[rubygems/rubygems] Load "bundler/setup" in lib/rubygems.rb

Ruby interpreter loads some special gems at startup: did_you_mean,
error_highlight, and syntax_suggest. These gems are loaded before
`bundler/setup` is loaded by `RUBYOPT=-rbundler/setup`.
So, the versions of the gems are not controllable by Gemfile.

This change will `require "bundler/setup"` in rubygems.rb (i.e., before
the special gems are loaded). Now `bundle exec` sets an environment
variable `BUNDLER_SETUP`, and rubygems requires the variable if defined.

See also: https://bugs.ruby-lang.org/issues/19089

https://github.com/rubygems/rubygems/commit/963cb65a2d

lib/bundler/environment_preserver.rb

@@ -7,6 +7,7 @@ module Bundler
       BUNDLE_BIN_PATH
       BUNDLE_GEMFILE
       BUNDLER_VERSION
+      BUNDLER_SETUP
       GEM_HOME
       GEM_PATH
       MANPATH

lib/bundler/shared_helpers.rb

@@ -284,6 +284,7 @@ module Bundler
       Bundler::SharedHelpers.set_env "BUNDLE_BIN_PATH", exe_file
       Bundler::SharedHelpers.set_env "BUNDLE_GEMFILE", find_gemfile.to_s
       Bundler::SharedHelpers.set_env "BUNDLER_VERSION", Bundler::VERSION
+      Bundler::SharedHelpers.set_env "BUNDLER_SETUP", File.expand_path("setup", __dir__)
     end
 
     def set_path

lib/rubygems.rb

@@ -1348,3 +1348,5 @@ Gem::Specification.load_defaults
 require_relative "rubygems/core_ext/kernel_gem"
 require_relative "rubygems/core_ext/kernel_require"
 require_relative "rubygems/core_ext/kernel_warn"
+
+require ENV["BUNDLER_SETUP"] if ENV["BUNDLER_SETUP"]

spec/bundler/bundler/shared_helpers_spec.rb

@@ -246,6 +246,13 @@ RSpec.describe Bundler::SharedHelpers do
       end
     end
 
+    shared_examples_for "ENV['BUNDLER_SETUP'] gets set correctly" do
+      it "ensures bundler/setup is set in ENV['BUNDLE_SETUP']" do
+        subject.set_bundle_environment
+        expect(ENV["BUNDLER_SETUP"]).to eq("#{source_lib_dir}/bundler/setup")
+      end
+    end
+
     shared_examples_for "ENV['RUBYLIB'] gets set correctly" do
       let(:ruby_lib_path) { "stubbed_ruby_lib_dir" }