length

declare function length<V extends vec2 | vec3 | vec4>(a0: V): (f32)
declare function length<P0 extends number>(a0: P0): ([P0] extends [boolean] ? bool : typeof f32Tag extends keyof P0 ? f32 : typeof i32Tag extends keyof P0 ? i32 : typeof u32Tag extends keyof P0 ? u32 : typeof f64Tag extends keyof P0 ? f64 : number)
declare function length<T extends Numeric | Vec64Any>(a0: T): T extends Vec64Any ? f64 : number

A number in a parameter or a return position is the scalar slot. The ambient file declares a GPU scalar as a branded number whose brand is optional, so a literal and any branded scalar both fill it.

type f32 = number & { readonly [f32Tag]?: true }

A declaration you write still needs a width, and a bare number on a field or a parameter is refused; the TypeScript constructs page carries that row with the compiler's own message.

A signature may name a type the ambient file declares for its own use. These are those declarations.

Vec64Any

type Vec64Any = vec2f64 | vec3f64 | vec4f64

Numeric

type Numeric = number | vec2 | vec3 | vec4 | vec2i | vec3i | vec4i | vec2u | vec3u | vec4u