Don't change the default gem directory.

Ruby expects default gem specifications to be stored in a subdirectory
of default gem specifications directory. Change in default directory
makes the default gems unloadable.

Unfortunately, when '--install-dir' option is used, this might prevent
generating of documentation [1].

[1] https://github.com/rubygems/rubygems/issues/1470

operating_system.rb

@@ -87,22 +87,33 @@ module Gem
     # Remove methods we are going to override. This avoids "method redefined;"
     # warnings otherwise issued by Ruby.
 
+    remove_method :operating_system_defaults if method_defined? :operating_system_defaults
     remove_method :default_dir if method_defined? :default_dir
     remove_method :default_path if method_defined? :default_path
-    remove_method :default_bindir if method_defined? :default_bindir
     remove_method :default_ext_dir_for if method_defined? :default_ext_dir_for
 
+    ##
+    # Regular user installs into user directory, root manages /usr/local.
+
+    def operating_system_defaults
+      unless opt_build_root?
+        options = if Process.uid == 0
+          "--install-dir=#{Gem.default_dirs[:local][:gem_dir]} --bindir #{Gem.default_dirs[:local][:bin_dir]}"
+        else
+          "--user-install --bindir #{File.join [Dir.home, 'bin']}"
+        end
+
+        {"gem" => options}
+      else
+        {}
+      end
+    end
+
     ##
     # RubyGems default overrides.
 
     def default_dir
-      if opt_build_root?
-        Gem.default_dirs[:system][:gem_dir]
-      elsif Process.uid == 0
-        Gem.default_dirs[:local][:gem_dir]
-      else
-        Gem.user_dir
-      end
+      Gem.default_dirs[:system][:gem_dir]
     end
 
     def default_path
@@ -110,16 +121,6 @@ module Gem
       path.unshift Gem.user_dir if File.exist? Gem.user_home
     end
 
-    def default_bindir
-      if opt_build_root?
-        Gem.default_dirs[:system][:bin_dir]
-      elsif Process.uid == 0
-        Gem.default_dirs[:local][:bin_dir]
-      else
-        File.join [Dir.home, 'bin']
-      end
-    end
-
     def default_ext_dir_for base_dir
       dir = if rpmbuild?
         build_dir = base_dir.chomp Gem.default_dirs[:system][:gem_dir]

ruby-2.5.0-Add-Gem.operating_system_defaults.patch

@@ -0,0 +1,80 @@
+From 60eb961c25f801ee43ca1be9393ab2f0a0546677 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?V=C3=ADt=20Ondruch?= <vondruch@redhat.com>
+Date: Tue, 19 Dec 2017 14:00:20 +0100
+Subject: [PATCH] Add Gem.operating_system_defaults to allow packagers to
+ override defaults.
+
+This change allows Ruby packagers to override defaults and lazily query
+them.
+
+This is very much the same change as #1644 to treat the
+operating_system defaults the same way as platform defaults.
+---
+ lib/rubygems/config_file.rb |  2 +-
+ lib/rubygems/defaults.rb    | 21 ++++++++++++++++++++-
+ test/rubygems/test_gem.rb   |  7 +++++++
+ 3 files changed, 28 insertions(+), 2 deletions(-)
+
+diff --git a/lib/rubygems/config_file.rb b/lib/rubygems/config_file.rb
+index a4efed0f5a..deee38e6d9 100644
+--- a/lib/rubygems/config_file.rb
++++ b/lib/rubygems/config_file.rb
+@@ -48,7 +48,7 @@ class Gem::ConfigFile
+   # For Ruby packagers to set configuration defaults.  Set in
+   # rubygems/defaults/operating_system.rb
+ 
+-  OPERATING_SYSTEM_DEFAULTS = {}
++  OPERATING_SYSTEM_DEFAULTS = Gem.operating_system_defaults
+ 
+   ##
+   # For Ruby implementers to set configuration defaults.  Set in
+diff --git a/lib/rubygems/defaults.rb b/lib/rubygems/defaults.rb
+index 43d57fc808..b8222877ae 100644
+--- a/lib/rubygems/defaults.rb
++++ b/lib/rubygems/defaults.rb
+@@ -177,7 +177,26 @@ def self.vendor_dir # :nodoc:
+   end
+ 
+   ##
+-  # Default options for gem commands.
++  # Default options for gem commands for Ruby packagers.
++  #
++  # The options here should be structured as an array of string "gem"
++  # command names as keys and a string of the default options as values.
++  #
++  # Example:
++  #
++  # def self.operating_system_defaults
++  #   {
++  #       'install' => '--no-rdoc --no-ri --env-shebang',
++  #       'update' => '--no-rdoc --no-ri --env-shebang'
++  #   }
++  # end
++
++  def self.operating_system_defaults
++    {}
++  end
++
++  ##
++  # Default options for gem commands for Ruby implementers.
+   #
+   # The options here should be structured as an array of string "gem"
+   # command names as keys and a string of the default options as values.
+diff --git a/test/rubygems/test_gem.rb b/test/rubygems/test_gem.rb
+index 3225a05c6b..62b80c4945 100644
+--- a/test/rubygems/test_gem.rb
++++ b/test/rubygems/test_gem.rb
+@@ -1799,6 +1799,13 @@ def test_use_gemdeps_specific
+     ENV['RUBYGEMS_GEMDEPS'] = rubygems_gemdeps
+   end
+ 
++  def test_operating_system_defaults
++    operating_system_defaults = Gem.operating_system_defaults
++
++    assert operating_system_defaults != nil
++    assert operating_system_defaults.is_a? Hash
++  end
++
+   def test_platform_defaults
+     platform_defaults = Gem.platform_defaults
+ 

ruby.spec

@@ -132,6 +132,9 @@ Patch7: ruby-2.2.3-Generate-preludes-using-miniruby.patch
 # hardening features of glibc (rhbz#1361037).
 # https://bugs.ruby-lang.org/issues/12666
 Patch9: ruby-2.3.1-Rely-on-ldd-to-detect-glibc.patch
+# Add Gem.operating_system_defaults to allow packagers to override defaults.
+# https://github.com/rubygems/rubygems/pull/2116
+Patch10: ruby-2.5.0-Add-Gem.operating_system_defaults.patch
 
 Requires: %{name}-libs%{?_isa} = %{version}-%{release}
 Suggests: rubypick
@@ -512,6 +515,7 @@ rm -rf ext/fiddle/libffi*
 %patch6 -p1
 %patch7 -p1
 %patch9 -p1
+%patch10 -p1
 
 # Provide an example of usage of the tapset:
 cp -a %{SOURCE3} .