I’ve looked around for information on this in the mix format source, custom mix formatters, Elixir style guides, and haven’t found anything, so please forgive me if this has been covered…

mix format does a great job of cleaning up unnecessary spaces in Elixir code and breaks long lines into multiple lines very well.

However, while it’s great at adding newlines when needed, there doesn’t seem to be any provision for removing unnecessary newlines.

I’m working on a team where there’s a tendency to use extensive pattern matching in function definitions, etc, which results in many multiline statements. When this code is edited and shortened, often the revised statements will fit on one line, but because the formatter doesn’t do this for us, I frequently see code that has unnecessary line breaks in it. The below should illustrate what I’m seeking. Note that the entirety of this code block has mix format applied:

  # Functions w/ long params get split into multiple lines (expected, desired):
  def function(
        very_long_parameter_that_causes_line_break1,
        very_long_parameter_that_causes_line_break2
      ) do
    # ...
  end

  # Shortening the long variable names does not result in the function definition being shortened: (i would like it to)
  def function(
        shortened_param1,
        shortened_param1
      ) do
    # ...
  end

  # Manually shortening the params works, but it is laborious:
  def function(shortened_param1, shortened_param1) do
    # ...
  end

  # This applies to structs/maps, too. I'd like these unnecessary newlines to be removed...
  def function() do
    #
    %{
      a: 1
    }
  end

  # ... so that after mix format, I have:
  def function() do
    %{a: 1}
  end

Is it possible to detect and remove un-necessary newlines using mix format? I started going down the path of writing my own formatter, but am not up on all the details of the Code module and am hoping there’s an easier way - or, if not, perhaps someone can outline an example formatter that I could write which would do this.