#25157 Repro - File 1

interfaces.ts

// Interface returned by our RouteCreator function
export interface Route<Parts extends PathPart<any>> {
  template(): string;
  create(params: UnionToIntersection<OnlyParams<Parts>>): string;
}

export type PathPart<T extends string> = string | PathParam<T>;

export function param<T extends string>(t: T): PathParam<T> {
  return { param: t };
}

export interface PathParam<T extends string> {
  param: T;
}

// Pluck only the parameter types from a Route
export type OnlyParams<T> = T extends PathParam<infer K> ? Record<K, string> : {};

// Given the parameters of a route I want an object of { paramName: string }
// e.g. for const Route = route(['logbook', param('logbookId'), param('otherId')]);
// RouteParams<Route> = { logbookId: string, otherId: string }
export type RouteParams<T extends Route<any>> = T extends Route<infer Parts>
  ? UnionToIntersection<OnlyParams<Parts>>
  : never;

// Type Utils
export type GetKeys<U> = U extends Record<infer K, any> ? K : never;
export type UnionToIntersection<U extends object> = {
  [K in GetKeys<U>]: U extends Record<K, infer T> ? T : never
};