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:

  13c4cc3b5a/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.

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
 

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

actionview/test/template/digestor_test.rb

@@ -33,7 +33,6 @@ class TemplateDigestorTest < ActionView::TestCase
   def teardown
     Dir.chdir @cwd
     FileUtils.rm_r @tmp_dir
-    ActionView::Digestor.cache.clear
   end
 
   def test_top_level_change_reflected
@@ -301,12 +300,12 @@ class TemplateDigestorTest < ActionView::TestCase
 
     def assert_digest_difference(template_name, options = {})
       previous_digest = digest(template_name, options)
-      ActionView::Digestor.cache.clear
+      finder.digest_cache.clear
 
       yield
 
       assert_not_equal previous_digest, digest(template_name, options), "digest didn't change"
-      ActionView::Digestor.cache.clear
+      finder.digest_cache.clear
     end
 
     def digest(template_name, options = {})

railties/test/application/per_request_digest_cache_test.rb

@@ -50,12 +50,13 @@ class PerRequestDigestCacheTest < ActiveSupport::TestCase
     get '/customers'
     assert_equal 200, last_response.status
 
-    assert_equal [ '8ba099b7749542fe765ff34a6824d548' ], ActionView::Digestor.cache.values
+    values = ActionView::LookupContext::DetailsKey.digest_caches.first.values
+    assert_equal [ '8ba099b7749542fe765ff34a6824d548' ], values
     assert_equal %w(david dingus), last_response.body.split.map(&:strip)
   end
 
   test "template digests are cleared before a request" do
-    assert_called(ActionView::Digestor.cache, :clear) do
+    assert_called(ActionView::LookupContext::DetailsKey, :clear) do
       get '/customers'
       assert_equal 200, last_response.status
     end