Error in project with TS 2.6 and strictFunctionTypes

RxJS version: 5.5.2

Code to reproduce:

In tsconfig.json:

{
  "compilerOptions": {
    "skipLibCheck": false,
    "strictFunctionTypes": true
  }
}

import * as Rx from "rxjs";

Expected behavior:

Compiles successfully.

Actual behavior:

Compiler error:

../../node_modules/rxjs/scheduler/VirtualTimeScheduler.d.ts(22,22): error TS2415: Class 'VirtualAction<T>' incorrectly extends base class 'AsyncAction<T>'.
  Types of property 'work' are incompatible.
    Type '(this: VirtualAction<T>, state?: T | undefined) => void' is not assignable to type '(this: AsyncAction<T>, state?: T | undefined) => void'.
      The 'this' types of each signature are incompatible.
        Type 'AsyncAction<T>' is not assignable to type 'VirtualAction<T>'.
          Property 'index' is missing in type 'AsyncAction<T>'

Additional information:

Workaround: disable strictFunctionTypes OR enable skipLibCheck

I believe this is happening because work is not defined as a method (rather, it’s defined as a property), so its parameters are checked contravariantly. If it was defined as a method, the parameters would be checked covariantly.

This could be fixed by defining work as a method in both classes, or defining it as (this: AsyncAction<T>, state?: T) => void in VirtualAction.

[craftytrickster]

To workaround this issue, you need, "skipLibCheck": true, not false. In generally, I would say it is bad practice to skipLibCheck, but since RxJs typings are broken, it is the only way around the issue.

[colindekker]

The issue in the VirtualTimeScheduler.d.ts file is there with TS 2…7.1 too. Changing the type if the this parameter of the work method from VirtualAction to its basetype AsyncAction in the VirtualTimeScheduler.d.ts file fixes the build issue.