log errors when an exception happens when streaming.

actionpack/lib/action_view/context.rb

@@ -15,6 +15,8 @@ module Context
     include CompiledTemplates
     attr_accessor :output_buffer, :view_flow
 
+    # TODO Provide an easy method that initializes all variables?
+
     # Returns the contents that are yielded to a layout, given a name or a block.
     #
     # You can think of a layout as a method that is called with a block. If the user calls

actionpack/lib/action_view/renderer/streaming_template_renderer.rb

@@ -60,11 +60,26 @@ def initialize(&start)
       def each(&block)
         begin
           @start.call(block)
-        rescue
+        rescue Exception => exception
+          log_error(exception)
           block.call ActionView::Base.streaming_completion_on_exception
         end
         self
       end
+
+      private
+
+      # This is the same logging logic as in ShowExceptions middleware.
+      # TODO Once "exceptron" is in, refactor this piece to simply re-use exceptron.
+      def log_error(exception) #:nodoc:
+        logger = ActionController::Base.logger
+        return unless logger
+
+        message = "\n#{exception.class} (#{exception.message}):\n"
+        message << exception.annoted_source_code.to_s if exception.respond_to?(:annoted_source_code)
+        message << "  " << exception.backtrace.join("\n  ")
+        logger.fatal("#{message}\n\n")
+      end
     end
 
     # For streaming, instead of rendering a given a template, we return a Body

actionpack/test/controller/new_base/render_streaming_test.rb

@@ -83,6 +83,19 @@ class StreamingTest < Rack::TestCase
       assert_streaming!
     end
 
+    test "rendering with template exception logs the exception" do
+      io = StringIO.new
+      _old, ActionController::Base.logger = ActionController::Base.logger, Logger.new(io)
+
+      begin
+        get "/render_streaming/basic/template_exception"
+        io.rewind
+        assert_match "(undefined method `invalid!' for nil:NilClass)", io.read
+      ensure
+        ActionController::Base.logger = _old
+      end
+    end
+
     test "do not stream on HTTP/1.0" do
       get "/render_streaming/basic/hello_world", nil, "HTTP_VERSION" => "HTTP/1.0"
       assert_body "Hello world, I'm here!"

actionpack/test/template/streaming_render_test.rb

@@ -13,8 +13,12 @@ def setup
     @controller_view = TestController.new.view_context
   end
 
+  def render_body(options)
+    @view.view_renderer.render_body(@view, options)
+  end
+
   def buffered_render(options)
-    body = @view.render_body(options)
+    body = render_body(options)
     string = ""
     body.each do |piece|
       string << piece
@@ -24,7 +28,7 @@ def buffered_render(options)
 
   def test_streaming_works
     content = []
-    body = @view.render_body(:template => "test/hello_world.erb", :layout => "layouts/yield")
+    body = render_body(:template => "test/hello_world.erb", :layout => "layouts/yield")
 
     body.each do |piece|
       content << piece