Significantly improved internal encoding heuristics and support.

* Default Encoding.default_internal to UTF-8
* Eliminated the use of file-wide magic comments to coerce code evaluated inside the file
* Read templates as BINARY, use default_external or template-wide magic comments
  inside the Template to set the initial encoding
  * This means that template handlers in Ruby 1.9 will receive Strings encoded
    in default_internal (UTF-8 by default)
* Create a better Exception for encoding issues, and use it when the template
  source has bytes that are not compatible with the specified encoding
* Allow template handlers to opt-into handling BINARY. If they do so, they
  need to do some of their own manual encoding work
* Added a "Configuration Gotchas" section to the intro Rails Guide instructing
  users to use UTF-8 for everything
* Use config.encoding= in Ruby 1.8, and raise if a value that is an invalid
  $KCODE value is used

Also:
* Fixed a few tests that were assert() rather than assert_equal() and
  were caught by Minitest requiring a String for the message
* Fixed a test where an assert_select was misformed, also caught by
  Minitest being more restrictive
* Fixed a test where a Rack response was returning a String rather
  than an Enumerable

actionpack/lib/action_view.rb

@@ -51,15 +51,17 @@ module ActionView
 
     autoload :MissingTemplate,    'action_view/template/error'
     autoload :ActionViewError,    'action_view/template/error'
-    autoload :TemplateError,     'action_view/template/error'
+    autoload :EncodingError,      'action_view/template/error'
+    autoload :TemplateError,      'action_view/template/error'
+    autoload :WrongEncodingError, 'action_view/template/error'
 
     autoload :TemplateHandler,   'action_view/template'
     autoload :TemplateHandlers,  'action_view/template'
   end
 
   autoload :TestCase, 'action_view/test_case'
 
-  ENCODING_FLAG = "#.*coding[:=]\s*(\S+)[ \t]*"
+  ENCODING_FLAG = '#.*coding[:=]\s*(\S+)[ \t]*'
 end
 
 require 'active_support/i18n'

actionpack/lib/action_view/template.rb

@@ -1,12 +1,89 @@
-# encoding: utf-8
-# This is so that templates compiled in this file are UTF-8
 require 'active_support/core_ext/array/wrap'
 require 'active_support/core_ext/object/blank'
+require 'active_support/core_ext/kernel/singleton_class'
 
 module ActionView
   class Template
     extend ActiveSupport::Autoload
 
+    # === Encodings in ActionView::Template
+    #
+    # ActionView::Template is one of a few sources of potential
+    # encoding issues in Rails. This is because the source for
+    # templates are usually read from disk, and Ruby (like most
+    # encoding-aware programming languages) assumes that the
+    # String retrieved through File IO is encoded in the
+    # <tt>default_external</tt> encoding. In Rails, the default
+    # <tt>default_external</tt> encoding is UTF-8.
+    #
+    # As a result, if a user saves their template as ISO-8859-1
+    # (for instance, using a non-Unicode-aware text editor),
+    # and uses characters outside of the ASCII range, their
+    # users will see diamonds with question marks in them in
+    # the browser.
+    #
+    # To mitigate this problem, we use a few strategies:
+    # 1. If the source is not valid UTF-8, we raise an exception
+    #    when the template is compiled to alert the user
+    #    to the problem.
+    # 2. The user can specify the encoding using Ruby-style
+    #    encoding comments in any template engine. If such
+    #    a comment is supplied, Rails will apply that encoding
+    #    to the resulting compiled source returned by the
+    #    template handler.
+    # 3. In all cases, we transcode the resulting String to
+    #    the <tt>default_internal</tt> encoding (which defaults
+    #    to UTF-8).
+    #
+    # This means that other parts of Rails can always assume
+    # that templates are encoded in UTF-8, even if the original
+    # source of the template was not UTF-8.
+    #
+    # From a user's perspective, the easiest thing to do is
+    # to save your templates as UTF-8. If you do this, you
+    # do not need to do anything else for things to "just work".
+    #
+    # === Instructions for template handlers
+    #
+    # The easiest thing for you to do is to simply ignore
+    # encodings. Rails will hand you the template source
+    # as the default_internal (generally UTF-8), raising
+    # an exception for the user before sending the template
+    # to you if it could not determine the original encoding.
+    #
+    # For the greatest simplicity, you can support only
+    # UTF-8 as the <tt>default_internal</tt>. This means
+    # that from the perspective of your handler, the
+    # entire pipeline is just UTF-8.
+    #
+    # === Advanced: Handlers with alternate metadata sources
+    #
+    # If you want to provide an alternate mechanism for
+    # specifying encodings (like ERB does via <%# encoding: ... %>),
+    # you may indicate that you are willing to accept
+    # BINARY data by implementing <tt>self.accepts_binary?</tt>
+    # on your handler.
+    #
+    # If you do, Rails will not raise an exception if
+    # the template's encoding could not be determined,
+    # assuming that you have another mechanism for
+    # making the determination.
+    #
+    # In this case, make sure you return a String from
+    # your handler encoded in the default_internal. Since
+    # you are handling out-of-band metadata, you are
+    # also responsible for alerting the user to any
+    # problems with converting the user's data to
+    # the default_internal.
+    #
+    # To do so, simply raise the raise WrongEncodingError
+    # as follows:
+    #
+    #     raise WrongEncodingError.new(
+    #       problematic_string,
+    #       expected_encoding
+    #     )
+
     eager_autoload do
       autoload :Error
       autoload :Handler
@@ -16,26 +93,22 @@ class Template
 
     extend Template::Handlers
 
-    attr_reader :source, :identifier, :handler, :virtual_path, :formats
+    attr_reader :source, :identifier, :handler, :virtual_path, :formats,
+                :original_encoding
 
-    Finalizer = proc do |method_name|
+    Finalizer = proc do |method_name, mod|
       proc do
-        ActionView::CompiledTemplates.module_eval do
+        mod.module_eval do
           remove_possible_method method_name
         end
       end
     end
 
     def initialize(source, identifier, handler, details)
-      if source.encoding_aware? && source =~ %r{\A#{ENCODING_FLAG}}
-        # don't snip off the \n to preserve line numbers
-        source.sub!(/\A[^\n]*/, '')
-        source.force_encoding($1).encode
-      end
-
-      @source     = source
-      @identifier = identifier
-      @handler    = handler
+      @source             = source
+      @identifier         = identifier
+      @handler            = handler
+      @original_encoding  = nil
 
       @virtual_path = details[:virtual_path]
       @method_names = {}
@@ -48,15 +121,21 @@ def render(view, locals, &block)
       # Notice that we use a bang in this instrumentation because you don't want to
       # consume this in production. This is only slow if it's being listened to.
       ActiveSupport::Notifications.instrument("!render_template.action_view", :virtual_path => @virtual_path) do
-        method_name = compile(locals, view)
+        if view.is_a?(ActionView::CompiledTemplates)
+          mod = ActionView::CompiledTemplates
+        else
+          mod = view.singleton_class
+        end
+
+        method_name = compile(locals, view, mod)
         view.send(method_name, locals, &block)
       end
     rescue Exception => e
       if e.is_a?(Template::Error)
         e.sub_template_of(self)
         raise e
       else
-        raise Template::Error.new(self, view.assigns, e)
+        raise Template::Error.new(self, view.respond_to?(:assigns) ? view.assigns : {}, e)
       end
     end
 
@@ -81,37 +160,97 @@ def inspect
     end
 
     private
-      def compile(locals, view)
+      # Among other things, this method is responsible for properly setting
+      # the encoding of the source. Until this point, we assume that the
+      # source is BINARY data. If no additional information is supplied,
+      # we assume the encoding is the same as Encoding.default_external.
+      #
+      # The user can also specify the encoding via a comment on the first
+      # line of the template (# encoding: NAME-OF-ENCODING). This will work
+      # with any template engine, as we process out the encoding comment
+      # before passing the source on to the template engine, leaving a
+      # blank line in its stead.
+      #
+      # Note that after we figure out the correct encoding, we then
+      # encode the source into Encoding.default_internal. In general,
+      # this means that templates will be UTF-8 inside of Rails,
+      # regardless of the original source encoding.
+      def compile(locals, view, mod)
         method_name = build_method_name(locals)
         return method_name if view.respond_to?(method_name)
 
         locals_code = locals.keys.map! { |key| "#{key} = local_assigns[:#{key}];" }.join
 
-        code = @handler.call(self)
-        if code.sub!(/\A(#.*coding.*)\n/, '')
-          encoding_comment = $1
-        elsif defined?(Encoding) && Encoding.respond_to?(:default_external)
-          encoding_comment = "#coding:#{Encoding.default_external}"
+        if source.encoding_aware?
+          if source.sub!(/\A#{ENCODING_FLAG}/, '')
+            encoding = $1
+          else
+            encoding = Encoding.default_external
+          end
+
+          # Tag the source with the default external encoding
+          # or the encoding specified in the file
+          source.force_encoding(encoding)
+
+          # If the original encoding is BINARY, the actual
+          # encoding is either stored out-of-band (such as
+          # in ERB <%# %> style magic comments) or missing.
+          # This is also true if the original encoding is
+          # something other than BINARY, but it's invalid.
+          if source.encoding != Encoding::BINARY && source.valid_encoding?
+            source.encode!
+          # If the assumed encoding is incorrect, check to
+          # see whether the handler accepts BINARY. If it
+          # does, it has another mechanism for determining
+          # the true encoding of the String.
+          elsif @handler.respond_to?(:accepts_binary?) && @handler.accepts_binary?
+            source.force_encoding(Encoding::BINARY)
+          # If the handler does not accept BINARY, the
+          # assumed encoding (either the default_external,
+          # or the explicit encoding specified by the user)
+          # is incorrect. We raise an exception here.
+          else
+            raise WrongEncodingError.new(source, encoding)
+          end
+
+          # Don't validate the encoding yet -- the handler
+          # may treat the String as raw bytes and extract
+          # the encoding some other way
         end
 
+        code = @handler.call(self)
+
         source = <<-end_src
           def #{method_name}(local_assigns)
-            _old_virtual_path, @_virtual_path = @_virtual_path, #{@virtual_path.inspect};_old_output_buffer = output_buffer;#{locals_code};#{code}
+            _old_virtual_path, @_virtual_path = @_virtual_path, #{@virtual_path.inspect};_old_output_buffer = @output_buffer;#{locals_code};#{code}
           ensure
-            @_virtual_path, self.output_buffer = _old_virtual_path, _old_output_buffer
+            @_virtual_path, @output_buffer = _old_virtual_path, _old_output_buffer
           end
         end_src
 
-        if encoding_comment
-          source = "#{encoding_comment}\n#{source}"
-          line = -1
-        else
-          line = 0
+        if source.encoding_aware?
+          # Handlers should return their source Strings in either the
+          # default_internal or BINARY. If the handler returns a BINARY
+          # String, we assume its encoding is the one we determined
+          # earlier, and encode the resulting source in the default_internal.
+          if source.encoding == Encoding::BINARY
+            source.force_encoding(Encoding.default_internal)
+          end
+
+          # In case we get back a String from a handler that is not in
+          # BINARY or the default_internal, encode it to the default_internal
+          source.encode!
+
+          # Now, validate that the source we got back from the template
+          # handler is valid in the default_internal
+          unless source.valid_encoding?
+            raise WrongEncodingError.new(@source, Encoding.default_internal)
+          end
         end
 
         begin
-          ActionView::CompiledTemplates.module_eval(source, identifier, line)
-          ObjectSpace.define_finalizer(self, Finalizer[method_name])
+          mod.module_eval(source, identifier, 0)
+          ObjectSpace.define_finalizer(self, Finalizer[method_name, mod])
 
           method_name
         rescue Exception => e # errors from template code

actionpack/lib/action_view/template/error.rb

@@ -4,6 +4,24 @@ module ActionView
   class ActionViewError < StandardError #:nodoc:
   end
 
+  class EncodingError < StandardError #:nodoc:
+  end
+
+  class WrongEncodingError < EncodingError #:nodoc:
+    def initialize(string, encoding)
+      @string, @encoding = string, encoding
+    end
+
+    def message
+      "Your template was not saved as valid #{@encoding}. Please " \
+      "either specify #{@encoding} as the encoding for your template " \
+      "in your text editor, or mark the template with its " \
+      "encoding by inserting the following as the first line " \
+      "of the template:\n\n# encoding: <name of correct encoding>.\n\n" \
+      "The source of your template was:\n\n#{@string}"
+    end
+  end
+
   class MissingTemplate < ActionViewError #:nodoc:
     attr_reader :path
 

actionpack/lib/action_view/template/handlers/erb.rb

@@ -5,6 +5,11 @@
 
 module ActionView
   class OutputBuffer < ActiveSupport::SafeBuffer
+    def initialize(*)
+      super
+      encode!
+    end
+
     def <<(value)
       super(value.to_s)
     end
@@ -72,16 +77,50 @@ class ERB < Handler
         cattr_accessor :erb_implementation
         self.erb_implementation = Erubis
 
-        ENCODING_TAG = Regexp.new("\A(<%#{ENCODING_FLAG}-?%>)[ \t]*")
+        ENCODING_TAG = Regexp.new("\\A(<%#{ENCODING_FLAG}-?%>)[ \\t]*")
+
+        def self.accepts_binary?
+          true
+        end
 
         def compile(template)
-          erb = template.source.gsub(ENCODING_TAG, '')
+          if template.source.encoding_aware?
+            # Even though Rails has given us a String tagged with the
+            # default_internal encoding (likely UTF-8), it is possible
+            # that the String is actually encoded using a different
+            # encoding, specified via an ERB magic comment. If the
+            # String is not actually UTF-8, the regular expression
+            # engine will (correctly) raise an exception. For now,
+            # we'll reset the String to BINARY so we can run regular
+            # expressions against it
+            template_source = template.source.dup.force_encoding("BINARY")
+
+            # Erubis does not have direct support for encodings.
+            # As a result, we will extract the ERB-style magic
+            # comment, give the String to Erubis as BINARY data,
+            # and then tag the resulting String with the extracted
+            # encoding later
+            erb = template_source.gsub(ENCODING_TAG, '')
+            encoding = $2
+
+            if !encoding && (template.source.encoding == Encoding::BINARY)
+              raise WrongEncodingError.new(template_source, Encoding.default_external)
+            end
+          end
+
           result = self.class.erb_implementation.new(
             erb,
             :trim => (self.class.erb_trim_mode == "-")
           ).src
 
-          result = "#{$2}\n#{result}" if $2
+          # If an encoding tag was found, tag the String
+          # we're returning with that encoding. Otherwise,
+          # return a BINARY String, which is what ERB
+          # returns. Note that if a magic comment was
+          # not specified, we will return the data to
+          # Rails as BINARY, which will then use its
+          # own encoding logic to create a UTF-8 String.
+          result = "\n#{result}".force_encoding(encoding).encode if encoding
           result
         end
       end

actionpack/lib/action_view/template/resolver.rb

@@ -70,7 +70,10 @@ def query(path, exts, formats)
 
       Dir[query].reject { |p| File.directory?(p) }.map do |p|
         handler, format = extract_handler_and_format(p, formats)
-        Template.new(File.read(p), File.expand_path(p), handler,
+
+        contents = File.open(p, "rb") {|io| io.read }
+
+        Template.new(contents, File.expand_path(p), handler,
           :virtual_path => path, :format => format)
       end
     end

actionpack/test/abstract_unit.rb

@@ -12,6 +12,10 @@
 
 ENV['TMPDIR'] = File.join(File.dirname(__FILE__), 'tmp')
 
+if defined?(Encoding.default_internal)
+  Encoding.default_internal = "UTF-8"
+end
+
 require 'test/unit'
 require 'abstract_controller'
 require 'action_controller'