Example Gemfile files preparing for the next rails upgrade (https://grant-ps.blog/2017/07/03/upgrading-ruby-on-rails-in-smallish-steps/)

_README.md

Preparing for rails 6

These files are examples of how you can start running your code against rails 6 in parallel while not affecting your ability to continue developing.

You will be able to:

• run rails 6 server
• run your specs against rails 6
• mark specs broken rails 6 specs
• find gems that don't have a upgrade path (yet)
• make decision with rails 6 in mind

Gemfile

@next_upgrade ||= false
source 'https://rubygems.org'

if @next_upgrade
  gem 'rails', '6.0.0.rc2'
else
  gem 'rails', '~> 5.2.0'
end

# rest of gems below ....

# examples of wrapping other gems
if @next_upgrade
  gem 'paranoia', :github => "radar/paranoia", branch: 'core'
else
  gem 'paranoia', '~> 2.0'
end

Gemfile-next

# BUNDLE_GEMFILE=Gemfile-next bundle install
@next_upgrade = true
main_gemfile = File.expand_path(File.dirname(__FILE__) + '/Gemfile')
eval File.read(main_gemfile), nil, main_gemfile

Gemfile_upgrade_run.sh

# do this only once so you have a starting lock file for the upgrade
cp Gemfile.lock Gemfile-next.lock 

# update your Gemfile-next.lock to rails 6
# * resolved conflicts. 
# * choose compatible rails 6 gems
# * notify gem authors if incompatible
# * fork the gem if you have to and create pull request for gem authors
BUNDLE_GEMFILE=Gemfile-next bundle update 

run_bundle.sh

#!/usr/bin/env bash
# a little helper script to use when installing new gems to keep both lock files up to date

bundle install # install gems for rails 5, creates Gemfile.lock
BUNDLE_GEMFILE=Gemfile-next bundle install # install gems for rails 6, creates Gemfile-next.lock

some_command_you_can_run.sh

## now you can run commands between rails 5 and 6

bundle install # install gems for rails 5, creates Gemfile.lock
BUNDLE_GEMFILE=Gemfile-next bundle install # install gems for rails 6, creates Gemfile-next.lock

bundle update # update gems for rails 5, creates Gemfile.lock
BUNDLE_GEMFILE=Gemfile-next bundle update # update gems for rails 6, creates Gemfile-next.lock

bundle exec rails s # runs code with rails 5
BUNDLE_GEMFILE=Gemfile-next bundle exec rails s # runs code with rails 6

bundle exec rspec # runs tests against rails 5
BUNDLE_GEMFILE=Gemfile-next bundle exec rspec # runs tests against rails 6

# etc

to_be_change_to_rails_helper.rb

def pending_on_upgrade
  pending "fix for rails upgrade" if Rails.version > "6"
end

## example of marking
it "does another thing" do
  pending_on_upgrade
end