So, I’m writing my home project with Elixir, everything’s going fine, decided to plug dialyxir to scan for some potential issues and it gives me this one error:

lib/http_server.ex:60:unmatched_return
The expression produces a value of type:

:ok | pid()

but this value is unmatched.

Code in question:

  defp accept_loop(listen_socket, %State{} = state) do
    state = %{state | total_calls: state.total_calls + 1}

    case :gen_tcp.accept(listen_socket) do # LINE 60, issue is here
      {:ok, client_socket} ->
        spawn(fn -> serve(client_socket, state) end)

      {:error, data} ->
        Logger.notice("Error accepting client socket - #{inspect(data)}")
    end

    accept_loop(listen_socket, state)
  end

Error about unmatched value from gen_tcp.accept. Everything’s working fine and according to documentation I’m matching values just fine - gen_tcp — OTP 29.0.2 (kernel 11.0.2) :

accept(ListenSocket) -> {ok, Socket} | {error, Reason}

I am matching both {:ok, socket} and {:error, reason} so I am at a loss now. What is going on?

Tried adding guard to :ok match - {:ok, client_socket} when is_port(client_socket) -> but mix dialyzer still returns same error.

Tried capturing first variable and checking whether it’s :ok or a pid - {test, client_socket} when test == :ok or is_pid(test) - still same error.