Autoload RubyGems internals by feature name

lib/rubygems.rb

@@ -1410,23 +1410,26 @@ def default_gem_load_paths
 
   MARSHAL_SPEC_DIR = "quick/Marshal.#{Gem.marshal_version}/".freeze
 
-  autoload :ConfigFile,         File.expand_path("rubygems/config_file", __dir__)
-  autoload :CIDetector,         File.expand_path("rubygems/ci_detector", __dir__)
-  autoload :Dependency,         File.expand_path("rubygems/dependency", __dir__)
-  autoload :DependencyList,     File.expand_path("rubygems/dependency_list", __dir__)
-  autoload :Installer,          File.expand_path("rubygems/installer", __dir__)
-  autoload :Licenses,           File.expand_path("rubygems/util/licenses", __dir__)
-  autoload :NameTuple,          File.expand_path("rubygems/name_tuple", __dir__)
-  autoload :PathSupport,        File.expand_path("rubygems/path_support", __dir__)
-  autoload :RequestSet,         File.expand_path("rubygems/request_set", __dir__)
-  autoload :Requirement,        File.expand_path("rubygems/requirement", __dir__)
-  autoload :Resolver,           File.expand_path("rubygems/resolver", __dir__)
-  autoload :Source,             File.expand_path("rubygems/source", __dir__)
-  autoload :SourceList,         File.expand_path("rubygems/source_list", __dir__)
-  autoload :SpecFetcher,        File.expand_path("rubygems/spec_fetcher", __dir__)
-  autoload :SpecificationPolicy, File.expand_path("rubygems/specification_policy", __dir__)
-  autoload :Util,               File.expand_path("rubygems/util", __dir__)
-  autoload :Version,            File.expand_path("rubygems/version", __dir__)
+  # Autoload by feature name. An absolute path skips the $LOADED_FEATURES
+  # check, so a second RubyGems tree on the load path gets loaded on top of
+  # this one.
+  autoload :ConfigFile,         "rubygems/config_file"
+  autoload :CIDetector,         "rubygems/ci_detector"
+  autoload :Dependency,         "rubygems/dependency"
+  autoload :DependencyList,     "rubygems/dependency_list"
+  autoload :Installer,          "rubygems/installer"
+  autoload :Licenses,           "rubygems/util/licenses"
+  autoload :NameTuple,          "rubygems/name_tuple"
+  autoload :PathSupport,        "rubygems/path_support"
+  autoload :RequestSet,         "rubygems/request_set"
+  autoload :Requirement,        "rubygems/requirement"
+  autoload :Resolver,           "rubygems/resolver"
+  autoload :Source,             "rubygems/source"
+  autoload :SourceList,         "rubygems/source_list"
+  autoload :SpecFetcher,        "rubygems/spec_fetcher"
+  autoload :SpecificationPolicy, "rubygems/specification_policy"
+  autoload :Util,               "rubygems/util"
+  autoload :Version,            "rubygems/version"
 end
 
 require_relative "rubygems/exceptions"

lib/rubygems/resolver/api_set.rb

@@ -5,7 +5,7 @@
 # Returns instances of APISpecification.
 
 class Gem::Resolver::APISet < Gem::Resolver::Set
-  autoload :GemParser, File.expand_path("api_set/gem_parser", __dir__)
+  autoload :GemParser, "rubygems/resolver/api_set/gem_parser"
 
   ##
   # The URI for the Compact Index API this APISet uses.

test/rubygems/test_rubygems.rb

@@ -52,8 +52,38 @@
     end
   end
 
+  def test_autoload_does_not_load_a_second_copy_of_the_same_file
+    # Two RubyGems trees on the load path, as when Bundler runs from a RubyGems
+    # checkout while the host RubyGems is already loaded.
+    path = util_install_name_tuple_rb
+
+    output = Gem::Util.popen(
+      *ruby_with_shadowing_rubygems_in_load_path(path),
+      "-e",
+      "require \"rubygems/name_tuple\"; puts $LOADED_FEATURES.count {|f| f.end_with?(\"rubygems/name_tuple.rb\") }",
+      { err: [:child, :out] }
+    ).strip
+
+    assert_equal "1", output
+  end
+
   private
 
+  def util_install_name_tuple_rb
+    dir = Dir.mktmpdir("test_shadowing_rubygems_lib", @tempdir)
+
+    name_tuple_rb = File.join dir, "rubygems", "name_tuple.rb"
+
+    FileUtils.mkdir_p File.dirname(name_tuple_rb)
+    FileUtils.cp File.join(rubygems_path, "rubygems", "name_tuple.rb"), name_tuple_rb
+
+    dir
+  end
+
+  def ruby_with_shadowing_rubygems_in_load_path(shadowing_path)
+    [Gem.ruby, "-I", shadowing_path, *ruby_with_rubygems_in_load_path.drop(1)]
+  end
+
   def util_install_operating_system_rb(content)
     dir_lib = Dir.mktmpdir("test_operating_system_lib", @tempdir)
     dir_lib_arg = File.join dir_lib, "lib"