Which project does this relate to?
Router
Describe the bug
Summary
Using the rsbuild, importing CSS via ?url emits the CSS file twice — once in dist/client/assets/css/ and again in dist/server/static/css/ — and both URLs end up in the SSR-rendered <head>.
- dev: both requests succeed (rsbuild's dev server serves both paths), but the page loads the same stylesheet twice with two HTTP round-trips.
- prod: the
/static/... URL 404s under the standard srvx --prod -s dist/client … start command, because only dist/client is exposed.
Reproduces with or without rsc.enabled.
After rsbuild build:
dist/client/assets/css/styles..css ✅ byte-identical
dist/server/static/css/styles..css ✅ byte-identical, unused at runtime
Rendered HTML:
<link rel="stylesheet" href="/static/css/styles.<hash>.css" data-precedence="default">
<link rel="stylesheet" href="/assets/css/styles.<hash>.css" data-precedence="default">
Complete minimal reproducer
https://github.com/ploskovytskyy/reproduce-start-rsbuild
Steps to Reproduce the Bug
- clone the repo and
pnpm install
- run
pnpm dev:rsbuild
- open localhost and check in browser inspector, there are two for styles
Optional:
- run
pnpm build:rsbuild
- run
pnpm start - it starts prod server
- now in the browser second styles request will fail with 404 since we only expose client assets
Expected behavior
A single <link rel="stylesheet"> in the rendered head, pointing at a file served from the client assets directory in both dev and prod.
Screenshots or Videos
No response
Platform
- Router / Start Version: [e.g. 1.121.0]
- OS: [e.g. macOS, Windows, Linux]
- Browser: [e.g. Chrome, Safari, Firefox]
- Browser Version: [e.g. 91.1]
- Bundler: [e.g. vite]
- Bundler Version: [e.g. 7.0.0]
Additional context
Root cause
createRsbuildEnvironmentPlan in packages/start-plugin-core/src/rsbuild/planning.ts defines two independent Rspack compilations:
Client env (lines 121-138) explicitly sets distPath.{css, cssAsync, svg, font, wasm, image, media, assets} under RSBUILD_CLIENT_ASSETS_DIR and assetPrefix: opts.publicBase.
Server env (lines 168-177) sets only distPath.root. Everything else falls back to rspack defaults — cssFilename = static/css/[name].[contenthash:8].css and no assetPrefix.
Each compilation runs its own CSS extract pipeline and produces its own ?url resolution. Since the source CSS is identical, the content hashes match, but the URLs differ (/assets/css/... vs /static/css/...). SSR picks up the server URL; client hydration produces a fresh for the client URL.
This is rspack-specific. Affects any asset imported via ?url in code that runs on both server and client (CSS, SVG, fonts, images). CSS is just the most visible because of the broken in prod and the doubled payload in dev.
Workaround
A top-level output.distPath override cascades into both environments and aligns the URLs:
// rsbuild.config.ts
export default defineConfig({
output: {
distPath: {
css: "assets/css",
// cssAsync: "assets/css/async", // if you use async CSS chunks
},
},
plugins: [pluginReact(), tanstackStart()],
});The duplicate file still gets emitted in dist/server/assets/css/ (unused), but the SSR'd URL and the client URL match.
Proposed fix
Apply the same mirroring inside createRsbuildEnvironmentPlan's server env.
Leaves the duplicate emit on disk but removes the visible bug.
For example, here is my branch with the patch and a draft commit: https://github.com/ploskovytskyy/router/tree/fix/start-rsbuild-client-assets-duplicate
Which project does this relate to?
Router
Describe the bug
Summary
Using the rsbuild, importing CSS via
?urlemits the CSS file twice — once indist/client/assets/css/and again indist/server/static/css/— and both URLs end up in the SSR-rendered<head>./static/...URL 404s under the standardsrvx --prod -s dist/client …start command, because onlydist/clientis exposed.Reproduces with or without
rsc.enabled.After rsbuild build:
dist/client/assets/css/styles..css ✅ byte-identical
dist/server/static/css/styles..css ✅ byte-identical, unused at runtime
Rendered HTML:
Complete minimal reproducer
https://github.com/ploskovytskyy/reproduce-start-rsbuild
Steps to Reproduce the Bug
pnpm installpnpm dev:rsbuildOptional:
pnpm build:rsbuildpnpm start- it starts prod serverExpected behavior
A single
<link rel="stylesheet">in the rendered head, pointing at a file served from the client assets directory in both dev and prod.Screenshots or Videos
No response
Platform
Additional context
Root cause
createRsbuildEnvironmentPlan in packages/start-plugin-core/src/rsbuild/planning.ts defines two independent Rspack compilations:
Client env (lines 121-138) explicitly sets distPath.{css, cssAsync, svg, font, wasm, image, media, assets} under RSBUILD_CLIENT_ASSETS_DIR and assetPrefix: opts.publicBase.
Server env (lines 168-177) sets only distPath.root. Everything else falls back to rspack defaults — cssFilename = static/css/[name].[contenthash:8].css and no assetPrefix.
Each compilation runs its own CSS extract pipeline and produces its own ?url resolution. Since the source CSS is identical, the content hashes match, but the URLs differ (/assets/css/... vs /static/css/...). SSR picks up the server URL; client hydration produces a fresh for the client URL.
This is rspack-specific. Affects any asset imported via ?url in code that runs on both server and client (CSS, SVG, fonts, images). CSS is just the most visible because of the broken in prod and the doubled payload in dev.
Workaround
A top-level
output.distPathoverride cascades into both environments and aligns the URLs:The duplicate file still gets emitted in dist/server/assets/css/ (unused), but the SSR'd URL and the client URL match.
Proposed fix
Apply the same mirroring inside createRsbuildEnvironmentPlan's server env.
Leaves the duplicate emit on disk but removes the visible bug.
For example, here is my branch with the patch and a draft commit: https://github.com/ploskovytskyy/router/tree/fix/start-rsbuild-client-assets-duplicate