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, 7 insertions, 9 deletions

diff --git a/actionview/lib/action_view/digestor.rb b/actionview/lib/action_view/digestor.rb
index 657026fa14..f3c5d6c8df 100644
--- a/actionview/lib/action_view/digestor.rb
+++ b/actionview/lib/action_view/digestor.rb
@@ -4,13 +4,11 @@ require 'monitor'
 
 module ActionView
   class Digestor
-    cattr_reader(:cache)
-    @@cache          = Concurrent::Map.new
     @@digest_monitor = Monitor.new
 
     class PerRequestDigestCacheExpiry < Struct.new(:app) # :nodoc:
       def call(env)
-        ActionView::Digestor.cache.clear
+        ActionView::LookupContext::DetailsKey.clear
         app.call(env)
       end
     end
@@ -25,12 +23,12 @@ module ActionView
       def digest(name:, finder:, **options)
         options.assert_valid_keys(:dependencies, :partial)
 
-        cache_key = ([ name, finder.details_key.hash ].compact + Array.wrap(options[:dependencies])).join('.')
+        cache_key = ([ name ].compact + Array.wrap(options[:dependencies])).join('.')
 
         # this is a correctly done double-checked locking idiom
         # (Concurrent::Map's lookups have volatile semantics)
-        @@cache[cache_key] || @@digest_monitor.synchronize do
-          @@cache.fetch(cache_key) do # re-check under lock
+        finder.digest_cache[cache_key] || @@digest_monitor.synchronize do
+          finder.digest_cache.fetch(cache_key) do # re-check under lock
             compute_and_store_digest(cache_key, name, finder, options)
           end
         end
@@ -42,16 +40,16 @@ module ActionView
             # Prevent re-entry or else recursive templates will blow the stack.
             # There is no need to worry about other threads seeing the +false+ value,
             # as they will then have to wait for this thread to let go of the @@digest_monitor lock.
-            pre_stored = @@cache.put_if_absent(cache_key, false).nil? # put_if_absent returns nil on insertion
+            pre_stored = finder.digest_cache.put_if_absent(cache_key, false).nil? # put_if_absent returns nil on insertion
             PartialDigestor
           else
             Digestor
           end
 
-          @@cache[cache_key] = stored_digest = klass.new(name, finder, options).digest
+          finder.digest_cache[cache_key] = stored_digest = klass.new(name, finder, options).digest
         ensure
           # something went wrong or ActionView::Resolver.caching? is false, make sure not to corrupt the @@cache
-          @@cache.delete_pair(cache_key, false) if pre_stored && !stored_digest
+          finder.digest_cache.delete_pair(cache_key, false) if pre_stored && !stored_digest
         end
     end