puyopuyotetr.is/db/migrate/20200620164023_add_fixed_lowercase_index_to_accounts.rb

class AddFixedLowercaseIndexToAccounts < ActiveRecord::Migration[5.2]
  disable_ddl_transaction!

  class CorruptionError < StandardError
    def cause
      nil
    end

    def backtrace
      []
    end
  end

  def up
    if index_name_exists?(:accounts, 'old_index_accounts_on_username_and_domain_lower') && index_name_exists?(:accounts, 'index_accounts_on_username_and_domain_lower')
      remove_index :accounts, name: 'index_accounts_on_username_and_domain_lower'
    elsif index_name_exists?(:accounts, 'index_accounts_on_username_and_domain_lower')
      rename_index :accounts, 'index_accounts_on_username_and_domain_lower', 'old_index_accounts_on_username_and_domain_lower'
    end

    begin
      add_index :accounts, "lower (username), COALESCE(lower(domain), '')", name: 'index_accounts_on_username_and_domain_lower', unique: true, algorithm: :concurrently
    rescue ActiveRecord::RecordNotUnique
      raise CorruptionError, 'Migration failed because of index corruption, see https://docs.joinmastodon.org/admin/troubleshooting/index-corruption/#fixing'
    end

    remove_index :accounts, name: 'old_index_accounts_on_username_and_domain_lower' if index_name_exists?(:accounts, 'old_index_accounts_on_username_and_domain_lower')
  end

  def down
    add_index :accounts, 'lower (username), lower(domain)', name: 'old_index_accounts_on_username_and_domain_lower', unique: true, algorithm: :concurrently
    remove_index :accounts, name: 'index_accounts_on_username_and_domain_lower'
    rename_index :accounts, 'old_index_accounts_on_username_and_domain_lower', 'index_accounts_on_username_and_domain_lower'
  end
end