[uncaught exception]: TypeError: this._state.then is not a function

[mjbvz]

Steps to Reproduce:

On MacOS with Node 7.8

1. Clone master
2. Do clean install and build
3. Open editor. Try opening a file

Bug
Cannot open any files. See [uncaught exception]: TypeError: this._state.then is not a function errors

A bisect identifies f24ea58 as the cause of this

[mjbvz]

Both @rebornix and I have hit this.

I think this line where we call Promise.resolve(detectMimeAndEncodingFromBuffer(...)) may be the root cause of the problem

[rebornix]

After reading #32381 (comment) I suppose Promise/TPromise is the thing.

[mjbvz]

Root cause of this seems to be that:

1. detectMimeAndEncodingFromBuffer returns a TPromise
2. When this TPromise is resolved, it swaps out its .then method.
3. At this point, I believe Promise.resolve has already grabbed the old .then implementation. It then invokes this invalid .thenlater on, triggering this error

Tested this by changing the code to:

const p: any = detectMimeAndEncodingFromBuffer(
    { buffer: chunkBuffer, bytesRead },
    options && options.autoGuessEncoding || this.configuredAutoGuessEncoding(resource));
Promise.resolve(p.then ?
    ({ then: (x) => p.then(x) })
    : p)

This does seem to work

[jrieken]

😱 wow... Stupid WinJS.Promise...