use the source returned from encode!

actionview/lib/action_view/template.rb

@@ -202,7 +202,9 @@ def inspect
     # before passing the source on to the template engine, leaving a
     # blank line in its stead.
     def encode!
-      return unless source.encoding == Encoding::BINARY
+      source = self.source
+
+      return source unless source.encoding == Encoding::BINARY
 
       # Look for # encoding: *. If we find one, we'll encode the
       # String in that encoding, otherwise, we'll use the
@@ -290,7 +292,7 @@ def compile!(view)
       # In general, this means that templates will be UTF-8 inside of Rails,
       # regardless of the original source encoding.
       def compile(mod)
-        encode!
+        source = encode!
         code = @handler.call(self)
 
         # Make sure that the resulting String to be eval'd is in the
@@ -312,7 +314,7 @@ def #{method_name}(local_assigns, output_buffer)
         # handler is valid in the default_internal. This is for handlers
         # that handle encoding but screw up
         unless source.valid_encoding?
-          raise WrongEncodingError.new(@source, Encoding.default_internal)
+          raise WrongEncodingError.new(source, Encoding.default_internal)
         end
 
         mod.module_eval(source, identifier, 0)