Add deprecation notices for <% %>.

  * The approach is to compile <% %> into a method call that checks whether
    the value returned from a block is a String. If it is, it concats to the buffer and
    prints a deprecation warning.
  * <%= %> uses exactly the same logic to compile the template, which first checks
    to see whether it's compiling a block.
  * This should have no impact on other uses of block in templates. For instance, in
    <% [1,2,3].each do |i| %><%= i %><% end %>, the call to each returns an Array,
    not a String, so the result is not concatenated
  * In two cases (#capture and #cache), a String can be returned that should *never*
    be concatenated. We have temporarily created a String subclass called NonConcattingString
    which behaves (and is serialized) identically to String, but is not concatenated
    by the code that handles deprecated <% %> block helpers. Once we remove support
    for <% %> block helpers, we can remove NonConcattingString.

1 files changed, 11 insertions, 5 deletions

diff --git a/actionpack/lib/action_controller/caching/fragments.rb b/actionpack/lib/action_controller/caching/fragments.rb
index 89787727bd..a07fe2b255 100644
--- a/actionpack/lib/action_controller/caching/fragments.rb
+++ b/actionpack/lib/action_controller/caching/fragments.rb
@@ -34,17 +34,23 @@ module ActionController #:nodoc:
         ActiveSupport::Cache.expand_cache_key(key.is_a?(Hash) ? url_for(key).split("://").last : key, :views)
       end
 
-      def fragment_for(buffer, name = {}, options = nil, &block) #:nodoc:
+      def fragment_for(name = {}, options = nil, &block) #:nodoc:
         if perform_caching
           if fragment_exist?(name, options)
-            buffer.safe_concat(read_fragment(name, options))
+            read_fragment(name, options)
           else
+            # VIEW TODO: Make #capture usable outside of ERB
+            # This dance is needed because Builder can't use capture
+            buffer = view_context.output_buffer
             pos = buffer.length
-            block.call
-            write_fragment(name, buffer[pos..-1], options)
+            yield
+            fragment = buffer[pos..-1]
+            write_fragment(name, fragment, options)
+            ActionView::NonConcattingString.new(fragment)
           end
         else
-          block.call
+          ret = yield
+          ActiveSupport::SafeBuffer.new(ret) if ret.is_a?(String)
         end
       end