Credo.Check.Refactor.LongQuoteBlocks (Credo v1.7.12)

Basics

This check has a base priority of high and works with any version of Elixir.

Explanation

Long quote blocks are generally an indication that too much is done inside them.

Let's look at why this is problematic:

defmodule MetaCommand do
  def __using__(opts \\ []) do
    modes = opts[:modes]
    command_name = opts[:command_name]

    quote do
      def run(filename) do
        contents =
          if File.exists?(filename) do
            {:ok, file} = File.open(filename, unquote(modes))
            {:ok, contents} = IO.read(file, :line)
            File.close(file)
            contents
          else
            ""
          end

        case contents do
          "" ->
            # ...
          unquote(command_name) <> rest ->
            # ...
        end
      end

      # ...
    end
  end
end

A cleaner solution would be to call "regular" functions outside the quote block to perform the actual work.

defmodule MyMetaCommand do
  def __using__(opts \\ []) do
    modes = opts[:modes]
    command_name = opts[:command_name]

    quote do
      def run(filename) do
        MyMetaCommand.run_on_file(filename, unquote(modes), unquote(command_name))
      end

      # ...
    end
  end

  def run_on_file(filename, modes, command_name) do
    contents =
      # actual implementation
  end
end

This way it is easier to reason about what is actually happening. And to debug it.

Check-Specific Parameters

Use the following parameters to configure this check:

:max_line_count

The maximum number of lines a quote block should be allowed to have.

This parameter defaults to 150.

:ignore_comments

Ignores comments when counting the lines of a quote block.

This parameter defaults to false.

General Parameters

Like with all checks, general params can be applied.

Parameters can be configured via the .credo.exs config file.