Enable and fix doctests on 2.13 (#3155)

* Enable and fix doctests on 2.13

* Avoid collections toString in doctests

build.sbt

@@ -63,12 +63,7 @@ lazy val commonSettings = commonScalaVersionSettings ++ Seq(
   Test / unmanagedSourceDirectories ++= scalaVersionSpecificFolders("test", baseDirectory.value, scalaVersion.value),
   resolvers ++= Seq(Resolver.sonatypeRepo("releases"), Resolver.sonatypeRepo("snapshots")),
   parallelExecution in Test := false,
-  scalacOptions in (Compile, doc) := (scalacOptions in (Compile, doc)).value.filter(_ != "-Xfatal-warnings"),
-  // TODO: reenable doctests on 2.13 once it's officially released. it's disabled for now due to changes to the `toString` impl of collections
-  doctestGenTests := {
-    val unchanged = doctestGenTests.value
-    if (priorTo2_13(scalaVersion.value)) unchanged else Nil
-  }
+  scalacOptions in (Compile, doc) := (scalacOptions in (Compile, doc)).value.filter(_ != "-Xfatal-warnings")
 ) ++ warnUnusedImport
 
 def macroDependencies(scalaVersion: String) =

core/src/main/scala/cats/NonEmptyTraverse.scala

@@ -20,8 +20,12 @@ import simulacrum.typeclass
    * scala> import cats.implicits._
    * scala> import cats.data.NonEmptyList
    * scala> def countWords(words: List[String]): Map[String, Int] = words.groupBy(identity).map { case (k, v) => (k, v.length) }
-   * scala> NonEmptyList.of(List("How", "do", "you", "fly"), List("What", "do", "you", "do")).nonEmptyTraverse(countWords)
-   * res0: Map[String,cats.data.NonEmptyList[Int]] = Map(do -> NonEmptyList(1, 2), you -> NonEmptyList(1, 1))
+   * scala> val expectedResult = Map("do" -> NonEmptyList.of(1, 2), "you" -> NonEmptyList.of(1, 1))
+   * scala> val x = List("How", "do", "you", "fly")
+   * scala> val y = List("What", "do", "you", "do")
+   * scala> val result = NonEmptyList.of(x, y).nonEmptyTraverse(countWords)
+   * scala> result === expectedResult
+   * res0: Boolean = true
    * }}}
    */
   def nonEmptyTraverse[G[_]: Apply, A, B](fa: F[A])(f: A => G[B]): G[F[B]]

core/src/main/scala/cats/arrow/Choice.scala

@@ -13,8 +13,8 @@ import simulacrum.typeclass
    * Example:
    * {{{
    * scala> import cats.implicits._
-   * scala> val b: Boolean => String = _ + " is a boolean"
-   * scala> val i: Int => String =  _ + " is an integer"
+   * scala> val b: Boolean => String = _.toString + " is a boolean"
+   * scala> val i: Int => String =  _.toString + " is an integer"
    * scala> val f: (Either[Boolean, Int]) => String = b ||| i
    *
    * scala> f(Right(3))

core/src/main/scala/cats/data/NonEmptyChain.scala

@@ -384,7 +384,7 @@ class NonEmptyChainOps[A](private val value: NonEmptyChain[A]) extends AnyVal {
    * scala> import cats.data.NonEmptyChain
    * scala> val as = NonEmptyChain(1, 2, 3)
    * scala> val bs = NonEmptyChain("A", "B", "C")
-   * scala> as.zipWith(bs)(_ + _)
+   * scala> as.zipWith(bs)(_.toString + _)
    * res0: cats.data.NonEmptyChain[String] = Chain(1A, 2B, 3C)
    * }}}
    */

core/src/main/scala/cats/data/NonEmptyList.scala

@@ -295,7 +295,7 @@ final case class NonEmptyList[+A](head: A, tail: List[A]) {
    * scala> import cats.data.NonEmptyList
    * scala> val as = NonEmptyList.of(1, 2, 3)
    * scala> val bs = NonEmptyList.of("A", "B", "C")
-   * scala> as.zipWith(bs)(_ + _)
+   * scala> as.zipWith(bs)(_.toString + _)
    * res0: cats.data.NonEmptyList[String] = NonEmptyList(1A, 2B, 3C)
    * }}}
    */
@@ -369,10 +369,12 @@ final case class NonEmptyList[+A](head: A, tail: List[A]) {
    * {{{
    * scala> import scala.collection.immutable.SortedMap
    * scala> import cats.data.NonEmptyList
-   * scala> import cats.instances.boolean._
+   * scala> import cats.implicits._
    * scala> val nel = NonEmptyList.of(12, -2, 3, -5)
-   * scala> nel.groupBy(_ >= 0)
-   * res0: SortedMap[Boolean, cats.data.NonEmptyList[Int]] = Map(false -> NonEmptyList(-2, -5), true -> NonEmptyList(12, 3))
+   * scala> val expectedResult = SortedMap(false -> NonEmptyList.of(-2, -5), true -> NonEmptyList.of(12, 3))
+   * scala> val result = nel.groupBy(_ >= 0)
+   * scala> result === expectedResult
+   * res0: Boolean = true
    * }}}
    */
   def groupBy[B](f: A => B)(implicit B: Order[B]): SortedMap[B, NonEmptyList[A]] = {
@@ -398,11 +400,13 @@ final case class NonEmptyList[+A](head: A, tail: List[A]) {
    * of the keys produced by the given mapping function.
    *
    * {{{
-   * scala> import cats.data._
-   * scala> import cats.instances.boolean._
+   * scala> import cats.data.{NonEmptyList, NonEmptyMap}
+   * scala> import cats.implicits._
    * scala> val nel = NonEmptyList.of(12, -2, 3, -5)
-   * scala> nel.groupByNem(_ >= 0)
-   * res0: NonEmptyMap[Boolean, NonEmptyList[Int]] = Map(false -> NonEmptyList(-2, -5), true -> NonEmptyList(12, 3))
+   * scala> val expectedResult = NonEmptyMap.of(false -> NonEmptyList.of(-2, -5), true -> NonEmptyList.of(12, 3))
+   * scala> val result = nel.groupByNem(_ >= 0)
+   * scala> result === expectedResult
+   * res0: Boolean = true
    * }}}
    */
   def groupByNem[B](f: A => B)(implicit B: Order[B]): NonEmptyMap[B, NonEmptyList[A]] =
@@ -411,11 +415,13 @@ final case class NonEmptyList[+A](head: A, tail: List[A]) {
   /**
    * Creates new `NonEmptyMap`, similarly to List#toMap from scala standard library.
    *{{{
-   * scala> import cats.data._
-   * scala> import cats.instances.int._
+   * scala> import cats.data.{NonEmptyList, NonEmptyMap}
+   * scala> import cats.implicits._
    * scala> val nel = NonEmptyList((0, "a"), List((1, "b"),(0, "c"), (2, "d")))
-   * scala> nel.toNem
-   * res0: NonEmptyMap[Int,String] = Map(0 -> c, 1 -> b, 2 -> d)
+   * scala> val expectedResult = NonEmptyMap.of(0 -> "c", 1 -> "b", 2 -> "d")
+   * scala> val result = nel.toNem
+   * scala> result === expectedResult
+   * res0: Boolean = true
    *}}}
    *
    */

core/src/main/scala/cats/data/NonEmptySet.scala

@@ -332,7 +332,7 @@ sealed class NonEmptySetOps[A](val value: NonEmptySet[A]) {
    * scala> import cats.implicits._
    * scala> val as = NonEmptySet.of(1, 2, 3)
    * scala> val bs = NonEmptySet.of("A", "B", "C")
-   * scala> as.zipWith(bs)(_ + _)
+   * scala> as.zipWith(bs)(_.toString + _)
    * res0: cats.data.NonEmptySet[String] = TreeSet(1A, 2B, 3C)
    * }}}
    */

core/src/main/scala/cats/data/NonEmptyVector.scala

@@ -215,7 +215,7 @@ final class NonEmptyVector[+A] private (val toVector: Vector[A]) extends AnyVal
    * scala> import cats.data.NonEmptyVector
    * scala> val as = NonEmptyVector.of(1, 2, 3)
    * scala> val bs = NonEmptyVector.of("A", "B", "C")
-   * scala> as.zipWith(bs)(_ + _)
+   * scala> as.zipWith(bs)(_.toString + _)
    * res0: cats.data.NonEmptyVector[String] = NonEmptyVector(1A, 2B, 3C)
    * }}}
    */

core/src/main/scala/cats/syntax/flatMap.scala

@@ -66,7 +66,7 @@ final class FlattenOps[F[_], A](private val ffa: F[F[A]]) extends AnyVal {
    * {{{
    * scala> import cats.implicits._
    * scala> type ErrorOr[A] = Either[String, A]
-   * scala> val x: ErrorOr[ErrorOr[Int]] = Right(Right(3))
+   * scala> val x: ErrorOr[ErrorOr[Int]] = 3.asRight.asRight
    * scala> x.flatten
    * res0: ErrorOr[Int] = Right(3)
    * }}}

core/src/main/scala/cats/syntax/list.scala

@@ -40,8 +40,10 @@ final class ListOps[A](private val la: List[A]) extends AnyVal {
    *
    * scala> val list = List(12, -2, 3, -5)
    *
-   * scala> list.groupByNel(_ >= 0)
-   * res0: SortedMap[Boolean, NonEmptyList[Int]] = Map(false -> NonEmptyList(-2, -5), true -> NonEmptyList(12, 3))
+   * scala> val expectedResult = SortedMap(false -> NonEmptyList.of(-2, -5), true -> NonEmptyList.of(12, 3))
+   *
+   * scala> list.groupByNel(_ >= 0) === expectedResult
+   * res0: Boolean = true
    * }}}
    */
   def groupByNel[B](f: A => B)(implicit B: Order[B]): SortedMap[B, NonEmptyList[A]] = {
@@ -67,8 +69,10 @@ final private[syntax] class ListOpsBinCompat0[A](private val la: List[A]) extend
    *
    * scala> val list = List(12, -2, 3, -5)
    *
-   * scala> list.groupByNec(_ >= 0)
-   * res0: SortedMap[Boolean, NonEmptyChain[Int]] = Map(false -> Chain(-2, -5), true -> Chain(12, 3))
+   * scala> val expectedResult = SortedMap(false -> NonEmptyChain(-2, -5), true -> NonEmptyChain(12, 3))
+   *
+   * scala> list.groupByNec(_ >= 0) === expectedResult
+   * res0: Boolean = true
    * }}}
    */
   def groupByNec[B](f: A => B)(implicit B: Order[B]): SortedMap[B, NonEmptyChain[A]] = {

core/src/main/scala/cats/syntax/set.scala

@@ -41,8 +41,10 @@ final class SetOps[A](private val se: SortedSet[A]) extends AnyVal {
    *
    * scala> val sortedSet = SortedSet(12, -2, 3, -5)
    *
-   * scala> sortedSet.groupByNes(_ >= 0)
-   * res0: SortedMap[Boolean, NonEmptySet[Int]] = Map(false -> TreeSet(-5, -2), true -> TreeSet(3, 12))
+   * scala> val expectedResult = SortedMap(false -> NonEmptySet.of(-5, -2), true -> NonEmptySet.of(3, 12))
+   *
+   * scala> sortedSet.groupByNes(_ >= 0) === expectedResult
+   * res0: Boolean = true
    * }}}
    */
   def groupByNes[B](f: A => B)(implicit B: Order[B]): SortedMap[B, NonEmptySet[A]] = {