Reproduction

Failing integration test on the current main branch:

https://github.com/comp615/react-router/blob/5574f7ef87af726d1aedba2b2ed7520d71c40f3b/integration/bug-report-test.ts

The fixture configures Framework Mode with:

export default {
  splitRouteModules: "enforce",
} satisfies Config;

and uses the standard React Router and React Vite plugins:

export default defineConfig({
  plugins: [reactRouter(), react()],
});

The route has two otherwise independent JSX exports:

export function HydrateFallback() {
  return <p>Loading...</p>;
}

export default function Index() {
  return <h1>Ready</h1>;
}

Run:

pnpm install
pnpm build
pnpm test:integration:run bug-report --project chromium

The test first confirms that the production fixture build succeeds. Loading the same fixture through the Vite dev server then renders the error overlay:

Error splitting route module: routes/_index.tsx

- HydrateFallback

This export could not be split into its own chunk because it shares code with other exports.

System Info

System:
  OS: macOS 26.5.2
  CPU: (16) arm64 Apple M3 Max
  Memory: 2.36 GB / 64.00 GB
  Shell: 5.9 - /bin/zsh
Binaries:
  Node: 24.16.0
  npm: 11.13.0
  pnpm: 11.7.0
Browsers:
  Chrome: 150.0.7871.125
  Firefox: 152.0.5
  Safari: 26.5.2
npmPackages:
  @react-router/dev: workspace:* => 8.2.0
  @react-router/fs-routes: workspace:* => 8.2.0
  @react-router/serve: workspace:* => 8.2.0
  @vitejs/plugin-react: ^6.0.1 => 6.0.1
  react-router: workspace:* => 8.2.0
  vite: ^8.0.0 => 8.0.2

Used Package Manager

pnpm

Expected Behavior

splitRouteModules: "enforce" should accept this route in Vite dev because the two exports do not share user-authored module-local code and the production build can split them successfully.

Actual Behavior

The React JSX development transform emits a shared module-level _jsxFileName binding used by the jsxDEV source metadata for both JSX exports. Dev manifest generation runs route-chunk dependency analysis on that transformed output, treats _jsxFileName as shared application code, and rejects HydrateFallback.

Production output does not contain the same development-only dependency, so the production build succeeds. This makes dev enforcement stricter than—and inconsistent with—the build output it is intended to enforce.

Potential directions include skipping build-only split enforcement during dev manifest generation, analyzing pre-development-JSX source, or excluding compiler-generated JSX source metadata from shared-binding analysis.

🤖 Report and reproduction prepared with AI assistance.