From de2791a696380183502c830165467bd36b31bfd9 Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Sat, 20 Aug 2016 18:21:17 +0200
Subject: [PATCH] ensure consistent expression value for post-assignment unary
 expressions (#3650)

---
 .../src/index.js                                 | 16 ++++++++++++++++
 .../test/fixtures/regression/options.json        |  3 ---
 .../hoisting-bindings}/actual.js                 |  3 +++
 .../hoisting-bindings}/expected.js               |  6 ++++++
 .../test/fixtures/systemjs/remap/expected.js     |  2 +-
 5 files changed, 26 insertions(+), 4 deletions(-)
 delete mode 100644 packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/options.json
 rename packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/{regression/T6973 => systemjs/hoisting-bindings}/actual.js (72%)
 rename packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/{regression/T6973 => systemjs/hoisting-bindings}/expected.js (72%)

diff --git a/packages/babel-plugin-transform-es2015-modules-systemjs/src/index.js b/packages/babel-plugin-transform-es2015-modules-systemjs/src/index.js
index ee868a2e9198..5b1619d245b2 100644
--- a/packages/babel-plugin-transform-es2015-modules-systemjs/src/index.js
+++ b/packages/babel-plugin-transform-es2015-modules-systemjs/src/index.js
@@ -43,10 +43,26 @@ export default function ({ types: t }) {
 
       let node = path.node;
 
+      // if it is a non-prefix update expression (x++ etc)
+      // then we must replace with the expression (_export('x', x + 1), x++)
+      // in order to ensure the same update expression value
+      let isPostUpdateExpression = path.isUpdateExpression() && !node.prefix;
+      if (isPostUpdateExpression) {
+        if (node.operator === "++")
+          node = t.binaryExpression("+", node.argument, t.numericLiteral(1));
+        else if (node.operator === "--")
+          node = t.binaryExpression("-", node.argument, t.numericLiteral(1));
+        else
+          isPostUpdateExpression = false;
+      }
+
       for (let exportedName of exportedNames) {
         node = this.buildCall(exportedName, node).expression;
       }
 
+      if (isPostUpdateExpression)
+        node = t.sequenceExpression([node, path.node]);
+
       path.replaceWith(node);
     }
   };
diff --git a/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/options.json b/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/options.json
deleted file mode 100644
index 576c2a257caf..000000000000
--- a/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "plugins": ["external-helpers", "transform-es2015-modules-systemjs"]
-}
diff --git a/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/T6973/actual.js b/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/systemjs/hoisting-bindings/actual.js
similarity index 72%
rename from packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/T6973/actual.js
rename to packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/systemjs/hoisting-bindings/actual.js
index 9d1ab87d80f2..e8ab2a516e24 100644
--- a/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/T6973/actual.js
+++ b/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();
 }
diff --git a/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/T6973/expected.js b/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/systemjs/hoisting-bindings/expected.js
similarity index 72%
rename from packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/T6973/expected.js
rename to packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/systemjs/hoisting-bindings/expected.js
index c146273d8142..bc39479420f9 100644
--- a/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/regression/T6973/expected.js
+++ b/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();
     }
   };
diff --git a/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/systemjs/remap/expected.js b/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/systemjs/remap/expected.js
index 1522b5bfef0b..8859d20bf93d 100644
--- a/packages/babel-plugin-transform-es2015-modules-systemjs/test/fixtures/systemjs/remap/expected.js
+++ 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;