This makes sure we don't trigger the export step if we aren't exporting any static pages during a build. This also adds an invariant to ensure we don't attempt creating a progress with 0 items.
Fixes: https://github.com/vercel/next.js/issues/22994
This updates to not automatically export `/500` from `_error` if a custom `getInitialProps` is used since logic may be used inside of this method that causes the export to fail. Users can still opt-in to the static `/500` by adding a `pages/500.js` file.
This also refactors checking `_app` for custom `getInitialProps` to outside of the static check loop to prevent a potential race condition where we could run this check multiple times un-necessarily.
Fixes: https://github.com/vercel/next.js/issues/22815
Follow-up to https://github.com/vercel/next.js/pull/22139 this ensures the default 500 error page hydrates with the correct `statusCode` prop when updating query values on the client since currently it will switch the 404 `statusCode` when one isn't present. An additional test case has been added to ensure this is handled correctly.
This adds generating a static 500 status page when a `pages/500.js` file is added similar to how we handle generating static 404 pages when `pages/404.js` is present. This allows showing a customized error page when a 500 error occurs in an optimal way.
