Disallow usage of module/exports in ES6 modules.

packages/babel-plugin-transform-es2015-modules-commonjs/package.json

@@ -6,6 +6,7 @@
   "license": "MIT",
   "main": "lib/index.js",
   "dependencies": {
+    "babel-helper-simple-access": "7.0.0-beta.2",
     "babel-helper-module-transforms": "7.0.0-beta.2",
     "babel-types": "7.0.0-beta.2"
   },

packages/babel-plugin-transform-es2015-modules-commonjs/src/index.js

@@ -6,8 +6,82 @@ import {
   ensureStatementsHoisted,
   wrapInterop,
 } from "babel-helper-module-transforms";
+import simplifyAccess from "babel-helper-simple-access";
+
+export default function({ types: t, template }) {
+  const moduleAssertion = template(`
+    (function(){
+      throw new Error("The CommonJS 'module' variable is not available in ES6 modules.");
+    })();
+  `);
+  const exportsAssertion = template(`
+    (function(){
+      throw new Error("The CommonJS 'exports' variable is not available in ES6 modules.");
+    })();
+  `);
+  const getAssertion = localName =>
+    (localName === "module" ? moduleAssertion() : exportsAssertion())
+      .expression;
+
+  const moduleExportsVisitor = {
+    ReferencedIdentifier(path) {
+      const localName = path.node.name;
+      if (localName !== "module" && localName !== "exports") return;
+
+      const localBinding = path.scope.getBinding(localName);
+      const rootBinding = this.scope.getBinding(localName);
+
+      if (
+        // redeclared in this scope
+        rootBinding !== localBinding ||
+        (path.parentPath.isObjectProperty({ value: path.node }) &&
+          path.parentPath.parentPath.isObjectPattern()) ||
+        path.parentPath.isAssignmentExpression({ left: path.node }) ||
+        path.isAssignmentExpression({ left: path.node })
+      ) {
+        return;
+      }
+
+      path.replaceWith(getAssertion(localName));
+    },
+
+    AssignmentExpression(path) {
+      const left = path.get("left");
+      if (left.isIdentifier()) {
+        const localName = path.node.name;
+        if (localName !== "module" && localName !== "exports") return;
+
+        const localBinding = path.scope.getBinding(localName);
+        const rootBinding = this.scope.getBinding(localName);
+
+        // redeclared in this scope
+        if (rootBinding !== localBinding) return;
+
+        const right = path.get("right");
+        right.replaceWith(
+          t.sequenceExpression([right.node, getAssertion(localName)]),
+        );
+      } else if (left.isPattern()) {
+        const ids = left.getOuterBindingIdentifiers();
+        const localName = Object.keys(ids).filter(localName => {
+          if (localName !== "module" && localName !== "exports") return false;
+
+          return (
+            this.scope.getBinding(localName) ===
+            path.scope.getBinding(localName)
+          );
+        })[0];
+
+        if (localName) {
+          const right = path.get("right");
+          right.replaceWith(
+            t.sequenceExpression([right.node, getAssertion(localName)]),
+          );
+        }
+      }
+    },
+  };
 
-export default function({ types: t }) {
   return {
     visitor: {
       Program: {
@@ -22,6 +96,9 @@ export default function({ types: t }) {
             strict,
             strictMode,
             noInterop,
+
+            // Defaulting to 'true' for now. May change before 7.x major.
+            allowCommonJSExports = true,
           } = state.opts;
 
           // Rename the bindings auto-injected into the scope so there is no
@@ -32,6 +109,16 @@ export default function({ types: t }) {
           path.scope.rename("__filename");
           path.scope.rename("__dirname");
 
+          // Rewrite references to 'module' and 'exports' to throw exceptions.
+          // These objects are specific to CommonJS and are not available in
+          // real ES6 implementations.
+          if (!allowCommonJSExports) {
+            simplifyAccess(path, new Set(["module", "exports"]));
+            path.traverse(moduleExportsVisitor, {
+              scope: path.scope,
+            });
+          }
+
           let moduleName = this.getModuleName();
           if (moduleName) moduleName = t.stringLiteral(moduleName);
 

packages/babel-plugin-transform-es2015-modules-commonjs/test/fixtures/misc/module-exports/actual.js

@@ -0,0 +1,22 @@
+import "foo";
+
+console.log(exports);
+console.log(exports.prop);
+exports++;
+exports += 4;
+({ exports } = {});
+[ exports ] = [];
+exports = {};
+exports.prop = "";
+
+
+console.log(module);
+console.log(module.exports);
+module++;
+module += 4;
+({ module } = {});
+[ module ] = [];
+module = {};
+module.prop = "";
+
+

packages/babel-plugin-transform-es2015-modules-commonjs/test/fixtures/misc/module-exports/expected.js

@@ -0,0 +1,58 @@
+"use strict";
+
+require("foo");
+
+console.log(function () {
+  throw new Error("The CommonJS 'exports' variable is not available in ES6 modules.");
+}());
+console.log(function () {
+  throw new Error("The CommonJS 'exports' variable is not available in ES6 modules.");
+}().prop);
+
+exports = function () {
+  throw new Error("The CommonJS 'exports' variable is not available in ES6 modules.");
+}() + 1;
+
+exports = function () {
+  throw new Error("The CommonJS 'exports' variable is not available in ES6 modules.");
+}() + 4;
+
+({
+  exports
+} = ({}, function () {
+  throw new Error("The CommonJS 'exports' variable is not available in ES6 modules.");
+}()));
+[exports] = ([], function () {
+  throw new Error("The CommonJS 'exports' variable is not available in ES6 modules.");
+}());
+exports = {};
+(function () {
+  throw new Error("The CommonJS 'exports' variable is not available in ES6 modules.");
+})().prop = "";
+console.log(function () {
+  throw new Error("The CommonJS 'module' variable is not available in ES6 modules.");
+}());
+console.log(function () {
+  throw new Error("The CommonJS 'module' variable is not available in ES6 modules.");
+}().exports);
+
+module = function () {
+  throw new Error("The CommonJS 'module' variable is not available in ES6 modules.");
+}() + 1;
+
+module = function () {
+  throw new Error("The CommonJS 'module' variable is not available in ES6 modules.");
+}() + 4;
+
+({
+  module
+} = ({}, function () {
+  throw new Error("The CommonJS 'module' variable is not available in ES6 modules.");
+}()));
+[module] = ([], function () {
+  throw new Error("The CommonJS 'module' variable is not available in ES6 modules.");
+}());
+module = {};
+(function () {
+  throw new Error("The CommonJS 'module' variable is not available in ES6 modules.");
+})().prop = "";

packages/babel-plugin-transform-es2015-modules-commonjs/test/fixtures/misc/module-exports/options.json

@@ -0,0 +1,8 @@
+{
+  "plugins": [
+    [
+      "transform-es2015-modules-commonjs",
+      { "allowCommonJSExports": false }
+    ]
+  ]
+}