bundler vs bundler-explain: A real world Gemfile during an upgrade to Rails 5 https://github.com/jhawthorn/bundler-explain

bundler-explain.txt

Because quiet_assets 1.0.1 depends on railties ~> 3.1
  and quiet_assets 1.0.0 depends on rails ~> 3.1,
  quiet_assets 1.0.0 OR 1.0.1 requires railties ~> 3.1 or rails ~> 3.1.
And because quiet_assets >= 1.0.2, <= 1.1.0 depends on railties < 5.0, >= 3.1,
  either railties < 5.0, >= 3.1 or rails ~> 3.1.
So, because rails >= 5.0.0, <= 5.0.7 depends on railties ~> 5.0.0
  and root depends on rails ~> 5.0.0,
  version solving has failed.

bundler_error.txt

Bundler could not find compatible versions for gem "actionpack":
  In test1.rb:
    rails (~> 5.0.0) was resolved to 5.0.0, which depends on
      actionpack (= 5.0.0)

    rails-controller-testing was resolved to 1.0.1, which depends on
      actionpack (~> 5.x)

    rspec-rails (~> 3.7.2) was resolved to 3.7.2, which depends on
      actionpack (>= 3.0)

    simple_form (~> 3.2) was resolved to 3.5.1, which depends on
      actionpack (< 5.2, > 4)

Bundler could not find compatible versions for gem "activemodel":
  In test1.rb:
    paperclip (~> 4.2.0) was resolved to 4.2.4, which depends on
      activemodel (>= 3.2.0)

    rails (~> 5.0.0) was resolved to 5.0.0, which depends on
      activemodel (= 5.0.0)

    simple_form (~> 3.2) was resolved to 3.5.1, which depends on
      activemodel (< 5.2, > 4)

Bundler could not find compatible versions for gem "activerecord":
  In test1.rb:
    discard (~> 1.0) was resolved to 1.0.0, which depends on
      activerecord (< 6, >= 4.2)

    paper_trail was resolved to 9.2.0, which depends on
      activerecord (< 5.3, >= 4.2)

    rails (~> 5.0.0) was resolved to 5.0.0, which depends on
      activerecord (= 5.0.0)

Bundler could not find compatible versions for gem "activesupport":
  In test1.rb:
    paperclip (~> 4.2.0) was resolved to 4.2.4, which depends on
      activesupport (>= 3.2.0)

    pundit was resolved to 1.1.0, which depends on
      activesupport (>= 3.0.0)

    rails (~> 5.0.0) was resolved to 5.0.0, which depends on
      activesupport (= 5.0.0)

    rails-controller-testing was resolved to 1.0.1, which depends on
      activesupport (~> 5.x)

    rspec-rails (~> 3.7.2) was resolved to 3.7.2, which depends on
      activesupport (>= 3.0)

    webpacker (~> 3.4.1) was resolved to 3.4.3, which depends on
      activesupport (>= 4.2)

Bundler could not find compatible versions for gem "rails":
  In test1.rb:
    rails (~> 5.0.0)

Could not find gem 'rails (~> 5.0.0)' in any of the sources.

Bundler could not find compatible versions for gem "railties":
  In test1.rb:
    quiet_assets was resolved to 1.0.1, which depends on
      railties (~> 3.1)

    rails (~> 5.0.0) was resolved to 5.0.0, which depends on
      railties (= 5.0.0)

Gemfile

source 'https://rubygems.org'

gem 'rails', '~> 5.0.0'

# Soft-deletion
gem 'paper_trail'
gem 'discard', '~> 1.0'

# auth
gem 'pundit'
gem 'devise', '~> 4.1.1'

# Forms and uploads
gem 'simple_form', '~> 3.2'
gem 'paperclip', '~> 4.2.0'

# assets
gem 'font-awesome-rails', '~> 4.7.0'
gem 'jquery-rails'
gem 'quiet_assets' # <-- comment this out to fix it
gem 'sass-rails', '~> 5.0'
gem 'webpacker', '~> 3.4.1'

group :test do
  gem 'factory_bot_rails'
  gem 'rails-controller-testing'
  gem 'rspec-rails', '~> 3.7.2'
end