This worries me for the fact following gems which are not included in any blocks are ruled out:

gem 'json'
gem 'sqlite3'
gem "ruby-debug"

Can you please elaborate this?

Yes, these gems are not auto-required by Bundler as of right now. You do however get their lib load paths added to $LOAD_PATH (that is true for all gems in all of the groups :assets, :test, :cucumber, :ci etc), so manually issuing require 'ruby-debug' will work (as will require 'capybara' in :development mode Rails console).

This however is not the expected result of adding gem dependency into Gemfile of a typical Rails app.

@radar: what's your thought on this?

The reason this works:

gem 'json'
gem 'sqlite3'

is because Rails or other gems issue manual requires for the json and sqlite3 gems. If you were to change the Gemfile like this:

group :this_is_never_used do
  gem 'json'
  gem 'sqlite3'
end

everything would still work.

I'm also not sure about requiring ruby-debug all the time, maybe it should be moved into the :development group?

Why is this patching the spec/dummy generator? I am not sure what this is fixing.

@radar: This is fixing spree/dummy (not spec/dummy) generator template that is being used by the sandbox app. I was using the sandbox as it seemed to be the simplest way to test my rails-dev-boost (faster Rails dev. mode) plugin with Spree. See the ticket referenced right above your reply.

Ah right then. Seems logical to me.