Install default and bundled gems into dedicated directories

lib/rubygems/defaults/ruby.rb

@@ -0,0 +1,37 @@
+module Gem
+  class << self
+
+    def bundled_gems_dir
+      File.join(RbConfig::CONFIG["rubylibprefix"], "bundled_gems", RbConfig::CONFIG["ruby_version"])
+    end
+
+    def default_gems_dir
+      File.join(RbConfig::CONFIG["rubylibprefix"], "default_gems", RbConfig::CONFIG["ruby_version"])
+    end
+
+    undef :default_specifications_dir if method_defined? :default_specifications_dir
+
+    if method_defined? :default_path
+      alias orig_default_path default_path
+      undef :default_path
+    end
+
+    ##
+    # Path to specification files of default gems.
+
+    def default_specifications_dir
+      @default_specifications_dir ||= File.join(Gem.default_gems_dir, "specifications", "default")
+    end
+
+    ##
+    # Default gem load path
+
+    def default_path
+      path = orig_default_path
+      path << bundled_gems_dir
+      path << default_gems_dir
+      path
+    end
+
+  end
+end

test/rubygems/test_gem.rb

@@ -574,6 +574,8 @@ def test_self_default_exec_format_jruby
   end
 
   def test_default_path
+    original_gem_default_path?
+
     vendordir(File.join(@tempdir, "vendor")) do
       FileUtils.rm_rf Gem.user_home
 
@@ -584,6 +586,8 @@ def test_default_path
   end
 
   def test_default_path_missing_vendor
+    original_gem_default_path?
+
     vendordir(nil) do
       FileUtils.rm_rf Gem.user_home
 
@@ -594,6 +598,8 @@ def test_default_path_missing_vendor
   end
 
   def test_default_path_user_home
+    original_gem_default_path?
+
     vendordir(File.join(@tempdir, "vendor")) do
       expected = [Gem.user_dir, Gem.default_dir]
 
@@ -602,6 +608,8 @@ def test_default_path_user_home
   end
 
   def test_default_path_vendor_dir
+    original_gem_default_path?
+
     vendordir(File.join(@tempdir, "vendor")) do
       FileUtils.mkdir_p Gem.vendor_dir
 
@@ -1796,4 +1804,10 @@ def util_remove_interrupt_command
   def util_cache_dir
     File.join Gem.dir, "cache"
   end
+
+  def original_gem_default_path?
+    unless Gem.method(:default_path).source_location.first.match? "lib/rubygems/defaults.rb"
+      pend "Gem.default_path likely differs from original RubyGems implementation"
+    end
+  end
 end

tool/rbinstall.rb

@@ -942,7 +942,7 @@ def load_gemspec(file, base = nil)
 end
 
 def install_default_gem(dir, srcdir, bindir)
-  gem_dir = Gem.default_dir
+  gem_dir = Gem.default_gems_dir
   install_dir = with_destdir(gem_dir)
   prepare "default gems from #{dir}", gem_dir
   RbInstall.no_write do
@@ -991,7 +991,7 @@ def install_default_gem(dir, srcdir, bindir)
 end
 
 install?(:ext, :comm, :gem, :'bundled-gems') do
-  gem_dir = Gem.default_dir
+  gem_dir = Gem.bundled_gems_dir
   install_dir = with_destdir(gem_dir)
   prepare "bundled gems", gem_dir
   RbInstall.no_write do