SolidJS type safe for `useParam` from a `RouteDefinition`

solidjs-RouteDefinitionParams.d.ts

import type { RouteDefinition } from "@solidjs/router";

/**
 * Refine a Type
 * @example
 * ```ts
 * type Refined = Refine<{ foo: string, bar: unknown[] }, { foo: `${number}` }>
 * //   ^? { foo: `${number}`, bar: unknown[] }
 * ```
 */
export type Refine<T, P extends Partial<T>> = {
  [k in keyof T]: T[k] & P[k];
};

/**
 * Prettify helper
 * @see https://www.totaltypescript.com/concepts/the-prettify-helper
 */
export type Prettify<T> = {
  [k in keyof T]: T[k];
} & unknown;

// SHOULD be: import type { MatchFilter } from "@solidjs/router";
// but `@solidjs/router` does NOT expose this type
type MatchFilter = NonNullable<
  NonNullable<RouteDefinition["matchFilters"]>[string]
>;

// The `matchFilters` of a RouteDefinition describes its Params
type RD$matchFilters<RD extends RouteDefinition> = NonNullable<
  RD["matchFilters"]
>;

// Convert MatchFilter to string value
type MF$toString<MF extends MatchFilter | undefined> =
  MF extends readonly string[]
    ? MF[number]
    : MF extends RegExp
    ? `${string}`
    : MF extends (s: string) => boolean
    ? `${string}`
    : never;

// Params of a RouteDefinition {[keyof matchFilters]: `${any}`}
type RD$Params<RD extends RouteDefinition> = {
  [k in NonNullable<keyof RD$matchFilters<RD>>]: MF$toString<
    RD$matchFilters<RD>[k]
  >;
};

// Refine a defined RouteDefinition
type RD$RouteParams<
  RD extends RouteDefinition,
  tRD extends RouteDefinition = RouteDefinition<RD["path"]>
> = Refine<RD$Params<tRD>, RD$Params<RD>>;

/**
 * @example
 * ```ts
 * const path = "/:aNumberParam";
 * type TRouteDefinition = RouteDefinition<typeof path>;
 *
 * type TParams = RouteDefinitionParams<TRouteDefinition>;
 * // or with Refined param Type
 * type TParams = RouteDefinitionParams<TRouteDefinition, { aNumberParam: `${number}` }>;
 * const params = useParams<TParams>();
 * //    ^? Type is { aNumberParam: `${number}` }
 * ```
 */
export type RouteDefinitionParams<
  RD extends RouteDefinition,
  P extends Partial<RD$RouteParams<RD>> = NonNullable<unknown>
> = Prettify<Refine<RD$RouteParams<RD>, P>>;