ruby · hsbt · Aug 28, 2026 · Aug 28, 2026 · Aug 28, 2026 · Aug 28, 2026
diff --git a/.github/workflows/rubygems.yml b/.github/workflows/rubygems.yml
@@ -60,6 +60,10 @@ jobs:
           - ruby: { name: no symlinks, value: 4.0.5 }
             os: { name: Windows, value: windows-2025 }
             symlink: off
+
+          - ruby: { name: head (RUBY_BOX=1), value: head }
+            os: { name: Ubuntu, value: ubuntu-24.04 }
+            ruby_box: true
     env:
       RUBYGEMS_USE_PSYCH: ${{ matrix.use_psych || 'false' }}
 
@@ -79,7 +83,10 @@ jobs:
         run: bin/rake setup
       - name: Run Test
         run: bin/rake test
-        if: matrix.ruby.name != 'truffleruby' && matrix.ruby.name != 'jruby' && matrix.symlink != 'off'
+        if: matrix.ruby.name != 'truffleruby' && matrix.ruby.name != 'jruby' && matrix.symlink != 'off' && !matrix.ruby_box
+      - name: Run Test (RUBY_BOX=1)
+        run: RUBY_BOX=1 bin/rake test
+        if: matrix.ruby_box
       - name: Run Test isolatedly
         run: bin/rake test:isolated
         if: matrix.ruby.name == '3.4' && matrix.os.name != 'Windows'

diff --git a/lib/bundler/gem_helper.rb b/lib/bundler/gem_helper.rb
@@ -216,7 +216,7 @@ def sh_with_status(cmd, &block)
       Bundler.ui.debug(cmd)
       SharedHelpers.chdir(base) do
         outbuf = IO.popen(cmd, err: [:child, :out], &:read)
-        status = $?
+        status = Process.last_status
         block&.call(outbuf) if status.success?
         [outbuf, status]
       end

diff --git a/lib/rubygems/ext/builder.rb b/lib/rubygems/ext/builder.rb
@@ -101,7 +101,8 @@ def self.run(command, results, command_name = nil, dir = Dir.pwd, env = {})
 
       require "open3"
       # Set $SOURCE_DATE_EPOCH for the subprocess.
-      # Under Ruby::Box mkmf makes RbConfig.expand recurse until SystemStackError.
+      # Under Ruby::Box defined?($gvar) does not see assignments made inside the
+      # box, so mkmf have_devel? never memoizes and recurses until SystemStackError.
       # Drop $RUBY_BOX last so no caller can restore it.
       build_env = { "SOURCE_DATE_EPOCH" => Gem.source_date_epoch_string }.merge(env).merge("RUBY_BOX" => nil)
       # A single-element command would be parsed as a shell command line,

diff --git a/lib/rubygems/source/git.rb b/lib/rubygems/source/git.rb
@@ -188,9 +188,10 @@ def rev_parse # :nodoc:
       hash = Gem::Util.popen(git_command, "rev-parse", @reference).strip
     end
 
+    # Process.last_status instead of $?, which Ruby::Box leaves uninitialized
     raise Gem::Exception,
           "unable to find reference #{@reference} in #{@repository}" unless
-            $?.success?
+            Process.last_status.success?
 
     hash
   end

diff --git a/spec/bundler/shared_helpers_spec.rb b/spec/bundler/shared_helpers_spec.rb
@@ -387,7 +387,11 @@
 
       before do
         ENV["RUBYOPT"] = "-r#{install_path}/bundler/setup"
-        allow(File).to receive(:expand_path).and_return("#{install_path}/bundler/setup")
+        # Only fake the resolution of bundler/setup itself. A blanket stub
+        # breaks unrelated RubyGems path lookups triggered lazily inside the
+        # example, see #set_rubyopt.
+        allow(File).to receive(:expand_path).and_call_original
+        allow(File).to receive(:expand_path).with("setup", anything).and_return("#{install_path}/bundler/setup")
         allow(Gem).to  receive(:bin_path).and_return("#{install_path}/bundler/setup")
       end
 
@@ -403,7 +407,8 @@
       let(:install_path) { "/opt/ruby with space/lib" }
 
       before do
-        allow(File).to receive(:expand_path).and_return("#{install_path}/bundler/setup")
+        allow(File).to receive(:expand_path).and_call_original
+        allow(File).to receive(:expand_path).with("setup", anything).and_return("#{install_path}/bundler/setup")
         allow(Gem).to receive(:bin_path).and_return("#{install_path}/bundler/setup")
       end
 

diff --git a/spec/commands/install_spec.rb b/spec/commands/install_spec.rb
@@ -2063,6 +2063,10 @@ def run
   end
 
   it "preserves bundled native extensions when BUNDLE_CLEAN removes another gem" do
+    # The command-line/RUBYOPT -r bypasses gem activation under RUBY_BOX=1
+    # (https://bugs.ruby-lang.org/issues/22295)
+    skip "-r cannot activate gems under Ruby::Box" if defined?(Ruby::Box) && Ruby::Box.enabled?
+
     build_repo4 do
       build_gem "native_child", "1.0", &:add_c_extension
       build_gem "native_parent", "1.0" do |s|

diff --git a/spec/support/command_execution.rb b/spec/support/command_execution.rb
@@ -2,6 +2,13 @@
 
 module Spec
   class CommandExecution
+    # Under RUBY_BOX, every spawned ruby prints an experimental warning to
+    # stderr, breaking specs that assert clean stderr.
+    RUBY_BOX_WARNING = Regexp.union(
+      /^[^\n]*: warning: Ruby::Box is experimental, and the behavior may change in the future!\n?/,
+      %r{^See https://docs\.ruby-lang\.org/\S+ for known issues, etc\.\n?}
+    )
+
     def initialize(command, timeout:)
       @command = command
       @timeout = timeout
@@ -72,7 +79,13 @@ def failure?
     attr_reader :failure_reason
 
     def normalize(string)
-      string.dup.force_encoding(Encoding::UTF_8).scrub.strip.gsub("\r\n", "\n")
+      string = string.dup.force_encoding(Encoding::UTF_8).scrub.gsub("\r\n", "\n")
+      string = string.gsub(RUBY_BOX_WARNING, "") if ruby_box_enabled?
+      string.strip
+    end
+
+    def ruby_box_enabled?
+      defined?(Ruby::Box) && Ruby::Box.enabled?
     end
   end
 end
diff --git a/test/rubygems/helper.rb b/test/rubygems/helper.rb
@@ -397,6 +397,10 @@ def setup
     ENV["BUNDLE_USER_HOME"] = nil
     ENV["RUBYGEMS_PREVENT_UPDATE_SUGGESTION"] = "true"
 
+    # Child ruby processes inherit RUBY_BOX and print an experimental
+    # warning on startup, breaking assertions on subprocess stderr.
+    ENV["RUBYOPT"] = [ENV["RUBYOPT"], "-W:no-experimental"].compact.join(" ") if ruby_box_enabled?
+
     @current_dir = Dir.pwd
     @fetcher     = nil
 
@@ -1367,6 +1371,32 @@ def ruby_repo?
     !ENV["GEM_COMMAND"].nil?
   end
 
+  ##
+  # Is this test running under Ruby::Box (RUBY_BOX=1)?
+
+  def ruby_box_enabled?
+    defined?(Ruby::Box) && Ruby::Box.enabled?
+  end
+
+  ##
+  # Ruby::Box gives each box detached copies of the stdio globals, so
+  # reassigning $stdout/$stderr cannot capture output written by Kernel#warn,
+  # Kernel#puts or subprocesses. Pends until the ruby-core fix for
+  # https://bugs.ruby-lang.org/issues/21867 lands.
+
+  def pend_for_ruby_box_stdio_capture
+    pend "Ruby::Box breaks $stdout/$stderr capture (https://bugs.ruby-lang.org/issues/21867)" if ruby_box_enabled?
+  end
+
+  ##
+  # Under Ruby::Box, Marshal in the main box cannot resolve Gem:: (and other
+  # boxed) constants. Pends until the ruby-core fix for
+  # https://bugs.ruby-lang.org/issues/22090 lands.
+
+  def pend_for_ruby_box_marshal
+    pend "Marshal cannot resolve boxed constants under Ruby::Box (https://bugs.ruby-lang.org/issues/22090)" if ruby_box_enabled?
+  end
+
   ##
   # Returns the make command for the current platform. For versions of Ruby
   # built on MS Windows with VC++ or Borland it will return 'nmake'. On all

diff --git a/test/rubygems/test_deprecate.rb b/test/rubygems/test_deprecate.rb
@@ -132,6 +132,7 @@ def test_deprecated_method_calls_the_old_method
   end
 
   def test_deprecated_method_outputs_a_warning
+    pend_for_ruby_box_stdio_capture
     out, err = capture_output do
       thing = Thing.new
       thing.foo
@@ -165,6 +166,7 @@ def execute
   end
 
   def test_deprecated_method_outputs_a_warning_old_way
+    pend_for_ruby_box_stdio_capture
     out, err = capture_output do
       thing = OtherThing.new
       thing.foo
@@ -180,6 +182,7 @@ def test_deprecated_method_outputs_a_warning_old_way
   end
 
   def test_deprecated_method_when_class_overrides_format
+    pend_for_ruby_box_stdio_capture
     out, err = capture_output do
       thing = ThingWithFormat.new
       thing.foo

diff --git a/test/rubygems/test_exit.rb b/test/rubygems/test_exit.rb
@@ -6,7 +6,8 @@
 class TestGemExit < Gem::TestCase
   def test_exit
     system(*ruby_with_rubygems_in_load_path, "-e", "raise Gem::SystemExitException.new(2)")
-    assert_equal 2, $?.exitstatus
+    # Process.last_status instead of $?, which Ruby::Box leaves uninitialized
+    assert_equal 2, Process.last_status.exitstatus
   end
 
   def test_status

diff --git a/test/rubygems/test_gem.rb b/test/rubygems/test_gem.rb
@@ -1291,6 +1291,7 @@ def test_self_try_activate_missing_prerelease
   end
 
   def test_self_try_activate_missing_extensions
+    pend_for_ruby_box_stdio_capture
     spec = util_spec "ext", "1" do |s|
       s.extensions = %w[ext/extconf.rb]
       s.installed_by_version = v("2.2")
@@ -1346,6 +1347,7 @@ def test_setting_paths_does_not_mutate_parameter_object
   end
 
   def test_deprecated_paths=
+    pend_for_ruby_box_stdio_capture
     stdout, stderr = capture_output do
       Gem.paths = { "GEM_HOME" => Gem.paths.home,
                     "GEM_PATH" => [Gem.paths.home, "foo"] }

diff --git a/test/rubygems/test_gem_commands_build_command.rb b/test/rubygems/test_gem_commands_build_command.rb
@@ -195,6 +195,7 @@ def test_execute_strict_with_warnings
   end
 
   def test_execute_bad_spec
+    pend_for_ruby_box_stdio_capture
     @gem.date = "2010-11-08"
 
     gemspec_file = File.join(@tempdir, @gem.spec_name)

diff --git a/test/rubygems/test_gem_commands_open_command.rb b/test/rubygems/test_gem_commands_open_command.rb
@@ -21,6 +21,7 @@ def gem(name, version = "1.0")
   end
 
   def test_execute
+    pend_for_ruby_box_stdio_capture
     omit "JRuby on Windows spawns the editor with a different cwd" if Gem.win_platform? && Gem.java_platform?
 
     @cmd.options[:args] = %w[foo]

diff --git a/test/rubygems/test_gem_commands_specification_command.rb b/test/rubygems/test_gem_commands_specification_command.rb
@@ -137,6 +137,7 @@ def test_execute_file
   end
 
   def test_execute_marshal
+    pend_for_ruby_box_marshal
     foo = util_spec "foo", "2"
 
     install_specs foo

diff --git a/test/rubygems/test_gem_config_file.rb b/test/rubygems/test_gem_config_file.rb
@@ -314,6 +314,7 @@ def test_handle_arguments_backtrace
   end
 
   def test_handle_arguments_debug
+    pend_for_ruby_box_stdio_capture
     assert_equal false, $DEBUG
 
     args = %w[--debug]

diff --git a/test/rubygems/test_gem_dependency_installer.rb b/test/rubygems/test_gem_dependency_installer.rb
@@ -1103,6 +1103,7 @@ def test_install_version_default
   end
 
   def test_install_legacy_spec_with_nil_required_ruby_version
+    pend_for_ruby_box_marshal
     path = File.expand_path "data/null-required-ruby-version.gemspec.rz", __dir__
     spec = Marshal.load Gem.read_binary(path)
     def spec.validate(*args); end
@@ -1128,6 +1129,7 @@ def spec.validate(*args); end
   end
 
   def test_install_legacy_spec_with_nil_required_rubygems_version
+    pend_for_ruby_box_marshal
     path = File.expand_path "data/null-required-rubygems-version.gemspec.rz", __dir__
     spec = Marshal.load Gem.read_binary(path)
     def spec.validate(*args); end

diff --git a/test/rubygems/test_gem_ext_builder.rb b/test/rubygems/test_gem_ext_builder.rb
@@ -494,7 +494,7 @@ def self.expand(val, config = CONFIG); val; end
       system(Gem.ruby, "-rmkmf", "-e", "exit MakeMakefile::RbConfig::CONFIG['host_os'] == 'fake_os'",
              "--", "--target-rbconfig=#{fake_rbconfig}")
     end
-    unless $?.success?
+    unless Process.last_status.success?
       assert_include(stderr, "uninitialized constant MakeMakefile::RbConfig")
       pend "This version of mkmf does not support --target-rbconfig"
     end

diff --git a/test/rubygems/test_gem_ext_cargo_builder.rb b/test/rubygems/test_gem_ext_cargo_builder.rb
@@ -111,7 +111,8 @@ def test_full_integration
         Open3.capture2e(*gem, "build", "rust_ruby_example.gemspec", "--output", built_gem)
         Open3.capture2e(*gem, "install", "--verbose", "--local", built_gem, *ARGV)
 
-        stdout_and_stderr_str, status = Open3.capture2e(env_for_subprocess, *ruby_with_rubygems_in_load_path, "-rrust_ruby_example", "-e", "puts 'Result: ' + RustRubyExample.reverse('hello world')")
+        # Require inside -e because -r bypasses gem activation under RUBY_BOX=1
+        stdout_and_stderr_str, status = Open3.capture2e(env_for_subprocess, *ruby_with_rubygems_in_load_path, "-e", "require 'rust_ruby_example'; puts 'Result: ' + RustRubyExample.reverse('hello world')")
         assert status.success?, stdout_and_stderr_str
         assert_match "Result: #{"hello world".reverse}", stdout_and_stderr_str
       end
@@ -134,7 +135,7 @@ def test_custom_name
         Open3.capture2e(*gem, "install", "--verbose", "--local", built_gem, *ARGV)
       end
 
-      stdout_and_stderr_str, status = Open3.capture2e(env_for_subprocess, *ruby_with_rubygems_in_load_path, "-rcustom_name", "-e", "puts 'Result: ' + CustomName.say_hello")
+      stdout_and_stderr_str, status = Open3.capture2e(env_for_subprocess, *ruby_with_rubygems_in_load_path, "-e", "require 'custom_name'; puts 'Result: ' + CustomName.say_hello")
 
       assert status.success?, stdout_and_stderr_str
       assert_match "Result: Hello world!", stdout_and_stderr_str
@@ -199,7 +200,7 @@ def skip_unsupported_platforms!
     pend "jruby not supported" if Gem.java_platform?
     pend "truffleruby not supported (yet)" if RUBY_ENGINE == "truffleruby"
     system(@rust_envs, "cargo", "-V", out: IO::NULL, err: [:child, :out])
-    pend "cargo not present" unless $?.success?
+    pend "cargo not present" unless Process.last_status.success?
     pend "ruby.h is not provided by ruby repo" if ruby_repo?
     pend "rust toolchain of mingw is broken" if mingw_windows?
   end

diff --git a/test/rubygems/test_gem_package.rb b/test/rubygems/test_gem_package.rb
@@ -1077,6 +1077,7 @@ def test_verify_corrupt
   end
 
   def test_verify_corrupt_tar_metadata_entry
+    pend_for_ruby_box_stdio_capture
     gem = tar_file_header("metadata.gz", "", 0, 999, Time.now)
 
     File.open "corrupt.gem", "wb" do |io|
@@ -1113,6 +1114,7 @@ def test_verify_corrupt_tar_checksums_entry
   end
 
   def test_verify_corrupt_tar_data_entry
+    pend_for_ruby_box_stdio_capture
     gem = tar_file_header("data.tar.gz", "", 0, 100, Time.now)
 
     File.open "corrupt.gem", "wb" do |io|

diff --git a/test/rubygems/test_gem_package_tar_header_ractor.rb b/test/rubygems/test_gem_package_tar_header_ractor.rb
@@ -8,6 +8,11 @@
 end
 
 class TestGemPackageTarHeaderRactor < Gem::Package::TarTestCase
+  def setup
+    super
+    pend "Ruby::Box ignores $VERBOSE=, so assert_ractor cannot keep the Ractor experimental warning out of the child stderr (https://bugs.ruby-lang.org/issues/22282)" if ruby_box_enabled?
+  end
+
   SETUP = <<~RUBY
     header = {
       name: "x",

diff --git a/test/rubygems/test_gem_request_set.rb b/test/rubygems/test_gem_request_set.rb
@@ -71,6 +71,7 @@ def test_install_from_gemdeps
   end
 
   def test_install_from_gemdeps_explain
+    pend_for_ruby_box_stdio_capture
     spec_fetcher do |fetcher|
       fetcher.gem "a", 2
     end
@@ -94,6 +95,7 @@ def test_install_from_gemdeps_explain
   end
 
   def test_install_from_gemdeps_explain_verbose
+    pend_for_ruby_box_stdio_capture
     spec_fetcher do |fetcher|
       fetcher.gem "a", 2
     end

diff --git a/test/rubygems/test_gem_request_set_gem_dependency_api.rb b/test/rubygems/test_gem_request_set_gem_dependency_api.rb
@@ -78,6 +78,7 @@ def test_gem
   end
 
   def test_gem_duplicate
+    pend_for_ruby_box_stdio_capture
     @gda.gem "a"
 
     _, err = capture_output do
@@ -128,6 +129,7 @@ def test_gem_bitbucket_expand_path
   end
 
   def test_gem_git_branch
+    pend_for_ruby_box_stdio_capture
     _, err = capture_output do
       @gda.gem "a", git: "git/a", branch: "other", tag: "v1"
     end
@@ -149,6 +151,7 @@ def test_gem_git_gist
   end
 
   def test_gem_git_ref
+    pend_for_ruby_box_stdio_capture
     _, err = capture_output do
       @gda.gem "a", git: "git/a", ref: "abcd123", branch: "other"
     end

diff --git a/test/rubygems/test_gem_requirement.rb b/test/rubygems/test_gem_requirement.rb
@@ -431,6 +431,7 @@ def self.exploit(arg)
   end
 
   def test_marshal_load_attack
+    pend_for_ruby_box_marshal
     wa = Gem::Net::WriteAdapter.allocate
     wa.instance_variable_set(:@socket, self.class)
     wa.instance_variable_set(:@method_id, :exploit)