Precompiling assets for deployment within a Rails Engine

[demsullivan]

There's a couple of threads on here about Rails engines, but we ran into trouble pretty quickly following the advice from #95 and the example engine code in examples/

This post is intended to illustrate an issue we ran into with gem version mismatches, and how we solved it, in the hopes that this might help others who are using Rails Engines!

Setup

Our setup follows the example engine almost exactly:

# engine_root/lib/my_engine/engine.rb
module MyEngine do
  class Engine < ::Rails::Engine
    isolate_namespace MyEngine
    delegate :vite_ruby, to: :class

    def self.vite_ruby
      @vite_ruby ||= ViteRuby.new(root: root)
    end

    config.app_middleware.use(Rack::Static,
                              urls: ["/#{vite_ruby.config.public_output_dir}"],
                              root: root.join(vite_ruby.config.public_dir))

    initializer 'vite_rails_engine.proxy' do |app|
      if vite_ruby.run_proxy?
        app.middleware.insert_before 0, ViteRuby::DevServerProxy, ssl_verify_none: true, vite_ruby: vite_ruby
      end
    end

    initializer 'vite_rails_engine.logger' do
      config.after_initialize do
        vite_ruby.logger = Rails.logger
      end
    end
  end
end

# engine_root/app/helpers/my_engine/application_helper.rb
module MyEngine
  class ApplicationHelper
    def vite_manifest
      MyEngine::Engine.vite_ruby.manifest
    end
  end
end

// engine_root/config/vite.json
{
  "all": {
    "sourceCodeDir": "app/frontend",
    "publicOutputDir": "my-engine-vite",
    "watchAdditionalPaths": []
  },
  "development": {
    "autoBuild": true,
    "host": "my_engine_vite",
    "port": 3115
  },
  "test": {
    "autoBuild": true,
    "port": 3117
  }
}

Deployment Issues

This setup works great for development - as long as we're running a separate bin/vite dev within the engine's root, we get full HMR on the engine, etc.

For precompiling and deployment, however, we ran into problems when the gem versions in the engine's Gemfile.lock differ from the host app. In this case, when we run bin/vite build from within the engine, we get the following error:

$ cd `bundle show my_engine` && bin/vite build
0.839 /bundle/gems/bundler-2.5.5/lib/bundler/definition.rb:570:in `materialize': Could not find nio4r-2.7.0, activesupport-7.1.3, irb-1.11.2, reline-0.4.2, railties-7.1.3, actionpack-7.1.3, rack-3.0.9, actionview-7.1.3, activemodel-7.1.3, nokogiri-1.16.2-x86_64-linux, rails-7.1.3, sidekiq-7.2.1, actioncable-7.1.3, httpx-1.2.2, bigdecimal-3.1.6, minitest-5.22.2, thor-1.3.0, actionmailbox-7.1.3, actionmailer-7.1.3, actiontext-7.1.3, activejob-7.1.3, activerecord-7.1.3, activestorage-7.1.3, redis-client-0.19.1, ruby-next-core-1.0.1, ffi-compiler-1.0.1, net-smtp-0.4.0.1, marcel-1.0.2 in locally installed gems (Bundler::GemNotFound)
0.839   from /bundle/gems/bundler-2.5.5/lib/bundler/definition.rb:203:in `specs'
0.839   from /bundle/gems/bundler-2.5.5/lib/bundler/definition.rb:270:in `specs_for'
0.839   from /bundle/gems/bundler-2.5.5/lib/bundler/runtime.rb:18:in `setup'
0.839   from /bundle/gems/bundler-2.5.5/lib/bundler.rb:162:in `setup'
0.839   from /bundle/gems/bundler-2.5.5/lib/bundler/setup.rb:26:in `block in <top (required)>'
0.839   from /bundle/gems/bundler-2.5.5/lib/bundler/ui/shell.rb:159:in `with_level'
0.839   from /bundle/gems/bundler-2.5.5/lib/bundler/ui/shell.rb:111:in `silence'
0.839   from /bundle/gems/bundler-2.5.5/lib/bundler/setup.rb:26:in `<top (required)>'
0.839   from <internal:/usr/local/lib/ruby/3.3.0/rubygems/core_ext/kernel_require.rb>:127:in `require'
0.839   from <internal:/usr/local/lib/ruby/3.3.0/rubygems/core_ext/kernel_require.rb>:127:in `require'
0.839   from /bundle/ruby/3.3.0/bundler/gems/my_engine-89a07ebe7438/bin/vite:25:in `<main>'

Solution

As a preliminary solution, we found that running bin/vite within the host app and overriding the config with environment variables allowed us to successfully compile the engine's assets.

Following the above example:

VITE_RUBY_ROOT=`bundle show my_engine` VITE_RUBY_PUBLIC_OUTPUT_DIR=my-engine-vite bin/vite build

As a next step, I'm looking into automating this... possibly by hooking into the vite:build Rake task, iterating over all of the gems that have a config/vite.json, reading the values from it, and running the above command from the host app's root.

If anyone has any additional suggestions, happy to hear them! Otherwise, hope this helps someone ❤️