Gracefully deal with YAML::PrivateType objects in Marshal'd gemspecs

lib/rubygems.rb

@@ -671,6 +671,7 @@ def self.load_yaml
           YAML::ENGINE.yamler = "psych"
         end
 
+        require 'rubygems/psych_additions'
         require 'rubygems/psych_tree'
       end
     end

lib/rubygems/psych_additions.rb

@@ -0,0 +1,9 @@
+# This exists just to satify bugs in marshal'd gemspecs that
+# contain a reference to YAML::PrivateType. We prune these out
+# in Specification._load, but if we don't have the constant, Marshal
+# blows up.
+
+module Psych
+  class PrivateType
+  end
+end

lib/rubygems/specification.rb

@@ -666,6 +666,11 @@ def self._load(str)
       raise TypeError, "invalid Gem::Specification format #{array.inspect}"
     end
 
+    # Cleanup any YAML::PrivateType. They only show up for an old bug
+    # where nil => null, so just convert them to nil based on the type.
+
+    array.map! { |e| e.kind_of?(YAML::PrivateType) ? nil : e }
+
     spec.instance_variable_set :@rubygems_version,          array[0]
     # spec version
     spec.instance_variable_set :@name,                      array[2]