Regression: Promise-related type inferencing failing in 2.4.1

[jklmli]

TypeScript Version: 2.4.1

After upgrading from 2.3.4, some tests fail to inference correctly. An overloaded method that's called resolves to the wrong version, and the only workaround I can find is explicitly declaring the correct variable type to choose the correct overloaded method.

Here is a repo/branch/CI with a repro:

1. Baseline - master on 2.3.4
2. Trying to upgrade to 2.4.1 - note the errors (lint needs to compile the files)
3. Forced type casts - tests pass now

Each CI run is a single commit, you can jump to the Github links to see what changed.

[yuit]

@jiaweihli could you share the small repo of the issue? also from reading the description, I think this may be the cause (https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#stricter-variance-in-callback-parameters)

[jklmli]

Here is the full branch I repro'd this on: https://github.com/jiaweihli/monapt/commits/upgrade-to-ts-2.4

[kitsonk]

could you share the small repo of the issue?

Here is the full branch I repro'd this on

😖

[jklmli]

The code is open-source, and I documented each step I took in a separate commit. Each of these has also been run independently through CI.

Do you still need a small repro?

[kitsonk]

Do you still need a small repro?

I am not part of the TypeScript team, but I think the answer will be yes. It is like saying "go read through the TypeScript source code to find your issue, it is open source, all the commits are there."

[jklmli]

Similar to DefinitelyTyped/DefinitelyTyped#11027