Rails 3: define plugin gem dependency - ruby-on-rails

Question

I wrote a plugin that requires a gem as a dependency.
Where do I have to define this dependency?
I have tried to create a Gemfile in vendor/plugins/my_plugin/, but bundle install doesn‛t find this file.

Answer 1

Ok. I have solved.
1) Create a Gemfile in vendor/plugins/my_plugin like:
# Gemfile
source "http://rubygems.org"
gemspec
2) Create a gemspec file. In the folder vendor/plugins run this command:
bundle gem my_plugin
(Note this command ask you for overwrite some files. Check the files before answer: Y)
3) Open gemspec file in vendor/plugins/my_plugin/ and add before the keyword end:
s.add_dependency('will_paginate', '~> 3.0.pre2')
(In this example I have used will_paginate how required dipendency of my_plugin)
4) Now go in your rails app and edit Gemfile, add:
gem 'my_plugin', :path=>'vendor/plugins/my_plugin'
The path specified supposed that your plugin is already in vendor/plugins folder of your rails app.
Of course when deploy rails app you don't need anymore to specify :path argument.
5) Now in rails app root do:
bundle install
And dependency of my_plugin (will_paginate in this case) is installed.
Thank to Sinetris for initial input.

Answer 2

Create a Gemfile in your vendor/plugins/my_plugin/ like:
# Gemfile
source "http://rubygems.org"
gemspec
gem "your-dependency-gem-name"
note the gemspec directive.
Take a look at Using Bundler with Rubygem gemspecs for more information.

Answer 3

Sebtm's own answer is quite good, but it still didn't work as Tiago and orangechicken described. I had to add
require 'your-dependency-gem-name'
on top of lib/my_plugin.rb right before the engine of my_plugin is loaded.
See http://guides.rubyonrails.org/engines.html#other-gem-dependencies

Answer 4

Gemfile in the application folder.
# Bundle the extra gems:
# gem 'bj'
# gem 'nokogiri'
# gem 'sqlite3-ruby', :require => 'sqlite3'
# gem 'aws-s3', :require => 'aws/s3

Answer 5

Reference for myself. If you're making a plugin that should work with Rails as a RailTie, use rails plugin my_plugin to create the gem instead of bundle gem my_plugin. It saves you (me) a lot of trouble.
Edit: When do you need the gem to work as a RailTie? Whenever you want to add rails generator, rake tasks or add your code to a Rails app (Called Rails Engine).
/Edit
$ rails plugin new my_plugin
then you add dependencies
Gem::Specification.new do |s|
#...
s.add_dependency "rails"
s.add_runtime_dependency "heroku"
s.add_development_dependency "sqlite3"
end
to include it in your rails app, use path: as described by #Sebtm
or release it to rubygems.
$ gem build my_plugin.gemspec
$ gem push my_plugin-0.7.0.gem #replace version number
#in Gemfile, as always
gem 'my_plugin'
or tag it on github. (use their release UI) and depend on it using
gem 'my_plugin', github: 'accountname/my_plugin', tag: 'v0.7.0'