properly handle export default shorthand, also consider export default foo; and export { foo as default } to be equivalent

src/babel/transformation/modules/_default.js

@@ -63,7 +63,10 @@ var exportsVisitor = traverse.explode({
       }
 
       if (!t.isExportDefaultDeclaration(node)) {
-        formatter.hasNonDefaultExports = true;
+        var onlyDefault = node.specifiers && t.isExportDefaultSpecifier(node.specifiers[0]) && node.specifiers.length === 1;
+        if (!onlyDefault) {
+          formatter.hasNonDefaultExports = true;
+        }
       }
 
       if (node.source) {
@@ -95,7 +98,7 @@ export default class DefaultFormatter {
   }
 
   doDefaultExportInterop(node) {
-    return t.isExportDefaultDeclaration(node) && !this.noInteropRequireExport && !this.hasNonDefaultExports;
+    return (t.isExportDefaultDeclaration(node) || t.isSpecifierDefault(node)) && !this.noInteropRequireExport && !this.hasNonDefaultExports;
   }
 
   bumpImportOccurences(node) {

src/babel/transformation/modules/common.js

@@ -61,6 +61,17 @@ export default class CommonJSFormatter extends DefaultFormatter {
     }, true));
   }
 
+  exportSpecifier(specifier, node, nodes) {
+    if (this.doDefaultExportInterop(specifier)) {
+      nodes.push(util.template("exports-default-assign", {
+        VALUE: specifier.local
+      }, true));
+      return;
+    } else {
+      DefaultFormatter.prototype.exportSpecifier.apply(this, arguments);
+    }
+  }
+
   exportDeclaration(node, nodes) {
     if (this.doDefaultExportInterop(node)) {
       var declar = node.declaration;

src/babel/transformation/transformers/es7/export-extensions.js

@@ -21,7 +21,7 @@ export function ExportNamedDeclaration(node, parent, scope) {
     var uid = scope.generateUidIdentifier(specifier.exported.name);
     nodes.push(
       t.importDeclaration([t.importSpecifier(uid, specifier.exported)], node.source),
-      t.exportNamedDeclaration(null, [t.exportSpecifier(uid, specifier.exported)])
+      t.exportNamedDeclaration(null, [t.exportSpecifier(uid, t.identifier("default"))])
     );
   }
 

test/core/fixtures/transformation/es7-export-extensions/default-commonjs/expected.js

@@ -1,9 +1,5 @@
 "use strict";
 
-Object.defineProperty(exports, "__esModule", {
-  value: true
-});
-
 var _foo = require("bar").foo;
 
-exports.foo = _foo;
+module.exports = _foo;

test/core/fixtures/transformation/es7-export-extensions/default-es6/expected.js

@@ -1,4 +1,4 @@
 "use strict";
 
 import { foo as _foo } from "bar";
-export { _foo as foo };
+export { _foo as default };