Revert friends-of-friends follow recommendation query to using a CTE (#29619)

app/models/account_suggestions/friends_of_friends_source.rb

@@ -7,14 +7,35 @@ class AccountSuggestions::FriendsOfFriendsSource < AccountSuggestions::Source
   end
 
   def source_query(account, limit: DEFAULT_LIMIT)
-    first_degree = account.following.where.not(hide_collections: true).select(:id).reorder(nil)
+    Account.find_by_sql([<<~SQL.squish, { id: account.id, limit: limit }]).map { |row| [row.id, row.frequency, row.followers_count] }
-    base_account_scope(account)
+      WITH first_degree AS (
-      .joins(:account_stat)
+          SELECT target_account_id
-      .joins(:passive_relationships).where(passive_relationships: { account_id: first_degree })
+          FROM follows
-      .group('accounts.id, account_stats.id')
+          JOIN accounts AS target_accounts ON follows.target_account_id = target_accounts.id
-      .reorder(frequency: :desc, followers_count: :desc)
+          WHERE account_id = :id
-      .limit(limit)
+            AND NOT target_accounts.hide_collections
-      .pluck(Arel.sql('accounts.id, COUNT(*) AS frequency, followers_count'))
+      )
+      SELECT accounts.id, COUNT(*) AS frequency, account_stats.followers_count as followers_count
+      FROM accounts
+      JOIN follows ON follows.target_account_id = accounts.id
+      JOIN account_stats ON account_stats.account_id = accounts.id
+      LEFT OUTER JOIN follow_recommendation_mutes ON follow_recommendation_mutes.target_account_id = accounts.id AND follow_recommendation_mutes.account_id = :id
+      WHERE follows.account_id IN (SELECT * FROM first_degree)
+        AND NOT EXISTS (SELECT 1 FROM blocks b WHERE b.target_account_id = follows.target_account_id AND b.account_id = :id)
+        AND NOT EXISTS (SELECT 1 FROM blocks b WHERE b.target_account_id = :id AND b.account_id = follows.target_account_id)
+        AND NOT EXISTS (SELECT 1 FROM mutes m WHERE m.target_account_id = follows.target_account_id AND m.account_id = :id)
+        AND (accounts.domain IS NULL OR NOT EXISTS (SELECT 1 FROM account_domain_blocks b WHERE b.account_id = :id AND b.domain = accounts.domain))
+        AND NOT EXISTS (SELECT 1 FROM follows f WHERE f.target_account_id = follows.target_account_id AND f.account_id = :id)
+        AND follows.target_account_id <> :id
+        AND accounts.discoverable
+        AND accounts.suspended_at IS NULL
+        AND accounts.silenced_at IS NULL
+        AND accounts.moved_to_account_id IS NULL
+        AND follow_recommendation_mutes.target_account_id IS NULL
+      GROUP BY accounts.id, account_stats.id
+      ORDER BY frequency DESC, account_stats.followers_count ASC
+      LIMIT :limit
+    SQL
   end
 
   private

spec/models/account_suggestions/friends_of_friends_source_spec.rb

@@ -76,19 +76,19 @@ RSpec.describe AccountSuggestions::FriendsOfFriendsSource do
       it 'contains correct underlying source data' do
         expect(source_query_values)
           .to contain_exactly(
-            [eugen.id, 2, 3], # Followed by 2 friends of bob (eve, mallory), 3 followers total (breaks tie)
+            [john.id, 2, 2],  # Followed by 2 friends of bob (eve, mallory), 2 followers total (breaks tie)
-            [john.id, 2, 2],  # Followed by 2 friends of bob (eve, mallory), 2 followers total
+            [eugen.id, 2, 3], # Followed by 2 friends of bob (eve, mallory), 3 followers total
-            [neil.id, 1, 2],  # Followed by 1 friends of bob (mallory), 2 followers total (breaks tie)
+            [jerk.id, 1, 1],  # Followed by 1 friends of bob (eve), 1 followers total (breaks tie)
-            [jerk.id, 1, 1]   # Followed by 1 friends of bob (eve), 1 followers total
+            [neil.id, 1, 2]   # Followed by 1 friends of bob (mallory), 2 followers total
           )
       end
 
       def expected_results
         [
-          [eugen.id, :friends_of_friends],
           [john.id, :friends_of_friends],
-          [neil.id, :friends_of_friends],
+          [eugen.id, :friends_of_friends],
           [jerk.id, :friends_of_friends],
+          [neil.id, :friends_of_friends],
         ]
       end