Fix Marshal.dump for String/Regexp with instance variables

spec/core/marshal/dump_spec.rb

@@ -358,9 +358,7 @@ def _dump(level)
     it "dumps a String with instance variables" do
       str = +""
       str.instance_variable_set("@foo", "bar")
-      NATFIXME 'dumps a String with instance variables', exception: SpecFailedException do
-        Marshal.dump(str.force_encoding("binary")).should == "\x04\bI\"\x00\x06:\t@foo\"\bbar"
-      end
+      Marshal.dump(str.force_encoding("binary")).should == "\x04\bI\"\x00\x06:\t@foo\"\bbar"
     end
 
     it "dumps a US-ASCII String" do
@@ -400,9 +398,7 @@ def _dump(level)
     it "dumps a Regexp with instance variables" do
       o = Regexp.new("")
       o.instance_variable_set(:@ivar, :ivar)
-      NATFIXME 'dumps a Regexp with instance variables', exception: SpecFailedException do
-        Marshal.dump(o).should == "\x04\bI/\x00\x00\a:\x06EF:\n@ivar:\tivar"
-      end
+      Marshal.dump(o).should == "\x04\bI/\x00\x00\a:\x06EF:\n@ivar:\tivar"
     end
 
     it "dumps an extended Regexp" do

spec/core/marshal/shared/load.rb

@@ -613,7 +613,7 @@
       h = { key: s }
       h.instance_variable_set :@hash_ivar, 'hash ivar'
 
-      NATFIXME 'preserves hash ivars when hash contains a string having ivar', exception: SpecFailedException do
+      NATFIXME 'issue with additional @ in ivar name', exception: NameError do
         unmarshalled = Marshal.send(@method, Marshal.dump(h))
         unmarshalled.instance_variable_get(:@hash_ivar).should == 'hash ivar'
         unmarshalled[:key].instance_variable_get(:@string_ivar).should == 'string ivar'

src/marshal.rb

@@ -102,15 +102,17 @@ def write_string_bytes(value)
     end
 
     def write_encoding_bytes(value)
+      ivars = value.instance_variables.map { |ivar_name| [ivar_name, value.instance_variable_get(ivar_name)] }
       case value.encoding
       when Encoding::US_ASCII
-        write_integer_bytes(1)
-        write_symbol(:E)
-        write_false
+        ivars.prepend([:E, false])
       when Encoding::UTF_8
-        write_integer_bytes(1)
-        write_symbol(:E)
-        write_true
+        ivars.prepend([:E, true])
+      end
+      write_integer_bytes(ivars.size) unless ivars.empty?
+      ivars.each do |ivar_name, ivar_value|
+        write(ivar_name)
+        write(ivar_value)
       end
     end
 
@@ -141,10 +143,10 @@ def write_integer(value)
     end
 
     def write_string(value)
-      write_char('I') if value.encoding != Encoding::ASCII_8BIT
+      write_char('I') if value.encoding != Encoding::ASCII_8BIT || !value.instance_variables.empty?
       write_char('"')
       write_string_bytes(value)
-      write_encoding_bytes(value) if value.encoding != Encoding::ASCII_8BIT
+      write_encoding_bytes(value)
     end
 
     def write_symbol(value)