commit 00a4e37e5a4f2c035627e8127391ebc1ffc42aff
Author: Pavel Skrylev <majioa@altlinux.org>
Date:   Mon Aug 15 21:26:44 2022 +0300

    feat: single instantination feature
    
    + single instantination feature allowing to optimize gem folder tree

diff --git a/configure.ac b/configure.ac
index 2ab04193e7..b345c3e69a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -4182,6 +4182,12 @@ AC_ARG_WITH(cachedir,
 	    AS_HELP_STRING([--with-cachedir=DIR], [specify ruby cache dir]),
 	    [cachedir=$withval])
 
+single_instantiating=no
+AC_ARG_ENABLE(single-instantiating,
+           AS_HELP_STRING([--enable-single-instantiating], [enable single ruby versions in tree]),
+           [single_instantiating=$enableval], [single_instantiating=no])
+AC_SUBST(single_instantiating)dnl
+
 AC_SUBST(rubyhdrdir)dnl
 AC_SUBST(sitehdrdir)dnl
 AC_SUBST(vendorhdrdir)dnl
diff --git a/lib/rubygems/config_file.rb b/lib/rubygems/config_file.rb
index 5dd2bfe88d..9f519b6a2a 100644
--- a/lib/rubygems/config_file.rb
+++ b/lib/rubygems/config_file.rb
@@ -223,6 +223,13 @@ def initialize(args)
     handle_arguments args
   end
 
+  ##
+  # Has the ruby build single instantiated, defaulting to false/nil
+
+  def single_instantiating?
+    @single_instantiating ||= RbConfig::CONFIG["single_instantiating"] == 'yes'
+  end
+
   ##
   # Hash of RubyGems.org and alternate API keys
 
diff --git a/lib/rubygems/defaults.rb b/lib/rubygems/defaults.rb
index d9f7fab1e8..228748fe57 100644
--- a/lib/rubygems/defaults.rb
+++ b/lib/rubygems/defaults.rb
@@ -38,7 +38,14 @@ def self.default_spec_cache_dir
   # specified in the environment
 
   def self.default_dir
-    @default_dir ||= File.join(RbConfig::CONFIG['rubylibprefix'], 'gems', RbConfig::CONFIG['ruby_version'])
+    subpath = if Gem.configuration.single_instantiating?
+                ['gemie']
+              else
+                ['gems', RbConfig::CONFIG['ruby_version']]
+              end
+    path = [RbConfig::CONFIG['rubylibprefix']] + subpath
+
+    @default_dir ||= File.join(*path)
   end
 
   ##
@@ -49,7 +56,18 @@ def self.default_dir
   # Ruby counterparts, therefore nil is returned
 
   def self.default_ext_dir_for(base_dir)
-    nil
+    if Gem.configuration.single_instantiating?
+      parts =
+        if base_dir.nil?
+          [RbConfig::CONFIG['rubyarchdir'], 'gemie']
+        elsif base_dir[0...RbConfig::CONFIG['rubylibprefix'].size] == RbConfig::CONFIG['rubylibprefix']
+          [RbConfig::CONFIG['rubyarchdir'], base_dir[RbConfig::CONFIG['rubylibprefix'].size..-1]]
+        else
+          [base_dir, 'gemie']
+        end + ['extensions']
+
+      File.join(parts)
+    end
   end
 
   ##
@@ -81,7 +81,12 @@ module Gem
   # Path to specification files of default gems.
 
   def self.default_specifications_dir
-    @default_specifications_dir ||= File.join(Gem.default_dir, "specifications", "default")
+    @default_specifications_dir ||=
+      if Gem.configuration.single_instantiating?
+        File.join(RbConfig::CONFIG['rubylibprefix'], "specifications")
+      else
+        File.join(Gem.default_dir, "specifications", "default")
+      end
   end
 
   ##
@@ -237,8 +255,13 @@ def self.vendor_dir # :nodoc:
 
     return nil unless RbConfig::CONFIG.key? 'vendordir'
 
-    File.join RbConfig::CONFIG['vendordir'], 'gems',
-              RbConfig::CONFIG['ruby_version']
+    subpath = if Gem.configuration.single_instantiating?
+                ['gemie']
+              else
+                ['gems', RbConfig::CONFIG['ruby_version']]
+              end
+
+    File.join RbConfig::CONFIG['vendordir'], *subpath
   end
 
   ##
diff --git a/lib/rubygems/basic_specification.rb b/lib/rubygems/basic_specification.rb
index b3b63b51aa..e77a316012 100644
--- a/lib/rubygems/basic_specification.rb
+++ b/lib/rubygems/basic_specification.rb
@@ -190,7 +190,12 @@ def to_fullpath(path)
   # eg: /usr/local/lib/ruby/1.8/gems/mygem-1.0
 
   def gem_dir
-    @gem_dir ||= File.expand_path File.join(gems_dir, full_name)
+    @gem_dir ||=
+      if default_gem?
+        File.expand_path(gems_dir)
+      else
+        File.expand_path File.join(gems_dir, full_name)
+      end
   end
 
   ##
diff --git a/lib/rubygems/specification.rb b/lib/rubygems/specification.rb
index cb8ee063b4..168a3060b1 100644
--- a/lib/rubygems/specification.rb
+++ b/lib/rubygems/specification.rb
@@ -1915,7 +1920,12 @@ def gem_dir # :nodoc:
   end
 
   def gems_dir
-    @gems_dir ||= File.join(base_dir, "gems")
+    @gems_dir ||=
+      if default_gem?
+        base_dir
+      else
+        File.join(base_dir, "gems")
+      end
   end
 
   ##
@@ -2032,7 +2032,7 @@ def initialize_copy(other_spec)
 
   def base_dir
     return Gem.dir unless loaded_from
-    @base_dir ||= if default_gem?
+    @base_dir ||= if !Gem.configuration.single_instantiating? && default_gem?
       File.dirname File.dirname File.dirname loaded_from
     else
       File.dirname File.dirname loaded_from
--- a/template/ruby.pc.in	2022-08-15 22:32:35.948000000 +0000
+++ b/template/ruby.pc.in	2022-08-16 10:29:49.008000000 +0000
@@ -23,6 +23,7 @@ sitearchincludedir=@sitearchincludedir@
 rubylibprefix=@rubylibprefix@
 rubyarchprefix=@rubyarchprefix@
 use_system_dirs=@use_system_dirs@
+single_instantiating=@single_instantiating@
 rubysitearchprefix=@rubysitearchprefix@
 rubylibdir=@rubylibdir@
 vendordir=@vendordir@