MONGOID-5204 default_scopes duplication, query scope inconsistency (#5137)

* MONGOID-5204 dont add duplicates to selector

* MONGOID-5204 add criteria tests

* MONGOID-5204 move subclass to its own file

* MONGOID-5204 remove trailing whitespace

Author: neilshweky

lib/mongoid/criteria/queryable/storable.rb

@@ -54,7 +54,7 @@ def add_field_expression(field, value)
               # adding them to the existing hash.
               new_value = selector[field].merge(value)
               selector.store(field, new_value)
-            else
+            elsif selector[field] != value
               add_operator_expression('$and', [{field => value}])
             end
           else

spec/mongoid/criteria_spec.rb

@@ -3508,6 +3508,23 @@ def self.ages; self; end
           'foo' => 1, '$and' => [{'foo' => 2}], 'bar' => 3)
       end
     end
+
+    context "when duplicating where conditions" do
+      let(:criteria) { Sound.where(active: true).where(active: true) }
+
+      it 'does not duplicate criteria' do
+        expect(criteria.selector).to eq('active' => true)
+      end
+    end
+
+    context "when duplicating where conditions with different values" do
+      let(:criteria) { Sound.where(active: true).where(active: false).where(active: true).where(active: false) }
+
+      it 'does not duplicate criteria' do
+        expect(criteria.selector).to eq(
+          'active' => true, '$and' => [{'active' => false}])
+      end
+    end
   end
 
   describe "#for_js" do

spec/mongoid/scopable_spec.rb

@@ -110,6 +110,17 @@
         expect(Band).to be_default_scoping
       end
     end
+
+    context "when parent class has default scope" do
+
+      let (:selector) do
+        AudibleSound.all.selector
+      end
+
+      it "the subclass doesn't duplicate the default scope in the selector" do
+        expect(selector).to eq({'active' => true})
+      end
+    end
   end
 
   describe ".default_scopable?" do

spec/support/models/audible_sound.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+class AudibleSound < Sound; end