fix(validators): backport memory leak fix for isImmutable (#9973) (#10031)

lib/instance-validator.js

 'use strict';
 
 const validator = require('./utils/validator-extras').validator;
-const extendModelValidations = require('./utils/validator-extras').extendModelValidations;
 const Utils = require('./utils');
 const sequelizeError = require('./errors');
 const Promise = require('./promise');
@@ -54,8 +53,6 @@ class InstanceValidator {
      * @private
      */
     this.inProgress = false;
-
-    extendModelValidations(modelInstance);
   }
 
   /**
@@ -298,7 +295,7 @@ class InstanceValidator {
 
     if (!Array.isArray(validatorArgs)) {
       if (validatorType === 'isImmutable') {
-        validatorArgs = [validatorArgs, field];
+        validatorArgs = [validatorArgs, field, this.modelInstance];
       } else if (isLocalizedValidator || validatorType === 'isIP') {
         validatorArgs = [];
       } else {

lib/utils/validator-extras.js

@@ -64,18 +64,10 @@ const extensions = {
 };
 exports.extensions = extensions;
 
-function extendModelValidations(modelInstance) {
-  const extensions = {
-    isImmutable(str, param, field) {
-      return modelInstance.isNewRecord || modelInstance.dataValues[field] === modelInstance._previousDataValues[field];
-    }
-  };
-
-  _.forEach(extensions, (extend, key) => {
-    validator[key] = extend;
-  });
-}
-exports.extendModelValidations = extendModelValidations;
+/** Instance based validators */
+validator.isImmutable = function(value, validatorArgs, field, modelInstance) {
+  return modelInstance.isNewRecord || modelInstance.dataValues[field] === modelInstance._previousDataValues[field];
+};
 
 // Deprecate this.
 validator.notNull = function() {