Add new Rails/PrivateTransactionOption cop

This PR adds a new cop called `Rails/PrivateTransactionOption`.

This cop checks whether `ActiveRecord::Base.transaction(joinable: _)`
is used. The `joinable` option is a private API and is not intended
to be called from outside Active Record core.

rails/rails#39912 (comment)
rails/rails#46182 (comment)

Passing `joinable: false` may cause unexpected behavior such as the
`after_commit` callback not firing at the appropriate time.

changelog/new_add_rails_private_transaction_option_cop.md

@@ -0,0 +1 @@
+* [#1236](https://github.com/rubocop/rubocop-rails/pull/1236): Add new `Rails/PrivateTransactionOption`. ([@wata727][])

config/default.yml

@@ -782,6 +782,12 @@ Rails/Present:
   # Convert usages of `unless blank?` to `if present?`
   UnlessBlank: true
 
+Rails/PrivateTransactionOption:
+  Description: 'Avoid use of `ActiveRecord::Base.transaction(joinable: _)`.'
+  Enabled: pending
+  Safe: false
+  VersionAdded: '<<next>>'
+
 Rails/RakeEnvironment:
   Description: 'Include `:environment` as a dependency for all Rake tasks.'
   Enabled: true

lib/rubocop/cop/rails/private_transaction_option.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # Checks whether `ActiveRecord::Base.transaction(joinable: _)` is used.
+      #
+      # The `joinable` option is a private API and is not intended to be called
+      # from outside Active Record core.
+      # https://github.com/rails/rails/issues/39912#issuecomment-665483779
+      # https://github.com/rails/rails/issues/46182#issuecomment-1265966330
+      #
+      # Passing `joinable: false` may cause unexpected behavior such as the
+      # `after_commit` callback not firing at the appropriate time.
+      #
+      # @safety
+      #   This Cop is unsafe because it cannot accurately identify
+      #   the `ActiveRecord::Base.transaction` method call.
+      #
+      # @example
+      #   # bad
+      #   ActiveRecord::Base.transaction(requires_new: true, joinable: false)
+      #
+      #   # good
+      #   ActiveRecord::Base.transaction(requires_new: true)
+      #
+      class PrivateTransactionOption < Base
+        MSG = 'Do not use `ActiveRecord::Base.transaction(joinable: _)`.'
+        RESTRICT_ON_SEND = %i[transaction].freeze
+
+        # @!method match_transaction_with_joinable(node)
+        def_node_matcher :match_transaction_with_joinable, <<~PATTERN
+          (send _ :transaction (hash <$(pair (sym :joinable) {true false}) ...>))
+        PATTERN
+
+        def on_send(node)
+          match_transaction_with_joinable(node) do |option_node|
+            add_offense(option_node)
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -88,6 +88,7 @@
 require_relative 'rails/pluralization_grammar'
 require_relative 'rails/presence'
 require_relative 'rails/present'
+require_relative 'rails/private_transaction_option'
 require_relative 'rails/rake_environment'
 require_relative 'rails/read_write_attribute'
 require_relative 'rails/redundant_active_record_all_method'

spec/rubocop/cop/rails/private_transaction_option_spec.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::PrivateTransactionOption, :config do
+  it 'registers an offense when using `joinable: false`' do
+    expect_offense(<<~RUBY)
+      ActiveRecord::Base.transaction(requires_new: true, joinable: false)
+                                                         ^^^^^^^^^^^^^^^ Do not use `ActiveRecord::Base.transaction(joinable: _)`.
+    RUBY
+  end
+
+  it 'does not register an offense when using only `requires_new: true`' do
+    expect_no_offenses(<<~RUBY)
+      ActiveRecord::Base.transaction(requires_new: true)
+    RUBY
+  end
+end