[help-needed] Rollup TypeScript support

[martonlederer]

This pull request contains a script to set up TypeScript with Rollup (there are some bugs, so help is needed). It would make sense to merge this after #1402 and would also solve my issue #251

[benmccann]

We should bump the version number in package.json to the latest (0.28.4). The type definitions were added in 0.28.1 and make using TypeScript with Sapper easier to setup

[Steakeye]

I'm just gonna leave this here in case you'd like to see how I wrote mine a couple of weeks ago https://gist.github.com/Steakeye/59db68c59e8fffba788f9de47f12c2ce

[Steakeye]

Also, my sapper typings, not sure where I lifted them from but they are as follows

///typings/@sapper/index.d.ts
declare module '@sapper/app' {
    // from sapper/runtime/src/app/types.ts
    // sapper doesn't export its types yet
    interface Redirect {
        statusCode: number
        location: string
    }
    // end

    interface gotoOpts {
        replaceState: boolean
    }
    function goto(
        href: string,
        opts: gotoOpts /*= { replaceState: false }*/
    ): Promise<unknown>
    function prefetch(
        href: string
    ): Promise<{ redirect?: Redirect; data?: unknown }>
    function prefetchRoutes(pathnames: string[]): Promise<unknown>
    function start(opts: { target: Node }): Promise<unknown>
    const stores: () => unknown

    export { goto, prefetch, prefetchRoutes, start, stores }
}

declare module '@sapper/server' {
    interface MiddlewareOptions {
        session?: (req: Express.Request, res: Express.Response) => unknown
        ignore?: unknown
    }

    function middleware(opts?: MiddlewareOptions): Express.RequestHandler

    export { middleware }
}

declare module '@sapper/service-worker' {
    const timestamp: number
    const files: string[]
    const shell: string[]
    const routes: { pattern: RegExp }[]

    export { timestamp, files, files as assets, shell, routes }
}

[benmccann]

The types are already included in Sapper. The template doesn't need to provide them

[benmccann]

Closing in favor of https://github.com/sveltejs/sapper-template/pull/262. Thanks for getting the ball rolling!