perf(document): avoid copying all properties into cloneOptions, just the necessary ones

Re: #14394

Author: vkarpov15

lib/document.js

@@ -3830,14 +3830,18 @@ Document.prototype.$toObject = function(options, json) {
   // `clone()` will recursively call `$toObject()` on embedded docs, so we
   // need the original options the user passed in, plus `_isNested` and
   // `_parentOptions` for checking whether we need to depopulate.
-  const cloneOptions = Object.assign({}, options, {
+  const cloneOptions = {
     _isNested: true,
     json: json,
     minimize: _minimize,
     flattenMaps: flattenMaps,
     flattenObjectIds: flattenObjectIds,
-    _seen: (options && options._seen) || new Map()
-  });
+    _seen: (options && options._seen) || new Map(),
+    _calledWithOptions: options._calledWithOptions,
+    virtuals: options.virtuals,
+    getters: options.getters,
+    depopulate: options.depopulate
+  };
 
   const depopulate = options.depopulate ||
     (options._parentOptions && options._parentOptions.depopulate || false);

test/document.test.js

@@ -722,32 +722,27 @@ describe('document', function() {
         lastName: String,
         password: String
       });
-
       userSchema.virtual('fullName').get(function() {
         return this.firstName + ' ' + this.lastName;
       });
-
       userSchema.set('toObject', { virtuals: false });
 
       const postSchema = new Schema({
         owner: { type: Schema.Types.ObjectId, ref: 'User' },
         content: String
       });
-
       postSchema.virtual('capContent').get(function() {
         return this.content.toUpperCase();
       });
-
       postSchema.set('toObject', { virtuals: true });
+      
       const User = db.model('User', userSchema);
       const Post = db.model('BlogPost', postSchema);
 
       const user = new User({ firstName: 'Joe', lastName: 'Smith', password: 'password' });
-
       const savedUser = await user.save();
 
       const post = await Post.create({ owner: savedUser._id, content: 'lorem ipsum' });
-
       const newPost = await Post.findById(post._id).populate('owner').exec();
 
       const obj = newPost.toObject();

test/model.populate.test.js

@@ -2976,33 +2976,27 @@ describe('model: populate:', function() {
           return ret;
         }
       });
-
       const Team = db.model('Test', teamSchema);
 
       const userSchema = new Schema({
         username: String
       });
-
       userSchema.set('toJSON', {
         transform: function(doc, ret) {
           return ret;
         }
       });
-
       const User = db.model('User', userSchema);
 
       const user = new User({ username: 'Test' });
-
       await user.save();
 
       const team = new Team({ members: [{ user: user }] });
-
       await team.save();
-
       await team.populate('members.user');
 
+      assert.equal(calls, 0);
       team.toJSON();
-
       assert.equal(calls, 1);
     });