Vfrdtyky

I have some code that is failing dialyzer and I cannot understand why. No matter what I put into the @spec at the top of the function, calls to that function return a puzzling dialyzer error. Here is a simplification of the function. As far as I can tell, I have spec'd the function correctly.

@spec balances(uuid :: String.t(), retries :: non_neg_integer) ::

        {:ok, list()}

        | {:internal_server_error, String.t(), String.t()}

        | {:internal_server_error, map | list, String.t()}

def fakebal(uuid, retries \ 0) do

  url = "/url/for/balances" |> process_url



  case HTTPoison.get(

         url,

         [, {"Content-Type", "application/json"}],

         

       ) do

    {:ok, %HTTPoison.Response{status_code: 200, body: body}} ->

      response = Poison.decode!(body, as: %{"message" => [%Currency{}]})



      cond response["message"] do

        length(bal) > 0 ->

          {:ok, bal}



        retries >= 1 ->

          {:ok, }



        true ->

          init(uuid)

          balances(uuid, retries + 1)

      end



    {:error, %HTTPoison.Error{reason: reason}} ->

      Notifier.notify(url, reason, Helpers.line_info(__ENV__))

      {:internal_server_error, reason, url}



    {_, %HTTPoison.Response{body: body} = res} ->

      response = Poison.decode!(body)

      Notifier.notify(url, response, Helpers.line_info(__ENV__))



      {:internal_server_error, response, url}

  end

end

My issue is that every call across the codebase to this function is failing if I expect to get anything other than {:ok, balances}:

  user_balances =

    case balances(uuid) do

      {:ok, user_balances} -> user_balances

      _ ->  # Dialyzer error here

    end

Dialyzer warns that The variable _ can never match since previous clauses completely covered the type {'ok',[map()]}. I read this to mean that any call to balances will always return {:ok, balances}, but that can't be true as the case statement for HTTPoison.get is the last thing evaluated in the function, and it appears to have only three possible results:

• {:ok, list}


• {:internal_server_error, String.t(), String.t()}


• 
  {:internal_server_error, map | list, String.t()}.

I understand that I am likely missing something very obvious but I can't figure out what it is. Any help would be greatly appreciated. Thank You!

Thanks to @legoscia's comment, I investigated the call to Notifier.notify, and sure enough there is a dialyzer warning in that function as well (I have PR out to an open source project to fix the spec that is causing the notify function to fail dialyzer). If I modify the notify function such that no warning occurs, sure enough the calls to balances no longer produce dialyzer warnings.

tl;dr If dialyzer gives you a warning about a function that doesn't appear to be incorrectly specified, start going through the function calls within your function to find a downstream dialyzer error.