Add more deprecations scheduled to v1.18

Author: josevalim

CHANGELOG.md

@@ -17,6 +17,11 @@ This release no longer supports WERL (a graphical user interface for the Erlang
   * [EEx] `<%#` is deprecated in favor of `<%!--` or `<% #`
   * [EEx] `c:EEx.handle_text/2` is deprecated in favor of `c:EEx.handle_text/3`
 
+#### Elixir
+
+  * [Enumerable] Deprecate returning a two-arity function in `Enumerable.slice/1`
+  * [Range] Deprecate inferring negative ranges on `Range.new/2`
+
 #### Mix
 
   * [mix cmd] Deprecate `mix cmd --app APP` in favor of `mix do --app APP`

lib/elixir/lib/enum.ex

@@ -2416,13 +2416,17 @@ defmodule Enum do
         {:ok, count, fun} when is_function(fun, 1) ->
           slice_list(fun.(enumerable), random_count(count), 1, 1)
 
-        # TODO: Deprecate me in Elixir v1.18.
-        {:ok, count, fun} when is_function(fun, 2) ->
-          fun.(random_count(count), 1)
-
         {:ok, count, fun} when is_function(fun, 3) ->
           fun.(random_count(count), 1, 1)
 
+        # TODO: Remove deprecation on Elixir v1.20.
+        {:ok, count, fun} when is_function(fun, 2) ->
+          IO.warn(
+            "#{inspect(Enumerable.impl_for(enumerable))} must return a three arity function on slice/1"
+          )
+
+          fun.(random_count(count), 1)
+
         {:error, _} ->
           take_random(enumerable, 1)
       end
@@ -4492,8 +4496,16 @@ defmodule Enum do
         amount = Kernel.min(amount, count - start) |> amount_with_step(step)
         enumerable |> fun.() |> slice_exact(start, amount, step, count)
 
-      # TODO: Deprecate me in Elixir v1.18.
+      {:ok, count, fun} when is_function(fun, 3) ->
+        amount = Kernel.min(amount, count - start) |> amount_with_step(step)
+        fun.(start, amount, step)
+
+      # TODO: Remove me on v2.0.
       {:ok, count, fun} when is_function(fun, 2) ->
+        IO.warn(
+          "#{inspect(Enumerable.impl_for(enumerable))} must return a three arity function on slice/1"
+        )
+
         amount = Kernel.min(amount, count - start)
 
         if step == 1 do
@@ -4503,10 +4515,6 @@ defmodule Enum do
           |> take_every_list(amount, step - 1)
         end
 
-      {:ok, count, fun} when is_function(fun, 3) ->
-        amount = Kernel.min(amount, count - start) |> amount_with_step(step)
-        fun.(start, amount, step)
-
       {:error, module} ->
         slice_enum(enumerable, module, start, amount, step)
     end
@@ -4565,11 +4573,18 @@ defmodule Enum do
 
   defp slice_count_and_fun(enumerable, step) do
     case Enumerable.slice(enumerable) do
+      {:ok, count, fun} when is_function(fun, 1) ->
+        {count, &slice_exact(fun.(enumerable), &1, &2, &3, count)}
+
       {:ok, count, fun} when is_function(fun, 3) ->
         {count, fun}
 
-      # TODO: Deprecate me in Elixir v1.18.
+      # TODO: Remove me on v2.0
       {:ok, count, fun} when is_function(fun, 2) ->
+        IO.warn(
+          "#{inspect(Enumerable.impl_for(enumerable))} must return a three arity function on slice/1"
+        )
+
         if step == 1 do
           {count, fn start, amount, 1 -> fun.(start, amount) end}
         else
@@ -4580,9 +4595,6 @@ defmodule Enum do
            end}
         end
 
-      {:ok, count, fun} when is_function(fun, 1) ->
-        {count, &slice_exact(fun.(enumerable), &1, &2, &3, count)}
-
       {:error, module} ->
         {list, count} =
           enumerable

lib/elixir/lib/module/behaviour.ex

@@ -144,7 +144,7 @@ defmodule Module.Behaviour do
   end
 
   defp impl_behaviours({function, arity}, defaults, kind, value, behaviours, callbacks) do
-    impls = for n <- arity..(arity - defaults), do: {function, n}
+    impls = for n <- (arity - defaults)..arity, do: {function, n}
     impl_behaviours(impls, kind, value, behaviours, callbacks)
   end
 

lib/elixir/lib/range.ex

@@ -184,8 +184,22 @@ defmodule Range do
 
   @spec new(limit, limit) :: t
   def new(first, last) when is_integer(first) and is_integer(last) do
-    # TODO: Deprecate inferring a range with a step of -1 on Elixir v1.18
-    step = if first <= last, do: 1, else: -1
+    step =
+      if first <= last do
+        1
+      else
+        # TODO: Remove me on v2.0
+        IO.warn_once(
+          {__MODULE__, :new},
+          fn ->
+            "Range.new/2 has a default step of -1, please call Range.new/3 explicitly passing the step of -1 instead"
+          end,
+          3
+        )
+
+        -1
+      end
+
     %Range{first: first, last: last, step: step}
   end
 

lib/elixir/unicode/tokenizer.ex

@@ -42,7 +42,7 @@ defmodule String.Tokenizer do
         case name do
           "<" <> _ when is_integer(first) ->
             last = String.to_integer(codepoint, 16)
-            {Enum.to_list(last..first), nil}
+            {Enum.to_list(last..first//-1), nil}
 
           "<" <> _ ->
             first = String.to_integer(codepoint, 16)