Do not set step to nil in ranges

Closes #12076

Author: josevalim

lib/elixir/lib/kernel.ex

@@ -3862,8 +3862,18 @@ defmodule Kernel do
   end
 
   defp range(:guard, first, last) do
+    # We need to compute the step using guards. We don't have conditionals,
+    # but we can emulate them using a map access.
+    step =
+      quote do
+        :erlang.map_get(
+          :erlang.>(unquote(first), unquote(last)),
+          %{false: unquote(1), true: unquote(-1)}
+        )
+      end
+
     # TODO: Deprecate me inside guard when sides are not integers on Elixir v1.17
-    {:%{}, [], [__struct__: Elixir.Range, first: first, last: last, step: nil]}
+    {:%{}, [], [__struct__: Elixir.Range, first: first, last: last, step: step]}
   end
 
   defp range(:match, first, last) do
@@ -4355,18 +4365,6 @@ defmodule Kernel do
 
   defp small_literal_list?(_list), do: false
 
-  defp in_range(left, first, last, nil) do
-    # TODO: nil steps are only supported due to x..y in guards. Remove me on Elixir 2.0.
-    quote do
-      :erlang.is_integer(unquote(left)) and :erlang.is_integer(unquote(first)) and
-        :erlang.is_integer(unquote(last)) and
-        ((:erlang."=<"(unquote(first), unquote(last)) and
-            unquote(increasing_compare(left, first, last))) or
-           (:erlang.<(unquote(last), unquote(first)) and
-              unquote(decreasing_compare(left, first, last))))
-    end
-  end
-
   defp in_range(left, first, last, step) when is_integer(step) do
     in_range_literal(left, first, last, step)
   end

lib/elixir/test/elixir/range_test.exs

@@ -35,7 +35,7 @@ defmodule RangeTest do
     assert Range.new(3, 1, -2) == 3..1//-2
   end
 
-  test "op" do
+  test "fields" do
     assert (1..3).first == 1
     assert (1..3).last == 3
     assert (1..3).step == 1
@@ -57,6 +57,12 @@ defmodule RangeTest do
     assert Range.shift(10..0//-2, -2) == 14..4//-2
   end
 
+  test "in guard equality" do
+    case {1, 1..1} do
+      {n, range} when range == n..n -> true
+    end
+  end
+
   test "limits are integer only" do
     first = 1.0
     last = 3.0