Support js_root generator option for controller and manifest tasks.

[jhirn]

This PR aims to support paths other than app/javascript for the root path in generator and manifest tasks. Similar attempts have been made/requested, but this PR uses config.generators instead of an initializer to set js_root. A small drawback is the manifest tasks load :environment to access configuration from application.rb, but it plays nicely with generator help message and doesn't pollute the Stimulus namespace. Here's the usage:

module Rails4Lyfe
  class Application < Rails::Application
    ...

    config.generators do |g|
      ...
      g.stimulus          :stimulus, skip_manifest: true, js_root: 'app/frontend'
      ...
    end
  end
end

I like using the generator because it keeps the controller consistent with the // Connects to data-controller=.. comment and naming conventions which get tricky with camelCase, under_score and dash-erized in play. Because the path is hard coded in the generator, the only option is to monkey patch it. Monkey patching the generator in my project made it difficult to reference the template from inside the gem requiring me to copy template as well.

If there's support for this option I'd be happy to proceed with updating docs and tests, although I had a pretty tough time getting the suite to run locally. Also open to suggestions for the name js_root and if we should respect this configuration for the stimulus:install tasks, but didn't want to make changes bigger without a green light.

Thank you for considering this PR.

[dhh]

Wouldn't js_root always be set, given that you have a default for the class_option? If so, I don't think we need to repeat the default here. And in fact, I'd just inline the entire call in the Rails.root.join.

[jhirn]

I love the idea of using the class_option, however the value in Rails.application.config.generators is not set on the class without instantiating an instance with the options. I actually quite like this approach as the default is only in one place:

def controllers_path
  Rails.root.join(StimulusGenerator.new(['stimulus'], generator_options, {}).options.js_root, "controllers")
end

def generator_options
  Rails.application.config.generators.options.dig(:stimulus)
end

I also had to add the following require statement to load StimulusGenerator.

# stimulus_tasks.rake
require "generators/stimulus/stimulus_generator"

# This worked in the rake task, but perhaps more appropriate in stimulus_generator.rb
# Let me know if its better to have them in the rake task instead of the generator. 
require 'rails/generators'
require 'rails/generators/actions'
require "rails/generators/named_base" # already present

This also eliminates needing to add :environment to the rake tasks for a reason I do not fully grok, but I'm totally ok with.

[jhirn]

I pushed up this change. LMK what you think.

However this pans out, thanks for the code review 👍

[dhh]

Always use " instead of ' for strings.