From 3680bcd506649bd6b7ef753742309c243826dd8f Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Fri, 28 Aug 2026 10:13:26 +0900
Subject: [PATCH 1/9] Suppress the Ruby::Box experimental warning in test
 subprocesses

Under RUBY_BOX=1 every spawned ruby prints an experimental warning to
stderr, which breaks tests asserting on subprocess output. Prepend
-W:no-experimental to RUBYOPT for child processes and add a
ruby_box_enabled? helper for box-specific guards.
---
 test/rubygems/helper.rb | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/test/rubygems/helper.rb b/test/rubygems/helper.rb
index 1fe8577b4fc9..44690f68555b 100644
--- 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 +1371,13 @@ 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
+
   ##
   # 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

From 64481df749ef1d5a3cfd614d0236f0dba7314c91 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Fri, 28 Aug 2026 10:13:36 +0900
Subject: [PATCH 2/9] Use Process.last_status instead of $?

Ruby::Box leaves $? uninitialized, so exit status checks read exit 0
regardless of the real status. Under RUBY_BOX=1 this made
Gem::Source::Git#rev_parse swallow git rev-parse failures, and made the
cargo availability pend in the test suite misjudge a broken toolchain as
usable. Process.last_status reports the real status in both modes.
---
 lib/bundler/gem_helper.rb                   | 2 +-
 lib/rubygems/source/git.rb                  | 3 ++-
 test/rubygems/test_exit.rb                  | 3 ++-
 test/rubygems/test_gem_ext_builder.rb       | 2 +-
 test/rubygems/test_gem_ext_cargo_builder.rb | 2 +-
 test/rubygems/test_require.rb               | 4 ++--
 test/rubygems/test_rubygems.rb              | 4 ++--
 7 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/lib/bundler/gem_helper.rb b/lib/bundler/gem_helper.rb
index e3af1b957f35..ea02e7e7712b 100644
--- 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/source/git.rb b/lib/rubygems/source/git.rb
index baf2f9dd4c09..1e1b99b95fe5 100644
--- 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/test/rubygems/test_exit.rb b/test/rubygems/test_exit.rb
index 396837edadfa..c339c39a67af 100644
--- 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_ext_builder.rb b/test/rubygems/test_gem_ext_builder.rb
index 8f90687ede30..3c773fe0f3f7 100644
--- 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
index b970e442c250..94673a478c4e 100644
--- a/test/rubygems/test_gem_ext_cargo_builder.rb
+++ b/test/rubygems/test_gem_ext_cargo_builder.rb
@@ -199,7 +199,7 @@ 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_require.rb b/test/rubygems/test_require.rb
index db86a3090565..6816e42bfe13 100644
--- a/test/rubygems/test_require.rb
+++ b/test/rubygems/test_require.rb
@@ -484,7 +484,7 @@ def test_realworld_default_gem
       puts Gem.loaded_specs["json"]
     RUBY
     output = Gem::Util.popen(*ruby_with_rubygems_in_load_path, "-e", cmd).strip
-    assert $?.success?
+    assert Process.last_status.success?
     refute_empty output
   end
 
@@ -508,7 +508,7 @@ def test_realworld_upgraded_default_gem
     assert_equal "999.99.9", output.lines[0].chomp
     # Make sure only files from the newer json gem are loaded, and no files from the default json gem
     assert_equal ["#{@gemhome}/gems/json-999.99.9/lib/json.rb"], output.lines.grep(%r{/gems/json-}).map(&:chomp)
-    assert $?.success?
+    assert Process.last_status.success?
   end
 
   def test_default_gem_and_normal_gem
diff --git a/test/rubygems/test_rubygems.rb b/test/rubygems/test_rubygems.rb
index 6566b5981e69..02393c57fcae 100644
--- a/test/rubygems/test_rubygems.rb
+++ b/test/rubygems/test_rubygems.rb
@@ -5,7 +5,7 @@
 class GemTest < Gem::TestCase
   def test_rubygems_normal_behaviour
     _ = Gem::Util.popen(*ruby_with_rubygems_in_load_path, "-e", "'require \"rubygems\"'", { err: [:child, :out] }).strip
-    assert $?.success?
+    assert Process.last_status.success?
   end
 
   def test_operating_system_other_exceptions
@@ -17,7 +17,7 @@ def test_operating_system_other_exceptions
     RUBY
 
     output = Gem::Util.popen(*ruby_with_rubygems_and_fake_operating_system_in_load_path(path), "-e", "'require \"rubygems\"'", { err: [:child, :out] }).strip
-    assert !$?.success?
+    assert !Process.last_status.success?
     assert_match(/undefined local variable or method [`']intentionally_not_implemented_method'/, output)
     assert_includes output, "Loading the #{operating_system_rb_at(path)} file caused an error. " \
     "This file is owned by your OS, not by rubygems upstream. " \

From 3692d9012e0abdaf9eca58d1c36be5fa39bca0a8 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Fri, 28 Aug 2026 10:13:55 +0900
Subject: [PATCH 3/9] Pend tests that capture stdio under Ruby::Box

Ruby::Box gives each box detached copies of the stdio globals, so
reassigning or reopening $stdout/$stderr cannot capture output written
by Kernel#warn, Kernel#puts or subprocesses, and $VERBOSE = nil cannot
silence category warnings in assert_ractor children. Pend the affected
tests until https://bugs.ruby-lang.org/issues/21867 is resolved.
---
 test/rubygems/helper.rb                               | 11 +++++++++++
 test/rubygems/test_deprecate.rb                       |  3 +++
 test/rubygems/test_gem.rb                             |  2 ++
 test/rubygems/test_gem_commands_build_command.rb      |  1 +
 test/rubygems/test_gem_commands_open_command.rb       |  1 +
 test/rubygems/test_gem_config_file.rb                 |  1 +
 test/rubygems/test_gem_package.rb                     |  2 ++
 test/rubygems/test_gem_package_tar_header_ractor.rb   |  5 +++++
 test/rubygems/test_gem_request_set.rb                 |  2 ++
 .../test_gem_request_set_gem_dependency_api.rb        |  3 +++
 test/rubygems/test_gem_specification.rb               |  5 +++++
 test/rubygems/test_gem_stub_specification.rb          |  1 +
 test/rubygems/test_require.rb                         |  4 ++++
 13 files changed, 41 insertions(+)

diff --git a/test/rubygems/helper.rb b/test/rubygems/helper.rb
index 44690f68555b..80df3b7d49b1 100644
--- a/test/rubygems/helper.rb
+++ b/test/rubygems/helper.rb
@@ -1378,6 +1378,17 @@ 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
+
+
   ##
   # 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
index bb6a0b5ceaaf..5700d356e756 100644
--- 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_gem.rb b/test/rubygems/test_gem.rb
index c81b0b0547ae..7862ef5f4d2f 100644
--- 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
index cd88421c0754..a46a6447ee34 100644
--- 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
index 3a774a9343c0..c30117a58ecc 100644
--- 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_config_file.rb b/test/rubygems/test_gem_config_file.rb
index 2c33192a4b3a..7120c49e327a 100644
--- 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_package.rb b/test/rubygems/test_gem_package.rb
index 7b8ac4736d2f..d70e8f60a819 100644
--- 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
index 57140648052e..676822f79bc3 100644
--- 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 (ruby-core bug, same family as https://bugs.ruby-lang.org/issues/21867)" 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
index 8c8be04fb9f9..60ff8724aef4 100644
--- 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
index 4b5eaa38eda8..d8f4e7f6e92b 100644
--- 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_specification.rb b/test/rubygems/test_gem_specification.rb
index c63e68be47dd..fba0bc36e334 100644
--- a/test/rubygems/test_gem_specification.rb
+++ b/test/rubygems/test_gem_specification.rb
@@ -1575,6 +1575,7 @@ def test_contains_requirable_file_eh
   end
 
   def test_contains_requirable_file_eh_extension
+    pend_for_ruby_box_stdio_capture
     ext_spec
 
     _, err = capture_output do
@@ -3180,6 +3181,7 @@ def test_validate_files
   end
 
   def test_unresolved_specs
+    pend_for_ruby_box_stdio_capture
     specification = Gem::Specification.clone
 
     set_orig specification
@@ -3206,6 +3208,7 @@ def test_unresolved_specs
   end
 
   def test_unresolved_specs_with_versions
+    pend_for_ruby_box_stdio_capture
     specification = Gem::Specification.clone
 
     set_orig specification
@@ -3238,6 +3241,7 @@ def test_unresolved_specs_with_versions
   end
 
   def test_unresolved_specs_with_duplicated_versions
+    pend_for_ruby_box_stdio_capture
     specification = Gem::Specification.clone
 
     set_orig specification
@@ -3291,6 +3295,7 @@ def test_unresolved_specs_with_unrestricted_deps_on_default_gems
   end
 
   def test_duplicate_runtime_dependency
+    pend_for_ruby_box_stdio_capture
     expected = "WARNING: duplicated b dependency [\"~> 3.0\", \"~> 3.0\"]\n"
     out, err = capture_output do
       @a1.add_dependency "b", "~> 3.0", "~> 3.0"
diff --git a/test/rubygems/test_gem_stub_specification.rb b/test/rubygems/test_gem_stub_specification.rb
index 744ffa7d059e..bbdd96c6cb63 100644
--- a/test/rubygems/test_gem_stub_specification.rb
+++ b/test/rubygems/test_gem_stub_specification.rb
@@ -66,6 +66,7 @@ def test_contains_requirable_file_eh
   end
 
   def test_contains_requirable_file_eh_extension
+    pend_for_ruby_box_stdio_capture
     stub_with_extension do |stub|
       _, err = capture_output do
         if RUBY_ENGINE == "jruby"
diff --git a/test/rubygems/test_require.rb b/test/rubygems/test_require.rb
index 6816e42bfe13..ef1bb2e465a2 100644
--- a/test/rubygems/test_require.rb
+++ b/test/rubygems/test_require.rb
@@ -718,6 +718,7 @@ def test_require_bundler
 
   ["", "Kernel."].each do |prefix|
     define_method "test_no_kernel_require_in_#{prefix.tr(".", "_")}warn_with_uplevel" do
+      pend_for_ruby_box_stdio_capture
       Dir.mktmpdir("warn_test") do |dir|
         File.write(dir + "/sub.rb", "#{prefix}warn 'uplevel', 'test', uplevel: 1\n")
         File.write(dir + "/main.rb", "require 'sub'\n")
@@ -733,6 +734,7 @@ def test_require_bundler
     end
 
     define_method "test_no_other_behavioral_changes_with_#{prefix.tr(".", "_")}warn" do
+      pend_for_ruby_box_stdio_capture
       Dir.mktmpdir("warn_test") do |dir|
         File.write(dir + "/main.rb", "#{prefix}warn({x:1}, {y:2}, [])\n")
         _, err = capture_subprocess_io do
@@ -748,6 +750,7 @@ def test_require_bundler
   end
 
   def test_no_crash_when_overriding_warn_with_warning_module
+    pend_for_ruby_box_stdio_capture
     Dir.mktmpdir("warn_test") do |dir|
       File.write(dir + "/main.rb", "module Warning; def warn(str); super; end; end; warn 'Foo Bar'")
       _, err = capture_subprocess_io do
@@ -762,6 +765,7 @@ def test_no_crash_when_overriding_warn_with_warning_module
   end
 
   def test_expected_backtrace_location_when_inheriting_from_basic_object_and_including_kernel
+    pend_for_ruby_box_stdio_capture
     Dir.mktmpdir("warn_test") do |dir|
       File.write(dir + "/main.rb", "\nrequire 'sub'\n")
       File.write(dir + "/sub.rb", <<-'RUBY')

From 47e1282a00f16d61d23f044ba9d5afe727183172 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Fri, 28 Aug 2026 10:14:03 +0900
Subject: [PATCH 4/9] Pend Marshal round-trip tests under Ruby::Box

Marshal in the main box cannot resolve Gem:: and other boxed constants,
so loading dumps of Gem::Specification, Gem::Version or Date raises
ArgumentError under RUBY_BOX=1. Pend the affected tests until
https://bugs.ruby-lang.org/issues/22090 is resolved.
---
 test/rubygems/helper.rb                                |  8 ++++++++
 .../test_gem_commands_specification_command.rb         |  1 +
 test/rubygems/test_gem_dependency_installer.rb         |  2 ++
 test/rubygems/test_gem_requirement.rb                  |  1 +
 test/rubygems/test_gem_safe_marshal.rb                 | 10 +++++++++-
 test/rubygems/test_gem_specification.rb                |  5 +++++
 6 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/test/rubygems/helper.rb b/test/rubygems/helper.rb
index 80df3b7d49b1..83f5b111fa4b 100644
--- a/test/rubygems/helper.rb
+++ b/test/rubygems/helper.rb
@@ -1388,6 +1388,14 @@ 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
diff --git a/test/rubygems/test_gem_commands_specification_command.rb b/test/rubygems/test_gem_commands_specification_command.rb
index 454d6ea1c6f7..ee96eaa892a5 100644
--- 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_dependency_installer.rb b/test/rubygems/test_gem_dependency_installer.rb
index 27fad9513536..1c189911b4c7 100644
--- 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_requirement.rb b/test/rubygems/test_gem_requirement.rb
index 00634dc7f43f..bd3988b32300 100644
--- 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)
diff --git a/test/rubygems/test_gem_safe_marshal.rb b/test/rubygems/test_gem_safe_marshal.rb
index 1937c02be0cb..806fb3149f2b 100644
--- a/test/rubygems/test_gem_safe_marshal.rb
+++ b/test/rubygems/test_gem_safe_marshal.rb
@@ -317,10 +317,12 @@ def test_array_subclass
   end
 
   def test_frozen_object
+    pend_for_ruby_box_marshal
     assert_safe_load_as Gem::Version.new("1.abc").freeze
   end
 
   def test_date
+    pend_for_ruby_box_marshal
     assert_safe_load_as Date.new(1994, 12, 9)
   end
 
@@ -369,6 +371,7 @@ def test_gem_spec_unmarshall_license
   end
 
   def test_gem_spec_unmarshall_required_ruby_rubygems_version
+    pend_for_ruby_box_marshal
     spec = Gem::Specification.new do |s|
       s.name = "hi"
       s.version = "1.2.3"
@@ -500,7 +503,12 @@ def test_date_user_defined_rejected
 
   def assert_safe_load_marshal(dumped, additional_methods: [], permitted_ivars: nil, equality: true, marshal_dump_equality: true,
     inspect: true, to_s: true)
-    loaded = Marshal.load(dumped)
+    loaded = begin
+      Marshal.load(dumped)
+    rescue ArgumentError => e
+      pend_for_ruby_box_marshal if e.message.include?("undefined class/module")
+      raise
+    end
     safe_loaded =
       assert_nothing_raised("dumped: #{dumped.b.inspect} loaded: #{loaded.inspect}") do
         if permitted_ivars
diff --git a/test/rubygems/test_gem_specification.rb b/test/rubygems/test_gem_specification.rb
index fba0bc36e334..f01b5534331b 100644
--- a/test/rubygems/test_gem_specification.rb
+++ b/test/rubygems/test_gem_specification.rb
@@ -710,6 +710,7 @@ def test_self_attribute_names
   end
 
   def test_self__load_future
+    pend_for_ruby_box_marshal
     spec = Gem::Specification.new
     spec.name = "a"
     spec.version = "1"
@@ -1064,6 +1065,7 @@ def test_self_stubs_returns_only_specified_named_specs
   end
 
   def test_handles_private_null_type
+    pend_for_ruby_box_marshal
     yaml_defined = Object.const_defined?("YAML")
 
     path = File.expand_path "data/pry-0.4.7.gemspec.rz", __dir__
@@ -1076,6 +1078,7 @@ def test_handles_private_null_type
   end
 
   def test_handles_dependencies_with_syck_requirements_bug
+    pend_for_ruby_box_marshal
     yaml_defined = Object.const_defined?("YAML")
 
     path = File.expand_path "data/excon-0.7.7.gemspec.rz", __dir__
@@ -1281,6 +1284,7 @@ def test_set_version_to_nil_after_setting_version
   end
 
   def test__dump
+    pend_for_ruby_box_marshal
     @a2.platform = Gem::Platform.local
     @a2.instance_variable_set :@original_platform, "old_platform"
 
@@ -3794,6 +3798,7 @@ def test_version_change_reset_cache_file
   end
 
   def test__load_fixes_Date_objects
+    pend_for_ruby_box_marshal
     spec = util_spec "a", 1
     spec.instance_variable_set :@date, Date.today
 

From 3b2655a97861757b1e2b4515d7a0ab60729c9f33 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Fri, 28 Aug 2026 11:42:52 +0900
Subject: [PATCH 5/9] Add a RUBY_BOX=1 CI lane on ruby-head

The suite is green under RUBY_BOX=1 now, so run it on ruby-head as a
canary to catch regressions on either side early.
---
 .github/workflows/rubygems.yml | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/rubygems.yml b/.github/workflows/rubygems.yml
index efa2a7ffeeb6..2e83ad6f2f09 100644
--- 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'

From eb392aabd8a7d3935e5e6c4ddc2580f4a674c862 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Mon, 31 Aug 2026 13:19:06 +0900
Subject: [PATCH 6/9] Fix the RUBY_BOX=1 lane failures

yamllint rejects the redundantly quoted matrix name. The cargo tests
require the installed gem with -r, which bypasses gem activation under
RUBY_BOX=1 because the command line require does not go through the
RubyGems Kernel#require override, so require inside -e instead.
---
 .github/workflows/rubygems.yml              | 2 +-
 test/rubygems/test_gem_ext_cargo_builder.rb | 5 +++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/rubygems.yml b/.github/workflows/rubygems.yml
index 2e83ad6f2f09..b1f8f4e28217 100644
--- a/.github/workflows/rubygems.yml
+++ b/.github/workflows/rubygems.yml
@@ -61,7 +61,7 @@ jobs:
             os: { name: Windows, value: windows-2025 }
             symlink: off
 
-          - ruby: { name: "head (RUBY_BOX=1)", value: head }
+          - ruby: { name: head (RUBY_BOX=1), value: head }
             os: { name: Ubuntu, value: ubuntu-24.04 }
             ruby_box: true
     env:
diff --git a/test/rubygems/test_gem_ext_cargo_builder.rb b/test/rubygems/test_gem_ext_cargo_builder.rb
index 94673a478c4e..ae94475f65ae 100644
--- 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

From 861044c050cc0bd763b9939e4ec8280f3f0f68ea Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Mon, 31 Aug 2026 14:14:04 +0900
Subject: [PATCH 7/9] Filter Ruby::Box experimental warnings from captured spec
 stderr

Under RUBY_BOX every ruby subprocess spawned by the specs prints a
two-line experimental warning to stderr, breaking specs that assert
clean stderr. Strip those lines when the host ruby has boxes enabled,
instead of injecting -W:no-experimental into RUBYOPT, because several
specs assert the exact RUBYOPT propagated to subprocesses.
---
 spec/support/command_execution.rb | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/spec/support/command_execution.rb b/spec/support/command_execution.rb
index e2915b996d9d..14da54dca4da 100644
--- 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

From 2c7725c78abc847e52ca37178362e4a25638caad Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Mon, 31 Aug 2026 14:47:00 +0900
Subject: [PATCH 8/9] Scope the File.expand_path stub in shared_helpers_spec

The special-characters and whitespace contexts stubbed File.expand_path
for every argument. Under RUBY_BOX=1 with the turbo_tests workers,
Bundler::Settings is still unloaded when these examples run, and reading
the repository .bundle/config triggers a lazy require of
rubygems/yaml_serializer. The default gem activation path in
Kernel#require then resolves paths through the stub and crashes with
Errno::ENOENT on a fake gemspec path. Stub only the expansion of
bundler/setup, which is all these examples need faked.
---
 spec/bundler/shared_helpers_spec.rb | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/spec/bundler/shared_helpers_spec.rb b/spec/bundler/shared_helpers_spec.rb
index 1619b0a14a59..232da4143a24 100644
--- 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
 

From 5f2d4815dc283d05265f481f00463753d1ace990 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Mon, 31 Aug 2026 15:33:20 +0900
Subject: [PATCH 9/9] Skip the RUBYOPT -r native extension example under
 Ruby::Box

The example passes RUBYOPT=-rnative_child to the bundle install
subprocess, but under RUBY_BOX=1 require_libraries_in_main_box calls
rb_require_string directly and bypasses the RubyGems Kernel#require
override, so the gem is never activated and the require raises
LoadError. This is an unreported ruby-core bug related to [Bug #21760]
item 3, and the scenario itself is legitimate, so skip it until the
Ruby::Box require semantics are settled upstream.
---
 spec/commands/install_spec.rb | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/spec/commands/install_spec.rb b/spec/commands/install_spec.rb
index a0b56a3d2970..dc9efb11e57f 100644
--- 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, a
+    # ruby-core bug (unreported, related to [Bug #21760] item 3)
+    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|