Add frozen_string_literal to every file and enforce Rubocop rule

Adds the magic `frozen_string_literal: true` comment to every file and
enables a Rubocop rule to make sure that it's always going to be there
going forward as well.

See here for more background [1], but the basic idea is that unlike many
other languages, static strings in code are mutable by default. This has
since been acknowledged as not a particularly good idea, and the
intention is to rectify the mistake when Ruby 3 comes out, where all
string literals will be frozen. The `frozen_string_literal` magic
comment was introduced in Ruby 2.3 as a way of easing the transition,
and allows libraries and projects to freeze their literals in advance.

I don't think this is breaking in any way: it's possible that users
might've been pulling out one of are literals somehow and mutating it,
but that would probably not have been useful for anything and would
certainly not be recommended, so I'm quite comfortable pushing this
change through as a minor version.

As discussed in stripe#641.

[1] https://stackoverflow.com/a/37799399

.rubocop.yml

@@ -13,6 +13,9 @@ Layout/IndentArray:
 Layout/IndentHash:
   EnforcedStyle: consistent
 
+Style/FrozenStringLiteralComment:
+  EnforcedStyle: always
+
 Style/StringLiterals:
   EnforcedStyle: double_quotes
 

Gemfile

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source "https://rubygems.org"
 
 gemspec

Rakefile

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "rake/testtask"
 require "rubocop/rake_task"
 

bin/stripe-console

@@ -1,5 +1,7 @@
 #!/usr/bin/env ruby
 
+# frozen_string_literal: true
+
 require "irb"
 require "irb/completion"
 

lib/stripe.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Stripe Ruby bindings
 # API spec at https://stripe.com/docs/api
 require "cgi"

lib/stripe/account.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Account < APIResource
     extend Gem::Deprecate

lib/stripe/alipay_account.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class AlipayAccount < APIResource
     include Stripe::APIOperations::Save

lib/stripe/api_operations/create.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   module APIOperations
     module Create

lib/stripe/api_operations/delete.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   module APIOperations
     module Delete

lib/stripe/api_operations/list.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   module APIOperations
     module List

lib/stripe/api_operations/nested_resource.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   module APIOperations
     # Adds methods to help manipulate a subresource from its parent resource so

lib/stripe/api_operations/request.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   module APIOperations
     module Request

lib/stripe/api_operations/save.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   module APIOperations
     module Save

lib/stripe/api_resource.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class APIResource < StripeObject
     include Stripe::APIOperations::Request

lib/stripe/apple_pay_domain.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   # Domains registered for Apple Pay on the Web
   class ApplePayDomain < APIResource

lib/stripe/application_fee.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class ApplicationFee < APIResource
     extend Stripe::APIOperations::List

lib/stripe/application_fee_refund.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class ApplicationFeeRefund < APIResource
     include Stripe::APIOperations::Save

lib/stripe/balance.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Balance < SingletonAPIResource
     OBJECT_NAME = "balance".freeze

lib/stripe/balance_transaction.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class BalanceTransaction < APIResource
     extend Stripe::APIOperations::List

lib/stripe/bank_account.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class BankAccount < APIResource
     include Stripe::APIOperations::Save

lib/stripe/bitcoin_receiver.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class BitcoinReceiver < APIResource
     # Directly creating or retrieving BitcoinReceivers is deprecated. Please use

lib/stripe/bitcoin_transaction.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class BitcoinTransaction < APIResource
     # Directly retrieving BitcoinTransactions is deprecated. Please use the

lib/stripe/card.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Card < APIResource
     include Stripe::APIOperations::Save

lib/stripe/charge.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Charge < APIResource
     extend Stripe::APIOperations::List

lib/stripe/country_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class CountrySpec < APIResource
     extend Stripe::APIOperations::List

lib/stripe/coupon.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Coupon < APIResource
     extend Stripe::APIOperations::Create

lib/stripe/customer.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Customer < APIResource
     extend Stripe::APIOperations::Create

lib/stripe/dispute.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Dispute < APIResource
     extend Stripe::APIOperations::List

lib/stripe/ephemeral_key.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class EphemeralKey < APIResource
     extend Stripe::APIOperations::Create

lib/stripe/errors.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   # StripeError is the base error from which all other more specific Stripe
   # errors derive.

lib/stripe/event.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Event < APIResource
     extend Stripe::APIOperations::List

lib/stripe/exchange_rate.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class ExchangeRate < APIResource
     extend Stripe::APIOperations::List

lib/stripe/file_upload.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class FileUpload < APIResource
     extend Stripe::APIOperations::Create

lib/stripe/invoice.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Invoice < APIResource
     extend Stripe::APIOperations::List

lib/stripe/invoice_item.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class InvoiceItem < APIResource
     extend Stripe::APIOperations::List

lib/stripe/invoice_line_item.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class InvoiceLineItem < StripeObject
     OBJECT_NAME = "line_item".freeze

lib/stripe/issuer_fraud_record.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class IssuerFraudRecord < APIResource
     extend Stripe::APIOperations::List

lib/stripe/list_object.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class ListObject < StripeObject
     include Enumerable

lib/stripe/login_link.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class LoginLink < APIResource
     OBJECT_NAME = "login_link".freeze

lib/stripe/oauth.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   module OAuth
     module OAuthOperations

lib/stripe/order.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Order < APIResource
     extend Stripe::APIOperations::List

lib/stripe/order_return.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class OrderReturn < APIResource
     extend Stripe::APIOperations::List

lib/stripe/payout.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Payout < APIResource
     extend Stripe::APIOperations::List

lib/stripe/plan.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Plan < APIResource
     extend Stripe::APIOperations::Create

lib/stripe/product.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Product < APIResource
     extend Stripe::APIOperations::List

lib/stripe/recipient.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   # Recipients objects are deprecated. Please use Stripe Connect instead.
   class Recipient < APIResource

lib/stripe/recipient_transfer.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class RecipientTransfer < StripeObject
     OBJECT_NAME = "recipient_transfer".freeze

lib/stripe/refund.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Refund < APIResource
     extend Stripe::APIOperations::Create

lib/stripe/reversal.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Reversal < APIResource
     extend Stripe::APIOperations::List

lib/stripe/singleton_api_resource.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class SingletonAPIResource < APIResource
     def self.resource_url

lib/stripe/sku.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class SKU < APIResource
     extend Stripe::APIOperations::List

lib/stripe/source.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Source < APIResource
     extend Stripe::APIOperations::Create

lib/stripe/source_transaction.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class SourceTransaction < StripeObject
     OBJECT_NAME = "source_transaction".freeze

lib/stripe/stripe_client.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   # StripeClient executes requests against the Stripe API and allows a user to
   # recover both a resource a call returns as well as a response object that

lib/stripe/stripe_object.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class StripeObject
     include Enumerable

lib/stripe/stripe_response.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   # StripeResponse encapsulates some vitals of a response that came back from
   # the Stripe API.

lib/stripe/subscription.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Subscription < APIResource
     extend Stripe::APIOperations::List

lib/stripe/subscription_item.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class SubscriptionItem < APIResource
     extend Stripe::APIOperations::Create

lib/stripe/three_d_secure.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class ThreeDSecure < APIResource
     extend Stripe::APIOperations::Create

lib/stripe/token.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Token < APIResource
     extend Stripe::APIOperations::Create

lib/stripe/topup.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Topup < APIResource
     extend Stripe::APIOperations::List

lib/stripe/transfer.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class Transfer < APIResource
     extend Stripe::APIOperations::List

lib/stripe/usage_record.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   class UsageRecord < APIResource
     def self.create(params = {}, opts = {})

lib/stripe/util.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cgi"
 
 module Stripe

lib/stripe/version.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Stripe
   VERSION = "3.14.0".freeze
 end