add GeneratorFunction assertion for app.use(). Closes #120

breaks old old shit but thats ok, super early in the game

lib/application.js

@@ -10,6 +10,7 @@ var request = require('./request');
 var response = require('./response');
 var Cookies = require('cookies');
 var Keygrip = require('keygrip');
+var assert = require('assert');
 var Stream = require('stream');
 var http = require('http');
 var co = require('co');
@@ -71,12 +72,13 @@ app.listen = function(){
 /**
  * Use the given middleware `fn`.
  *
- * @param {Function} fn
+ * @param {GeneratorFunction} fn
  * @return {Application} self
  * @api public
  */
 
 app.use = function(fn){
+  assert('GeneratorFunction' == fn.constructor.name, 'app.use() requires a generator function');
   debug('use %s', fn.name || '-');
   this.middleware.push(fn);
   return this;

test/application.js

@@ -58,6 +58,17 @@ describe('app.use(fn)', function(){
       done();
     });
   })
+
+  it('should error when a non-generator function is passed', function(done){
+    var app = koa();
+
+    try {
+      app.use(function(){});
+    } catch (err) {
+      err.message.should.equal('app.use() requires a generator function');
+      done();
+    }
+  })
 })
 
 describe('app.respond', function(){

test/response/status.js

@@ -40,8 +40,7 @@ describe('res.status=', function(){
     it('should strip content related header fields', function(done){
       var app = koa();
 
-      app.use(function(next){
-        return function *(){
+      app.use(function *(){
         this.body = { foo: 'bar' };
         this.set('Content-Type', 'application/json');
         this.set('Content-Length', '15');
@@ -50,7 +49,6 @@ describe('res.status=', function(){
         assert(null == this.response.header['content-type']);
         assert(null == this.response.header['content-length']);
         assert(null == this.response.header['transfer-encoding']);
-        }
       });
 
       request(app.listen())