Allow SSR during development when ssr: false

[futursolo]

react-router dev will refuse to start when you have a loader but no prerender paths when ssr: false.

Prerender: 1 invalid route export in `routes/sitemap-index[.]xml` when pre-rendering with `ssr:false`: `loader`. See https://reactrouter.com/how-to/pre-rendering#invalid-exports for more information.

This is fine and preferable when building production. But it is hard to use when doing development.

I’d imagine a normal development workflow for a new path is:

1. add routes/new-path.tsx
2. add loader
3. add export default function Component
4. Make loader / Component work
5. add paths to prerender

Adding path to prerender is usually the last step after loader and Component is completed.
But React Router will refuse to start as soon as a loader is added.

This makes developers have to add prerender or dummy route before 2, which is not only counterintuitive but also hard sometimes when the new route is a dynamic route with params since you have to write logic to collect these from some datasource.

In addition:

• When you rename the path, you have to fix prerender.
• If you want to preview a new path with params, such as /posts/post-i-just-wrote, you have to add to prerender first.
• If you use async function to collect paths, it doesn’t rerun automatically.

I feel the developer experience will be much better if ssr is allowed during development.