plugin-rsc: a server component's CSS is not linked in production when its module has no final newline #1495

Related plugins

• plugin-rsc

Describe the bug

Hi, and thank you for plugin-rsc! It made it possible for us to run the Payload CMS 4 admin panel on React Router 8's RSC Framework Mode, and the automatic CSS injection for server components has been a pleasure to rely on.

We found one case where that injection silently does nothing, in production builds only: when a server component's module has no final newline and ends with a line comment, its CSS file is built and listed in the assets manifest, but no <link> reaches the page.

How we found it. Our admin pages rendered unstyled in production while vite dev looked fine. The affected parts were all server components from @payloadcms/ui: the login and create-first-user templates (the form spread over the full viewport width instead of its centered 400px column), the navigation, and the account settings. On the login page:

• the production build emitted 12 CSS files, and the page linked only 6 of them;
• the ones not linked included Root-*.css (which holds the .template-minimal rules), Default-*.css, adminViews-*.css and Verify-*.css, although __vite_rsc_assets_manifest.js correctly maps templates/Minimal/index.js to Root-*.css;
• in the RSC chunk, MinimalTemplate was never wrapped: the wrapper assignment sat inside a comment.

Every compiled file of @payloadcms/ui ends with //# sourceMappingURL=index.js.map and no final newline. transformRscCssExport turned the end of templates/Minimal/index.js into:

//# sourceMappingURL=index.js.mapMinimalTemplate = /* #__PURE__ */ __vite_rsc_wrap_css__(MinimalTemplate, "MinimalTemplate");
export { MinimalTemplate };

Cause. transformWrapExport moves the rewritten export declaration to the end of the module (output.move(start, end, input.length)), and the moved code starts without a newline. When the input has no final newline, the moved code joins the last line. If that line is a comment, the __vite_rsc_wrap_css__(...) call becomes part of it, never runs, and loadCss() is never rendered for that component. vite dev is not affected because it collects CSS from the module graph.

I have opened #1494 with a fix: it adds a newline before the first moved block, only when the input does not end with one, so modules that already end with a newline produce the same output as before. I hope that is useful, and I am happy to change the approach if you prefer another one.

Reproduction

https://github.com/Mheaus/vite-plugin-rsc-final-newline-repro

Steps to reproduce

The reproduction starts from examples/starter and adds two local packages that look like a compiled UI library. Each exports a server component that imports ./card.css. They are identical except for the last byte of dist/index.js:

Both are loaded with await import() so that each gets its own chunk and CSS file, and the RSC build bundles them (resolve.noExternal), as a framework does for UI packages that import CSS.

pnpm install
./check.sh   # vite build, vite preview, then inspects the served HTML

Result with @vitejs/plugin-rsc 0.5.35 and 0.5.36 (vite 8.3.4):

compiled-card: css built=dist-S79n46Dc.css linked=0 rendered=1
source-card: css built=dist-CEWtfTe8.css linked=1 rendered=1

Both cards render, but only source-card gets its stylesheet. With the change from #1494 applied to the installed plugin, both are linked:

compiled-card: css built=dist-S79n46Dc.css linked=1 rendered=1
source-card: css built=dist-CEWtfTe8.css linked=1 rendered=1

Some notes from investigating, in case they help:

• A module inside the project (.tsx or .js under src/) does not reproduce it: the comment is gone before rsc:rsc-css-export-transform sees the code. It reproduces with files that come from a package in node_modules, which is where compiled libraries live.
• "use server" modules go through transformModuleExportEffect, which already surrounds moved code with newlines (\n${code}\n), so they do not have this problem.
• Until a release ships, a small enforce: 'pre' plugin that appends \n to modules without a final newline in the rsc environment works around it. That is what we ship in our adapter today.

System Info

  System:
    OS: macOS 27.0
    CPU: (18) arm64 Apple M5 Pro
    Memory: 1.45 GB / 48.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 26.5.0 - /opt/homebrew/bin/node
    npm: 11.17.0 - /opt/homebrew/bin/npm
    pnpm: 11.17.0
  Browsers:
    Chrome: 154.0.8037.98
    Firefox: 153.0
    Safari: 27.0
  npmPackages:
    @vitejs/plugin-react: 6.0.1 => 6.0.1
    @vitejs/plugin-rsc: 0.5.36 => 0.5.36
    vite: 8.3.4 => 8.3.4

Also reproduced on Node 24.15.0.

Used Package Manager

pnpm

Logs

No error is logged: the build succeeds and the page renders, only without the component's stylesheet.

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue.

Thanks a lot for your time!