How to `bundle install` when your Gemfile requires an older version of bundler?

Question

I am in an older Rails project that has a Gemfile. I tried to add a gem to the Gemfile and bundle install but got an error:

Bundler could not find compatible versions for gem "bundler":   In Gemfile:     rails (= 3.0.0) ruby depends on       bundler (~> 1.0.0) ruby    Current Bundler version:     bundler (1.1.5)  This Gemfile requires a different version of Bundler. 

The version of Rails it's using requires bundler ~>1.0.0 but I have 1.1.5 installed and am using it for my other projects. Usually I would use bundle exec ... but since this is bundler we are talking about, it's a little more complicated than that. How can I add a gem to my Gemfile and run bundle install while using the version of bundler that it requires?

Answer 1

First you need to install the appropriate version of bundler:

% gem install bundler -v '~> 1.0.0' Successfully installed bundler-1.0.22 

Then force rubygems to use the version you want (see this post):

% bundle _1.0.22_ install 

Answer 2

The error message In Gemfile: bundler (~> 1.16) is a bit inaccurate, since the version number requirement can come from other places, such as the .gemspec file, which was the case for me:

spec.add_development_dependency "bundler", "~> 1.16" 

Removing the version number from the .gemspec file solved the issue for me:

spec.add_development_dependency "bundler"