Use YAMLSerializer in Specification with Psych fallback

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: hsbt

lib/rubygems/safe_marshal.rb

@@ -54,6 +54,7 @@ module SafeMarshal
       "Gem::NameTuple" => %w[@name @version @platform],
       "Gem::Platform" => %w[@os @cpu @version],
       "Psych::PrivateType" => %w[@value @type_id],
+      "YAML::PrivateType" => %w[@value @type_id],
     }.freeze
     private_constant :PERMITTED_IVARS
 

lib/rubygems/specification.rb

@@ -1275,7 +1275,7 @@ def self._load(str)
       raise unless message.include?("YAML::")
 
       unless Object.const_defined?(:YAML)
-        Object.const_set "YAML", Psych
+        Object.const_set "YAML", Module.new
         yaml_set = true
       end
 
@@ -1284,7 +1284,7 @@ def self._load(str)
 
         YAML::Syck.const_set "DefaultKey", Class.new if message.include?("YAML::Syck::DefaultKey") && !YAML::Syck.const_defined?(:DefaultKey)
       elsif message.include?("YAML::PrivateType") && !YAML.const_defined?(:PrivateType)
-        YAML.const_set "PrivateType", Class.new
+        YAML.const_set "PrivateType", Class.new { attr_accessor :type_id, :value }
       end
 
       retry_count += 1
@@ -2455,24 +2455,28 @@ def to_spec
   def to_yaml(opts = {}) # :nodoc:
     Gem.load_yaml
 
-    # Because the user can switch the YAML engine behind our
-    # back, we have to check again here to make sure that our
-    # psych code was properly loaded, and load it if not.
-    unless Gem.const_defined?(:NoAliasYAMLTree)
-      require_relative "psych_tree"
-    end
+    if Gem.use_psych?
+      # Because the user can switch the YAML engine behind our
+      # back, we have to check again here to make sure that our
+      # psych code was properly loaded, and load it if not.
+      unless Gem.const_defined?(:NoAliasYAMLTree)
+        require_relative "psych_tree"
+      end
 
-    builder = Gem::NoAliasYAMLTree.create
-    builder << self
-    ast = builder.tree
+      builder = Gem::NoAliasYAMLTree.create
+      builder << self
+      ast = builder.tree
 
-    require "stringio"
-    io = StringIO.new
-    io.set_encoding Encoding::UTF_8
+      require "stringio"
+      io = StringIO.new
+      io.set_encoding Encoding::UTF_8
 
-    Psych::Visitors::Emitter.new(io).accept(ast)
+      Psych::Visitors::Emitter.new(io).accept(ast)
 
-    io.string.gsub(/ !!null \n/, " \n")
+      io.string.gsub(/ !!null \n/, " \n")
+    else
+      Gem::YAMLSerializer.dump(self)
+    end
   end
 
   ##