mix format does not respect max line length

[albertored]

Environment

Erlang/OTP 23 [erts-11.2.2.4] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1]
Elixir 1.12.2 (compiled with Erlang/OTP 23)

Problem

mix format behaves differently in version 1.12.2 with respect with 1.10.4.

In .formatter.exs the line length is set to 120 and with elixir 1.10.4 this file is formatted as follows:

defmodule A do
  defp info(version, exclude) do
    %Info{
      title: "XXX",
      version: "1.2.3",
      description: """

      #{
        :app
        |> Application.fetch_env!(:doc_resources_changelog_path)
        |> read_or_empty_string()
        |> clean_tagged_string(exclude)
      }

      #{
        :app
        |> Application.fetch_env!(:doc_schema_version_path)
        |> read_or_empty_string()
        |> clean_lines_containing(exclude)
      }

      """
    }
  end
end

With elixir 1.12.2 it is instead formatted with the pipes on single lines despite they both exceed the maximum line length (129 and 127 chars)

defmodule A do
  defp info(version, exclude) do
    %Info{
      title: "XXX",
      version: "1.2.3",
      description: """

      #{:app |> Application.fetch_env!(:doc_resources_changelog_path) |> read_or_empty_string() |> clean_tagged_string(exclude)}

      #{:app |> Application.fetch_env!(:doc_schema_version_path) |> read_or_empty_string() |> clean_lines_containing(exclude)}

      """
    }
  end
end

[josevalim]

Yes, the formatter tries to break where it can, but in many occasions it cannot. It is your responsibility to break it apart.

The change in v1.12 is because the large interpolations in the middle of strings were largely unhelpful and the code will almost always be clearer if you move the logic to outside. :) So yeah, the formatter is hinting you to break it apart. :)

Thanks for the report!