Fix Macro.to_string/1 for large negative integers

Author: sabiwara

lib/elixir/lib/code/formatter.ex

@@ -1621,18 +1621,27 @@ defmodule Code.Formatter do
       byte_size(digits) >= 6 ->
         digits
         |> String.to_charlist()
-        |> Enum.reverse()
-        |> Enum.chunk_every(3)
-        |> Enum.intersperse(~c"_")
-        |> List.flatten()
-        |> Enum.reverse()
+        |> insert_underscores_charlist()
         |> List.to_string()
 
       true ->
         digits
     end
   end
 
+  defp insert_underscores_charlist([?- | rest]) do
+    [?- | insert_underscores_charlist(rest)]
+  end
+
+  defp insert_underscores_charlist(digits) do
+    digits
+    |> Enum.reverse()
+    |> Enum.chunk_every(3)
+    |> Enum.intersperse(~c"_")
+    |> List.flatten()
+    |> Enum.reverse()
+  end
+
   defp escape_heredoc(string, escape) do
     string = String.replace(string, escape, "\\" <> escape)
     heredoc_to_algebra(["" | String.split(string, "\n")])

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