Generic TypeScript function that infers the literal type of any primitive, object, or tuple (literal JSON type inference)

ts_literal_json_inference.ts

type Primitive = string | number | boolean | null | undefined;
type Compound<U extends Primitive = Primitive> =
  | U
  | { [name: string]: Compound<U> }
  | []
  | [Compound<U>]
  | [Compound<U>, ...Compound<U>[]];
type Json<U extends Primitive> = U | Compound<U>;

// this function infers the EXACT type of the value passed into it
// and returns it as a const will full type information
const inferLiteral = <U extends Primitive,T extends Json<U>>(arg: T): T  => {
  return arg; 
};

// equivalent to using "as const";
const whatever = inferLiteral("whatever");
const whatever = "whatever" as const;