Added deprecation message when adding an extra anchor in behalf of th…

…e user. (vercel#797)

lib/link.js

@@ -1,6 +1,7 @@
 import { resolve } from 'url'
 import React, { Component, Children, PropTypes } from 'react'
 import Router from './router'
+import { warn, execOnce } from './utils'
 
 export default class Link extends Component {
   constructor (props) {
@@ -69,6 +70,7 @@ export default class Link extends Component {
       if (isAnchor) {
         return React.cloneElement(child, props)
       } else {
+        warnLink(`Warning: Every Link must be the parent of an anchor, this pattern is deprecated. Please add an anchor inside the <Link>.`)
         return <a {...props}>{child}</a>
       }
     })
@@ -82,3 +84,5 @@ export function isLocal (href) {
   return !/^(https?:)?\/\//.test(href) ||
     origin === href.substr(0, origin.length)
 }
+
+const warnLink = execOnce(warn)

lib/utils.js

@@ -4,6 +4,16 @@ export function warn (message) {
   }
 }
 
+export function execOnce (fn) {
+  let used = false
+  return (...args) => {
+    if (!used) {
+      used = true
+      fn.apply(this, args)
+    }
+  }
+}
+
 export function deprecated (fn, message) {
   if (process.env.NODE_ENV === 'production') return fn