How to add dependency of a local gem to a rails plugin/engine, in .gemspec file

Question

I had tried in this way：

 s.add_dependency 'gem', :path => '../gem'

like add gem in the gemfile, but it doesn't work, and will cause this error:

/Users/chenqh/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/requirement.rb:81:in `parse': Illformed requirement 

Answer 1

It's likely not possible to add local dependencies because other users will not be able to access the gem as it is local dependent and hence of no use after publish. Instead of that, Add remote dependency in your own plugin's gemspec.

Steps -

1) Open gemspec file of your own plugin 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 required dependency of my_plugin)

2) Now go in your rails app and edit Gemfile, add:

gem 'my_plugin', path: 'vendor/plugins/my_plugin'

3) Now in rails app root do:

bundle install

And dependency of my_plugin (will_paginate in this case) is installed.

Answer 2

While developing 2 gems, gem1 and gem2, requiring that gem1 locally depends on gem2 is quite handy.

You can't do this in your gemspec, however, you can do so in your gem's Gemfile!

# Gemfile
source "https://rubygems.org"

gem 'gem2', :path => '../gem2'

# Specify your gem's dependencies in gem1.gemspec
gemspec

And then in your gemspec, require your gem like you would normally if that gem was already published:

# gem1.gemspec
spec.add_runtime_dependency "gem2"

Just make sure you don't accidentally push that Gemfile change!

Answer 3

Sometimes you want to embed one gem into another gem, nevermind why. You can reference one gempec from another to completely encapsulate a local gem.

require "rubygems"

embedded_gemspec = Gem::Specification::load("path/to/internal.gemspec")

Gem::Specification.new do |spec|
  spec.name          = "gem_that_contains_another_gem"
  # spec.whatever,   = whole bunch of other info

  #                     our files               + other gem's files
  spec.files         = ['file1.rb', 'file2.rb'] + embedded_gemspec.files

  # our dependencies
  spec.add_dependency 'nokogiri'
  # other gem's dependencies
  embedded_gemspec.runtime_dependencies.each { |d| spec.add_dependency d }

end

EDIT: this appears to only work locally. If you try to install this gemspec from, say, a git repo, it won't know where to get embedded_gemspec (even though embedded_gemspec's dependencies come in just fine).