I’m trying to build a recursive type in TypeScript that will resolve each possible route path, including nested paths, from a given route configuration. However, I’m encountering issues with type constraints and inference.

I have defined the routes using a TypedRoute interface and a createRoute function:

interface TypedRoute<
  Path extends string,
  QueryParams extends Record<string, string> = {}
> {
  path: Path;
  queryParams?: QueryParams;
  children?: TypedRoute<any, any>[];
}

function createRoute<
  Path extends string,
  QueryParams extends Record<string, string> = {}
>(config: TypedRoute<Path, QueryParams>) {
  return config;
}

const routes = [
  createRoute({
    path: 'results/:id/foo/:bar'
  }),
  createRoute({
    path: 'home',
    children: [
      createRoute({
        path: 'bar',
        children: [
          createRoute({ path: 'baz' })
        ]
      }),
    ],
  }),
]

Now, I’m trying to create a type ExtractRoutePaths that recursively extracts all possible paths:

type ExtractRoutePaths<T extends readonly TypedRoute<any, any>[]> = 
  T extends readonly []
    ? never
    : T extends readonly [infer First, ...infer Rest]
      ? First extends TypedRoute<infer P, any>
        ? First extends { children: infer C }
          ? C extends readonly TypedRoute<any, any>[]
            ? `{P}` | ExtractRoutePaths<C, `${P}/`> | ExtractRoutePaths<Rest extends readonly TypedRoute<any, any>[] ? Rest : never>
            : `${P}` | ExtractRoutePaths<Rest extends readonly TypedRoute<any, any>[] ? Rest : never>
          : `${P}` | ExtractRoutePaths<Rest extends readonly TypedRoute<any, any>[] ? Rest : never>
        : ExtractRoutePaths<Rest extends readonly TypedRoute<any, any>[] ? Rest : never>
      : never;

I expect the Routes to be:

results/:id/foo/:bar | home | home/bar | home/bar/baz

What am I doing wrong, and how can I correctly build this recursive type to extract all possible paths, including nested ones?