Potential formatter bug - newlines don't seem to be added as expected

[pdgonzalez872]

Elixir and Erlang/OTP versions

latest main, Erlang 27

Operating system

Linux + Mac

Current behavior

Hi!

This came up in the Elixir forum: https://elixir-lang.slack.com/archives/C03EPRA3B/p1727466551251699

I had a little bit of time yesterday after Jason (@axelson) shared his snippet, so I chatted with him and played around with the code.

The following test case fails but it seems like it should pass?

# place it in lib/elixir/test/elixir/code_formatter/general_test.exs
test "with def followed by module attribute" do
  bad = """
  defmodule Example do
    @impl FooA
    def a(), do: :something
    @impl FooB
    def b() do
      :something_else
    end
  end
  """

  good = """
  defmodule Example do
    @impl FooA
    def a(), do: :something

    @impl FooB
    def b() do
      :something_else
    end
  end
  """

  assert_format bad, good
end

with this error (note only one \n):

  1) test blocks with def followed by module attribute (Code.Formatter.GeneralTest)
     lib/elixir/test/elixir/code_formatter/general_test.exs:873
     Assertion with == failed
     code:  assert IO.iodata_to_binary(Code.format_string!(bad, opts)) == result
     left:  "defmodule Example do\n  @impl FooA\n  def a(), do: :something\n  @impl FooB\n  def b() do\n    :something_else\n  end\nend"
     right: "defmodule Example do\n  @impl FooA\n  def a(), do: :something\n\n  @impl FooB\n  def b() do\n    :something_else\n  end\nend"
     stacktrace:
       lib/elixir/test/elixir/code_formatter/general_test.exs:897: (test)

I have a commit that makes the above pass, I'll push it up shortly.

Expected behavior

The test should pass