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

Question

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!