Add cop for has_many :through without disabled autoloadingfix-n-plus-one-when-getting-notification-settings-for-recipients

Goldiloader is great, but has several issues with has_many :through relations:

* https://github.com/salsify/goldiloader/issues/12
* https://github.com/salsify/goldiloader/issues/14
* https://github.com/salsify/goldiloader/issues/18

Rather than try to figure out which applies in each case, we should just do the
drudge work of manually disabling autoloading for all relations of this type. We
can always use regular preloading for specific cases, but this way we avoid
generating invalid queries through Goldiloader's magic.

2 files changed, 47 insertions, 1 deletions

diff --git a/rubocop/cop/gitlab/has_many_through_scope.rb b/rubocop/cop/gitlab/has_many_through_scope.rb
new file mode 100644
index 00000000000..770a2a0529f
--- /dev/null
+++ b/rubocop/cop/gitlab/has_many_through_scope.rb
@@ -0,0 +1,45 @@
+require 'gitlab/styles/rubocop/model_helpers'
+
+module RuboCop
+  module Cop
+    module Gitlab
+      class HasManyThroughScope < RuboCop::Cop::Cop
+        include ::Gitlab::Styles::Rubocop::ModelHelpers
+
+        MSG = 'Always provide an explicit scope calling auto_include(false) when using has_many :through'.freeze
+
+        def_node_search :through?, <<~PATTERN
+          (pair (sym :through) _)
+        PATTERN
+
+        def_node_matcher :has_many_through?, <<~PATTERN
+          (send nil? :has_many ... #through?)
+        PATTERN
+
+        def_node_search :disables_auto_include?, <<~PATTERN
+          (send _ :auto_include false)
+        PATTERN
+
+        def_node_matcher :scope_disables_auto_include?, <<~PATTERN
+          (block (send nil? :lambda) _ #disables_auto_include?)
+        PATTERN
+
+        def on_send(node)
+          return unless in_model?(node)
+          return unless has_many_through?(node)
+
+          target = node
+          scope_argument = node.children[3]
+
+          if scope_argument.children[0].children.last == :lambda
+            return if scope_disables_auto_include?(scope_argument)
+
+            target = scope_argument
+          end
+
+          add_offense(target, location: :expression)
+        end
+      end
+    end
+  end
+end
diff --git a/rubocop/rubocop.rb b/rubocop/rubocop.rb
index 406ec95ffc9..c2254332e7d 100644
--- a/rubocop/rubocop.rb
+++ b/rubocop/rubocop.rb
@@ -1,7 +1,8 @@
 # rubocop:disable Naming/FileName
+require_relative 'cop/gitlab/has_many_through_scope'
+require_relative 'cop/gitlab/httparty'
 require_relative 'cop/gitlab/module_with_instance_variables'
 require_relative 'cop/gitlab/predicate_memoization'
-require_relative 'cop/gitlab/httparty'
 require_relative 'cop/include_sidekiq_worker'
 require_relative 'cop/line_break_around_conditional_block'
 require_relative 'cop/migration/add_column'