* ext/psych/lib/psych/visitors/to_ruby.rb: Added support for loading

  subclasses of String with ivars
* ext/psych/lib/psych/visitors/yaml_tree.rb: Added support for dumping
  subclasses of String with ivars
* test/psych/test_string.rb: corresponding tests

2 files changed, 22 insertions, 4 deletions

diff --git a/lib/psych/visitors/to_ruby.rb b/lib/psych/visitors/to_ruby.rb
index bb29c8b..3db67a3 100644
--- a/lib/psych/visitors/to_ruby.rb
+++ b/lib/psych/visitors/to_ruby.rb
@@ -50,8 +50,13 @@ module Psych
         case o.tag
         when '!binary', 'tag:yaml.org,2002:binary'
           o.value.unpack('m').first
-        when '!str', 'tag:yaml.org,2002:str'
-          o.value
+        when /^!(?:str|ruby\/string)(?::(.*))?/, 'tag:yaml.org,2002:str'
+          klass = resolve_class($1)
+          if klass
+            klass.allocate.replace o.value
+          else
+            o.value
+          end
         when '!ruby/object:BigDecimal'
           require 'bigdecimal'
           BigDecimal._load o.value
@@ -136,9 +141,16 @@ module Psych
         return revive_hash({}, o) unless o.tag
 
         case o.tag
-        when '!str', 'tag:yaml.org,2002:str'
+        when /^!(?:str|ruby\/string)(?::(.*))?/, 'tag:yaml.org,2002:str'
+          klass = resolve_class($1)
           members = Hash[*o.children.map { |c| accept c }]
           string = members.delete 'str'
+
+          if klass
+            string = klass.allocate
+            string.replace string
+          end
+
           init_with(string, members.map { |k,v| [k.to_s.sub(/^@/, ''),v] }, o)
         when /^!ruby\/array:(.*)$/
           klass = resolve_class($1)
diff --git a/lib/psych/visitors/yaml_tree.rb b/lib/psych/visitors/yaml_tree.rb
index 1e22501..80af046 100644
--- a/lib/psych/visitors/yaml_tree.rb
+++ b/lib/psych/visitors/yaml_tree.rb
@@ -245,9 +245,15 @@ module Psych
         ivars = find_ivars o
 
         if ivars.empty?
+          unless o.class == ::String
+            tag = "!ruby/string:#{o.class}"
+          end
           @emitter.scalar str, nil, tag, plain, quote, style
         else
-          @emitter.start_mapping nil, '!str', false, Nodes::Mapping::BLOCK
+          maptag = '!ruby/string'
+          maptag << ":#{o.class}" unless o.class == ::String
+
+          @emitter.start_mapping nil, maptag, false, Nodes::Mapping::BLOCK
           @emitter.scalar 'str', nil, nil, true, false, Nodes::Scalar::ANY
           @emitter.scalar str, nil, tag, plain, quote, style