Upgrading from 0.8.1 to 0.23.3: module Plug.Swoosh.MailboxPreview is not available

[justinbkay]

When I try to compile after updating the package to 0.23.3 from 0.8.1, I get an error saying that the Plug.Swoosh.MailboxPreview module is not available. As far as I can tell everything is set up in the application correctly. The error comes from the router.ex file:

== Compilation error in file lib/refleq_web/router.ex == ** (UndefinedFunctionError) function Plug.Swoosh.MailboxPreview.init/1 is undefined (module Plug.Swoosh.MailboxPreview is not available) Plug.Swoosh.MailboxPreview.init([base_path: "/dev/mailbox"])

Router:

scope "/dev" do
  pipe_through [:browser]
  forward "/mailbox", Plug.Swoosh.MailboxPreview, base_path: "/dev/mailbox"
end

[justinbkay]

Seems as though I needed to add {:plug_cowboy, "~> 1.0"} to my mix.exs file for this to work.

[7stud]

I already had {:plug_cowboy, "~> 2.5"} in my mix.exs deps, and I was getting the warning:

 warning: Plug.Swoosh.MailboxPreview.init/1 is undefined (module Plug.Swoosh.MailboxPreview is not available or is yet to be defined)
    │
 41 │       forward "/mailbox", Plug.Swoosh.MailboxPreview
    │       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    │
    └─ lib/auction_web/router.ex:41

I searched for Plug.Swoosh.MailboxPreview and the first hit was:

HexDocs
Plug.Swoosh.MailboxPreview — Swoosh v1.14.2

So, I looked at the Swoosh docs, and Swoosh contains the module Plug.Swoosh.MailboxPreview, so I added Swoosh as a dependency in mix.exs:

defp deps do
    [
      {:phoenix, "~> 1.7.10"},
      {:phoenix_html, "~> 3.3"},
      {:phoenix_live_reload, "~> 1.2", only: :dev},
      {:phoenix_live_view, "~> 0.20.1"},
      {:floki, ">= 0.30.0", only: :test},
      {:phoenix_live_dashboard, "~> 0.8.2"},
      {:esbuild, "~> 0.8", runtime: Mix.env() == :dev},
      {:tailwind, "~> 0.2.0", runtime: Mix.env() == :dev},
      {:telemetry_metrics, "~> 0.6"},
      {:telemetry_poller, "~> 1.0"},
      {:gettext, "~> 0.20"},
      {:jason, "~> 1.2"},
      {:plug_cowboy, "~> 2.5"},
      {:auction, in_umbrella: true},
      {:swoosh, "~> 1.14.3"},
      {:hackney, "~> 1.20.1"}
    ]
  end

Then I did mix.deps get, then I started up my server: mix phx.server. Yeah, the warning:

 warning: Plug.Swoosh.MailboxPreview.init/1 is undefined (module Plug.Swoosh.MailboxPreview is not available or is yet to be defined)
    │
 41 │       forward "/mailbox", Plug.Swoosh.MailboxPreview
    │       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    │
    └─ lib/auction_web/router.ex:41

was gone...but it was replaced by this:

00:29:05.113 [notice] Application runtime_tools exited: :stopped
** (Mix) Could not start application swoosh: exited in: Swoosh.Application.start(:normal, [])
    ** (EXIT) an exception was raised:
        ** (RuntimeError) missing hackney dependency
            (swoosh 1.14.3) lib/swoosh/api_client/hackney.ex:26: Swoosh.ApiClient.Hackney.init/0
            (swoosh 1.14.3) lib/swoosh/api_client.ex:43: Swoosh.ApiClient.init/0
            (swoosh 1.14.3) lib/swoosh/application.ex:7: Swoosh.Application.start/2
            (kernel 9.1) application_master.erl:293: :application_master.start_it_old/4

What the heck, mix deps.get ??! I checked the Swoosh docs, and sure enough you have to add hackney as a dependency. I was left with this:

defp deps do
    [
      {:phoenix, "~> 1.7.10"},
      {:phoenix_html, "~> 3.3"},
      {:phoenix_live_reload, "~> 1.2", only: :dev},
      {:phoenix_live_view, "~> 0.20.1"},
      {:floki, ">= 0.30.0", only: :test},
      {:phoenix_live_dashboard, "~> 0.8.2"},
      {:esbuild, "~> 0.8", runtime: Mix.env() == :dev},
      {:tailwind, "~> 0.2.0", runtime: Mix.env() == :dev},
      {:telemetry_metrics, "~> 0.6"},
      {:telemetry_poller, "~> 1.0"},
      {:gettext, "~> 0.20"},
      {:jason, "~> 1.2"},
      {:plug_cowboy, "~> 2.5"},
      {:auction, in_umbrella: true},
      {:swoosh, "~> 1.14.3"},
      {:hackney, "~> 1.20.1"}
    ]
  end

After mix deps.get and mix phx.server: Ta da! No more warnings or errors. Good luck.