Add missing :erlang.size/1 guard, closes #9789

Author: josevalim

lib/elixir/lib/module/types/pattern.ex

@@ -275,6 +275,7 @@ defmodule Module.Types.Pattern do
     {:binary_part, 3} => {[:binary, :integer, :integer], :binary},
     {:bit_size, 1} => {[:binary], :integer},
     {:byte_size, 1} => {[:binary], :integer},
+    {:size, 1} => {[{:union, [:binary, :tuple]}], :boolean},
     {:div, 2} => {[:integer, :integer], :integer},
     {:rem, 2} => {[:integer, :integer], :integer},
     {:node, 0} => {[], :atom},

lib/elixir/test/elixir/module/types_test.exs

@@ -161,6 +161,11 @@ defmodule Module.TypesTest do
                quoted_head([x], [is_tuple(is_atom(x))])
     end
 
+    test "erlang-only guards" do
+      assert quoted_head([x], [:erlang.size(x)]) ==
+               {:ok, [{:union, [:binary, :tuple]}]}
+    end
+
     test "failing guard functions" do
       assert quoted_head([x], [length([])]) == {:ok, [{:var, 0}]}