How to load rubygems_plugin.rb when running bundle install

[impostorsguides]

I'm reading the RBENV codebase, and I came upon its rubygems_plugin.rb file. It includes the following code:

if defined?(Bundler::Installer) && Bundler::Installer.respond_to?(:install) && !Bundler::Installer.respond_to?(:install_without_rbenv_rehash)
  Bundler::Installer.class_eval do
  ...
end

According to the PR that introduced it, the goal of this code is to ensure that RBENV rebuilds its shims only at the end of the bundle install process, as opposed to after each gem installation. To me, this implies that bundle install will run the rubygems_plugin.rb file.

I wanted to step through the code to see how it works, so I did the following:

• added debugger statements to the rubygems_plugin.rb file inside my ~/.rbenv directory (both just before, as well as inside, the above if block)
• installed a fresh Ruby version (v3.1.4) via rbenv install 3.1.4 to make sure that any gems in a Gemfile would not yet be installed
• created a fresh Rails project (rails new foobar) using that new Ruby version, so that I could run bundle install on its Gemfile
• Added a gem to the Gemfile (wisper) which I knew contained an executable, and would therefore return true for this line of code and result in a shim being generated.
• ran bundle install inside that project.

I was surprised to see that I didn't hit my debuggers. I also checked ~/.rbenv/shims for the wisper shim, but I didn't find it.
Both of these things imply that the file isn't being loaded during a bundle install. However, when I run a simple gem install wisper, I do hit the debugger outside the if block, and I do see the wisper shim.

I also tried to install the version of Ruby which was active at the time of the original PR (v2.1.2), but it's no longer supported (and in fact, can no longer be installed on my 2023 Macbook).

I read through the Bundler CHANGELOG.md file from the deprecated Bundler repo, to see if maybe support for this file was removed from the bundle install command. Nothing stood out to me, but maybe I missed something.

I'm guessing this is user error, and that I'm simply missing something. But I thought I'd post this question anyway, in case this file no longer loaded when bundle install is run?

Also FYI: I also read through the Bundler git history, and I saw this PR from June 2018 that introduced a GEM_AFTER_INSTALL_ALL hook to Bundler. This appears to address the same goal that the above RBENV PR from 2015 addressed. Thought I'd call that out in case it's useful.

[mislav]

Thanks for the detailed dive! I didn't know this, and you're right: in my testing it looks like bundle commands no longer cause the rubygems_plugin.rb file to be loaded from LOAD_PATH.

You are also right that Bundler now has its own plugin API, but it doesn't look like rbenv can automatically inject its own plugin via environment variables. Instead, it looks like a user needs to explicitly enable a plugin via a bundle command.

I'd be fine with giving up on rbenv hooking into bundle install, and instead just leaving the gem install hook. People who use bundler can easily generate binstubs for their own project, which alleviates the need for rbenv to keep its shims up to date.

[impostorsguides]

Thanks for the clarification. If the Bundler-specific code is no longer executed, is it worthwhile to restore rubygems_plugin.rb to its pre-Bundler state? If so, I'd be happy to put up a PR changing it to something like this:

hook = lambda do |installer|
  begin
    # Ignore gems that aren't installed in locations that rbenv searches for binstubs
    if installer.spec.executables.any? &&
        [Gem.default_bindir, Gem.bindir(Gem.user_dir)].include?(installer.bin_dir)
      `rbenv rehash`
    end
  rescue
    warn "rbenv: error in gem-rehash (#{$!.class.name}: #{$!.message})"
  end
end

begin
  Gem.post_install(&hook)
  Gem.post_uninstall(&hook)
rescue
  warn "rbenv: error installing gem-rehash hooks (#{$!.class.name}: #{$!.message})"
end

[impostorsguides]

If you're as curious as I was:

Upon further research, it looks like this unexpected behavior was caused by this PR in the Bundler repo, specifically the removal of this line in lib/bundler/cli/install.rb:

Gem.load_env_plugins if Gem.respond_to?(:load_env_plugins)

When I edit this file on my machine to add this line back and re-run bundle install in my toy Rails project, I once again hit the debugger statements in RBENV's rubygems_plugin.rb file.

This change was, in fact, mentioned in the Bundler CHANGELOG.md file, I simply glossed over it the first time around:

load all rubygems plugins when installing gems (rubygems/bundler#2824, @segiddins)

I found the Bundler released which introduced this behavior by installing every Bundler version from the last 8 years (not that many, really), and running bundle _version_number_ install (i.e. bundle _1.14.0_ install) on each one until I started hitting my breakpoints again, then combing through the release notes for that version.

I've already got a question open on the RubyGems repo here, and I'll add the above remarks to the question and see if they think it's worth a PR.

[impostorsguides]

I was curious how one would go about hooking into Bundler to run rbenv rehash, so I took the liberty of creating this Ruby gem as a very rough proof-of-concept. No worries if you'd rather not go down this route- it was still a useful learning exercise for me.

TL;DR- running gem install rbenv_bundler_rehash followed by bundle install plugin rbenv_bundler_rehash will result in gems being shimmed whenever bundle install is run.

I'm having credential-related problems while trying to run rake release in order to push this gem up to RubyGems, so for now gem install rbenv_bundler_rehash won't work. But feel free to inspect the code.

Lastly, it turns out that there is no "AFTER_UNINSTALL_ALL" lifecycle hook in Bundler (presumably because there's no bundle uninstall command), so there's no way to add this logic to uninstalling gems.