Dialyzer has inferred that check_rating_to_play and check_rank_to_play can ONLY return :ok, so it deduces that those branches of the cond are dead.

The issue is sneaky, but ultimately comes from get_failed_rating_check_text and get_failed_rank_check_text returning the wrong type.

A walkthrough of what’s happening. Start in this code, from check_rating_to_play:

    cond do
      state.minimum_rating_to_play != nil and player_rating < state.minimum_rating_to_play ->
        msg = get_failed_rating_check_text(player_rating, state, rating_type)
        {:error, msg}
# maximum clause omitted
      true ->
        # All good
        :ok
    end

What’s the type of msg? It’s the return type of get_failed_rating_check_text.

What’s that type? It’s [String.t()]!

  def get_failed_rating_check_text(player_rating, consul_state, rating_type) do
    bounds = get_rating_bounds_for_title(consul_state)
    player_rating_text = player_rating |> Decimal.from_float() |> Decimal.round(2)

    [
      @splitter,
      "You don't meet the rating requirements for this lobby (#{bounds}). Your #{rating_type} match rating is #{player_rating_text}. Learn more about rating here:",
      "https://www.beyondallreason.info/guide/rating-and-lobby-balance#openskill"
    ]
  end

Dialyzer sees this and infers that the minimum_rating_to_play branch of the cond would make the function return {:error, [String.t()]}.

The function is not specced to return that type, so Dialyzer infers that that branch does not execute, so check_rating_to_play “always” returns :ok.

When I run Dialyzer locally, it also complains about get_coordinator_userid not being called - further evidence it has deduced that those branches are dead.

Replacing the lists in get_failed_rating_check_text and get_failed_rank_check_text with a literal string makes all three messages go away, verifying the diagnosis.

Possible fixes:

• join the strings together in get_failed_rating_check_text etc

• widen the type of check_rating_to_play etc to :ok, {:error, iodata()}