narrow down possible status codes for redirects to 300-308

[ivanhofer]

closes #7614

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[ghost]

Can't we make the type more generic ?

type RangeStartArray<
	LENGTH extends number,
	ACC extends unknown[] = [],
> = ACC['length'] extends LENGTH
	? ACC
	: RangeStartArray<LENGTH, [...ACC, 1]>

type NumericRangeBuilder<
	START_ARR extends number[],
	END extends number,
	ACC extends number = never>
	= START_ARR['length'] extends END
	? ACC | END
	: NumericRangeBuilder<[...START_ARR, 1], END, ACC | START_ARR['length']>

/**
 * A type that represents a range of numbers 'FROM' to `END` (inclusive)
 * 
 * @example
 * type Range = NumericRange<100, 200> // 100 | 101 ... 199 | 200
 */
export type NumericRange<FROM extends number, TO extends number> = NumericRangeBuilder<RangeStartArray<FROM>, TO>

/**
 * 
 * @property {number} informational - 1xx
 * @property {number} success - 2xx
 * @property {number} redirection - 3xx
 * @property {number} clientError - 4xx
 * @property {number} serverError - 5xx
 * 
 * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Status
 */
export type HttpStatusCode = {
	informational: NumericRange<1, 199>;
	success: NumericRange<200, 299>;
	redirect: NumericRange<300, 399>;
	clientError: NumericRange<400, 499>;
	serverError: NumericRange<500, 599>;
}

/**
 * Creates a `Redirect` object. If thrown during request handling, SvelteKit will
 * return a redirect response.
 * @param status The HTTP redirect status code (300-399)
 * @param location The location to redirect to
 */
export function redirect(status: HttpStatusCode['redirect'], location: string): Redirect;

[ivanhofer]

Can't we make the type more generic ?

If it would be more performant.. then probably yes.
I haven't seen any performant NumberRange implementation yet. This one takes a few minutes on my machine to tell me that 500 is not allowed.

[dummdidumm]

Number range generator is something for another PR, if ever - I'd rather have more simple types. In this case it's ok because it's only a handful of numbers, which can be hardcoded.

[Rich-Harris]

thank you!