Use recyclable cache keys (#29092)

5 files changed, 23 insertions, 15 deletions

diff --git a/actionview/lib/action_view/helpers/cache_helper.rb b/actionview/lib/action_view/helpers/cache_helper.rb
index 15ab7e304f..c3aecadcd6 100644
--- a/actionview/lib/action_view/helpers/cache_helper.rb
+++ b/actionview/lib/action_view/helpers/cache_helper.rb
@@ -8,10 +8,9 @@ module ActionView
       # fragments, and so on. This method takes a block that contains
       # the content you wish to cache.
       #
-      # The best way to use this is by doing key-based cache expiration
-      # on top of a cache store like Memcached that'll automatically
-      # kick out old entries. For more on key-based expiration, see:
-      # http://signalvnoise.com/posts/3113-how-key-based-cache-expiration-works
+      # The best way to use this is by doing recyclable key-based cache expiration
+      # on top of a cache store like Memcached or Redis that'll automatically
+      # kick out old entries.
       #
       # When using this method, you list the cache dependency as the name of the cache, like so:
       #
@@ -23,10 +22,14 @@ module ActionView
       # This approach will assume that when a new topic is added, you'll touch
       # the project. The cache key generated from this call will be something like:
       #
-      #   views/projects/123-20120806214154/7a1156131a6928cb0026877f8b749ac9
-      #         ^class   ^id ^updated_at    ^template tree digest
+      #   views/template/action.html.erb:7a1156131a6928cb0026877f8b749ac9/projects/123
+      #         ^template path           ^template tree digest            ^class   ^id
       #
-      # The cache is thus automatically bumped whenever the project updated_at is touched.
+      # This cache key is stable, but it's combined with a cache version derived from the project
+      # record. When the project updated_at is touched, the #cache_version changes, even
+      # if the key stays stable. This means that unlike a traditional key-based cache expiration
+      # approach, you won't be generating cache trash, unused keys, simply because the dependent
+      # record is updated.
       #
       # If your template cache depends on multiple sources (try to avoid this to keep things simple),
       # you can name all these dependencies as part of an array:
@@ -217,10 +220,15 @@ module ActionView
 
       def fragment_name_with_digest(name, virtual_path)
         virtual_path ||= @virtual_path
+
         if virtual_path
           name = controller.url_for(name).split("://").last if name.is_a?(Hash)
-          digest = Digestor.digest name: virtual_path, finder: lookup_context, dependencies: view_cache_dependencies
-          [ name, digest ]
+
+          if digest = Digestor.digest(name: virtual_path, finder: lookup_context, dependencies: view_cache_dependencies).presence
+            [ "#{virtual_path}:#{digest}", name ]
+          else
+            [ virtual_path, name ]
+          end
         else
           name
         end
diff --git a/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb b/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
index 1fbe209200..847256ac78 100644
--- a/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
+++ b/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
@@ -38,7 +38,7 @@ module ActionView
       end
 
       def expanded_cache_key(key)
-        key = @view.fragment_cache_key(@view.cache_fragment_name(key, virtual_path: @template.virtual_path))
+        key = @view.combined_fragment_cache_key(@view.cache_fragment_name(key, virtual_path: @template.virtual_path))
         key.frozen? ? key.dup : key # #read_multi & #write may require mutability, Dalli 2.6.0.
       end
 
diff --git a/actionview/test/activerecord/relation_cache_test.rb b/actionview/test/activerecord/relation_cache_test.rb
index 43f7242ee9..fbab512c41 100644
--- a/actionview/test/activerecord/relation_cache_test.rb
+++ b/actionview/test/activerecord/relation_cache_test.rb
@@ -10,7 +10,7 @@ class RelationCacheTest < ActionView::TestCase
 
   def test_cache_relation_other
     cache(Project.all) { concat("Hello World") }
-    assert_equal "Hello World", controller.cache_store.read("views/projects-#{Project.count}/")
+    assert_equal "Hello World", controller.cache_store.read("views/path/projects-#{Project.count}")
   end
 
   def view_cache_dependencies; end
diff --git a/actionview/test/template/log_subscriber_test.rb b/actionview/test/template/log_subscriber_test.rb
index 7f358add7e..584666d54b 100644
--- a/actionview/test/template/log_subscriber_test.rb
+++ b/actionview/test/template/log_subscriber_test.rb
@@ -39,7 +39,7 @@ class AVLogSubscriberTest < ActiveSupport::TestCase
 
   def set_view_cache_dependencies
     def @view.view_cache_dependencies; []; end
-    def @view.fragment_cache_key(*); "ahoy `controller` dependency"; end
+    def @view.combined_fragment_cache_key(*); "ahoy `controller` dependency"; end
   end
 
   def test_render_file_template
diff --git a/actionview/test/template/render_test.rb b/actionview/test/template/render_test.rb
index 3f66ab3ed3..fef78807d1 100644
--- a/actionview/test/template/render_test.rb
+++ b/actionview/test/template/render_test.rb
@@ -10,8 +10,8 @@ module RenderTestCases
     @view = Class.new(ActionView::Base) do
       def view_cache_dependencies; end
 
-      def fragment_cache_key(key)
-        ActiveSupport::Cache.expand_cache_key(key, :views)
+      def combined_fragment_cache_key(key)
+        [ :views, key ]
       end
     end.new(paths, @assigns)
 
@@ -718,6 +718,6 @@ class CachedCollectionViewRenderTest < ActiveSupport::TestCase
   private
     def cache_key(*names, virtual_path)
       digest = ActionView::Digestor.digest name: virtual_path, finder: @view.lookup_context, dependencies: []
-      @view.fragment_cache_key([ *names, digest ])
+      @view.combined_fragment_cache_key([ "#{virtual_path}:#{digest}", *names ])
     end
 end