Heroku部署Rails应用时Bundler报undefined method `present?`，gem安装失败

我在尝试将Rails应用推送到Heroku时遇到了如下异常错误：

remote: -----> Building on the Heroku-20 stack
remote: -----> Using buildpack: heroku/ruby
remote: -----> Ruby app detected
remote: -----> Installing bundler 2.2.16
remote: -----> Removing BUNDLED WITH version in the Gemfile.lock
remote: -----> Compiling Ruby/Rails
remote: -----> Using Ruby version: ruby-3.0.1
remote: -----> Installing dependencies using bundler 2.2.16
remote:        Running: BUNDLE_WITHOUT='development:test' BUNDLE_PATH=vendor/bundle BUNDLE_BIN=vendor/bundle/bin BUNDLE_DEPLOYMENT=1 bundle install -j4
remote:        /tmp/build_ae8e646d/bin/bundle:42:in `gemfile': undefined method `present?' for "/tmp/build_ae8e646d/Gemfile":String (NoMethodError)
remote:        Did you mean?  prepend
remote:         from /tmp/build_ae8e646d/bin/bundle:49:in `lockfile'
remote:         from /tmp/build_ae8e646d/bin/bundle:57:in `lockfile_version'
remote:         from /tmp/build_ae8e646d/bin/bundle:68:in `bundler_version'
remote:         from /tmp/build_ae8e646d/bin/bundle:72:in `bundler_requirement'
remote:         from /tmp/build_ae8e646d/bin/bundle:100:in `activate_bundler'
remote:         from /tmp/build_ae8e646d/bin/bundle:88:in `load_bundler!'
remote:         from /tmp/build_ae8e646d/bin/bundle:116:in `<main>'
remote:        Bundler Output: /tmp/build_ae8e646d/bin/bundle:42:in `gemfile': undefined method `present?' for "/tmp/build_ae8e646d/Gemfile":String (NoMethodError)
remote:        Did you mean?  prepend
remote:         from /tmp/build_ae8e646d/bin/bundle:49:in `lockfile'
remote:         from /tmp/build_ae8e646d/bin/bundle:57:in `lockfile_version'
remote:         from /tmp/build_ae8e646d/bin/bundle:68:in `bundler_version'
remote:         from /tmp/build_ae8e646d/bin/bundle:72:in `bundler_requirement'
remote:         from /tmp/build_ae8e646d/bin/bundle:100:in `activate_bundler'
remote:         from /tmp/build_ae8e646d/bin/bundle:88:in `load_bundler!'
remote:         from /tmp/build_ae8e646d/bin/bundle:116:in `<main>'
remote: 
remote:  !
remote:  !     Failed to install gems via Bundler.
remote:  !
remote:  !     Push rejected, failed to compile Ruby app.

此前我已将该应用的脚手架版本部署到Heroku，运行一切正常。后续开发一段时间再推送变更时就出现了该错误。我已经尝试重新生成Gemfile.lock、执行bundle update操作，均未解决问题。本地运行一切正常，本地使用的Ruby和Bundler版本与Heroku上的版本完全一致。目前暂无排查思路，请问有人遇到过同类错误吗？

根因分析 #

该错误的核心原因是项目下的bin/bundle可执行文件被修改，使用了仅Rails Active Support库提供的present?扩展方法。Heroku在构建阶段执行bundler安装时，还未加载Rails相关依赖，纯Ruby环境没有为字符串类型提供present?方法，因此抛出NoMethodError。
本地运行正常是因为本地执行时已加载Rails运行环境，Active Support的核心扩展已经被注入到字符串类中，不会触发方法不存在的错误。

修复步骤 #

• 打开项目根目录下的bin/bundle文件，定位第42行调用present?的代码段
• 将字符串调用present?的代码替换为纯Ruby原生写法，例如将gemfile_path.present?改为!gemfile_path.nil? && !gemfile_path.empty?
• 若不确定如何修改，可直接执行本地命令rails app:update:bin，选择覆盖bin/bundle文件，恢复为Rails官方默认的binstub内容
• 提交修改后的bin/bundle文件到代码仓库，重新推送到Heroku即可完成正常构建

内容的提问来源于stack exchange，提问作者Alex Riabukha