Use one-indexed args for clarity, closes #10518

lib/elixir/lib/kernel/utils.ex

@@ -267,7 +267,7 @@ defmodule Kernel.Utils do
                   {new_var, acc}
 
                 %{} ->
-                  generated = String.to_atom("arg" <> Integer.to_string(map_size(acc)))
+                  generated = String.to_atom("arg" <> Integer.to_string(map_size(acc) + 1))
                   new_var = Macro.var(generated, Elixir)
                   {new_var, Map.put(acc, pair, {new_var, var})}
               end

lib/elixir/test/elixir/kernel/guard_test.exs

@@ -428,8 +428,8 @@ defmodule Kernel.GuardTest do
 
       assert expand_defguard_to_string(:with_unused_vars, args, nil) == """
              (
-               {arg0, arg1} = {1 + 1, 2 + 2}
-               :erlang.+(arg0, arg1)
+               {arg1, arg2} = {1 + 1, 2 + 2}
+               :erlang.+(arg1, arg2)
              )
              """
     end
@@ -445,8 +445,8 @@ defmodule Kernel.GuardTest do
 
       assert expand_defguard_to_string(:with_reused_vars, args, nil) == """
              (
-               {arg0, arg1, arg2} = {1 + 1, 2 + 2, 3 + 3}
-               :erlang.+(:erlang.+(:erlang.+(arg0, arg0), arg1), arg2)
+               {arg1, arg2, arg3} = {1 + 1, 2 + 2, 3 + 3}
+               :erlang.+(:erlang.+(:erlang.+(arg1, arg1), arg2), arg3)
              )
              """
     end