Undo the last change in lib

lib/bundler.rb

@@ -299,7 +299,7 @@ def unbundled_env
       env.delete_if {|k, _| k[0, 7] == "BUNDLE_" }
 
       if env.key?("RUBYOPT")
-        env["RUBYOPT"] = env["RUBYOPT"].sub "-r#{File.expand_path("bundler/setup", __dir__)}", ""
+        env["RUBYOPT"] = env["RUBYOPT"].sub "-rbundler/setup", ""
       end
 
       if env.key?("RUBYLIB")

spec/runtime/with_unbundled_env_spec.rb

@@ -1,15 +1,15 @@
 # frozen_string_literal: true
 
 RSpec.describe "Bundler.with_env helpers" do
-  def bundle_exec_ruby!(code)
-    build_bundler_context
-    bundle! "exec '#{Gem.ruby}' -e #{code}"
+  def bundle_exec_ruby!(code, options = {})
+    build_bundler_context options
+    bundle! "exec '#{Gem.ruby}' -e #{code}", options
   end
 
-  def build_bundler_context
+  def build_bundler_context(options = {})
     bundle "config set path vendor/bundle"
     gemfile ""
-    bundle "install"
+    bundle "install", options
   end
 
   describe "Bundler.original_env" do
@@ -74,9 +74,9 @@ def build_bundler_context
 
     it "should remove '-rbundler/setup' from RUBYOPT" do
       code = "print #{modified_env}['RUBYOPT']"
-      ENV["RUBYOPT"] = "-W2 -r#{lib}/bundler/setup #{ENV["RUBYOPT"]}"
-      bundle_exec_ruby! code.dump
-      expect(last_command.stdboth).not_to include("-r#{lib}/bundler/setup")
+      ENV["RUBYOPT"] = "-W2 -rbundler/setup #{ENV["RUBYOPT"]}"
+      bundle_exec_ruby! code.dump, :env => { "BUNDLER_SPEC_DISABLE_DEFAULT_BUNDLER_GEM" => "true" }
+      expect(last_command.stdboth).not_to include("-rbundler/setup")
     end
 
     it "should restore RUBYLIB", :ruby_repo do

spec/support/hax.rb

@@ -14,7 +14,7 @@ class Platform
   @platforms = [Gem::Platform::RUBY, Gem::Platform.local]
 
   # We only need this hack for rubygems versions without the BundlerVersionFinder
-  if Gem::Version.new(Gem::VERSION) < Gem::Version.new("2.7.0")
+  if Gem::Version.new(Gem::VERSION) < Gem::Version.new("2.7.0") || ENV["BUNDLER_SPEC_DISABLE_DEFAULT_BUNDLER_GEM"]
     @path_to_default_spec_map.delete_if do |_path, spec|
       spec.name == "bundler"
     end