util.warn: add stack trace using Vue.config.debug

Author: yyx990803

src/directives/view.js

@@ -39,14 +39,6 @@ export default function (Vue) {
         this.keepAlive = false
         warn('<router-view> does not support keep-alive.')
       }
-      /* istanbul ignore if */
-      if (this.waitForEvent) {
-        this.waitForEvent = null
-        warn(
-          '<router-view> does not support wait-for. Use ' +
-          'the acitvate route hook instead.'
-        )
-      }
 
       // all we need to do here is registering this view
       // in the router. actual component switching will be

src/util.js

@@ -9,15 +9,15 @@ export default exports
  * Warn stuff.
  *
  * @param {String} msg
- * @param {Error} [err]
  */
 
-export function warn (msg, err) {
+export function warn (msg) {
   /* istanbul ignore next */
   if (window.console) {
     console.warn('[vue-router] ' + msg)
-    if (err) {
-      console.warn(err.stack)
+    /* istanbul ignore if */
+    if (!exports.Vue || exports.Vue.config.debug) {
+      console.warn(new Error('warning stack trace:').stack)
     }
   }
 }