Cannot launch Elixir desktop app when MIX_ENV=test

Question

Background

I have Phoenix umbrella application. When inside said application, I can run it without issues if MIX_ENV=prod. However, if I do mix test while MIX_ENV=dev, I get an error.

Problem

The error I have is as follows:

18:39:42.101 [error] ** wx object server {:local, WebInterface} terminating
** Last message in was {:"$gen_cast", {:show, &WebInterface.Endpoint.url/0}}
** When Server state == %Desktop.Window{
  module: nil,
  taskbar: nil,
  frame: {:wx_ref, 35, :wxFrame, []},
  notifications: %{},
  webview: {:wx_ref, 49, :wxWebView, []},
  home_url: &WebInterface.Endpoint.url/0,
  last_url: nil,
  title: "Market Manager",
  rebuild: 0,
  rebuild_timer: {:interval, #Reference<0.2679771817.2635857922.255366>}
}
** Reason for termination ==
** {:badarg,
 [
   {:erlang, :binary_to_existing_atom,
    ["Elixir.WebInterface.Endpoint.HTTP", :utf8],
    [error_info: %{module: :erl_erts_errors}]},
   {:elixir_aliases, :safe_concat, 1,
    [file: ~c"src/elixir_aliases.erl", line: 139]},
   {WebInterface.Endpoint, :url, 0,
    [file: ~c"lib/web_interface/endpoint.ex", line: 4]},
   {Desktop.Window, :prepare_url, 1,
    [file: ~c"lib/desktop/window.ex", line: 666]},
   {Desktop.Window, :handle_cast, 2,
    [file: ~c"lib/desktop/window.ex", line: 604]},
   {:wx_object, :handle_msg, 5, [file: ~c"wx_object.erl", line: 493]},
   {:proc_lib, :init_p_do_apply, 3, [file: ~c"proc_lib.erl", line: 241]}
 ]}

Reading this, I understand the problem comes from my application.ex, namely:

@impl true
  def start(_type, _args) do
    children = [
      Telemetry,
      {Phoenix.PubSub, name: PubSub},
      Endpoint,
      Manager,
      %{
        id: Desktop.Window,
        start:
          {Desktop.Window, :start_link,
           [
             [
               app: :web_interface,
               id: WebInterface,
               title: "Market Manager",
               size: WindowUtils.calculate_window_size(0.6, 0.8),
               menubar: MenuBar,
               icon: "static/images/resized_logo_5_32x32.png",
               url: &WebInterface.Endpoint.url/0    # This line seems to be a problem
             ]
           ]},
        restart: :transient,
        shutdown: 5_000
      }
    ]

    opts = [strategy: :one_for_one, name: WebInterface.Supervisor]

    Supervisor.start_link(children, opts)
  end

After reading more on the subject I changed my config/test.exs to this:

import Config

config :web_interface, WebInterface.Endpoint,
  http: [ip: {127, 0, 0, 1}, port: 4002],
  secret_key_base: "some_key",
  server: true,
  check_origin: false

But this still does not fix the issue.

In contrast, this is my config/prod.exs:

config :web_interface, WebInterface.Endpoint,
  http: [ip: {127, 0, 0, 1}, port: 80],
  cache_static_manifest: "priv/static/cache_manifest.json",
  secret_key_base: "some_key",
  check_origin: false,
  server: true

But the issue still occurs.

Questions

• Why am I having this issue?
• How can I fix it?

Answer 1

Answer

Turns out that in a previous launch of the application, wxWidgets (the process) had exited in a bad state. Perhaps it crashed or something else happened, but what matters here is that trying to restart it was impossible.

I had to restart my machine to start everything in a new clean state. I also deleted the _build folder to be sure.

This solved the issue.

Answer 2

That error message is indicating a problem with wxWidgets. I'd guess that Desktop.Window is using wxWidgets. One way to insure that wxWidgets is working correctly is to try to start Erlang observer. Do this within iex:

:observer.start()

If observer starts correctly then wxWidgets is fine and the problem lies elsewhere. If it doesn't start then you'll need to figure out what's wrong with wxWidgets.

I'm not sure why Desktop would behave differently from test vs. production.