Soft deprecate size/1

Closes #2356

Author: José Valim

CHANGELOG.md

@@ -15,6 +15,7 @@
   * [Kernel] Ensure Mix `_build` structure works on Windows when copying projects
 
 * Soft deprecations (no warnings emitted)
+  * [Kernel] `size/1` is deprecated, please use `byte_size/1` or `tuple_size/1` instead
   * [ExUnit] `teardown/2` and `teardown_all/2` are deprecated in favor of `on_exit/1` callbacks
 
 * Deprecations

lib/elixir/lib/kernel.ex

@@ -225,6 +225,11 @@ defmodule Kernel do
     :erlang.setelement(index + 1, tuple, value)
   end
 
+  @doc false
+  def size(arg) do
+    :erlang.size(arg)
+  end
+
   ## END OF DEPRECATED
 
   @doc """
@@ -665,18 +670,6 @@ defmodule Kernel do
     :erlang.self()
   end
 
-  @doc """
-  Returns the size of the given argument, which must be a tuple or a binary.
-
-  Prefer using `tuple_size/1` or `byte_size/1` instead.
-
-  Allowed in guard tests. Inlined by the compiler.
-  """
-  @spec size(tuple|binary) :: non_neg_integer
-  def size(arg) do
-    :erlang.size(arg)
-  end
-
   @doc """
   Spawns the given function and returns its pid.
 

lib/elixir/src/elixir_dispatch.erl

@@ -444,7 +444,6 @@ inline(?kernel, 'rem', 2) -> {erlang, 'rem'};
 inline(?kernel, round, 1) -> {erlang, round};
 inline(?kernel, self, 0) -> {erlang, self};
 inline(?kernel, send, 2) -> {erlang, send};
-inline(?kernel, size, 1) -> {erlang, size};
 inline(?kernel, spawn, 1) -> {erlang, spawn};
 inline(?kernel, spawn, 3) -> {erlang, spawn};
 inline(?kernel, spawn_link, 1) -> {erlang, spawn_link};
@@ -483,6 +482,9 @@ inline(?string, to_integer, 2) -> {erlang, binary_to_integer};
 inline(?system, stacktrace, 0) -> {erlang, get_stacktrace};
 inline(?tuple, to_list, 1) -> {erlang, tuple_to_list};
 
+%% DEPRECATED
+inline(?kernel, size, 1) -> {erlang, size};
+
 inline(_, _, _) -> false.
 
 check_deprecation(Meta, Receiver, Name, Arity, #{file := File}) ->