PERF: introduce site/global emoji cache (#15899)

Previously calls such as `Emoji["smile"]` would force a full dehydration of
objects from Redis.

This introduces a version safe site and global emoji cache so lookups are
cheap. It eliminates iterating through the list of emojis and pulling from
redis.

Distributed cache uses a normalized name as the key and stores an Array tuple
with version and Emoji. Successful hits always confirm version matches.

Interface to Emoji object remains unchanged.

We opted for 2 caches to improve reuse on multisites. misses though will be
stored in both caches. If there is a hit on the global cache we can avoid
looking up in site local cache and storing a miss there.

app/models/emoji.rb

@@ -12,6 +12,14 @@ class Emoji
 
   attr_accessor :name, :url, :tonable, :group
 
+  def self.global_emoji_cache
+    @global_emoji_cache ||= DistributedCache.new("global_emoji_cache", namespace: false)
+  end
+
+  def self.site_emoji_cache
+    @site_emoji_cache ||= DistributedCache.new("site_emoji_cache")
+  end
+
   def self.all
     Discourse.cache.fetch(cache_key("all_emojis")) { standard | custom }
   end
@@ -54,10 +62,28 @@ class Emoji
     is_toned = name.match?(/.+:t[1-6]/)
     normalized_name = name.gsub(/(.+):t[1-6]/, '\1')
 
-    Emoji.all.detect do |e|
+    found_emoji = nil
+
+    [[global_emoji_cache, :standard], [site_emoji_cache, :custom]].each do |cache, list_key|
+      cache_postfix, found_emoji = cache.defer_get_set(normalized_name) do
+        emoji = Emoji.public_send(list_key).detect do |e|
           e.name == normalized_name &&
           (!is_toned || (is_toned && e.tonable))
         end
+        [self.cache_postfix, emoji]
+      end
+
+      if found_emoji && (cache_postfix != self.cache_postfix)
+        cache.delete(normalized_name)
+        redo
+      end
+
+      if found_emoji
+        break
+      end
+    end
+
+    found_emoji
   end
 
   def self.create_from_db_item(emoji)
@@ -81,13 +107,19 @@ class Emoji
   end
 
   def self.cache_key(name)
-    "#{name}:v#{EMOJI_VERSION}:#{Plugin::CustomEmoji.cache_key}"
+    "#{name}#{cache_postfix}"
+  end
+
+  def self.cache_postfix
+    ":v#{EMOJI_VERSION}:#{Plugin::CustomEmoji.cache_key}"
   end
 
   def self.clear_cache
     %w{custom standard aliases search_aliases translations all tonable}.each do |key|
       Discourse.cache.delete(cache_key("#{key}_emojis"))
     end
+    global_emoji_cache.clear
+    site_emoji_cache.clear
   end
 
   def self.db_file

spec/models/emoji_spec.rb

@@ -87,6 +87,37 @@ describe Emoji do
     end
   end
 
+  describe 'version updates' do
+    it 'should correct cache when global emojis cache is stale' do
+      Emoji.global_emoji_cache["blonde_man"] = [
+        "invalid",
+        Emoji.new
+      ]
+
+      emoji = Emoji[":blonde_man:t3"]
+
+      expect(emoji.name).to eq('blonde_man')
+      expect(emoji.tonable).to eq(true)
+    end
+
+    it 'should correct cache when site emojis cache is stale' do
+      CustomEmoji.create!(name: 'test123', upload_id: 9999)
+      Emoji.clear_cache
+
+      Emoji.site_emoji_cache["test123"] = [
+        "invalid",
+        Emoji.new
+      ]
+
+      emoji = Emoji[":test123:"]
+
+      expect(emoji.name).to eq('test123')
+      expect(emoji.tonable).to be_falsey
+
+      Emoji.clear_cache
+    end
+  end
+
   describe '.codes_to_img' do
     before { Plugin::CustomEmoji.clear_cache }
     after { Plugin::CustomEmoji.clear_cache }