ensure consistent expression value for post-assignment unary expressions (#3650)

packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/options.json

@@ -1,3 +0,0 @@
-{
-  "plugins": ["external-helpers", "transform-es2015-modules-systemjs"]
-}

packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/systemjs/hoisting-bindings/actual.js

@@ -1,7 +1,10 @@
 export function a() {
   alert("a");
+  c++;
 }
 
+export var c = 5;
+
 function b() {
   a();
 }

packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/systemjs/hoisting-bindings/expected.js

@@ -1,8 +1,10 @@
 System.register([], function (_export, _context) {
   "use strict";
 
+  var c;
   function a() {
     alert("a");
+    _export("c", c + 1), c++;
   }
 
   _export("a", a);
@@ -14,6 +16,10 @@ System.register([], function (_export, _context) {
   return {
     setters: [],
     execute: function () {
+      _export("c", c = 5);
+
+      _export("c", c);
+
       b();
     }
   };

packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/systemjs/remap/expected.js

@@ -10,7 +10,7 @@ System.register([], function (_export, _context) {
       _export("test", test);
 
       _export("test", test = 5);
-      _export("test", test++);
+      _export("test", test + 1), test++;
 
       (function () {
         var test = 2;