rules:
  - id: enum_map_join
    message: >-
      Using `Enum.map_join/3` is more efficient than using `Enum.map/2 |> Enum.join/2`.
    severity: WARNING
    languages:
      - elixir
    pattern-either:
      - pattern: |
          Enum.join(Enum.map($E, $FUN), $JOINER)
      - pattern: |
          Enum.map($E, $FUN)
          |> Enum.join($JOINER)
      - pattern: |
          $E
          |> Enum.map($FUN)
          |> Enum.join($JOINER)
    fix: |
      $E
      |> Enum.map_join($JOINER, $FUN end)
    metadata:
      references:
        - https://github.com/rrrene/credo/blob/master/lib/credo/check/refactor/map_join.ex
      category: best-practice
      technology:
        - elixir