fix(rsc): remove duplicate server css on initial render

packages/plugin-rsc/e2e/basic.test.ts

@@ -473,6 +473,22 @@ function defineTest(f: Fixture) {
         'color',
         'rgb(255, 165, 0)',
       )
+      await expectNoDuplicateServerCss(page)
+    })
+
+    async function expectNoDuplicateServerCss(page: Page) {
+      // check only manually inserted stylesheet link exists
+      // (toHaveAttribute passes only when locator matches single element)
+      await expect(page.locator('link[rel="stylesheet"]')).toHaveAttribute(
+        'href',
+        '/test-style-server-manual.css',
+      )
+    }
+
+    test('no duplicate server css', async ({ page }) => {
+      await page.goto(f.url())
+      await waitForHydration(page)
+      await expectNoDuplicateServerCss(page)
     })
 
     test('adding/removing css client @js', async ({ page }) => {
@@ -557,6 +573,7 @@ function defineTest(f: Fixture) {
         'color',
         'rgb(255, 165, 0)',
       )
+      await expectNoDuplicateServerCss(page)
     })
 
     // TODO: need a way to add/remove links on server hmr. for now, it requires a manually reload.

packages/plugin-rsc/examples/basic/src/routes/style-server/server.tsx

@@ -10,7 +10,7 @@ export function TestStyleServer() {
       </div>
       <link
         rel="stylesheet"
-        href="/test.css"
+        href="/test-style-server-manual.css"
         precedence="test-style-server-manual"
       />
       <div className="test-style-server-manual">test-style-server-manual</div>

packages/plugin-rsc/src/plugin.ts

@@ -837,7 +837,8 @@ window.__vite_plugin_react_preamble_installed__ = true;
         const resolvedEntry = await this.resolve(source)
         assert(resolvedEntry, `[vite-rsc] failed to resolve entry '${source}'`)
         code += `await import(${JSON.stringify(resolvedEntry.id)});`
-        // TODO: this doesn't have to wait for "vite:beforeUpdate" and should do it right after browser css import.
+        // server css is normally removed via `RemoveDuplicateServerCss` on useEffect.
+        // this also makes sure they are removed on hmr in case initial rendering failed.
         code += /* js */ `
 const ssrCss = document.querySelectorAll("link[rel='stylesheet']");
 import.meta.hot.on("vite:beforeUpdate", () => {
@@ -1910,6 +1911,36 @@ export function vitePluginRscCss(
         }
       },
     },
+    createVirtualPlugin(
+      'vite-rsc/remove-duplicate-server-css',
+      async function () {
+        // Remove duplicate css during dev due to server rendered <link> and client inline <style>
+        // https://github.com/remix-run/react-router/blob/166fd940e7d5df9ed005ca68e12de53b1d88324a/packages/react-router/lib/dom-export/hydrated-router.tsx#L245-L274
+        assert.equal(this.environment.mode, 'dev')
+        function removeFn() {
+          document
+            .querySelectorAll("link[rel='stylesheet']")
+            .forEach((node) => {
+              if (
+                node instanceof HTMLElement &&
+                node.dataset.precedence?.startsWith('vite-rsc/')
+              ) {
+                node.remove()
+              }
+            })
+        }
+        return `\
+"use client"
+import React from "react";
+export default function RemoveDuplicateServerCss() {
+  React.useEffect(() => {
+    (${removeFn.toString()})();
+  }, []);
+  return null;
+}
+`
+      },
+    ),
   ]
 }
 
@@ -1940,6 +1971,7 @@ function generateResourcesCode(depsCode: string) {
   const ResourcesFn = (
     React: typeof import('react'),
     deps: ResolvedAssetDeps,
+    RemoveDuplicateServerCss?: React.FC,
   ) => {
     return function Resources() {
       return React.createElement(React.Fragment, null, [
@@ -1960,14 +1992,29 @@ function generateResourcesCode(depsCode: string) {
             src: href,
           }),
         ),
+        RemoveDuplicateServerCss &&
+          React.createElement(RemoveDuplicateServerCss, {
+            key: 'remove-duplicate-css',
+          }),
       ])
     }
   }
 
   return `
-    import __vite_rsc_react__ from "react";
-    export const Resources = (${ResourcesFn.toString()})(__vite_rsc_react__, ${depsCode});
-  `
+import __vite_rsc_react__ from "react";
+
+${
+  config.command === 'serve'
+    ? `import RemoveDuplicateServerCss from "virtual:vite-rsc/remove-duplicate-server-css";`
+    : `const RemoveDuplicateServerCss = undefined;`
+}
+
+export const Resources = (${ResourcesFn.toString()})(
+  __vite_rsc_react__,
+  ${depsCode},
+  RemoveDuplicateServerCss,
+);
+`
 }
 
 export async function transformRscCssExport(options: {