`mix openapi.spec.json` task could not start application.

[alishir]

I have a project that connects to a message broker on startup. When I tried to generate API specs using mix openapi.spec.json --spec MyProj.ApiSpec, I got the following error, because my application could not connect to the broker from the build server.

** (Mix) Could not start application my_proj: MyProj.Application.start(:normal, []) returned an error: shutdown: failed to start child: MyProj.BrokerConn

Do you know how should I generate API spec without trying to connect to the broker?

[mbuhot]

I'd create a custom mix task, giving you control over how much of the app is running at the time the spec is generated.
It could be as simple as:

defmodule Mix.Tasks.MyApp.OpenApiSpec do
  def run([output_file]) do
    json =
      MyApp.ApiSpec.spec()
      |> Jason.encode!(pretty: true)

    :ok = File.write!(output_file, json)
  end
end

Although I'm not sure if there's some amount of initialisation that would be required to allow you to discover the phoenix routes? The phx.routes doesn't seem to require anything special.