WeakMapConstructor and WeakSetConstructor should be able to take `undefined` and `null`

[AlexErrant]

lib Update Request

Configuration Check

My compilation target is ES2015 and my lib is es2021.

Missing / Incorrect Definition

The es2015.iterable type definitions for WeakMap and WeakSet's ctors are missing undefined and null, contrary to the weakmap spec and the weakset spec:

4. If iterable is either undefined or null, return map.
5. If iterable is either undefined or null, return set.

TypeScript/src/lib/es2015.iterable.d.ts

Lines 146 to 148 in 03951f2

	interface WeakMapConstructor {
	new <K extends WeakKey, V>(iterable: Iterable<readonly [K, V]>): WeakMap<K, V>;
	}

TypeScript/src/lib/es2015.iterable.d.ts

Lines 194 to 196 in 03951f2

	interface WeakSetConstructor {
	new <T extends WeakKey = WeakKey>(iterable: Iterable<T>): WeakSet<T>;
	}

The (non-weak) Map ctor was made optional/nullable in this PR from 2021 - I assume that WeakMap/WeakSet was missed as an oversight.

I began to address this issue in this branch, but the PR template required an issue so here I am :)

[RyanCavanaugh]

What are you trying to address? This is already legal:

// Not an error
const p1 = new WeakMap(null);
// Not an error
const p2 = new WeakMap(undefined);
// Not an error
const p3 = new WeakSet(null);
// Not an error
const p4 = new WeakSet(undefined);

[fatcerberus]

That’s interesting, since the only construct signature defined (as shown in the quoted type definition) is one that takes an Iterable

[AlexErrant]

I ran into this issue in the course of this PR. I didn't run into this issue in the course of run/compile-time analysis; I only, uh, noticed it during "copy/paste time analysis". I noticed it while trying to copy TypeScript's Map/Set constructor type definitions to the above library's Map/Set wrapper. (The above library defines a special Map/Set wrapper that something special in the SolidJS UI framework.)

I believe your example works because it uses WeakMapConstructorand WeakSetConstructor from https://github.com/microsoft/TypeScript/blob/main/src/lib/es2015.collection.d.ts , which correctly handles null/undefined. My issue is with es2015.iterable. (I've no idea what determines whether collection or iterable is used.)

[fatcerberus]

Ah, now this makes sense. There's nothing to be fixed here.

I've no idea what determines whether collection or iterable is used.

Assuming both are used in a project, then whichever one matches a given call. The two definitions aren't mutually exclusive; the declarations merge at compile time and create overloads.

tl;dr: You're not looking at the full definition