Further preparation for Rails 6 (#15916)

* Use ActiveRecord::Result#to_ary instead of deprecated to_hash

They do the same thing, and to_hash has been removed from Rails 6.1

* Explicitly name polymorphic indexes to workaround a bug in Rails 6.1

cf. https://github.com/rails/rails/issues/41693

* Fix incorrect usage of “foreign_key” in migration script

* Use `ActiveModel::Errors#delete` instead of deprecated clear method

* Fix link headers tests on Rails 6.1

Rails 6.1 adds values to the Link header by default, thus it is not a
LinkHeader object anymore. Fix the test to parse the Link header instead
of assuming it is a LinkHeader.

db/migrate/20161006213403_rails_settings_migration.rb

@@ -7,12 +7,12 @@ end
 class RailsSettingsMigration < MIGRATION_BASE_CLASS
   def self.up
     create_table :settings do |t|
-      t.string     :var, :null => false
+      t.string     :var, null: false
       t.text       :value
-      t.references :target, :null => false, :polymorphic => true
-      t.timestamps :null => true
+      t.references :target, null: false, polymorphic: true, index: { name: 'index_settings_on_target_type_and_target_id' }
+      t.timestamps null: true
     end
-    add_index :settings, [ :target_type, :target_id, :var ], :unique => true
+    add_index :settings, [ :target_type, :target_id, :var ], unique: true
   end
 
   def self.down

db/migrate/20171119172437_create_admin_action_logs.rb

@@ -3,7 +3,7 @@ class CreateAdminActionLogs < ActiveRecord::Migration[5.1]
     create_table :admin_action_logs do |t|
       t.belongs_to :account, foreign_key: { on_delete: :cascade }
       t.string :action, null: false, default: ''
-      t.references :target, polymorphic: true
+      t.references :target, polymorphic: true, index: { name: 'index_admin_action_logs_on_target_type_and_target_id' }
       t.text :recorded_changes, null: false, default: ''
 
       t.timestamps

db/migrate/20180528141303_fix_accounts_unique_index.rb

@@ -37,7 +37,7 @@ class FixAccountsUniqueIndex < ActiveRecord::Migration[5.2]
       end
     end
 
-    duplicates = Account.connection.select_all('SELECT string_agg(id::text, \',\') AS ids FROM accounts GROUP BY lower(username), lower(domain) HAVING count(*) > 1').to_hash
+    duplicates = Account.connection.select_all('SELECT string_agg(id::text, \',\') AS ids FROM accounts GROUP BY lower(username), lower(domain) HAVING count(*) > 1').to_ary
 
     duplicates.each do |row|
       deduplicate_account!(row['ids'].split(','))

db/migrate/20181024224956_migrate_account_conversations.rb

@@ -17,8 +17,8 @@ class MigrateAccountConversations < ActiveRecord::Migration[5.2]
     belongs_to :account, optional: true
     belongs_to :activity, polymorphic: true, optional: true
 
-    belongs_to :status,         foreign_type: 'Status',        foreign_key: 'activity_id', optional: true
-    belongs_to :mention,        foreign_type: 'Mention',       foreign_key: 'activity_id', optional: true
+    belongs_to :status,  foreign_key: 'activity_id', optional: true
+    belongs_to :mention, foreign_key: 'activity_id', optional: true
 
     def target_status
       mention&.status

db/migrate/20181207011115_downcase_custom_emoji_domains.rb

@@ -2,7 +2,7 @@ class DowncaseCustomEmojiDomains < ActiveRecord::Migration[5.2]
   disable_ddl_transaction!
 
   def up
-    duplicates = CustomEmoji.connection.select_all('SELECT string_agg(id::text, \',\') AS ids FROM custom_emojis GROUP BY shortcode, lower(domain) HAVING count(*) > 1').to_hash
+    duplicates = CustomEmoji.connection.select_all('SELECT string_agg(id::text, \',\') AS ids FROM custom_emojis GROUP BY shortcode, lower(domain) HAVING count(*) > 1').to_ary
 
     duplicates.each do |row|
       CustomEmoji.where(id: row['ids'].split(',')[0...-1]).destroy_all

db/migrate/20190726175042_add_case_insensitive_index_to_tags.rb

@@ -2,7 +2,7 @@ class AddCaseInsensitiveIndexToTags < ActiveRecord::Migration[5.2]
   disable_ddl_transaction!
 
   def up
-    Tag.connection.select_all('SELECT string_agg(id::text, \',\') AS ids FROM tags GROUP BY lower(name) HAVING count(*) > 1').to_hash.each do |row|
+    Tag.connection.select_all('SELECT string_agg(id::text, \',\') AS ids FROM tags GROUP BY lower(name) HAVING count(*) > 1').to_ary.each do |row|
       canonical_tag_id  = row['ids'].split(',').first
       redundant_tag_ids = row['ids'].split(',')[1..-1]