For performance reasons, you can no longer call html_safe! on Strings....

For performance reasons, you can no longer call html_safe! on Strings. Instead, all Strings are always not html_safe?. Instead, you can get a SafeBuffer from a String by calling #html_safe, which will SafeBuffer.new(self).

  * Additionally, instead of doing concat("</form>".html_safe), you can do
    safe_concat("</form>"), which will skip both the flag set, and the flag
    check.
  * For the first pass, I converted virtually all #html_safe!s to #html_safe,
    and the tests pass. A further optimization would be to try to use
    #safe_concat as much as possible, reducing the performance impact if
    we know up front that a String is safe.

actionpack/lib/action_view.rb

@@ -56,7 +56,9 @@ module ActionView
   autoload :TestCase, 'action_view/test_case'
 end
 
-require 'action_view/erb/util'
+require 'active_support/core_ext/string/output_safety'
 require 'action_view/base'
 
+ActionView::SafeBuffer = ActiveSupport::SafeBuffer
+
 I18n.load_path << "#{File.dirname(__FILE__)}/action_view/locale/en.yml"

actionpack/lib/action_view/base.rb

@@ -284,7 +284,7 @@ def initialize(view_paths = [], assigns_for_first_render = {}, controller = nil,
       @helpers = self.class.helpers || Module.new
 
       @_controller   = controller
-      @_content_for  = Hash.new {|h,k| h[k] = ActionView::SafeBuffer.new }
+      @_content_for  = Hash.new {|h,k| h[k] = ActiveSupport::SafeBuffer.new }
       @_virtual_path = nil
       self.view_paths = view_paths
     end

actionpack/lib/action_view/erb/util.rb

-require 'erb'
-
-class ERB
-  module Util
-    HTML_ESCAPE = { '&' => '&amp;',  '>' => '&gt;',   '<' => '&lt;', '"' => '&quot;' }
-    JSON_ESCAPE = { '&' => '\u0026', '>' => '\u003E', '<' => '\u003C' }
-
-    # A utility method for escaping HTML tag characters.
-    # This method is also aliased as <tt>h</tt>.
-    #
-    # In your ERb templates, use this method to escape any unsafe content. For example:
-    #   <%=h @person.name %>
-    #
-    # ==== Example:
-    #   puts html_escape("is a > 0 & a < 10?")
-    #   # => is a &gt; 0 &amp; a &lt; 10?
-    def html_escape(s)
-      s = s.to_s
-      if s.html_safe?
-        s
-      else
-        s.gsub(/[&"><]/) { |special| HTML_ESCAPE[special] }.html_safe!
-      end
-    end
-
-    undef :h
-    alias h html_escape
-
-    module_function :html_escape
-    module_function :h
-
-    # A utility method for escaping HTML entities in JSON strings.
-    # This method is also aliased as <tt>j</tt>.
-    #
-    # In your ERb templates, use this method to escape any HTML entities:
-    #   <%=j @person.to_json %>
-    #
-    # ==== Example:
-    #   puts json_escape("is a > 0 & a < 10?")
-    #   # => is a \u003E 0 \u0026 a \u003C 10?
-    def json_escape(s)
-      s.to_s.gsub(/[&"><]/) { |special| JSON_ESCAPE[special] }
-    end
-
-    alias j json_escape
-    module_function :j
-    module_function :json_escape
-  end
-end

actionpack/lib/action_view/helpers/active_model_helper.rb

@@ -6,7 +6,7 @@
 
 module ActionView
   class Base
-    @@field_error_proc = Proc.new{ |html_tag, instance| "<div class=\"fieldWithErrors\">#{html_tag}</div>".html_safe! }
+    @@field_error_proc = Proc.new{ |html_tag, instance| "<div class=\"fieldWithErrors\">#{html_tag}</div>".html_safe }
     cattr_accessor :field_error_proc
   end
 
@@ -86,12 +86,11 @@ def form(record_name, options = {})
         submit_value = options[:submit_value] || options[:action].gsub(/[^\w]/, '').capitalize
 
         contents = form_tag({:action => action}, :method =>(options[:method] || 'post'), :enctype => options[:multipart] ? 'multipart/form-data': nil)
-        contents << hidden_field(record_name, :id) unless record.new_record?
-        contents << all_input_tags(record, record_name, options)
+        contents.safe_concat hidden_field(record_name, :id) unless record.new_record?
+        contents.safe_concat all_input_tags(record, record_name, options)
         yield contents if block_given?
-        contents << submit_tag(submit_value)
-        contents << '</form>'
-        contents.html_safe!
+        contents.safe_concat submit_tag(submit_value)
+        contents.safe_concat('</form>')
       end
 
       # Returns a string containing the error message attached to the +method+ on the +object+ if one exists.

actionpack/lib/action_view/helpers/asset_tag_helper.rb

@@ -293,7 +293,7 @@ def javascript_include_tag(*sources)
         else
           sources = expand_javascript_sources(sources, recursive)
           ensure_javascript_sources!(sources) if cache
-          sources.collect { |source| javascript_src_tag(source, options) }.join("\n").html_safe!
+          sources.collect { |source| javascript_src_tag(source, options) }.join("\n").html_safe
         end
       end
 
@@ -444,7 +444,7 @@ def stylesheet_link_tag(*sources)
         else
           sources = expand_stylesheet_sources(sources, recursive)
           ensure_stylesheet_sources!(sources) if cache
-          sources.collect { |source| stylesheet_tag(source, options) }.join("\n").html_safe!
+          sources.collect { |source| stylesheet_tag(source, options) }.join("\n").html_safe
         end
       end
 
@@ -588,7 +588,7 @@ def video_tag(sources, options = {})
 
         if sources.is_a?(Array)
           content_tag("video", options) do
-            sources.map { |source| tag("source", :src => source) }.join.html_safe!
+            sources.map { |source| tag("source", :src => source) }.join.html_safe
           end
         else
           options[:src] = path_to_video(sources)

actionpack/lib/action_view/helpers/date_helper.rb

@@ -616,7 +616,7 @@ def select_datetime
 
           build_selects_from_types(order)
         else
-          "#{select_date}#{@options[:datetime_separator]}#{select_time}".html_safe!
+          "#{select_date}#{@options[:datetime_separator]}#{select_time}".html_safe
         end
       end
 
@@ -835,7 +835,7 @@ def build_select(type, select_options_as_html)
           select_html << prompt_option_tag(type, @options[:prompt]) + "\n" if @options[:prompt]
           select_html << select_options_as_html.to_s
 
-          (content_tag(:select, select_html, select_options) + "\n").html_safe!
+          (content_tag(:select, select_html, select_options) + "\n").html_safe
         end
 
         # Builds a prompt option tag with supplied options or from default options
@@ -865,7 +865,7 @@ def build_hidden(type, value)
             :id => input_id_from_type(type),
             :name => input_name_from_type(type),
             :value => value
-          }) + "\n").html_safe!
+          }) + "\n").html_safe
         end
 
         # Returns the name attribute for the input tag
@@ -896,7 +896,7 @@ def build_selects_from_types(order)
             separator = separator(type) unless type == order.first # don't add on last field
             select.insert(0, separator.to_s + send("select_#{type}").to_s)
           end
-          select.html_safe!
+          select.html_safe
         end
 
         # Returns the separator for a given datetime component
@@ -916,15 +916,15 @@ def separator(type)
 
     class InstanceTag #:nodoc:
       def to_date_select_tag(options = {}, html_options = {})
-        datetime_selector(options, html_options).select_date.html_safe!
+        datetime_selector(options, html_options).select_date.html_safe
       end
 
       def to_time_select_tag(options = {}, html_options = {})
-        datetime_selector(options, html_options).select_time.html_safe!
+        datetime_selector(options, html_options).select_time.html_safe
       end
 
       def to_datetime_select_tag(options = {}, html_options = {})
-        datetime_selector(options, html_options).select_datetime.html_safe!
+        datetime_selector(options, html_options).select_datetime.html_safe
       end
 
       private

actionpack/lib/action_view/helpers/debug_helper.rb

@@ -27,10 +27,10 @@ module DebugHelper
       def debug(object)
         begin
           Marshal::dump(object)
-          "<pre class='debug_dump'>#{h(object.to_yaml).gsub("  ", "&nbsp; ")}</pre>".html_safe!
+          "<pre class='debug_dump'>#{h(object.to_yaml).gsub("  ", "&nbsp; ")}</pre>".html_safe
         rescue Exception => e  # errors from Marshal or YAML
           # Object couldn't be dumped, perhaps because of singleton methods -- this is the fallback
-          "<code class='debug_dump'>#{h(object.inspect)}</code>".html_safe!
+          "<code class='debug_dump'>#{h(object.inspect)}</code>".html_safe
         end
       end
     end

actionpack/lib/action_view/helpers/form_helper.rb

@@ -311,7 +311,7 @@ def form_for(record_or_name_or_array, *args, &proc)
 
         concat(form_tag(options.delete(:url) || {}, options.delete(:html) || {}))
         fields_for(object_name, *(args << options), &proc)
-        concat('</form>'.html_safe!)
+        safe_concat('</form>')
       end
 
       def apply_form_for_options!(object_or_array, options) #:nodoc:
@@ -879,7 +879,7 @@ def to_check_box_tag(options = {}, checked_value = "1", unchecked_value = "0")
         end
         hidden = tag("input", "name" => options["name"], "type" => "hidden", "value" => options['disabled'] && checked ? checked_value : unchecked_value)
         checkbox = tag("input", options)
-        (hidden + checkbox).html_safe!
+        (hidden + checkbox).html_safe
       end
 
       def to_boolean_select_tag(options = {})

actionpack/lib/action_view/helpers/form_options_helper.rb

@@ -296,7 +296,7 @@ def options_for_select(container, selected = nil)
           options << %(<option value="#{html_escape(value.to_s)}"#{selected_attribute}#{disabled_attribute}>#{html_escape(text.to_s)}</option>)
         end
 
-        options_for_select.join("\n").html_safe!
+        options_for_select.join("\n").html_safe
       end
 
       # Returns a string of option tags that have been compiled by iterating over the +collection+ and assigning the

actionpack/lib/action_view/helpers/form_tag_helper.rb

@@ -446,7 +446,7 @@ def field_set_tag(legend = nil, options = nil, &block)
         concat(tag(:fieldset, options, true))
         concat(content_tag(:legend, legend)) unless legend.blank?
         concat(content)
-        concat("</fieldset>".html_safe!)
+        safe_concat("</fieldset>")
       end
 
       private
@@ -474,14 +474,14 @@ def extra_tags_for_form(html_options)
 
         def form_tag_html(html_options)
           extra_tags = extra_tags_for_form(html_options)
-          (tag(:form, html_options, true) + extra_tags).html_safe!
+          (tag(:form, html_options, true) + extra_tags).html_safe
         end
 
         def form_tag_in_block(html_options, &block)
           content = capture(&block)
           concat(form_tag_html(html_options))
           concat(content)
-          concat("</form>".html_safe!)
+          safe_concat("</form>")
         end
 
         def token_tag

actionpack/lib/action_view/helpers/number_helper.rb

@@ -92,7 +92,7 @@ def number_to_currency(number, options = {})
             :precision => precision,
             :delimiter => delimiter,
             :separator => separator)
-          ).gsub(/%u/, unit).html_safe!
+          ).gsub(/%u/, unit).html_safe
         rescue
           number
         end

actionpack/lib/action_view/helpers/prototype_helper.rb

@@ -610,7 +610,7 @@ def method_missing(method, *arguments)
       #     page.hide 'spinner'
       #   end
       def update_page(&block)
-        JavaScriptGenerator.new(@template, &block).to_s.html_safe!
+        JavaScriptGenerator.new(@template, &block).to_s.html_safe
       end
 
       # Works like update_page but wraps the generated JavaScript in a <script>

actionpack/lib/action_view/helpers/raw_output_helper.rb

@@ -2,7 +2,7 @@ module ActionView #:nodoc:
   module Helpers #:nodoc:
     module RawOutputHelper
       def raw(stringish)
-        stringish.to_s.html_safe!
+        stringish.to_s.html_safe
       end
     end
   end

actionpack/lib/action_view/helpers/sanitize_helper.rb

@@ -50,11 +50,7 @@ module SanitizeHelper
       # confuse browsers.
       #
       def sanitize(html, options = {})
-        returning self.class.white_list_sanitizer.sanitize(html, options) do |sanitized|
-          if sanitized
-            sanitized.html_safe!
-          end
-        end
+        self.class.white_list_sanitizer.sanitize(html, options).try(:html_safe)
       end
 
       # Sanitizes a block of CSS code. Used by +sanitize+ when it comes across a style attribute.
@@ -77,11 +73,7 @@ def sanitize_css(style)
       #   strip_tags("<div id='top-bar'>Welcome to my website!</div>")
       #   # => Welcome to my website!
       def strip_tags(html)
-        returning self.class.full_sanitizer.sanitize(html) do |sanitized|
-          if sanitized
-            sanitized.html_safe!
-          end
-        end
+        self.class.full_sanitizer.sanitize(html).try(:html_safe)
       end
 
       # Strips all link tags from +text+ leaving just the link text.

actionpack/lib/action_view/helpers/tag_helper.rb

@@ -41,7 +41,7 @@ module TagHelper
       #   tag("img", { :src => "open & shut.png" }, false, false)
       #   # => <img src="open &amp; shut.png" />
       def tag(name, options = nil, open = false, escape = true)
-        "<#{name}#{tag_options(options, escape) if options}#{open ? ">" : " />"}".html_safe!
+        "<#{name}#{tag_options(options, escape) if options}#{open ? ">" : " />"}".html_safe
       end
 
       # Returns an HTML block tag of type +name+ surrounding the +content+. Add
@@ -94,7 +94,7 @@ def content_tag(name, content_or_options_with_block = nil, options = nil, escape
       #   cdata_section(File.read("hello_world.txt"))
       #   # => <![CDATA[<hello from a text file]]>
       def cdata_section(content)
-        "<![CDATA[#{content}]]>".html_safe!
+        "<![CDATA[#{content}]]>".html_safe
       end
 
       # Returns an escaped version of +html+ without affecting existing escaped entities.
@@ -128,7 +128,7 @@ def block_called_from_erb?(block)
 
         def content_tag_string(name, content, options, escape = true)
           tag_options = tag_options(options, escape) if options
-          "<#{name}#{tag_options}>#{content}</#{name}>".html_safe!
+          "<#{name}#{tag_options}>#{content}</#{name}>".html_safe
         end
 
         def tag_options(options, escape = true)
@@ -143,7 +143,7 @@ def tag_options(options, escape = true)
                 attrs << %(#{key}="#{final_value}")
               end
             end
-            " #{attrs.sort * ' '}".html_safe! unless attrs.empty?
+            " #{attrs.sort * ' '}".html_safe unless attrs.empty?
           end
         end
     end

actionpack/lib/action_view/helpers/text_helper.rb

@@ -24,14 +24,14 @@ module TextHelper
       #       end
       #       # will either display "Logged in!" or a login link
       #   %>
-      def concat(string, unused_binding = nil)
-        if unused_binding
-          ActiveSupport::Deprecation.warn("The binding argument of #concat is no longer needed.  Please remove it from your views and helpers.", caller)
-        end
-
+      def concat(string)
         output_buffer << string
       end
 
+      def safe_concat(string)
+        output_buffer.safe_concat(string)
+      end
+
       # Truncates a given +text+ after a given <tt>:length</tt> if +text+ is longer than <tt>:length</tt>
       # (defaults to 30). The last characters will be replaced with the <tt>:omission</tt> (defaults to "...")
       # for a total length not exceeding <tt>:length</tt>.

actionpack/lib/action_view/helpers/translation_helper.rb

@@ -12,7 +12,7 @@ module TranslationHelper
       # prepend the key with a period, nothing is converted.
       def translate(key, options = {})
         options[:raise] = true
-        I18n.translate(scope_key_by_partial(key), options).html_safe!
+        I18n.translate(scope_key_by_partial(key), options).html_safe
       rescue I18n::MissingTranslationData => e
         keys = I18n.send(:normalize_translation_keys, e.locale, e.key, e.options[:scope])
         content_tag('span', keys.join(', '), :class => 'translation_missing')

actionpack/lib/action_view/helpers/url_helper.rb

@@ -98,7 +98,7 @@ def url_for(options = {})
           polymorphic_path(options)
         end
 
-        escape ? escape_once(url).html_safe! : url
+        escape ? escape_once(url).html_safe : url
       end
 
       # Creates a link tag of the given +name+ using a URL created by the set
@@ -208,7 +208,7 @@ def link_to(*args, &block)
         if block_given?
           options      = args.first || {}
           html_options = args.second
-          concat(link_to(capture(&block), options, html_options).html_safe!)
+          safe_concat(link_to(capture(&block), options, html_options))
         else
           name         = args[0]
           options      = args[1] || {}
@@ -226,7 +226,7 @@ def link_to(*args, &block)
           end
 
           href_attr = "href=\"#{url}\"" unless href
-          "<a #{href_attr}#{tag_options}>#{ERB::Util.h(name || url)}</a>".html_safe!
+          "<a #{href_attr}#{tag_options}>#{ERB::Util.h(name || url)}</a>".html_safe
         end
       end
 
@@ -312,7 +312,7 @@ def button_to(name, options = {}, html_options = {})
         html_options.merge!("type" => "submit", "value" => name)
 
         ("<form method=\"#{form_method}\" action=\"#{escape_once url}\" #{"data-remote=\"true\"" if remote} class=\"button-to\"><div>" +
-          method_tag + tag("input", html_options) + request_token_tag + "</div></form>").html_safe!
+          method_tag + tag("input", html_options) + request_token_tag + "</div></form>").html_safe
       end
 
 

actionpack/lib/action_view/render/partials.rb

@@ -240,7 +240,7 @@ def render_collection
         end
 
         result = @template ? collection_with_template : collection_without_template
-        result.join(spacer).html_safe!
+        result.join(spacer).html_safe
       end
 
       def collection_with_template(template = @template)

actionpack/lib/action_view/safe_buffer.rb

-module ActionView #:nodoc:
-  class SafeBuffer < String
-    def <<(value)
-      if value.html_safe?
-        super(value)
-      else
-        super(ERB::Util.h(value))
-      end
-    end
-
-    def concat(value)
-      self << value
-    end
-
-    def html_safe?
-      true
-    end
-
-    def html_safe!
-      self
-    end
-
-    def to_s
-      self
-    end
-  end
-end
\ No newline at end of file

actionpack/lib/action_view/test_case.rb

@@ -53,7 +53,7 @@ def initialize
     setup :setup_with_controller
     def setup_with_controller
       @controller = TestController.new
-      @output_buffer = ActionView::SafeBuffer.new
+      @output_buffer = ActiveSupport::SafeBuffer.new
       @rendered = ''
 
       self.class.send(:include_helper_modules!)

actionpack/test/controller/caching_test.rb

@@ -611,7 +611,7 @@ def test_fragment_for_with_disabled_caching
     @store.write('views/expensive', 'fragment content')
     fragment_computed = false
 
-    buffer = 'generated till now -> '
+    buffer = 'generated till now -> '.html_safe
     @controller.fragment_for(buffer, 'expensive') { fragment_computed = true }
 
     assert fragment_computed
@@ -622,7 +622,7 @@ def test_fragment_for
     @store.write('views/expensive', 'fragment content')
     fragment_computed = false
 
-    buffer = 'generated till now -> '
+    buffer = 'generated till now -> '.html_safe
     @controller.fragment_for(buffer, 'expensive') { fragment_computed = true }
 
     assert !fragment_computed

actionpack/test/controller/output_escaping_test.rb

@@ -13,7 +13,7 @@ class OutputEscapingTest < ActiveSupport::TestCase
   test "escapeHTML shouldn't touch explicitly safe strings" do
     # TODO this seems easier to compose and reason about, but
     # this should be verified
-    assert_equal "<", ERB::Util.h("<".html_safe!)
+    assert_equal "<", ERB::Util.h("<".html_safe)
   end
 
 end

actionpack/test/template/erb_util_test.rb

@@ -22,7 +22,7 @@ def test_html_escape_is_html_safe
   end
 
   def test_html_escape_passes_html_escpe_unmodified
-    escaped = h("<p>".html_safe!)
+    escaped = h("<p>".html_safe)
     assert_equal "<p>", escaped
     assert escaped.html_safe?
   end

actionpack/test/template/form_helper_test.rb

@@ -1170,7 +1170,7 @@ class LabelledFormBuilder < ActionView::Helpers::FormBuilder
     (field_helpers - %w(hidden_field)).each do |selector|
       src = <<-END_SRC
         def #{selector}(field, *args, &proc)
-          ("<label for='\#{field}'>\#{field.to_s.humanize}:</label> " + super + "<br/>").html_safe!
+          ("<label for='\#{field}'>\#{field.to_s.humanize}:</label> " + super + "<br/>").html_safe
         end
       END_SRC
       class_eval src, __FILE__, __LINE__

actionpack/test/template/form_tag_helper_test.rb

@@ -335,19 +335,19 @@ def test_field_set_tag_in_erb
     expected = %(<fieldset><legend>Your details</legend>Hello world!</fieldset>)
     assert_dom_equal expected, output_buffer
 
-    self.output_buffer = ''
+    self.output_buffer = ''.html_safe
     field_set_tag { concat "Hello world!" }
 
     expected = %(<fieldset>Hello world!</fieldset>)
     assert_dom_equal expected, output_buffer
 
-    self.output_buffer = ''
+    self.output_buffer = ''.html_safe
     field_set_tag('') { concat "Hello world!" }
 
     expected = %(<fieldset>Hello world!</fieldset>)
     assert_dom_equal expected, output_buffer
 
-    self.output_buffer = ''
+    self.output_buffer = ''.html_safe
     field_set_tag('', :class => 'format') { concat "Hello world!" }
 
     expected = %(<fieldset class="format">Hello world!</fieldset>)

actionpack/test/template/safe_buffer_test.rb

@@ -16,7 +16,7 @@ def setup
   end
 
   test "Should NOT escape a safe value passed to it" do
-    @buffer << "<script>".html_safe!
+    @buffer << "<script>".html_safe
     assert_equal "<script>", @buffer
   end
 

actionpack/test/template/test_case_test.rb

@@ -160,7 +160,7 @@ def from_test_case; 'Word!'; end
     class AssertionsTest < ActionView::TestCase
       def render_from_helper
         form_tag('/foo') do
-          concat render(:text => '<ul><li>foo</li></ul>').html_safe!
+          safe_concat render(:text => '<ul><li>foo</li></ul>')
         end
       end
       helper_method :render_from_helper

activesupport/lib/active_support.rb

@@ -67,5 +67,6 @@ module ActiveSupport
     autoload :XmlMini
   end
 
+  autoload :SafeBuffer, "active_support/core_ext/string/output_safety"
   autoload :TestCase
 end

activesupport/lib/active_support/core_ext/string/output_safety.rb

+require "erb"
+
+class ERB
+  module Util
+    HTML_ESCAPE = { '&' => '&amp;',  '>' => '&gt;',   '<' => '&lt;', '"' => '&quot;' }
+    JSON_ESCAPE = { '&' => '\u0026', '>' => '\u003E', '<' => '\u003C' }
+
+    # A utility method for escaping HTML tag characters.
+    # This method is also aliased as <tt>h</tt>.
+    #
+    # In your ERb templates, use this method to escape any unsafe content. For example:
+    #   <%=h @person.name %>
+    #
+    # ==== Example:
+    #   puts html_escape("is a > 0 & a < 10?")
+    #   # => is a &gt; 0 &amp; a &lt; 10?
+    def html_escape(s)
+      s = s.to_s
+      if s.html_safe?
+        s
+      else
+        s.gsub(/[&"><]/) { |special| HTML_ESCAPE[special] }.html_safe
+      end
+    end
+
+    undef :h
+    alias h html_escape
+
+    module_function :html_escape
+    module_function :h
+
+    # A utility method for escaping HTML entities in JSON strings.
+    # This method is also aliased as <tt>j</tt>.
+    #
+    # In your ERb templates, use this method to escape any HTML entities:
+    #   <%=j @person.to_json %>
+    #
+    # ==== Example:
+    #   puts json_escape("is a > 0 & a < 10?")
+    #   # => is a \u003E 0 \u0026 a \u003C 10?
+    def json_escape(s)
+      s.to_s.gsub(/[&"><]/) { |special| JSON_ESCAPE[special] }
+    end
+
+    alias j json_escape
+    module_function :j
+    module_function :json_escape
+  end
+end
+
 class Object
   def html_safe?
     false
@@ -10,32 +60,46 @@ def html_safe?
   end
 end
 
-class String
-  attr_accessor :_rails_html_safe
-  alias html_safe? _rails_html_safe
+module ActiveSupport #:nodoc:
+  class SafeBuffer < String
+    alias safe_concat concat
 
-  def html_safe!
-    @_rails_html_safe = true
-    self
-  end
+    def concat(value)
+      if value.html_safe?
+        super(value)
+      else
+        super(ERB::Util.h(value))
+      end
+    end
 
-  def html_safe
-    dup.html_safe!
-  end
+    def +(other)
+      dup.concat(other)
+    end
+
+    def <<(value)
+      self.concat(value)
+    end
+
+    def html_safe?
+      true
+    end
+
+    def html_safe
+      self
+    end
 
-  alias original_plus +
-  def +(other)
-    result = original_plus(other)
-    result._rails_html_safe = html_safe? && other.html_safe?
-    result
+    def to_s
+      self
+    end
   end
+end
 
-  alias original_concat <<
-  alias safe_concat <<
-  def <<(other)
-    @_rails_html_safe = false unless other.html_safe?
-    result = original_concat(other)
+class String
+  def html_safe!
+    raise "You can't call html_safe! on a String"
   end
 
-  alias concat <<
+  def html_safe
+    ActiveSupport::SafeBuffer.new(self)
+  end
 end
\ No newline at end of file

activesupport/test/core_ext/string_ext_test.rb

@@ -342,12 +342,12 @@ def setup
   end
 
   test "A string can be marked safe" do
-    @string.html_safe!
-    assert @string.html_safe?
+    string = @string.html_safe
+    assert string.html_safe?
   end
 
   test "Marking a string safe returns the string" do
-    assert_equal @string, @string.html_safe!
+    assert_equal @string, @string.html_safe
   end
 
   test "A fixnum is safe by default" do
@@ -361,7 +361,7 @@ def to_str
       end
     end
 
-    @string.html_safe!
+    @string.html_safe
     @string << klass.new
 
     assert_equal "helloother", @string
@@ -369,44 +369,44 @@ def to_str
   end
 
   test "Adding a safe string to another safe string returns a safe string" do
-    @other_string = "other".html_safe!
-    @string.html_safe!
-    @combination = @other_string + @string
+    @other_string = "other".html_safe
+    string = @string.html_safe
+    @combination = @other_string + string
 
     assert_equal "otherhello", @combination
     assert @combination.html_safe?
   end
 
-  test "Adding an unsafe string to a safe string returns an unsafe string" do
-    @other_string = "other".html_safe!
-    @combination = @other_string + @string
-    @other_combination = @string + @other_string
+  test "Adding an unsafe string to a safe string escapes it and returns a safe string" do
+    @other_string = "other".html_safe
+    @combination = @other_string + "<foo>"
+    @other_combination = @string + "<foo>"
 
-    assert_equal "otherhello", @combination
-    assert_equal "helloother", @other_combination
+    assert_equal "other&lt;foo&gt;", @combination
+    assert_equal "hello<foo>", @other_combination
 
-    assert !@combination.html_safe?
+    assert @combination.html_safe?
     assert !@other_combination.html_safe?
   end
 
   test "Concatting safe onto unsafe yields unsafe" do
     @other_string = "other"
-    @string.html_safe!
+    @string.html_safe
 
     @other_string.concat(@string)
     assert !@other_string.html_safe?
   end
 
-  test "Concatting unsafe onto safe yields unsafe" do
-    @other_string = "other".html_safe!
-
-    @other_string.concat(@string)
-    assert !@other_string.html_safe?
+  test "Concatting unsafe onto safe yields escaped safe" do
+    @other_string = "other".html_safe
+    string = @other_string.concat("<foo>")
+    assert_equal "other&lt;foo&gt;", string
+    assert string.html_safe?
   end
 
   test "Concatting safe onto safe yields safe" do
-    @other_string = "other".html_safe!
-    @string.html_safe!
+    @other_string = "other".html_safe
+    @string.html_safe
 
     @other_string.concat(@string)
     assert @other_string.html_safe?
@@ -414,31 +414,32 @@ def to_str
 
   test "Concatting safe onto unsafe with << yields unsafe" do
     @other_string = "other"
-    @string.html_safe!
+    @string.html_safe
 
     @other_string << @string
     assert !@other_string.html_safe?
   end
 
-  test "Concatting unsafe onto safe with << yields unsafe" do
-    @other_string = "other".html_safe!
-
-    @other_string << @string
-    assert !@other_string.html_safe?
+  test "Concatting unsafe onto safe with << yields escaped safe" do
+    @other_string = "other".html_safe
+    string = @other_string << "<foo>"
+    assert_equal "other&lt;foo&gt;", string
+    assert string.html_safe?
   end
 
   test "Concatting safe onto safe with << yields safe" do
-    @other_string = "other".html_safe!
-    @string.html_safe!
+    @other_string = "other".html_safe
+    @string.html_safe
 
     @other_string << @string
     assert @other_string.html_safe?
   end
 
   test "Concatting a fixnum to safe always yields safe" do
-    @string.html_safe!
-    @string.concat(13)
-    assert @string.html_safe?
+    string = @string.html_safe
+    string = string.concat(13)
+    assert_equal "hello".concat(13), string
+    assert string.html_safe?
   end
 end