feat: +invariantK instance for Mid

modules/kernel/higherKind/src/main/scala-2/tofu/higherKind/Mid.scala

@@ -1,7 +1,7 @@
 package tofu.higherKind
 import cats.data.Chain
-import cats.tagless.ApplyK
-import cats.{Monoid, MonoidK, Semigroup}
+import cats.tagless.{ApplyK, InvariantK}
+import cats.{Monoid, MonoidK, Semigroup, ~>}
 import tofu.higherKind.Mid.MidCompose
 import tofu.syntax.funk.funK
 
@@ -47,13 +47,22 @@ trait MidInstances extends MidInstances1 {
 
 trait MidInstances1 {
   implicit def midAlgebraSemigroup[F[_], U[f[_]]: ApplyK]: Semigroup[U[Mid[F, *]]] = new MidAlgebraSemigroup[F, U]
+
+  private val midInvariantInstance: InvariantK[Mid[*[_], Any]] = new MidInvariantK()
+  implicit def midInvariantK[A]: InvariantK[Mid[*[_], A]]      = midInvariantInstance.asInstanceOf[InvariantK[Mid[*[_], A]]]
 }
 
 class MidMonoidK[F[_]] extends MonoidK[Mid[F, *]] {
   def empty[A]: Mid[F, A]                                = fa => fa
   def combineK[A](x: Mid[F, A], y: Mid[F, A]): Mid[F, A] = fa => x(y(fa))
 }
 
+class MidInvariantK extends InvariantK[Mid[*[_], Any]] {
+  def imapK[F[_], G[_]](af: Mid[F, Any])(fk: F ~> G)(gk: G ~> F): Mid[G, Any] = { ga =>
+    fk(af(gk(ga)))
+  }
+}
+
 class MidAlgebraMonoid[F[_], U[f[_]]: MonoidalK] extends MidAlgebraSemigroup[F, U] with Monoid[U[Mid[F, *]]] {
   def empty: U[Mid[F, *]] = Mid.point[F].pureK[U]
 }

modules/kernel/higherKind/src/test/scala-2/tofu/higherKind/MidSuite.scala

@@ -1,13 +1,14 @@
 package tofu.higherKind
 
-import cats.tagless.ApplyK
+import cats.tagless.{ApplyK, InvariantK}
 import cats.{Monoid, Semigroup}
 import tofu.higherKind.Mid._
 
 object MidSuite {
   def summonMidInstances[F[_], U[_[_]]: ApplyK, W[_[_]]: MonoidalK](): Unit = {
     implicitly[Semigroup[U[Mid[F, *]]]]
     implicitly[Monoid[W[Mid[F, *]]]]
+    implicitly[InvariantK[Mid[*[_], Any]]]
     ()
   }
 }