Get set helpers (#7687)

* Improve get/set helper

* fixtures

* Edge cases

* Add loose edge cases

* Spec compliant

* Add issue case

* Even more edge cases!

* Final updates

* Fix name

* Use Reflect.{get, set} when available

* Avoid block scoping in loose

* Remove semicolon

* Do not redefine a non-enumerable

* Get strictness from call site, not helpers

* Add called assertions

* Classes are always strict

* Update test fixture

packages/babel-plugin-transform-exponentiation-operator/test/fixtures/regression/4349/output.js

@@ -1,8 +1,14 @@
 var _obj;
 
-function _set(object, property, value, receiver) { var desc = Object.getOwnPropertyDescriptor(object, property); if (desc === undefined) { var parent = _getPrototypeOf(object); if (parent !== null) { _set(parent, property, value, receiver); } } else if ("value" in desc && desc.writable) { desc.value = value; } else { var setter = desc.set; if (setter !== undefined) { setter.call(receiver, value); } } return value; }
+function set(target, property, value, receiver) { if (typeof Reflect !== "undefined" && Reflect.set) { set = Reflect.set; } else { set = function set(target, property, value, receiver) { var base = _superPropBase(target, property); var desc; if (base) { desc = Object.getOwnPropertyDescriptor(base, property); if (desc.set) { desc.set.call(receiver, value); return true; } else if (!desc.writable) { return false; } } desc = Object.getOwnPropertyDescriptor(receiver, property); if (desc) { if (!desc.writable) { return false; } desc.value = value; Object.defineProperty(receiver, property, desc); } else { _defineProperty(receiver, property, value); } return true; }; } return set(target, property, value, receiver); }
 
-function _get(object, property, receiver) { if (object === null) object = Function.prototype; var desc = Object.getOwnPropertyDescriptor(object, property); if (desc === undefined) { var parent = _getPrototypeOf(object); if (parent === null) { return undefined; } else { return _get(parent, property, receiver); } } else if ("value" in desc) { return desc.value; } else { var getter = desc.get; if (getter === undefined) { return undefined; } return getter.call(receiver); } }
+function _set(target, property, value, receiver, isStrict) { const s = set(target, property, value, receiver || target); if (!s && isStrict) { throw new Error('failed to set property'); } return value; }
+
+function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
+
+function _get(target, property, receiver) { if (typeof Reflect !== "undefined" && Reflect.get) { _get = Reflect.get; } else { _get = function _get(target, property, receiver) { var base = _superPropBase(target, property); if (!base) return; var desc = Object.getOwnPropertyDescriptor(base, property); if (desc.get) { return desc.get.call(receiver); } return desc.value; }; } return _get(target, property, receiver || target); }
+
+function _superPropBase(object, property) { while (!Object.prototype.hasOwnProperty.call(object, property)) { object = _getPrototypeOf(object); if (object === null) break; } return object; }
 
 function _getPrototypeOf(o) { _getPrototypeOf = Object.getPrototypeOf || function _getPrototypeOf(o) { return o.__proto__; }; return _getPrototypeOf(o); }
 
@@ -10,7 +16,7 @@ foo = _obj = {
   bar() {
     var _ref;
 
-    return _ref = _get(_getPrototypeOf(_obj), "baz", this), _set(_getPrototypeOf(_obj), "baz", Math.pow(_ref, 12), this);
+    return _ref = _get(_getPrototypeOf(_obj), "baz", this), _set(_getPrototypeOf(_obj), "baz", Math.pow(_ref, 12), this, false);
   }
 
 };