Add new Rails/StrictLoadingAssociations cop

changelog/new_add_strict_loading_associations_cop.md

@@ -0,0 +1,2 @@
+- [#876](https://github.com/rubocop/rubocop-rails/pull/876): Add new
+  Rails/StrictLoadingAssociations cop. ([@drenmi][])

config/default.yml

@@ -977,6 +977,11 @@ Rails/SquishedSQLHeredocs:
   # to be preserved in order to work, thus autocorrection is not safe.
   SafeAutoCorrect: false
 
+Rails/StrictLoadingAssociations:
+  Description: 'Declare a `strict_loading` option on `has_many` associations.'
+  Enabled: pending
+  VersionAdded: '2.18'
+
 Rails/StripHeredoc:
   Description: 'Enforces the use of squiggly heredoc over `strip_heredoc`.'
   StyleGuide: 'https://rails.rubystyle.guide/#prefer-squiggly-heredoc'

lib/rubocop/cop/rails/strict_loading_associations.rb

@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # Declare a `strict_loading` option on `has_many` associations.
+      #
+      # @example
+      #
+      #   # bad
+      #   has_many :posts
+      #
+      #   # good
+      #   has_many :posts, strict_loading: true
+      #
+      #   # good
+      #   has_many :posts, strict_loading: false
+      #
+      class StrictLoadingAssociations < Base
+        extend TargetRailsVersion
+
+        minimum_target_rails_version 6.1
+
+        MSG = 'Declare a `strict_loading` option on `has_many` associations.'
+
+        RESTRICT_ON_SEND = %i[has_many].freeze
+
+        # @!method has_many(node)
+        def_node_matcher :has_many, <<~PATTERN
+          (send nil? :has_many _ $hash ?)
+        PATTERN
+
+        def on_send(node)
+          has_many(node) do |options|
+            add_offense(node) unless strict_loading_declared?(options.first)
+          end
+        end
+
+        private
+
+        def strict_loading_declared?(options)
+          return false if options.nil?
+
+          options.each_key.any? { |k| k.value.to_s == "strict_loading" }
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -112,6 +112,7 @@
 require_relative 'rails/short_i18n'
 require_relative 'rails/skips_model_validations'
 require_relative 'rails/squished_sql_heredocs'
+require_relative 'rails/strict_loading_associations'
 require_relative 'rails/strip_heredoc'
 require_relative 'rails/table_name_assignment'
 require_relative 'rails/time_zone'

spec/rubocop/cop/rails/strict_loading_associations_spec.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::StrictLoadingAssociations, :config do
+  context "when using Rails 6.1 or newer", :rails61 do
+    it 'registers an offense when not declaring `strict_loading`' do
+      expect_offense(<<~RUBY)
+        class Author < ApplicationRecord
+          has_many :posts
+          ^^^^^^^^^^^^^^^ Declare a `strict_loading` option on `has_many` associations.
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when declaring `strict_loading`' do
+      expect_no_offenses(<<~RUBY)
+        class Author < ApplicationRecord
+          has_many :posts, strict_loading: true
+        end
+      RUBY
+    end
+  end
+
+  context "when using Rails 6.0 or older", :rails60 do
+    it 'does not register an offense when not declaring `strict_loading`' do
+      expect_no_offenses(<<~RUBY)
+        class Author < ApplicationRecord
+          has_many :posts
+        end
+      RUBY
+    end
+  end
+end