Fix #3039 (#3126)

* Hash[Map[K, V]] has unnecessary constraint #3039

* fix binary compatibility

* Simplify names, adjust deprecation messages

* Make bincompat-only auxiliary constructor package-private

Author: travisbrown

core/src/main/scala/cats/instances/sortedSet.scala

@@ -73,7 +73,7 @@ trait SortedSetInstances extends SortedSetInstances1 {
 private[instances] trait SortedSetInstances1 {
   @deprecated("Use cats.kernel.instances.sortedSet.catsKernelStdHashForSortedSet", "2.0.0-RC2")
   private[instances] def catsKernelStdHashForSortedSet[A: Order: Hash]: Hash[SortedSet[A]] =
-    cats.kernel.instances.sortedSet.catsKernelStdHashForSortedSet[A]
+    cats.kernel.instances.sortedSet.catsKernelStdHashForSortedSet[A](Hash[A])
 
   @deprecated("Use cats.kernel.instances.sortedSet.catsKernelStdSemilatticeForSortedSet", "2.0.0-RC2")
   def catsKernelStdSemilatticeForSortedSet[A: Order]: BoundedSemilattice[SortedSet[A]] =
@@ -93,8 +93,12 @@ private[instances] trait SortedSetInstancesBinCompat0 {
 
 private[instances] trait SortedSetInstancesBinCompat1 extends LowPrioritySortedSetInstancesBinCompat1 {
   // TODO: Remove when this is no longer necessary for binary compatibility.
-  implicit override def catsKernelStdHashForSortedSet[A: Order: Hash]: Hash[SortedSet[A]] =
-    cats.kernel.instances.sortedSet.catsKernelStdHashForSortedSet[A]
+  // Note that the overrides here and below are only necessary because the
+  // definitions in `SortedSetInstances1` conflict with the ones in
+  // `cats.kernel.instances.SortedSetInstances`. Both are inherited here, so
+  // we have to "bubble" the "correct" ones up to the appropriate place.
+  implicit override def catsKernelStdHashForSortedSet[A: Hash]: Hash[SortedSet[A]] =
+    cats.kernel.instances.sortedSet.catsKernelStdHashForSortedSet[A](Hash[A])
 }
 
 private[instances] trait LowPrioritySortedSetInstancesBinCompat1
@@ -103,8 +107,12 @@ private[instances] trait LowPrioritySortedSetInstancesBinCompat1
   implicit override def catsKernelStdOrderForSortedSet[A: Order]: Order[SortedSet[A]] =
     cats.kernel.instances.sortedSet.catsKernelStdOrderForSortedSet[A]
 
+  implicit override def catsKernelStdHashForSortedSet[A: Hash]: Hash[SortedSet[A]] =
+    cats.kernel.instances.sortedSet.catsKernelStdHashForSortedSet[A](Hash[A])
+
+  @deprecated("Use cats.kernel.instances.sortedSet.catsKernelStdHashForSortedSet", "2.0.0-RC2")
   override def catsKernelStdHashForSortedSet[A: Order: Hash]: Hash[SortedSet[A]] =
-    cats.kernel.instances.sortedSet.catsKernelStdHashForSortedSet[A]
+    cats.kernel.instances.sortedSet.catsKernelStdHashForSortedSet[A](Hash[A])
 }
 
 @deprecated("Use cats.kernel.instances.SortedSetHash", "2.0.0-RC2")

kernel/src/main/scala/cats/kernel/instances/SortedSetInstances.scala

@@ -1,11 +1,14 @@
 package cats.kernel
 package instances
 
-import cats.kernel.{BoundedSemilattice, Hash, Order}
 import scala.collection.immutable.SortedSet
 
 trait SortedSetInstances extends SortedSetInstances1 {
-  implicit def catsKernelStdHashForSortedSet[A: Order: Hash]: Hash[SortedSet[A]] =
+  @deprecated("Use catsKernelStdHashForSortedSet override without Order", "2.1.0")
+  def catsKernelStdHashForSortedSet[A: Order: Hash]: Hash[SortedSet[A]] =
+    new SortedSetHash[A]
+
+  implicit def catsKernelStdHashForSortedSet[A: Hash]: Hash[SortedSet[A]] =
     new SortedSetHash[A]
 }
 
@@ -28,9 +31,13 @@ class SortedSetOrder[A: Order] extends Order[SortedSet[A]] {
     StaticMethods.iteratorEq(s1.iterator, s2.iterator)
 }
 
-class SortedSetHash[A: Order: Hash] extends Hash[SortedSet[A]] {
+// FIXME use context bound in 3.x
+class SortedSetHash[A](implicit hashA: Hash[A]) extends Hash[SortedSet[A]] {
   import scala.util.hashing.MurmurHash3._
 
+  @deprecated("Use the constructor _without_ Order instead, since Order is not required", "2.1.0")
+  private[instances] def this(o: Order[A], h: Hash[A]) = this()(h)
+
   // adapted from [[scala.util.hashing.MurmurHash3]],
   // but modified standard `Any#hashCode` to `ev.hash`.
   def hash(xs: SortedSet[A]): Int = {
@@ -50,7 +57,7 @@ class SortedSetHash[A: Order: Hash] extends Hash[SortedSet[A]] {
     finalizeHash(h, n)
   }
   override def eqv(s1: SortedSet[A], s2: SortedSet[A]): Boolean =
-    StaticMethods.iteratorEq(s1.iterator, s2.iterator)(Order[A])
+    StaticMethods.iteratorEq(s1.iterator, s2.iterator)(Eq[A])
 }
 
 class SortedSetSemilattice[A: Order] extends BoundedSemilattice[SortedSet[A]] {