backported #2834 added CommutativeMonoid[Option[A]] instance, in binary compatible way (#3334)

Author: gagandeepkalra

core/src/main/scala/cats/instances/all.scala

@@ -69,6 +69,7 @@ trait AllInstancesBinCompat7
     with VectorInstancesBinCompat1
     with EitherInstancesBinCompat0
     with StreamInstancesBinCompat1
+    with OptionInstancesBinCompat1
     with QueueInstancesBinCompat0
     with TailRecInstances
     with SortedSetInstancesBinCompat2

core/src/main/scala/cats/instances/option.scala

@@ -1,6 +1,8 @@
 package cats
 package instances
 
+import cats.kernel.instances.OptionInstances3
+
 import scala.annotation.tailrec
 import cats.data.Ior
 
@@ -172,3 +174,5 @@ private[instances] trait OptionInstancesBinCompat0 {
 
   }
 }
+
+private[instances] trait OptionInstancesBinCompat1 extends OptionInstances3

core/src/main/scala/cats/instances/package.scala

@@ -21,7 +21,7 @@ package object instances {
   object invariant extends InvariantMonoidalInstances
   object list extends ListInstances with ListInstancesBinCompat0 with ListInstancesBinCompat1
   object long extends LongInstances
-  object option extends OptionInstances with OptionInstancesBinCompat0
+  object option extends OptionInstances with OptionInstancesBinCompat0 with OptionInstancesBinCompat1
   object map extends MapInstances with MapInstancesBinCompat0 with MapInstancesBinCompat1
   object order extends OrderInstances
   object ordering extends OrderingInstances

kernel-laws/shared/src/test/scala/cats/kernel/laws/LawTests.scala

@@ -227,10 +227,8 @@ class Tests extends AnyFunSuiteLike with Discipline {
 
   checkAll("Monoid[String]", MonoidTests[String].monoid)
   checkAll("Monoid[String]", SerializableTests.serializable(Monoid[String]))
-  checkAll("Monoid[Option[Int]]", MonoidTests[Option[Int]].monoid)
-  checkAll("Monoid[Option[Int]]", SerializableTests.serializable(Monoid[String]))
   checkAll("Monoid[Option[String]]", MonoidTests[Option[String]].monoid)
-  checkAll("Monoid[Option[String]]", SerializableTests.serializable(Monoid[String]))
+  checkAll("Monoid[Option[String]]", SerializableTests.serializable(Monoid[Option[String]]))
   checkAll("Monoid[List[Int]]", MonoidTests[List[Int]].monoid)
   checkAll("Monoid[List[Int]]", SerializableTests.serializable(Monoid[List[Int]]))
   checkAll("Monoid[Vector[Int]]", MonoidTests[Vector[Int]].monoid)
@@ -246,6 +244,8 @@ class Tests extends AnyFunSuiteLike with Discipline {
   checkAll("Monoid[Queue[Int]]", MonoidTests[Queue[Int]].monoid)
   checkAll("Monoid[Queue[Int]]", SerializableTests.serializable(Monoid[Queue[Int]]))
 
+  checkAll("CommutativeMonoid[Option[Int]]", CommutativeMonoidTests[Option[Int]].commutativeMonoid)
+  checkAll("CommutativeMonoid[Option[Int]]", SerializableTests.serializable(CommutativeMonoid[Option[Int]]))
   checkAll("CommutativeMonoid[Map[String, Int]]", CommutativeMonoidTests[Map[String, Int]].commutativeMonoid)
   checkAll("CommutativeMonoid[Map[String, Int]]", SerializableTests.serializable(CommutativeMonoid[Map[String, Int]]))
   checkAll("CommutativeMonoid[SortedMap[String, Int]]",

kernel/src/main/scala/cats/kernel/instances/AllInstances.scala

@@ -37,4 +37,4 @@ private[instances] trait AllInstancesBinCompat0 extends FiniteDurationInstances
 
 private[instances] trait AllInstancesBinCompat1 extends SortedMapInstances with SortedSetInstances
 
-private[instances] trait AllInstancesBinCompat2 extends SortedSetInstances2
+private[instances] trait AllInstancesBinCompat2 extends OptionInstances3 with SortedSetInstances2

kernel/src/main/scala/cats/kernel/instances/OptionInstances.scala

@@ -23,6 +23,11 @@ private[instances] trait OptionInstances2 {
     new OptionEq[A]
 }
 
+trait OptionInstances3 {
+  implicit def catsKernelStdCommutativeMonoidForOption[A: CommutativeSemigroup]: CommutativeMonoid[Option[A]] =
+    new OptionCommutativeMonoid[A]
+}
+
 class OptionOrder[A](implicit A: Order[A]) extends Order[Option[A]] {
   def compare(x: Option[A], y: Option[A]): Int =
     x match {
@@ -80,3 +85,7 @@ class OptionMonoid[A](implicit A: Semigroup[A]) extends Monoid[Option[A]] {
         }
     }
 }
+
+private class OptionCommutativeMonoid[A](implicit A: CommutativeSemigroup[A])
+    extends OptionMonoid[A]()(A)
+    with CommutativeMonoid[Option[A]]