Changed behaviour in TS2.1 for Promise<void>

In typescript 2.0 any promise could be used a promise of type void, this does not seem to be the case in typescript 2.1.

I couldn’t find this listed as a breaking change or any existing tickets so raised this one.

TypeScript Version: 2.1.4

Code

function testVoidPromises(promiseA: Promise<void>, promiseB: Promise<void>): Promise<void> {
	return Promise.all([promiseA, promiseB]);
}

Expected behavior: This compiles without errors in typescript 2.0

Actual behavior: This fails to compile in typescript 2.1.4 with the following error: test.ts(2,9): error TS2322: Type ‘Promise<[void, void]>’ is not assignable to type ‘Promise<void>’. Type ‘[void, void]’ is not assignable to type ‘void’.

[jorenl]

So, almost four years later I still run into this issue continuously: https://www.typescriptlang.org/play/?ssl=18&ssc=26&pln=1&pc=1#code/JYOwLgpgTgZghgYwgAgEoQM4AdkG8BQyRyCA9gCYQBcyIArgLYBG0A3IcUxQJ40ZhRQAc3YBffPhh0QCMMFIhkYOAGsIAMRAAKGCBpaAlMgC8APmQA3UsHJGCxZFAhg6UEGIlSZchUtUQABShSBmAMDW1dfSMzZCCQsIgAHisbUzsOIicXNw98MhB+ZF0TZEMadGwTcy1cMkoaACYABmaAGmQucl5kACIAeQBpXtEDdgKirGDQ8M1S8rjpxKTKrHNY+JmIADonDFIAGwsIWpIKamQW9s6eGgHh5FH2fGU1TR0QMZf-TcT3qYSs0+rCAA

Afaik, () => T assigns to () => void just fine, but () => Promise<T> does not assign to () => Promise<void>. What’s the correct pattern/workaround here?

[advorkovyy]

let x: Promise<void> = Promise.resolve(1) 

gives TS2322:Type ‘Promise<number>’ is not assignable to type ‘Promise<void>’. Type ‘number’ is not assignable to type ‘void’.

So, this is obviously a bug in typescript compiler