Cannot use most CLI commands in a Rails app with Hanami slices

[sandbergja]

Describe the bug

We are working to incrementally migrate a Rails application to Hanami, gradually replacing an area of the Rails code with its own dedicated slice as we go (taking this post as inspiration and a template). As such, we have Hanami stuff in slices/**/* and config/initializers/load_hanami.rb, but nothing in config/app.rb.

To Reproduce

rails new ibis
cd ibis
bundle add hanami
cat << END_INITIALIZER > config/initializers/load_hanami.rb
require 'hanami'
module IbisHanami
  class App < Hanami::App
    prepare_container { |container| container.autoloader.ignore('app') }
  end
end
Hanami.boot
END_INITIALIZER
mkdir -p slices/osprey
cat << END_SLICE > slices/osprey/my_class.rb
module Osprey
  class MyClass
    def call = 'Hello from slice!'
  end
end
END_SLICE
hanami g slice pigeon # does not generate a new slice, instead gives the usage docs for creating a new Hanami app

Expected behavior

It would be nice if there were a way to use the convenient CLI commands in applications that use hanami, but define their Hanami::App somewhere other than config/app.rb

My environment

• Ruby version: 3.4
• OS: I have seen this on both Mac OS and Linux

[katafrakt]

I think it's a good callout to support that. However, looking into how the things are built, I see at least 3 layers of problems preventing us from doing so.

1. At the top level, Hanami CLI correctly detects we are not inside a Hanami app and only offers out-of-app commands (new and version)
2. Even if we trick it into thinking we are inside a Hanami app, the slice generator still looks for config/app.rb to load some configuration
3. Even if we trick the slice generator and it generates a slice, every followup command, such as hanami g action, again looks up for config/app.rb to load the configuration

Perhaps the way without rebuilding everything would be to support something like a env variable HANAMI_APP_FILE which in this case would point to config/initializers/load_hanami.rb and would cause a bypass of checks for config/app.rb, using the value from the env var instead. This is a bit convoluted though, so maybe others have better ideas.

[timriley]

This is a fantastic use case for us to support, @sandbergja, thank you for raising this!

I think @katafrakt is onto the right direction. As a first try, let's look for an ENV["HANAMI_APP_PATH"] in the places we currently check for the hard-coded "config/app" path.

This would need changes in:

• .within_hanami_app? in lib/hanami/cli/commands.rb
• Hanami.app_path in lib/hanami.rb in the hanami gem

Once those are changed, I think that should be enough for Hanami.setup to work even with a custom ENV-provided app path, which should be enough for the right commands to run and get the app-provided config they need.

Would you be up for giving that a go, @sandbergja? We might discover another missing step or two, but we can figure that out here :)

--

Also while I'm here, may I offer a suggestion about your app setup?

Your initializer both defines the Hanami app class and immediately boots it. This means you'll end up paying the full cost of app boot whenever you want to do simpler things like just running a generator.

If you move the app class to its own separate file, and then keep the boot step in your Rails initializer, this might give you more of Hanami's lazy loading code benefits.

For example, config/hanami.rb:

require "hanami"

module IbisHanami
  class App < Hanami::App
    prepare_container { |container| container.autoloader.ignore('app') }
  end
end

And then in config/initializers/load_hanami.rb:

require_relative "../hanami"
Hanami.boot

Or some variation of the above :)

A stretch goal from here would be to try and only fully boot the Hanami app when Rails is in production environment, and then allow Hanami's standard lazy loading to work in both Rails test and development environments. This would be the closest match of the standard Hanami experience and give you the full set of code loading benefits.

I see this mixing-and-matching of Hanami and Rails as a really important aspect of our future, so I'd love to do everything I can to support you here!

[sandbergja]

Thanks, @katafrakt and @timriley !

• Thank you for the guidance on separating the two files, @timriley ! While I was trying that, I realized... there's no reason that the config/hanami.rb couldn't simply be called config/app.rb, which got the CLI commands working for me in that application.
• I'd be happy to work on the HANAMI_APP_FILE approach if it would still be useful.