fix funK scala3 type infer

modules/kernel/higherKind/src/main/scala-3/tofu/syntax/functionK.scala

@@ -0,0 +1,33 @@
+package tofu.syntax
+
+import cats.~>
+
+object funk {
+
+  def makeFunctionK[F[_], G[_]](maker: ContextNT[F, G]): F ~> G = toFunK(maker)
+
+  def funK[F[_], G[_]](maker: ContextNT[F, G]) = toFunK(maker)
+
+  def funKFrom[F[_]] = new Applied1[F](true)
+
+  type ContextNT[F[_], G[_]] = (arb: { type _A }) ?=> F[arb._A] => G[arb._A]
+
+  private def toFunK[F[_], G[_]](maker: ContextNT[F, G]): F ~> G =
+    new ~>[F, G] {
+      def apply[A](fa: F[A]): G[A] =
+        given { type _A = A } = new { type _A = A }
+        maker(fa)
+    }
+
+  final class Applied1[F[_]](private val __ : Boolean) extends AnyVal {
+    def apply[G[_]](maker: ContextNT[F, G]): F ~> G =
+      toFunK[F, G](maker)
+  }
+
+  // RepresentableK uses Maker
+  abstract class Maker[F[_], G[_], Arbitrary] extends (F ~> G) {
+    def applyArbitrary(f: F[Arbitrary]): G[Arbitrary]
+
+    def apply[A](fa: F[A]): G[A] = applyArbitrary(fa.asInstanceOf[F[Arbitrary]]).asInstanceOf[G[A]]
+  }
+}

modules/kernel/higherKind/src/test/scala/tofu/syntax/functionKSpec.scala

@@ -0,0 +1,26 @@
+package tofu.syntax
+
+import org.scalatest.funsuite.AnyFunSuite
+import cats.{Id, ~>}
+
+class functionKSpec extends AnyFunSuite {
+  def infer1(x: Id ~> Option): Unit = ()
+
+  test("funK infers type args") {
+    assertCompiles(
+      """|import tofu.syntax.funk._
+         |infer1(funK(Some(_)))
+         |""".stripMargin
+    )
+  }
+
+  def infer2[F[_]](x: F ~> Option): Unit = ()
+
+  test("funKFrom infers type args") {
+    assertCompiles(
+      """|import tofu.syntax.funk._
+         |infer2(funKFrom[Id](Some(_)))
+         |""".stripMargin
+    )
+  }
+}