add allowTopLevelThis option to transform-modules-systemjs (#10780)

* feat: expose rewriteThis method

* feat: add allowTopLevelThis option to transform-modules-systemjs

packages/babel-helper-module-transforms/src/index.js

@@ -12,7 +12,7 @@ import normalizeAndLoadModuleMetadata, {
   isSideEffectImport,
 } from "./normalize-and-load-metadata";
 
-export { hasExports, isSideEffectImport, isModule };
+export { hasExports, isSideEffectImport, isModule, rewriteThis };
 
 /**
  * Perform all of the generic ES6 module rewriting needed to handle initial

packages/babel-plugin-transform-modules-systemjs/package.json

@@ -10,6 +10,7 @@
   "main": "lib/index.js",
   "dependencies": {
     "@babel/helper-hoist-variables": "^7.7.4",
+    "@babel/helper-module-transforms": "^7.7.4",
     "@babel/helper-plugin-utils": "^7.0.0",
     "babel-plugin-dynamic-import-node": "^2.3.0"
   },

packages/babel-plugin-transform-modules-systemjs/src/index.js

@@ -2,6 +2,7 @@ import { declare } from "@babel/helper-plugin-utils";
 import hoistVariables from "@babel/helper-hoist-variables";
 import { template, types as t } from "@babel/core";
 import { getImportSource } from "babel-plugin-dynamic-import-node/utils";
+import { rewriteThis } from "@babel/helper-module-transforms";
 
 const buildTemplate = template(`
   SYSTEM_REGISTER(MODULE_NAME, SOURCES, function (EXPORT_IDENTIFIER, CONTEXT_IDENTIFIER) {
@@ -106,7 +107,7 @@ function constructExportCall(
 export default declare((api, options) => {
   api.assertVersion(7);
 
-  const { systemGlobal = "System" } = options;
+  const { systemGlobal = "System", allowTopLevelThis = false } = options;
   const IGNORE_REASSIGNMENT_SYMBOL = Symbol();
 
   const reassignmentVisitor = {
@@ -227,6 +228,9 @@ export default declare((api, options) => {
       Program: {
         enter(path, state) {
           state.contextIdent = path.scope.generateUid("context");
+          if (!allowTopLevelThis) {
+            rewriteThis(path);
+          }
         },
         exit(path, state) {
           const undefinedIdent = path.scope.buildUndefinedNode();

packages/babel-plugin-transform-modules-systemjs/test/fixtures/allow-top-level-this/false/input.mjs

@@ -0,0 +1 @@
+export var v = this;

packages/babel-plugin-transform-modules-systemjs/test/fixtures/allow-top-level-this/false/options.json

@@ -0,0 +1,7 @@
+{
+  "plugins": [
+    ["transform-modules-systemjs", {
+      "allowTopLevelThis": false
+    }]
+  ]
+}

packages/babel-plugin-transform-modules-systemjs/test/fixtures/allow-top-level-this/false/output.mjs

@@ -0,0 +1,11 @@
+System.register([], function (_export, _context) {
+  "use strict";
+
+  var v;
+  return {
+    setters: [],
+    execute: function () {
+      _export("v", v = void 0);
+    }
+  };
+});

packages/babel-plugin-transform-modules-systemjs/test/fixtures/allow-top-level-this/true/input.mjs

@@ -0,0 +1 @@
+export var v = this;

packages/babel-plugin-transform-modules-systemjs/test/fixtures/allow-top-level-this/true/options.json

@@ -0,0 +1,7 @@
+{
+  "plugins": [
+    ["transform-modules-systemjs", {
+      "allowTopLevelThis": true
+    }]
+  ]
+}

packages/babel-plugin-transform-modules-systemjs/test/fixtures/allow-top-level-this/true/output.mjs

@@ -0,0 +1,11 @@
+System.register([], function (_export, _context) {
+  "use strict";
+
+  var v;
+  return {
+    setters: [],
+    execute: function () {
+      _export("v", v = this);
+    }
+  };
+});