Optimize Enum.to_list for ranges (#12384)

Closes #12383

2 files changed, 21 insertions, 0 deletions

diff --git a/lib/elixir/lib/enum.ex b/lib/elixir/lib/enum.ex
index bcea77bca..d9bcde75f 100644
--- a/lib/elixir/lib/enum.ex
+++ b/lib/elixir/lib/enum.ex
@@ -3675,6 +3675,7 @@ defmodule Enum do
   """
   @spec to_list(t) :: [element]
   def to_list(enumerable) when is_list(enumerable), do: enumerable
+  def to_list(%{__struct__: Range} = range), do: Range.to_list(range)
   def to_list(%_{} = enumerable), do: reverse(enumerable) |> :lists.reverse()
   def to_list(%{} = enumerable), do: Map.to_list(enumerable)
   def to_list(enumerable), do: reverse(enumerable) |> :lists.reverse()
diff --git a/lib/elixir/lib/range.ex b/lib/elixir/lib/range.ex
index 23af606af..7bde6701f 100644
--- a/lib/elixir/lib/range.ex
+++ b/lib/elixir/lib/range.ex
@@ -390,6 +390,26 @@ defmodule Range do
   end
 
   @doc """
+  Converts a range to a list.
+  """
+  @doc since: "1.15.0"
+  def to_list(first..last//step)
+      when step > 0 and first <= last
+      when step < 0 and first >= last do
+    :lists.seq(first, last, step)
+  end
+
+  def to_list(_first.._last//_step) do
+    []
+  end
+
+  # TODO: Remove me on v2.0
+  def to_list(%{__struct__: Range, first: first, last: last}) do
+    step = if first <= last, do: 1, else: -1
+    :lists.seq(first, last, step)
+  end
+
+  @doc """
   Checks if two ranges are disjoint.
 
   ## Examples