Rails 6.1、Ruby 3.0.0：测试错误，因为它们无法加载 rexml

Question

我使用 Ruby 3.0.0 从头开始​​创建了一个新的 Rails 6.1 应用程序。

我已经运行 db:create 并生成了一个带有一些字符串列的单个模型，然后是 rails db:migrate。

我跑了rails test，但得到了这个 require rexml 错误：

/Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:34:in `require': cannot load such file -- rexml/document (LoadError)
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/gems/3.0.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `block in require'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/gems/3.0.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:299:in `load_dependency'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/gems/3.0.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/selenium-webdriver-3.142.7/lib/selenium/webdriver/firefox.rb:22:in `<main>'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `require'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `block in require_with_bootsnap_lfi'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require_with_bootsnap_lfi'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in `require'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/gems/3.0.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `block in require'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/gems/3.0.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:299:in `load_dependency'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/gems/3.0.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/webdrivers-4.4.1/lib/webdrivers/geckodriver.rb:72:in `<main>'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `require'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `block in require_with_bootsnap_lfi'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require_with_bootsnap_lfi'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in `require'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/gems/3.0.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `block in require'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/gems/3.0.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:299:in `load_dependency'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/gems/3.0.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/webdrivers-4.4.1/lib/webdrivers.rb:4:in `<main>'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `require'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `block in require_with_bootsnap_lfi'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require_with_bootsnap_lfi'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/bootsnap-1.5.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in `require'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/3.0.0/bundler/runtime.rb:66:in `block (2 levels) in require'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/3.0.0/bundler/runtime.rb:61:in `each'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/3.0.0/bundler/runtime.rb:61:in `block in require'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/3.0.0/bundler/runtime.rb:50:in `each'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/3.0.0/bundler/runtime.rb:50:in `require'
  from /Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/3.0.0/bundler.rb:174:in `require'
  from /Users/froop/Rails/froop_app/config/application.rb:7:in `<top (required)>'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/spring-2.1.1/lib/spring/application.rb:92:in `require'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/spring-2.1.1/lib/spring/application.rb:92:in `preload'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/spring-2.1.1/lib/spring/application.rb:157:in `serve'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/spring-2.1.1/lib/spring/application.rb:145:in `block in run'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/spring-2.1.1/lib/spring/application.rb:139:in `loop'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/spring-2.1.1/lib/spring/application.rb:139:in `run'
  from /Users/froop/.rvm/gems/ruby-3.0.0/gems/spring-2.1.1/lib/spring/application/boot.rb:19:in `<top (required)>'
  from <internal:/Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
  from <internal:/Users/froop/.rvm/rubies/ruby-3.0.0/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
  from -e:1:in `<main>'

我完全不确定是什么原因造成的。 Rails 是最新的。谁能指出我正确的方向？

Answer 1

rexml gem 是自 Ruby 3.0.0 以来捆绑的 gem。 所以你必须将rexml添加到Gemfile。

在 Ruby 2.6 和 2.7 上，rexml gem 是默认 gem。 因此，如果Gemfile 不包含rexml，则使用默认rexml。 在这些版本的 ruby​​ 上，只有当您想使用特定的 rexml 版本时，您才必须将 rexml 添加到 Gemfile。

Answer 2

要安装 rexml，只需在 Gemfile 中粘贴：gem 'rexml', '~> 3.2', '>= 3.2.4'。你可以在https://rubygems.org/gems/rexml找到它

Answer 3

为什么现在会这样？

Ruby 经历了Gemifying Ruby 的过程——将 Ruby 从标准库分解为 Gems。

在 Ruby 2.7 中，rexml gem 是一个“默认 gem”，这意味着它不能被删除，并且可以在不将它们声明为 Gemfiles 中的依赖项的情况下被要求。

在 Ruby 3.0 中，rexml gem 是一个“捆绑的 gem”：

Bundled gems are regular gems that ship with the default Ruby installation. These libraries are maintained outside the Ruby core team and can be uninstalled if necessary. As with other 3rd-party gems, you have to include them into gemspec or gemfile.

Blog article by strzibny - What are default and bundled gems in Ruby anyway?

因此，在 Ruby 3.0.0 中更改为捆绑 gem（从 2.7 中的默认 Gem），因此如果使用它，则必须将其添加到 Gemfile。