Port contravariant to new scheme

core/src/main/scala-3/cats/derived/DerivedContravariant.scala

@@ -0,0 +1,35 @@
+package cats.derived
+
+import cats.{Contravariant, Functor}
+import shapeless3.deriving.{Const, K1}
+
+import scala.annotation.implicitNotFound
+import scala.compiletime.*
+
+@implicitNotFound("""Could not derive an instance of Contravariant[F] where F = ${F}.
+Make sure that F[_] satisfies one of the following conditions:
+  * it is a constant type [x] =>> T
+  * it is a nested type [x] =>> G[H[x]] where G: Functor and H: Contravariant
+  * it is a generic case class where all fields have a Contravariant instance
+  * it is a generic sealed trait where all subclasses have a Contravariant instance""")
+type DerivedContravariant[F[_]] = Derived[Contravariant[F]]
+object DerivedContravariant:
+  type Or[F[_]] = Derived.Or[Contravariant[F]]
+  inline def apply[F[_]]: Contravariant[F] =
+    import DerivedContravariant.given
+    summonInline[DerivedContravariant[F]].instance
+
+  given [T]: DerivedContravariant[Const[T]] = new Contravariant[Const[T]]:
+    def contramap[A, B](fa: T)(f: B => A): T = fa
+
+  given [F[_], G[_]](using F: DerivedFunctor.Or[F], G: Or[G]): DerivedContravariant[[x] =>> F[G[x]]] =
+    given Contravariant[G] = G.unify
+    F.unify.composeContravariant[G]
+
+  given [F[_]](using inst: => K1.Instances[Or, F]): DerivedContravariant[F] =
+    given K1.Instances[Contravariant, F] = inst.unify
+    new Generic[Contravariant, F] {}
+
+  trait Generic[T[x[_]] <: Contravariant[x], F[_]](using inst: K1.Instances[T, F]) extends Contravariant[F]:
+    final override def contramap[A, B](fa: F[A])(f: B => A): F[B] =
+      inst.map(fa: F[A])([f[_]] => (tf: T[f], fa: f[A]) => tf.contramap(fa)(f))

core/src/main/scala-3/cats/derived/package.scala

@@ -26,8 +26,9 @@ extension (x: Traverse.type) inline def derived[F[_]]: Traverse[F] = DerivedTrav
 extension (x: NonEmptyTraverse.type) inline def derived[F[_]]: NonEmptyTraverse[F] = DerivedNonEmptyTraverse[F]
 extension (x: SemigroupK.type) inline def derived[F[_]]: SemigroupK[F] = DerivedSemigroupK[F]
 extension (x: MonoidK.type) inline def derived[F[_]]: MonoidK[F] = DerivedMonoidK[F]
+extension (x: Contravariant.type) inline def derived[F[_]]: Contravariant[F] = DerivedContravariant[F]
 
-object semiauto extends ContravariantDerivation, InvariantDerivation, PartialOrderDerivation, Instances:
+object semiauto extends InvariantDerivation, PartialOrderDerivation, Instances:
 
   inline def eq[A]: Eq[A] = DerivedEq[A]
   inline def hash[A]: Hash[A] = DerivedHash[A]
@@ -49,6 +50,7 @@ object semiauto extends ContravariantDerivation, InvariantDerivation, PartialOrd
   inline def show[A]: Show[A] = DerivedShow[A]
   inline def semigroupK[F[_]]: SemigroupK[F] = DerivedSemigroupK[F]
   inline def monoidK[F[_]]: MonoidK[F] = DerivedMonoidK[F]
+  inline def contravariant[F[_]]: Contravariant[F] = DerivedContravariant[F]
 
 object auto:
   object eq:
@@ -110,3 +112,6 @@ object auto:
 
   object monoidK:
     inline given [F[_]](using NotGiven[MonoidK[F]]): MonoidK[F] = DerivedMonoidK[F]
+
+  object contravariant:
+    inline given [F[_]](using NotGiven[Contravariant[F]]): Contravariant[F] = DerivedContravariant[F]

core/src/test/scala-3/cats/derived/ContravariantSuite.scala

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2015 Miles Sabin
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cats
+package derived
+
+import cats.laws.discipline.*
+import cats.laws.discipline.arbitrary.*
+import cats.laws.discipline.eq.*
+import scala.compiletime.*
+
+class ContravariantSuite extends KittensSuite:
+  import ContravariantSuite.*
+  import TestDefns.*
+
+  inline def contravariantTests[F[_]]: ContravariantTests[F] = ContravariantTests[F](summonInline)
+
+  inline def testContravariant(context: String): Unit =
+    checkAll(s"$context.Contravariant[OptPred]", contravariantTests[OptPred].contravariant[MiniInt, String, Boolean])
+    checkAll(s"$context.Contravariant[TreePred]", contravariantTests[TreePred].contravariant[MiniInt, String, Boolean])
+    checkAll(s"$context.Contravariant[ListPred]", contravariantTests[ListPred].contravariant[MiniInt, String, Boolean])
+    checkAll(
+      s"$context.Contravariant[GenericAdtPred]",
+      contravariantTests[GenericAdtPred].contravariant[MiniInt, String, Boolean]
+    )
+    // TODO https://github.com/typelevel/kittens/issues/473
+    // checkAll(
+    //   s"$context.Contravariant[InterleavedPred]",
+    //   ContravariantTests[InterleavedPred].contravariant[MiniInt, String, Boolean]
+    // )
+    checkAll(
+      s"$context.Contravariant[AndCharPred]",
+      contravariantTests[AndCharPred].contravariant[MiniInt, String, Boolean]
+    )
+    checkAll(
+      s"$context.Contravariant[ListSnocF]",
+      contravariantTests[ListSnocF].contravariant[MiniInt, String, Boolean]
+    )
+    checkAll(
+      s"$context.Contravariant is Serializable",
+      SerializableTests.serializable(summonInline[Contravariant[TreePred]])
+    )
+
+    // TODO https://github.com/typelevel/kittens/issues/476
+    // test(s"$context.Contravariant.contramap is stack safe") {
+    //   val C = summonInline[Contravariant[ListSnocF]]
+    //   val n = 10000
+    //   val largeBoxed = Snoc.fromSeq((1 until n).map((j: Int) => (i: Int) => i + j)) :: Nil
+    //   val actualBoxed = C.contramap[Int, Int](largeBoxed)((j: Int) => j + 1).flatMap(Snoc.toList)
+    //   val expected = (3 until n + 2).toList
+    //   assert(actualBoxed.map(_.apply(1)) == expected)
+    // }
+
+  locally {
+    import auto.contravariant.given
+    testContravariant("auto")
+  }
+
+  locally {
+    import semiInstances.given
+    testContravariant("semiauto")
+  }
+
+object ContravariantSuite:
+  import TestDefns.*
+
+  type OptPred[A] = Option[A => Boolean]
+  type ListPred[A] = List[A => Boolean]
+  type GenericAdtPred[A] = GenericAdt[A => Boolean]
+  type ListSnocF[A] = List[Snoc[A => Int]]
+  type InterleavedPred[A] = Interleaved[A => Boolean]
+  type AndCharPred[A] = (A => Boolean, Char)
+  type TreePred[A] = Tree[A => Boolean]
+
+  object semiInstances:
+    implicit val optPred: Contravariant[OptPred] = semiauto.contravariant
+    implicit val treePred: Contravariant[TreePred] = semiauto.contravariant
+    implicit val listPred: Contravariant[ListPred] = semiauto.contravariant
+    implicit val genericAdtPred: Contravariant[GenericAdtPred] = semiauto.contravariant
+    // implicit val interleavePred: Contravariant[InterleavedPred] = semiauto.contravariant
+    implicit val andCharPred: Contravariant[AndCharPred] = semiauto.contravariant
+    implicit val listSnocF: Contravariant[ListSnocF] = semiauto.contravariant
+
+  case class Single[A](value: A => Unit) derives Contravariant
+
+  enum Many[-A] derives Contravariant:
+    case Naught
+    case More(value: A => Unit, rest: Many[A])
+
+  enum AtMostOne[-A] derives Contravariant:
+    case Naught
+    case Single(value: A => Unit)
+
+  enum AtLeastOne[-A] derives Contravariant:
+    case Single(value: A => Unit)
+    case More(value: A => Unit, rest: Option[AtLeastOne[A]])

core/src/test/scala-3/cats/derived/MonoidKSuite.scala

@@ -7,13 +7,13 @@ import cats.laws.discipline.{MonoidKTests, SerializableTests}
 import org.scalacheck.Arbitrary
 import scala.compiletime.*
 
-class MonoidKSuite extends KittensSuite {
+class MonoidKSuite extends KittensSuite:
   import MonoidKSuite.*
   import TestDefns.*
 
   inline def monoidKTests[F[_]]: MonoidKTests[F] = MonoidKTests[F](summonInline)
 
-  inline def testMonoidK(context: String): Unit = {
+  inline def testMonoidK(context: String): Unit =
     checkAll(s"$context.MonoidK[ComplexProduct]", monoidKTests[ComplexProduct].monoidK[Char])
     checkAll(s"$context.MonoidK[CaseClassWOption]", monoidKTests[CaseClassWOption].monoidK[Char])
     checkAll(s"$context.MonoidK[BoxMul]", monoidKTests[BoxMul].monoidK[Char])
@@ -24,32 +24,29 @@ class MonoidKSuite extends KittensSuite {
       assert(M.empty[Char] == Box(Mul[Char](1)))
       assert(M.combineK(Box(Mul[Char](5)), Box(Mul[Char](5))) == Box(Mul[Char](25)))
     }
-  }
 
-  {
+  locally {
     import auto.monoidK.given
     testMonoidK("auto")
   }
 
-  {
+  locally {
     import monInstances.given
     testMonoidK("semi")
   }
-}
 
-object MonoidKSuite {
+object MonoidKSuite:
   import TestDefns._
 
   type BoxMul[A] = Box[Mul[A]]
 
-  object monInstances {
+  object monInstances:
     implicit val complexProduct: MonoidK[ComplexProduct] = semiauto.monoidK
     implicit val caseClassWOption: MonoidK[CaseClassWOption] = semiauto.monoidK
     implicit val boxMul: MonoidK[BoxMul] = semiauto.monoidK
-  }
 
   final case class Mul[T](value: Int)
-  object Mul {
+  object Mul:
 
     implicit def eqv[T]: Eq[Mul[T]] = Eq.by(_.value)
 
@@ -60,8 +57,6 @@ object MonoidKSuite {
       def empty[A] = Mul(1)
       def combineK[A](x: Mul[A], y: Mul[A]) = Mul(x.value * y.value)
     }
-  }
 
   case class Simple[A](value1: List[A], value2: Set[A]) derives MonoidK
   case class Recursive[A](first: List[A], rest: Recursive[A]) derives MonoidK
-}

core/src/test/scala-3/cats/derived/SemigroupKSuite.scala

@@ -5,13 +5,13 @@ import cats.laws.discipline.{SemigroupKTests, SerializableTests}
 import org.scalacheck.Arbitrary
 import scala.compiletime.*
 
-class SemigroupKSuite extends KittensSuite {
+class SemigroupKSuite extends KittensSuite:
   import SemigroupKSuite.*
   import TestDefns.*
 
   inline def semigroupKTests[F[_]]: SemigroupKTests[F] = SemigroupKTests[F](summonInline)
 
-  inline def testSemigroupK(context: String): Unit = {
+  inline def testSemigroupK(context: String): Unit =
     checkAll(s"$context.SemigroupK[ComplexProduct]", semigroupKTests[ComplexProduct].semigroupK[Char])
     checkAll(s"$context.SemigroupK[CaseClassWOption]", semigroupKTests[CaseClassWOption].semigroupK[Char])
     checkAll(s"$context.SemigroupK[BoxMul]", semigroupKTests[BoxMul].semigroupK[Char])
@@ -23,7 +23,6 @@ class SemigroupKSuite extends KittensSuite {
     test(s"$context.SemigroupK respects existing instances") {
       assert(summonInline[SemigroupK[BoxMul]].combineK(Box(Mul[Char](5)), Box(Mul[Char](5))) == Box(Mul[Char](25)))
     }
-  }
 
   locally {
     import auto.semigroupK.given
@@ -34,21 +33,19 @@ class SemigroupKSuite extends KittensSuite {
     import semiInstances.given
     testSemigroupK("semiauto")
   }
-}
 
-object SemigroupKSuite {
-  import TestDefns._
+object SemigroupKSuite:
+  import TestDefns.*
 
   type BoxMul[A] = Box[Mul[A]]
 
-  object semiInstances {
+  object semiInstances:
     implicit val complexProduct: SemigroupK[ComplexProduct] = semiauto.semigroupK
     implicit val caseClassWOption: SemigroupK[CaseClassWOption] = semiauto.semigroupK
     implicit val boxMul: SemigroupK[BoxMul] = semiauto.semigroupK
-  }
 
   final case class Mul[T](value: Int)
-  object Mul {
+  object Mul:
 
     implicit def eqv[T]: Eq[Mul[T]] = Eq.by(_.value)
 
@@ -58,8 +55,6 @@ object SemigroupKSuite {
     implicit val semigroupK: SemigroupK[Mul] = new SemigroupK[Mul] {
       def combineK[A](x: Mul[A], y: Mul[A]) = Mul(x.value * y.value)
     }
-  }
 
   case class Simple[A](value1: List[A], value2: Set[A]) derives SemigroupK
   case class Recursive[A](first: List[A], rest: Recursive[A]) derives SemigroupK
-}