When your templates change, browser caches bust automatically.

New default: the template digest is automatically included in your ETags.
When you call `fresh_when @post`, the digest for `posts/show.html.erb`
is mixed in so future changes to the HTML will blow HTTP caches for you.
This makes it easy to HTTP-cache many more of your actions.

If you render a different template, you can now pass the `:template`
option to include its digest instead:

  fresh_when @post, template: 'widgets/show'

Pass `template: false` to skip the lookup. To turn this off entirely, set:

  config.action_controller.etag_with_template_digest = false

1 files changed, 34 insertions, 2 deletions

diff --git a/actionpack/test/controller/render_test.rb b/actionpack/test/controller/render_test.rb
index 9926130c02..b036b6c08e 100644
--- a/actionpack/test/controller/render_test.rb
+++ b/actionpack/test/controller/render_test.rb
@@ -10,11 +10,17 @@ class TestControllerWithExtraEtags < ActionController::Base
   etag { nil  }
 
   def fresh
-    render text: "stale" if stale?(etag: '123')
+    render text: "stale" if stale?(etag: '123', template: false)
   end
 
   def array
-    render text: "stale" if stale?(etag: %w(1 2 3))
+    render text: "stale" if stale?(etag: %w(1 2 3), template: false)
+  end
+
+  def with_template
+    if stale? template: 'test/hello_world'
+      render text: 'stale'
+    end
   end
 end
 
@@ -409,6 +415,32 @@ class EtagRenderTest < ActionController::TestCase
     assert_response :success
   end
 
+  def test_etag_reflects_template_digest
+    get :with_template
+    assert_response :ok
+    assert_not_nil etag = @response.etag
+
+    request.if_none_match = etag
+    get :with_template
+    assert_response :not_modified
+
+    # Modify the template digest
+    path = File.expand_path('../../fixtures/test/hello_world.erb', __FILE__)
+    old = File.read(path)
+
+    begin
+      File.write path, 'foo'
+      ActionView::Digestor.cache.clear
+
+      request.if_none_match = etag
+      get :with_template
+      assert_response :ok
+      assert_not_equal etag, @response.etag
+    ensure
+      File.write path, old
+    end
+  end
+
   def etag(record)
     Digest::MD5.hexdigest(ActiveSupport::Cache.expand_cache_key(record)).inspect
   end