Dialyzer error - the pattern can never match the type

Questions / Help
,
1

I’m getting the following error:

________________________________________________________________________________
lib/teiserver_web/live/account/profile/overview.ex:315:pattern_match
The pattern can never match the type.

Pattern:
true

Type:
{:failure, binary()}

Here is the line it is referencing:

This is calling another function that looks like

  @spec server_allows_join?(T.userid(), integer(), String.t() | nil) ::
          {:failure, String.t()} | true
  def server_allows_join?(userid, lobby_id, password \\ nil) do
    lobby = get_lobby(lobby_id)
    user = Account.get_user_by_id(userid)

    # In theory this would never happen but it's possible to see this at startup when
    # not everything is loaded and ready, hence the case statement
    {consul_response, consul_reason} =
      case Coordinator.call_consul(lobby_id, {:request_user_join_lobby, userid}) do
        {a, b} ->
          {a, b}

        nil ->
          {true, nil}

        v ->
          Logger.error("ConsulServer can_join? error, response #{Kernel.inspect(v)}")
          {false, "ConsulServer error on can_join? call"}
      end

    ignore_password =
      Enum.any?([
        CacheUser.is_moderator?(user),
        Enum.member?(user.roles, "Caster"),
        consul_reason in [:override_approve, :allow_friends]
      ])

    ignore_locked =
      Enum.any?([
        CacheUser.is_moderator?(user),
        Enum.member?(user.roles, "Caster"),
        consul_reason == :override_approve
      ])

    cond do
      user == nil ->
        {:failure, "You are not a user"}

      lobby == nil ->
        {:failure, "No lobby found (type 1, lobby is nil for server_allows_join?)"}

      lobby.locked == true and ignore_locked == false ->
        {:failure, "Battle locked"}

      lobby.password != nil and password != lobby.password and not ignore_password ->
        {:failure, "Invalid password"}

      consul_response == false ->
        {:failure, consul_reason}

      CacheUser.is_restricted?(user, ["All lobbies", "Joining existing lobbies"]) ->
        {:failure, "You are currently banned from joining lobbies"}

      true ->
        true
    end
  end

It seems like this function can return true so not sure what’s going on.

2

I believe that dialyzer is saying that Account.get_user_by_default can never return anything that isn’t covered by the prior clauses of the cond expression.

Dialyzer is saying it can never reach the true clause of the cond - that the other clauses exhaustively covers what it believes it will see.

3

Not sure if it’s directly causing the failure you’re seeing, but some of the functions in CacheUser are incorrectly typed. For instance, is_restricted?:

The first argument is typed as T.userid() | T.user(), but there are heads for T.userid() | T.user() | nil.

The second argument is typed as String.t() but there are also heads that support list(String.t())

1 Like
4

That worked! Thanks.