Add `NonEmptyArray` to `lib` (but **not** `length > 0` narrowing)

⚙ Compilation target

ES2023

⚙ Library

ES2023

Missing / Incorrect Definition

type NonEmptyArray<T> = [T, ...T[]]
type ReadonlyNonEmptyArray<T> = readonly [T, ...readonly T[]]

Sample Code

const is_non_empty = <T>(a: ReadonlyArray<T>): a is ReadonlyNonEmptyArray<T> =>
	a.length > 0

function sum(a: ReadonlyNonEmptyArray<number>): number
function sum(a: ReadonlyNonEmptyArray<bigint>): bigint
function sum(a:
	ReadonlyNonEmptyArray<number> |
	ReadonlyNonEmptyArray<bigint>
) {
	//@ts-expect-error
	return a.reduce((acc, x) => acc + x)
}

Documentation Link

There's no docs that I'm aware of. However, there are multiple issues using this boilerplate. See also: #60463

Here's a WIP example implementations of sum. The sample code is a simplified version of that. More info here

Start by locating the ES2023 library declaration files and the existing array type definitions; the issue names no specific file or test. Add the mutable and readonly NonEmptyArray aliases without introducing length-based narrowing, then verify the supplied type-checking example and relevant compiler tests.