dotty/tools/dotc/typer/Typer.scala       |  4 +++-
 library/src/scala/Tuple.scala                         |  2 +-
 tests/run/tuple-product.scala                         | 11 +++++++++++
 4 files changed, 16 insertions(+), 3 deletions(-)
 create mode 100644 tests/run/tuple-product.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Applications.scala b/compiler/src/dotty/tools/dotc/typer/Applications.scala
index 90b89ac04ae6..c4cd1d95f0b9 100644
--- a/compiler/src/dotty/tools/dotc/typer/Applications.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Applications.scala
@@ -116,7 +116,7 @@ object Applications {
       if (sel.exists) sel :: tupleSelectors(n + 1, tp) else Nil
     }
     def genTupleSelectors(n: Int, tp: Type): List[Type] = tp match {
-      case tp: AppliedType if !tp.derivesFrom(defn.ProductClass) && tp.derivesFrom(defn.PairClass) =>
+      case tp: AppliedType if !defn.isTupleClass(tp.typeSymbol) && tp.derivesFrom(defn.PairClass) =>
         val List(head, tail) = tp.args
         head :: genTupleSelectors(n, tail)
       case _ => tupleSelectors(n, tp)
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 63f7682a3003..890059da151c 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -1147,7 +1147,9 @@ class Typer extends Namer
 
     val desugared =
       if (protoFormals.length == 1 && params.length != 1 && ptIsCorrectProduct(protoFormals.head)) {
-        val isGenericTuple = !protoFormals.head.derivesFrom(defn.ProductClass)
+        val isGenericTuple =
+          protoFormals.head.derivesFrom(defn.TupleClass)
+          && !defn.isTupleClass(protoFormals.head.typeSymbol)
         desugar.makeTupledFunction(params, fnBody, isGenericTuple)
       }
       else {
diff --git a/library/src/scala/Tuple.scala b/library/src/scala/Tuple.scala
index 3575dcb6c628..e01f46df318a 100644
--- a/library/src/scala/Tuple.scala
+++ b/library/src/scala/Tuple.scala
@@ -186,7 +186,7 @@ object Tuple {
 }
 
 /** Tuple of arbitrary non-zero arity */
-sealed trait NonEmptyTuple extends Tuple {
+sealed trait NonEmptyTuple extends Tuple with Product {
   import Tuple._
 
   /** Get the i-th element of this tuple.
diff --git a/tests/run/tuple-product.scala b/tests/run/tuple-product.scala
new file mode 100644
index 000000000000..4441ee75f1af
--- /dev/null
+++ b/tests/run/tuple-product.scala
@@ -0,0 +1,11 @@
+@main def Test = {
+  val a: Product = 1 *: ()
+  assert(a.productArity == 1)
+  val b: Product = 1 *: 2 *: ()
+  assert(b.productArity == 2)
+  val c: Product = 1 *: 2 *: 3 *: 4 *: 5 *: 6 *: 7 *: 8 *: 9 *: 10 *: 11 *: 12 *: 13 *: 14 *: 15 *: 16 *: 17 *: 18 *: 19 *: 20 *: 21 *: 22 *: 23 *: 24 *: 25 *: ()
+  assert(c.productArity == 25)
+  val d: NonEmptyTuple = (1, 2)
+  val e: Product = d
+  assert(e.productArity == 2)
+}
\ No newline at end of file