fix(utils): clone attributes before mutating them (#13226)

lib/utils.js

@@ -186,6 +186,7 @@ exports.mapOptionFieldNames = mapOptionFieldNames;
 
 function mapWhereFieldNames(attributes, Model) {
   if (attributes) {
+    attributes = cloneDeep(attributes);
     getComplexKeys(attributes).forEach(attribute => {
       const rawAttribute = Model.rawAttributes[attribute];
 

test/integration/associations/scope.test.js

@@ -19,6 +19,7 @@ describe(Support.getTestDialectTeaser('associations'), () => {
         commentable: Sequelize.STRING,
         commentable_id: Sequelize.INTEGER,
         isMain: {
+          field: 'is_main',
           type: Sequelize.BOOLEAN,
           defaultValue: false
         }
@@ -298,6 +299,11 @@ describe(Support.getTestDialectTeaser('associations'), () => {
           expect(comment.type).to.match(/blue|green/);
         }
       });
+      it('should not mutate scope when running SELECT query (#12868)', async function() {
+        await this.sequelize.sync({ force: true });
+        await this.Post.findOne({ where: {}, include: [{ association: this.Post.associations.mainComment, attributes: ['id'], required: true, where: {} }] });
+        expect(this.Post.associations.mainComment.scope.isMain).to.equal(true);
+      });
     });
 
     if (Support.getTestDialect() !== 'sqlite') {