Does not work with node v6.5

Hi, I have a webapp that I built using the koa v2 framework. I use koa-convert, koa-generic-session and koa-redis to store user sessions in my redis instance. Since upgrading to node v6.5, my webapp fails with the following stacktrace:

TypeError: Cannot read property 'done' of undefined
      at next (/Users/dev/work/node_modules/co/index.js:98:14)
      at onFulfilled (/Users/dev/work/node_modules/co/index.js:69:7)
      at /Users/Stephen/dev/work/node_modules/co/index.js:54:5
      at Object.co (/Users/dev/work/node_modules/co/index.js:50:10)
      at next (/Users/dev/work/node_modules/co/index.js:99:29)
      at onFulfilled (/Users/dev/work/node_modules/co/index.js:69:7)

It worked fine with node v6.4. The stacktrace doesnt go past co, but through trial and error, I deleted a lot of third party libs and middleware and narrowed it down to this block of code:

app.use(convert(session({
  key: 'session',
  errorHandler(err, type, ctx) {
    console.error(err, type)
  },
  store: redisStore({ url: config.redis.url })
})))

which can be reduced to app.use(convert(session())) and still trigger the same bug.

I do not use the convert lib anywhere else in the app so I cannot quickly test to see if the issue is specifically in the convert or session lib.

[targos]

This is a bug in V8 with tail call optimization. The --harmony-tailcalls flag (implied by --harmony) is enough to trigger it. It will probably not be fixed in Node.js because the feature is not considered stable in V8 5.1. I suggest you drop the --harmony flag and if you really need one of the features that it activates, enable it directly. Here is the list: https://github.com/nodejs/node/blob/v6.5.0/deps/v8/src/flag-definitions.h#L211-L216

[bishtawi]

Did some more testing. Its due to the --harmony flag that I am including when running node.

Smallest failing test case:

const Koa = require('koa')
const convert = require('koa-convert')
const session = require('koa-generic-session')

const app = new Koa()
app.use(convert(session()))

app.listen(3000)

Running node --harmony index.js then hitting localhost:3000 in a webbrowser returns a 500 instead of the expected 404.

Running without the harmony flag works as expected.