Configurable entry file path names (routes, root, entry.client, entry.server)

[brettburley]

Configurable entry file path names

Summary

The standard entry file names (root, routes, entry.client, entry.server) should be configurable via the React Router configuration, allowing projects to use custom file names and paths while maintaining the same functionality.

Motivation

While the default conventions are clear and work well for new projects, we have found that with many React Router apps, it becomes cumbersome to manage all of these files for each application. For example, we have a shared root.tsx that is used in dozens of applications, and the contents of that file is effectively re-exporting all of the functionality from a shared package:

import App from '@internal/shared-runtime';

export * from '@internal/shared-runtime';
export default App;

Rather than having to manage all of these "shell" entry files, we'd like to centralize to a single implementation and point each application to that source root file.

Furthermore, this would offer a mechanism that library authors could use to provide custom implementations of the default entry files through exposing a configuration preset that points one or more of the entry files to their custom implementations.

Proposed Solution

Add configuration options to react-router.config.ts for specifying custom file names:

export default {
  // Existing options for file paths
  appDirectory: "app",
  
  // New options for file names
  rootRouteFile: "custom/root.tsx",
  routesFile: "custom/app-routes.ts",
  clientEntryFile: "custom/entry.client.tsx",
  serverEntryFile: "custom/entry.server.tsx"
}

Implementation Details

• These configurations would be optional, falling back to current defaults.
• If custom files are provided, their existence will be validated when the configuration is loaded.
• Entry files could point to a file relative to the appDirectory, or be an absolute path that doesn't necessarily live within the appDirectory to support shared configurations across multiple applications.

Breaking Changes

None. This is a purely additive change that maintains backward compatibility with existing projects.

[brettburley]

Created a draft PR for a possible implementation here in #13269.

[brettburley]

Having thought about this more, I think there are maybe two concerns here: the root file, which is potentially a routes.ts concern, and the configuration files (entry.client.tsx and entry.server.tsx).

Initially we grasped for using vite virtual modules to abstract how the entry and root files ares resolved, but currently they're read directly from the file system: https://github.com/remix-run/react-router/blob/main/packages/react-router-dev/config/config.ts#L748, but I think using virtual modules to resolve these files might make it easier to customize this behavior.