Check exported bindings are defined (#9589)

* Check exported bindings are defined

* Add tests

* Update flow whitelist

* Add tests for builtins

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-named-2/input.mjs

@@ -1 +1,2 @@
 export {foo, bar};
+var foo, bar;

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-named-2/output.mjs

@@ -1,12 +1,15 @@
 System.register([], function (_export, _context) {
   "use strict";
 
+  var foo, bar;
+
+  _export({
+    foo: void 0,
+    bar: void 0
+  });
+
   return {
     setters: [],
-    execute: function () {
-      _export("foo", foo);
-
-      _export("bar", bar);
-    }
+    execute: function () {}
   };
 });

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-named-3/input.mjs

@@ -1 +1,2 @@
 export {foo as bar};
+var foo;

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-named-3/output.mjs

@@ -1,10 +1,12 @@
 System.register([], function (_export, _context) {
   "use strict";
 
+  var foo;
+
+  _export("foo", void 0);
+
   return {
     setters: [],
-    execute: function () {
-      _export("bar", foo);
-    }
+    execute: function () {}
   };
 });

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-named-4/input.mjs

@@ -1 +1,2 @@
 export {foo as default};
+var foo;

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-named-4/output.mjs

@@ -1,10 +1,12 @@
 System.register([], function (_export, _context) {
   "use strict";
 
+  var foo;
+
+  _export("foo", void 0);
+
   return {
     setters: [],
-    execute: function () {
-      _export("default", foo);
-    }
+    execute: function () {}
   };
 });

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-named-5/input.mjs

@@ -1 +1,2 @@
 export {foo as default, bar};
+var foo, bar;

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-named-5/output.mjs

@@ -1,12 +1,15 @@
 System.register([], function (_export, _context) {
   "use strict";
 
+  var foo, bar;
+
+  _export({
+    foo: void 0,
+    bar: void 0
+  });
+
   return {
     setters: [],
-    execute: function () {
-      _export("default", foo);
-
-      _export("bar", bar);
-    }
+    execute: function () {}
   };
 });

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-named/input.mjs

@@ -1 +1,2 @@
 export {foo};
+var foo;

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-named/output.mjs

@@ -1,10 +1,12 @@
 System.register([], function (_export, _context) {
   "use strict";
 
+  var foo;
+
+  _export("foo", void 0);
+
   return {
     setters: [],
-    execute: function () {
-      _export("foo", foo);
-    }
+    execute: function () {}
   };
 });

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/overview/input.mjs

@@ -6,7 +6,7 @@ import * as foo2 from "foo";
 import {bar} from "foo";
 import {foo as bar2} from "foo";
 
-export {test};
+export {foo};
 export var test2 = 5;
 
-export default test;
+export default foo;

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/overview/output.mjs

@@ -10,11 +10,11 @@ System.register(["foo", "foo-bar", "./directory/foo-bar"], function (_export, _c
       bar2 = _foo.foo;
     }, function (_fooBar) {}, function (_directoryFooBar) {}],
     execute: function () {
-      _export("test", test);
+      _export("foo", foo);
 
       _export("test2", test2 = 5);
 
-      _export("default", test);
+      _export("default", foo);
     }
   };
 });