Fixes to laws.

Author: denisrosset

js/src/test/scala/cats/tests/FutureTests.scala

@@ -38,7 +38,7 @@ class FutureTests extends CatsSuite {
     }
 
   implicit val throwableEq: Eq[Throwable] =
-    Eq[String].on(_.toString)
+    Eq.by[Throwable, String](_.toString)
 
   implicit val comonad: Comonad[Future] = futureComonad(timeout)
 

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

@@ -94,7 +94,7 @@ class Tests extends FunSuite with Discipline {
 
   {
     // needed for Cogen[Map[...]]
-    implicit val ohe: Ordering[HasEq[Int]] = Ordering[Int].on(_.a)
+    implicit val ohe: Ordering[HasEq[Int]] = Ordering.by[HasEq[Int], Int](_.a)
     checkAll("Eq[Map[String, HasEq[Int]]]", EqTests[Map[String, HasEq[Int]]].eqv)
   }
 
@@ -365,7 +365,7 @@ class Tests extends FunSuite with Discipline {
 
   object HasHash {
     implicit def hasHash[A: Hash]: Hash[HasHash[A]] =
-      Hash.by(_.a) // not Hash[A].on(_.a) because of diamond inheritance problems with Eq
+      Hash.by(_.a)
     implicit def hasHashArbitrary[A: Arbitrary]: Arbitrary[HasHash[A]] =
       Arbitrary(arbitrary[A].map(HasHash(_)))
     implicit def hasCogen[A: Cogen]: Cogen[HasHash[A]] =