Fix partial caching ignore repeated items issue

This is because we only use hash to maintain the result. So when the key
are the same, the result would be skipped. The solution is to maintain
an array for tracking every item's position to restructure the result.

3 files changed, 43 insertions, 13 deletions

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 ed59033e27..ca692699a6 100644
--- a/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
+++ b/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
@@ -17,13 +17,13 @@ module ActionView
         # Result is a hash with the key represents the
         # key used for cache lookup and the value is the item
         # on which the partial is being rendered
-        keyed_collection = collection_by_cache_keys(view, template)
+        keyed_collection, ordered_keys = collection_by_cache_keys(view, template)
 
         # Pull all partials from cache
         # Result is a hash, key matches the entry in
         # `keyed_collection` where the cache was retrieved and the
         # value is the value that was present in the cache
-        cached_partials  = collection_cache.read_multi(*keyed_collection.keys)
+        cached_partials = collection_cache.read_multi(*keyed_collection.keys)
         instrumentation_payload[:cache_hits] = cached_partials.size
 
         # Extract the items for the keys that are not found
@@ -40,11 +40,15 @@ module ActionView
         rendered_partials = @collection.empty? ? [] : yield
 
         index = 0
-        fetch_or_cache_partial(cached_partials, template, order_by: keyed_collection.each_key) do
+        keyed_partials = fetch_or_cache_partial(cached_partials, template, order_by: keyed_collection.each_key) do
           # This block is called once
           # for every cache miss while preserving order.
           rendered_partials[index].tap { index += 1 }
         end
+
+        ordered_keys.map do |key|
+          keyed_partials[key]
+        end
       end
 
       def callable_cache_key?
@@ -56,8 +60,10 @@ module ActionView
 
         digest_path = view.digest_path_from_template(template)
 
-        @collection.each_with_object({}) do |item, hash|
-          hash[expanded_cache_key(seed.call(item), view, template, digest_path)] = item
+        @collection.each_with_object([{}, []]) do |item, (hash, ordered_keys)|
+          key = expanded_cache_key(seed.call(item), view, template, digest_path)
+          ordered_keys << key
+          hash[key] = item
         end
       end
 
@@ -82,15 +88,16 @@ module ActionView
       # If the partial is not already cached it will also be
       # written back to the underlying cache store.
       def fetch_or_cache_partial(cached_partials, template, order_by:)
-        order_by.map do |cache_key|
-          if content = cached_partials[cache_key]
-            build_rendered_template(content, template)
-          else
-            yield.tap do |rendered_partial|
-              collection_cache.write(cache_key, rendered_partial.body)
-            end
+        order_by.each_with_object({}) do |cache_key, hash|
+            hash[cache_key] =
+              if content = cached_partials[cache_key]
+                build_rendered_template(content, template)
+              else
+                yield.tap do |rendered_partial|
+                  collection_cache.write(cache_key, rendered_partial.body)
+                end
+              end
           end
-        end
       end
   end
 end
diff --git a/actionview/test/fixtures/test/_cached_set.erb b/actionview/test/fixtures/test/_cached_set.erb
new file mode 100644
index 0000000000..cd492fc519
--- /dev/null
+++ b/actionview/test/fixtures/test/_cached_set.erb
@@ -0,0 +1 @@
+<%= cached_set.first %> | <%= cached_set.second %> | <%= cached_set.third %> | <%= cached_set.fourth %> | <%= cached_set.fifth %>
diff --git a/actionview/test/template/render_test.rb b/actionview/test/template/render_test.rb
index 15c41051de..f0b5d7d95e 100644
--- a/actionview/test/template/render_test.rb
+++ b/actionview/test/template/render_test.rb
@@ -811,6 +811,28 @@ class CachedCollectionViewRenderTest < ActiveSupport::TestCase
     end
   end
 
+  test "collection caching with repeated collection" do
+    sets = [
+        [1, 2, 3, 4, 5],
+        [1, 2, 3, 4, 4],
+        [1, 2, 3, 4, 5],
+        [1, 2, 3, 4, 4],
+        [1, 2, 3, 4, 6]
+    ]
+
+    result = @view.render(partial: "test/cached_set", collection: sets, cached: true)
+
+    splited_result = result.split("\n")
+    assert_equal 5, splited_result.count
+    assert_equal [
+      "1 | 2 | 3 | 4 | 5",
+      "1 | 2 | 3 | 4 | 4",
+      "1 | 2 | 3 | 4 | 5",
+      "1 | 2 | 3 | 4 | 4",
+      "1 | 2 | 3 | 4 | 6"
+    ], splited_result
+  end
+
   private
     def cache_key(*names, virtual_path)
       digest = ActionView::Digestor.digest name: virtual_path, format: :html, finder: @view.lookup_context, dependencies: []