move digest cache on to the DetailsKey object

This moves digest calculation cache on to the details key object.
Before, the digest cache was a class level ivar, and one of the keys was
the hash value of the details key object:

  https://github.com/rails/rails/blob/13c4cc3b5aea02716b7459c0da641438077f5236/actionview/lib/action_view/digestor.rb#L28

An object's hash value is not unique, so it's possible for this cache
key to produce colliding keys with no resolution.  This commit move
cache on to the details key object itself, so we know that the digests
are always unique per details key object.

1 files changed, 16 insertions, 0 deletions

diff --git a/actionview/lib/action_view/lookup_context.rb b/actionview/lib/action_view/lookup_context.rb
index 2a1f4378f5..86afedaa2d 100644
--- a/actionview/lib/action_view/lookup_context.rb
+++ b/actionview/lib/action_view/lookup_context.rb
@@ -69,6 +69,18 @@ module ActionView
       def self.clear
         @details_keys.clear
       end
+
+      def self.empty?; @details_keys.empty?; end
+
+      def self.digest_caches
+        @details_keys.values.map(&:digest_cache)
+      end
+
+      attr_reader :digest_cache
+
+      def initialize
+        @digest_cache = Concurrent::Map.new
+      end
     end
 
     # Add caching behavior on top of Details.
@@ -194,6 +206,10 @@ module ActionView
       self.view_paths = view_paths
     end
 
+    def digest_cache
+      details_key.digest_cache
+    end
+
     def initialize_details(target, details)
       registered_details.each do |k|
         target[k] = details[k] || Accessors::DEFAULT_PROCS[k].call