Rails: Chaining Ruby gem dependencies? - ruby-on-rails

Question

I'm creating a Rails web application which uses a shared library of models (as a Rails Engine), stored in a subrepository (Git subtree.) This shared library contains dependencies on other Ruby gems (in my case, HTTParty and Dalli), of which I want to be automatically referenced by the parent project that includes this shared library.
However, my gem's dependencies don't appear to be resolving in the parent project, and when I start my web application, it has missing references to those gem dependencies in the shared library. (i.e. NameError: uninitialized constant ApiClient::HTTParty) If I explicitly add those references to my web app's Gemfile (as in uncomment the Gemfile lines below), everything works fine.
How do I get these dependencies to 'chain', and have the parent project automatically resolve these references?
Here's what my project looks like:
[MyRailsApp]
-- ...
-- [app]
-- [config]
-- [lib]
-- [MyLib]
-- ...
-- [app]
-- [config]
-- [lib]
-- [MyLib]
-- version.rb
-- engine.rb
-- MyLib.gemspec
-- Gemfile
-- Gemfile
MyRailsApp/Gemfile:
source 'https://rubygems.org'
gem 'activesupport', '3.2.13', :require => 'active_support'
gem 'actionpack', '3.2.13', :require => 'action_pack'
gem 'actionmailer', '3.2.13', :require => 'action_mailer'
gem 'railties', '3.2.13', :require => 'rails'
...
# gem 'dalli'
# gem 'httparty'
gem 'MyLib', :path => 'lib/MyLib'
MyLib/MyLib.gemspec:
$:.push File.expand_path("../lib", __FILE__)
# Maintain your gem's version:
require "mylib/version"
# Describe your gem and declare its dependencies:
Gem::Specification.new do |s|
s.name = "MyLib"
s.version = MyLib::VERSION
s.authors = ["David"]
s.email = ["ops#myemail.com"]
s.homepage = "http://www.mysite.com"
s.summary = "Shared Library"
s.description = "Shared Library"
s.files = Dir["{app,config,db,lib}/**/*"] + ["MIT-LICENSE", "Rakefile", "README.rdoc"]
s.add_dependency "rails", "~> 3.2.13"
s.add_dependency "dalli", ">= 2.6.4"
s.add_dependency "httparty", ">= 0.11.0"
end

Answer 1

Figured it out. I had the wrong line of thinking... I thought Gemspecs, used for installing gem dependencies (which was working just fine), would also be used by Rails to determine what dependencies need to be loaded into memory when the application starts. This is not the case, at least, not when using Rails engines.
For the average gem, it appears that a typical Rails web app has a line in the boot.rb file which loads all gems and dependencies in the application Gemfile. However, this autoloading does not appear to extend to Rails engines listed in the Gemfile. In this case, you must load your dependencies into application memory manually, by finding the engine.rb file (in your Rails engine) and adding require 'yourgem' at the beginning of the file. This will load the dependency when the engine loads.
A friend found and linked me this relevant question/answer, if this explanation isn't sufficient:
https://stackoverflow.com/a/5850503

Answer 2

If you want rubygems to understand your dependencies, package each of them with a proper .gemspec file. You don't have to publish your gem, it can be private and referenced via a git:// type URL.
The thing is, generally your .gemspec needs to be at the root level. You can't bury it in your project as Rubygems does not go out of its way to look for these.
In your use case, MyLib should be a separate thing.