search: optimize counting posts for fav: and pool: searches.

Optimize counting the number of posts returned by fav:<name> and
pool:<name> searches. Use cached counts to avoid slow count(*) queries
for users with lots of favorites.

app/logical/post_query_builder.rb

@@ -917,6 +917,20 @@ class PostQueryBuilder
         Tag.find_by(name: tags.first.name).try(:post_count)
       elsif is_metatag?(:rating)
         estimated_row_count
+      elsif is_metatag?(:pool) || is_metatag?(:ordpool)
+        name = find_metatag(:pool, :ordpool)
+        Pool.find_by_name(name)&.post_count || 0
+      elsif is_metatag?(:fav) || is_metatag?(:ordfav)
+        name = find_metatag(:fav, :ordfav)
+        user = User.find_by_name(name)
+
+        if user.nil?
+          0
+        elsif Pundit.policy!(current_user, user).can_see_favorites?
+          user.favorite_count
+        else
+          nil
+        end
       end
     end
 

test/factories/favorite.rb

@@ -1,3 +1,6 @@
 FactoryBot.define do
-  factory(:favorite)
+  factory(:favorite) do
+    user
+    post
+  end
 end

test/unit/post_query_builder_test.rb

@@ -1190,9 +1190,34 @@ class PostQueryBuilderTest < ActiveSupport::TestCase
       end
 
       should "return the correct cached count for a pool:<id> search" do
-        build(:tag, name: "pool:1234", post_count: -100).save(validate: false)
+        pool = create(:pool, post_ids: [1, 2, 3])
+
+        build(:tag, name: "pool:#{pool.id}", post_count: -100).save(validate: false)
         PostQueryBuilder.new("pool:1234").set_cached_count(100)
-        assert_fast_count(100, "pool:1234")
+
+        assert_fast_count(3, "pool:#{pool.id}")
+        assert_fast_count(3, "pool:#{pool.name}")
+      end
+
+      should "return the correct favorite count for a fav:<name> search" do
+        fav = create(:favorite)
+        fav.user.update!(favorite_count: 1)
+
+        assert_fast_count(1, "fav:#{fav.user.name}")
+        assert_fast_count(1, "ordfav:#{fav.user.name}")
+      end
+
+      should "return the correct favorite count for a fav:<name> search for a user with private favorites" do
+        fav = create(:favorite)
+        fav.user.update!(favorite_count: 1, enable_private_favorites: true)
+
+        assert_fast_count(0, "fav:#{fav.user.name}")
+        assert_fast_count(0, "ordfav:#{fav.user.name}")
+      end
+
+      should "return the correct favorite count for a fav:<name> search for a nonexistent user" do
+        assert_fast_count(0, "fav:doesnotexist")
+        assert_fast_count(0, "ordfav:doesnotexist")
       end
     end