• The issue
• bundler 1.x solutions
  • 🏆 Using BUNDLE_GEMFILE= + eval_gemfile()
  • Using BUNDLE_GEMFILE= env var setting or --gemfile flag
  • eval_gemfile()
    • Older alternatives to eval_gemfile
  • bootboot bundler plugin
  • appraisal gem
  • bundle config --local gemfile Gemfile.local
• bundler 2 solutions
• Other fun things
  • wwtd (local Travis simulator)

We want to bundle gems in a way that supports multiple platforms or versions of ruby. This might translate into different Gemfile version rules, and will almost certainly result in different versions recorded in Gemfile.lock.

This is sometimes referred to as "Dualbooting" (as in this conference talk by @rafaelfranca).

It seems like what we want is a Gemfile and Gemfile.lock for each supported platform/ruby. However, in practice, the actual Gemfile content will be mostly identical.

This would be useful when used with matrixed tests, like Travis CI's build matrix keyword gemfile:

matrix:
  include:
  - rvm: 2.5
    gemfile: gemfiles/Gemfile.rails-3.2.x
    env: ISOLATED=false
  - rvm: 2.5
    gemfile: gemfiles/Gemfile.rails-3.2.x
    env: ISOLATED=true

Approaches to this issue have been discussed and evolved over the years:

• 2018:
  • Multiple Gemfiles, Multiple Ruby Versions, One Rails (2018/11/12)
  • Proposal to allow defining different lockfile name not based on Gemfile name #6777
• 2017:
  • Bundler cop idea: recommend eval_gemfile #3903 rubocop-hq/rubocop issue
  • RailsConf 2017: Upgrading a big application to Rails 5 by Rafael França
• 2013:
  • A second Gemfile and lock? I.e. Gemfile.local, Gemfile.lock.local? (ruby-bundler Google group)
  • How to use different Gemfiles with Bundler
• 2010:
  • Multiple lockfiles? (ruby-bundler Google group)

See bundle_gemfile/ directory for an example

Multiple Gemfiles, Multiple Ruby Versions, One Rails reviews the current options (including the appraisal gem) and makes a strong case for just using BUNDLE_GEMFILE + eval_gemfile:

BUNDLE_GEMFILE=gemfiles/Gemfile.2.4.5 bundle install
BUNDLE_GEMFILE=gemfiles/Gemfile.2.4.5 rails server -p 4321

# Contents of Gemfile.2.4.5
ruby "2.4.5"

eval_gemfile "Gemfile"

A classic (2010-2013) solution, mentioned in the ruby=bunder Google group discussion, A second Gemfile and lock? I.e. Gemfile.local, Gemfile.lock.local?.

From the article How to use different Gemfiles with Bundler:

Bundler supports passing an environment variable called BUNDLE_GEMFILE to all of its commands. Here is an example how we can tell it to use a file called Gemfile-rails4:

BUNDLE_GEMFILE=Gemfile-rails4 bundle install --path vendor/bundle-rails4

You can then run tests in the similar way:

BUNDLE_GEMFILE=Gemfile-rails4 bundle exec rake spec

See eval_gemfile/ directory for an example

The eval_gemfile method has been available since bundler 1.2.0. It is a popular choice, but is not considered part of bundler's public API by its developers.

From @segiddins comment in Bundler cop idea: recommend eval_gemfile #3903:

Please note that eval_gemfile is still (purposefully) undocumented, and while we strive to support it, we do not fully consider it public API at this point

Before eval_gemfile, it was common to load another file with the Gemfile like so

From rubocop-hq/rubocop issue Bundler cop idea: recommend eval_gemfile #3903 (2017):

eval(File.read('Gemfile.local')) if File.exist?('Gemfile.local')

Mentioned in A second Gemfile and lock? I.e. Gemfile.local, Gemfile.lock.local? (ruby-bundler Google group):

load "#{File.dirname __FILE__}/Gemfile"

From phamkykhoi/redmine.tanphat.com

  instance_eval File.read(file), file

shopify/bootboot is a bundler plugin than natively supports dualbooting.

• The sync feature requires bundler >= 1.17
• ❌ Only supports two versions

`thoughtbot/appraisal is a bundler plugin than natively supports dualbooting.

Adds a new file, Appraisals:

appraise "rails-3" do
  gem "rails", "3.2.14"
end

appraise "rails-4" do
  gem "rails", "4.0.0"
end

These combine (and in the event of a collision, override) the dependencies in your Gemfile.

# In .travis.yml
gemfile:
  - gemfiles/3.0.gemfile
  - gemfiles/3.1.gemfile
  - gemfiles/3.2.gemfile

• bundler 2 has many features that can help
• Bundler 2.0 dropped support for Ruby < 2.3 (no legacy Puppet 4) and RubyGems < 3.0

Travis simulator: https://github.com/grosser/wwtd

• nicer than travish

wwtd --local        # Run all gemfiles on current ruby -> get rid of Appraisal