Fix Macro.to_string/1 for large negative integers

Author: sabiwara

lib/elixir/lib/code/formatter.ex

@@ -1613,6 +1613,10 @@ defmodule Code.Formatter do
     color(string, :number, inspect_otps)
   end
 
+  defp insert_underscores("-" <> digits) do
+    "-" <> insert_underscores(digits)
+  end
+
   defp insert_underscores(digits) do
     cond do
       digits =~ "_" ->

lib/elixir/test/elixir/macro_test.exs

@@ -429,6 +429,16 @@ defmodule MacroTest do
     test "converts quoted to string" do
       assert Macro.to_string(quote do: hello(world)) == "hello(world)"
     end
+
+    test "large number literals" do
+      # with quote
+      assert Macro.to_string(quote do: 576_460_752_303_423_455) == "576_460_752_303_423_455"
+      assert Macro.to_string(quote do: -576_460_752_303_423_455) == "-576_460_752_303_423_455"
+
+      # without quote
+      assert Macro.to_string(576_460_752_303_423_455) == "576_460_752_303_423_455"
+      assert Macro.to_string(-576_460_752_303_423_455) == "-576_460_752_303_423_455"
+    end
   end
 
   describe "to_string/2" do