move named exports check to generated code (fix #599)

Author: yyx990803

lib/component-normalizer.js

@@ -1,23 +1,17 @@
 module.exports = function normalizeComponent (
-  scriptExports,
+  rawScriptExports,
   compiledTemplate,
   scopeId,
   cssModules
 ) {
-  scriptExports = scriptExports || {}
+  var esModule
+  var scriptExports = rawScriptExports = rawScriptExports || {}
 
   // ES6 modules interop
-  var type = typeof scriptExports.default
+  var type = typeof rawScriptExports.default
   if (type === 'object' || type === 'function') {
-    // check named exports
-    if (process.env.NODE_ENV !== 'production') {
-      if (Object.keys(scriptExports).some(function (key) {
-        return key !== 'default' && key !== '__esModule'
-      })) {
-        console.error('named exports are not supported in *.vue files.')
-      }
-    }
-    scriptExports = scriptExports.default
+    esModule = rawScriptExports
+    scriptExports = rawScriptExports.default
   }
 
   // Vue.extend constructor export interop
@@ -46,6 +40,7 @@ module.exports = function normalizeComponent (
   }
 
   return {
+    esModule: esModule,
     exports: scriptExports,
     options: options
   }

lib/loader.js

@@ -299,6 +299,13 @@ module.exports = function (content) {
   if (!isProduction) {
     // add filename in dev
     output += 'Component.options.__file = ' + JSON.stringify(filePath) + '\n'
+    // check named exports
+    output +=
+      'if (Component.esModule && Object.keys(Component.esModule).some(function (key) {' +
+        'return key !== "default" && key !== "__esModule"' +
+      '})) {' +
+        'console.error("named exports are not supported in *.vue files.")' +
+      '}\n'
     // check functional components used with templates
     if (template) {
       output +=