From 73988a443c71e42606966d4891a95ce3bafab9b5 Mon Sep 17 00:00:00 2001
From: Filippo Mariotti <barambani@users.noreply.github.com>
Date: Thu, 11 Jun 2020 16:39:49 +0100
Subject: [PATCH] Added CommutativeMonoid for Option to scope (#3463)

* Added CommutativeMonoid for Option to scope

* Fix ambiguity when the base type has both Semigroup and CommutativeSemigroup
---
 .../src/test/scala/cats/kernel/laws/LawTests.scala   | 10 +++++++++-
 kernel/src/main/scala/cats/kernel/Semigroup.scala    | 12 ++++++++----
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/kernel-laws/shared/src/test/scala/cats/kernel/laws/LawTests.scala b/kernel-laws/shared/src/test/scala/cats/kernel/laws/LawTests.scala
index 61f9c98677..28c791f7b7 100644
--- a/kernel-laws/shared/src/test/scala/cats/kernel/laws/LawTests.scala
+++ b/kernel-laws/shared/src/test/scala/cats/kernel/laws/LawTests.scala
@@ -1,7 +1,6 @@
 package cats.kernel
 package laws
 
-import cats.kernel.instances.all._
 import cats.kernel.laws.discipline._
 import cats.platform.Platform
 
@@ -148,6 +147,15 @@ class Tests extends TestsConfig with AnyFunSuiteLike with FunSuiteDiscipline wit
 
   import KernelCheck._
 
+  test("The instances in scope are not ambiguous") {
+    implicitly[Monoid[Option[String]]]
+    implicitly[Semigroup[Option[String]]]
+    implicitly[Monoid[Option[Int]]]
+    implicitly[Semigroup[Option[Int]]]
+    implicitly[CommutativeSemigroup[Option[Int]]]
+    implicitly[CommutativeMonoid[Option[Int]]]
+  }
+
   {
     // needed for Cogen[Map[...]]
     implicit val ohe: Ordering[HasEq[Int]] = Ordering.by[HasEq[Int], Int](_.a)
diff --git a/kernel/src/main/scala/cats/kernel/Semigroup.scala b/kernel/src/main/scala/cats/kernel/Semigroup.scala
index f82eb5557c..aac2aa4e23 100644
--- a/kernel/src/main/scala/cats/kernel/Semigroup.scala
+++ b/kernel/src/main/scala/cats/kernel/Semigroup.scala
@@ -179,8 +179,6 @@ object Semigroup
 
   implicit def catsKernelMonoidForString: Monoid[String] = cats.kernel.instances.string.catsKernelStdMonoidForString
 
-  implicit def catsKernelMonoidForOption[A: Semigroup]: Monoid[Option[A]] =
-    cats.kernel.instances.option.catsKernelStdMonoidForOption[A]
   implicit def catsKernelMonoidForList[A]: Monoid[List[A]] = cats.kernel.instances.list.catsKernelStdMonoidForList[A]
   implicit def catsKernelMonoidForVector[A]: Monoid[Vector[A]] =
     cats.kernel.instances.vector.catsKernelStdMonoidForVector[A]
@@ -230,6 +228,8 @@ private[kernel] trait CommutativeMonoidInstances extends MonoidInstances {
     cats.kernel.instances.function.catsKernelCommutativeMonoidForFunction0[A]
   implicit def catsKernelCommutativeMonoidForFunction1[A, B: CommutativeMonoid]: CommutativeMonoid[A => B] =
     cats.kernel.instances.function.catsKernelCommutativeMonoidForFunction1[A, B]
+  implicit def catsKernelCommutativeMonoidForOption[A: CommutativeSemigroup]: CommutativeMonoid[Option[A]] =
+    cats.kernel.instances.option.catsKernelStdCommutativeMonoidForOption[A]
 }
 
 private[kernel] trait MonoidInstances extends BandInstances {
@@ -243,7 +243,10 @@ private[kernel] trait MonoidInstances extends BandInstances {
     cats.kernel.instances.sortedMap.catsKernelStdMonoidForSortedMap[K, V]
   implicit def catsKernelMonoidForEither[A, B: Monoid]: Monoid[Either[A, B]] =
     cats.kernel.instances.either.catsDataMonoidForEither[A, B]
-  implicit def catsKernelMonoidForTry[A: Monoid]: Monoid[Try[A]] = new TryMonoid[A](Monoid[A])
+  implicit def catsKernelMonoidForTry[A: Monoid]: Monoid[Try[A]] =
+    new TryMonoid[A](Monoid[A])
+  implicit def catsKernelMonoidForOption[A: Semigroup]: Monoid[Option[A]] =
+    cats.kernel.instances.option.catsKernelStdMonoidForOption[A]
 }
 
 private[kernel] trait BandInstances extends CommutativeSemigroupInstances {
@@ -267,7 +270,8 @@ private[kernel] trait SemigroupInstances {
     cats.kernel.instances.function.catsKernelSemigroupForFunction1[A, B]
   implicit def catsKernelSemigroupForEither[A, B: Semigroup]: Semigroup[Either[A, B]] =
     cats.kernel.instances.either.catsDataSemigroupForEither[A, B]
-  implicit def catsKernelSemigroupForTry[A: Semigroup]: Semigroup[Try[A]] = new TrySemigroup[A](Semigroup[A])
+  implicit def catsKernelSemigroupForTry[A: Semigroup]: Semigroup[Try[A]] =
+    new TrySemigroup[A](Semigroup[A])
 }
 
 private class TryMonoid[A](A: Monoid[A]) extends TrySemigroup[A](A) with Monoid[Try[A]] {