Optional arguments due to multiple constructors are not considered when resolving rest parameters in generics

[stephanemagnenat]

TypeScript Version: 3.8.3 and nightly from the playground as of today.

Search Terms: label:bug constructor rest parameter

Code

class A {
	constructor(value: number);
	constructor(sKey: string, sValue: string);
	constructor(sKeyOrValue: string | number, sValue?: string) {}
}

function test<T, S, A extends any[]>(ctor: new (...args: A) => T, ...params: A): T {
	return new ctor(...params);
}

test(A, 3);

Expected behavior:
I would expect this to compile without error, because class A has a valid constructor with one argument of type number.

Actual behavior:
Error: Expected 3 arguments, but got 2.(2554). It seems the compiler is not able to realise that class A has a matching constructor.

Playground Link: Playground link

Related Issues: #37142, #29707

[jcalz]

This is a design limitation: type inference from a type with multiple call or construct signatures only happens against the last such signature. See #32418, #35641, probably others...

[ahejlsberg]

Meanwhile, it works if you write it like this, though you loose the descriptive parameter names:

class A {
	constructor(...args: [number] | [string, string]);
	constructor(sKeyOrValue: string | number, sValue?: string) {}
}

function test<T, S, A extends any[]>(ctor: new (...args: A) => T, ...params: A): T {
	return new ctor(...params);
}

test(A, 3);
test(A, 'foo', 'bar');