Swoosh crashes if phx.new.ecto does not get run with --no-mailer

[adonig]

Environment

• Elixir version (elixir -v): 1.16.2
• Phoenix version (mix deps): 1.7.12
• Operating system: Fedora Linux 39 (Workstation Edition)

Actual behavior

$ mix phx.new.ecto domain
* creating domain/lib/domain/application.ex
* creating domain/lib/domain.ex
* creating domain/test/test_helper.exs
* creating domain/README.md
* creating domain/mix.exs
* creating domain/.gitignore
* creating domain/.formatter.exs
* creating domain/lib/domain/repo.ex
* creating domain/priv/repo/migrations/.formatter.exs
* creating domain/priv/repo/seeds.exs
* creating domain/test/support/data_case.ex

Fetch and install dependencies? [Yn] 
* running mix deps.get
* running mix deps.compile

We are almost there! The following steps are missing:

    $ cd domain

Then configure your database in config/dev.exs and run:

    $ mix ecto.create

You can run your app inside IEx (Interactive Elixir) as:

    $ iex -S mix

$ cd domain
$ mix ecto.create
Compiling 3 files (.ex)
Generated domain app
The database for Domain.Repo has been created
$ iex -S mix
10:40:25.899 [error] Could not find hackney dependency.

Please add :hackney to your dependencies:

    {:hackney, "~> 1.9"}

Or set your own Swoosh.ApiClient:

    config :swoosh, :api_client, MyAPIClient

10:40:25.907 [notice] Application swoosh exited: exited in: Swoosh.Application.start(:normal, [])
    ** (EXIT) an exception was raised:
        ** (RuntimeError) missing hackney dependency
            (swoosh 1.16.3) lib/swoosh/api_client/hackney.ex:26: Swoosh.ApiClient.Hackney.init/0
            (swoosh 1.16.3) lib/swoosh/api_client.ex:43: Swoosh.ApiClient.init/0
            (swoosh 1.16.3) lib/swoosh/application.ex:7: Swoosh.Application.start/2
            (kernel 9.2.2) application_master.erl:293: :application_master.start_it_old/4
10:40:25.932 [notice] Application finch exited: :stopped
10:40:25.932 [notice] Application nimble_options exited: :stopped
10:40:25.934 [notice] Application nimble_pool exited: :stopped
10:40:25.936 [notice] Application mint exited: :stopped
10:40:25.936 [notice] Application hpax exited: :stopped
10:40:25.936 [notice] Application castore exited: :stopped
10:40:25.936 [notice] Application mime exited: :stopped
10:40:25.936 [notice] Application xmerl exited: :stopped
10:40:25.938 [notice] Application ecto_sql exited: :stopped
10:40:25.938 [notice] Application postgrex exited: :stopped
10:40:25.939 [notice] Application db_connection exited: :stopped
10:40:25.940 [notice] Application ecto exited: :stopped
10:40:25.940 [notice] Application jason exited: :stopped
10:40:25.940 [notice] Application decimal exited: :stopped
10:40:25.941 [notice] Application telemetry exited: :stopped
10:40:25.941 [notice] Application eex exited: :stopped
10:40:25.941 [notice] Application phoenix_pubsub exited: :stopped
10:40:25.941 [notice] Application dns_cluster exited: :stopped
10:40:25.942 [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 1.16.3) lib/swoosh/api_client/hackney.ex:26: Swoosh.ApiClient.Hackney.init/0
            (swoosh 1.16.3) lib/swoosh/api_client.ex:43: Swoosh.ApiClient.init/0
            (swoosh 1.16.3) lib/swoosh/application.ex:7: Swoosh.Application.start/2
            (kernel 9.2.2) application_master.erl:293: :application_master.start_it_old/4

Expected behavior

I believe phx.new.ecto should by default run with --no-mailer.

$ mix phx.new.ecto domain --no-mailer
* creating domain/lib/domain/application.ex
* creating domain/lib/domain.ex
* creating domain/test/test_helper.exs
* creating domain/README.md
* creating domain/mix.exs
* creating domain/.gitignore
* creating domain/.formatter.exs
* creating domain/lib/domain/repo.ex
* creating domain/priv/repo/migrations/.formatter.exs
* creating domain/priv/repo/seeds.exs
* creating domain/test/support/data_case.ex

Fetch and install dependencies? [Yn] 
* running mix deps.get
* running mix deps.compile

We are almost there! The following steps are missing:

    $ cd domain

Then configure your database in config/dev.exs and run:

    $ mix ecto.create

You can run your app inside IEx (Interactive Elixir) as:

    $ iex -S mix

$ cd domain/
$ mix ecto.create
Compiling 1 file (.ex)
Generated domain app
The database for Domain.Repo has already been created
$ iex -S mix
Erlang/OTP 26 [erts-14.2.3] [source] [64-bit] [smp:20:20] [ds:20:20:10] [async-threads:1] [jit:ns]

Interactive Elixir (1.16.2) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> 

[adonig]

Okay, if we make --no-mailer the default, then it becomes impossible to create an Ecto project with Swoosh mailer files.

I believe Phoenix first needs boolean command line arguments that can be true and false, so it's possible to say:

$ mix phx.new.ecto domain --mailer

Now the default would create a new minimal Ecto project that just works as expected and at the same time it is still possible to add Swoosh if required.

EDIT: Nevermind, I realized it is already possible and it was just about setting the default value. See my PR.