Add cop for has_many :through without disabled autoloading

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.

1 files changed, 74 insertions, 0 deletions

diff --git a/spec/rubocop/cop/gitlab/has_many_through_scope_spec.rb b/spec/rubocop/cop/gitlab/has_many_through_scope_spec.rb
new file mode 100644
index 00000000000..6d769c8e6fd
--- /dev/null
+++ b/spec/rubocop/cop/gitlab/has_many_through_scope_spec.rb
@@ -0,0 +1,74 @@
+require 'spec_helper'
+
+require 'rubocop'
+require 'rubocop/rspec/support'
+
+require_relative '../../../../rubocop/cop/gitlab/has_many_through_scope'
+
+describe RuboCop::Cop::Gitlab::HasManyThroughScope do # rubocop:disable RSpec/FilePath
+  include CopHelper
+
+  subject(:cop) { described_class.new }
+
+  context 'in a model file' do
+    before do
+      allow(cop).to receive(:in_model?).and_return(true)
+    end
+
+    context 'when the model does not use has_many :through' do
+      it 'does not register an offense' do
+        expect_no_offenses(<<-RUBY)
+          class User < ActiveRecord::Base
+            has_many :tags, source: 'UserTag'
+          end
+        RUBY
+      end
+    end
+
+    context 'when the model uses has_many :through' do
+      context 'when the association has no scope defined' do
+        it 'registers an offense on the association' do
+          expect_offense(<<-RUBY)
+            class User < ActiveRecord::Base
+              has_many :tags, through: :user_tags
+              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ #{described_class::MSG}
+            end
+           RUBY
+        end
+      end
+
+      context 'when the association has a scope defined' do
+        context 'when the scope does not disable auto-loading' do
+          it 'registers an offense on the scope' do
+            expect_offense(<<-RUBY)
+              class User < ActiveRecord::Base
+                has_many :tags, -> { where(active: true) }, through: :user_tags
+                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ #{described_class::MSG}
+              end
+             RUBY
+          end
+        end
+
+        context 'when the scope has auto_include(false)' do
+          it 'does not register an offense' do
+            expect_no_offenses(<<-RUBY)
+              class User < ActiveRecord::Base
+                has_many :tags, -> { where(active: true).auto_include(false).reorder(nil) }, through: :user_tags
+              end
+            RUBY
+          end
+        end
+      end
+    end
+  end
+
+  context 'outside of a migration spec file' do
+    it 'does not register an offense' do
+      expect_no_offenses(<<-RUBY)
+        class User < ActiveRecord::Base
+          has_many :tags, through: :user_tags
+        end
+      RUBY
+    end
+  end
+end