fix: lightningcss fails with html-proxy

packages/vite/src/node/plugins/css.ts

@@ -2183,6 +2183,10 @@ async function compileLightningCSS(
             if (filePath === filename) {
               return src
             }
+            // This happens with html-proxy (#13776)
+            if (!filePath.endsWith('.css')) {
+              return src
+            }
             return fs.readFileSync(toAbsolute(filePath), 'utf-8')
           },
           async resolve(id, from) {

playground/css-lightningcss-proxy/__tests__/css-lightningcss-proxy.spec.ts

@@ -0,0 +1,13 @@
+import { describe, expect, test } from 'vitest'
+import { port } from './serve'
+import { getColor, page } from '~utils'
+
+const url = `http://localhost:${port}`
+
+describe('injected inline style', () => {
+  test('injected inline style is present', async () => {
+    await page.goto(url)
+    const el = await page.$('.ssr-proxy')
+    expect(await getColor(el)).toBe('coral')
+  })
+})

playground/css-lightningcss-proxy/__tests__/serve.ts

@@ -0,0 +1,38 @@
+// this is automatically detected by playground/vitestSetup.ts and will replace
+// the default e2e test serve behavior
+
+import path from 'node:path'
+import kill from 'kill-port'
+import { hmrPorts, ports, rootDir } from '~utils'
+
+export const port = ports['css/lightningcss-proxy']
+
+export async function serve(): Promise<{ close(): Promise<void> }> {
+  await kill(port)
+
+  const { createServer } = await import(path.resolve(rootDir, 'server.js'))
+  const { app, vite } = await createServer(
+    rootDir,
+    hmrPorts['css/lightningcss-proxy'],
+  )
+
+  return new Promise((resolve, reject) => {
+    try {
+      const server = app.listen(port, () => {
+        resolve({
+          // for test teardown
+          async close() {
+            await new Promise((resolve) => {
+              server.close(resolve)
+            })
+            if (vite) {
+              await vite.close()
+            }
+          },
+        })
+      })
+    } catch (e) {
+      reject(e)
+    }
+  })
+}

playground/css-lightningcss-proxy/index.html

@@ -0,0 +1,5 @@
+<!--[inline-css]-->
+<div class="wrapper">
+  <p>Injected inline style with SSR Proxy</p>
+  <p class="ssr-proxy">This should be coral</p>
+</div>

playground/css-lightningcss-proxy/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "@vitejs/test-css-lightningcss-proxy",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "node server",
+    "serve": "NODE_ENV=production node server",
+    "debug": "node --inspect-brk server",
+    "preview": "vite preview"
+  },
+  "devDependencies": {
+    "lightningcss": "^1.21.5",
+    "express": "^4.18.2"
+  }
+}

playground/css-lightningcss-proxy/server.js

@@ -0,0 +1,89 @@
+import fs from 'node:fs'
+import path from 'node:path'
+import { fileURLToPath } from 'node:url'
+import express from 'express'
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
+const isTest = process.env.VITEST
+
+const DYNAMIC_STYLES = `
+  <style>
+  .ssr-proxy {
+    color: coral;
+  }
+  </style>
+`
+
+export async function createServer(root = process.cwd(), hmrPort) {
+  const resolve = (p) => path.resolve(__dirname, p)
+
+  const app = express()
+
+  /**
+   * @type {import('vite').ViteDevServer}
+   */
+  const vite = await (
+    await import('vite')
+  ).createServer({
+    root,
+    logLevel: isTest ? 'error' : 'info',
+    css: {
+      transformer: 'lightningcss',
+      lightningcss: {
+        drafts: { nesting: true },
+      },
+    },
+    server: {
+      middlewareMode: true,
+      watch: {
+        // During tests we edit the files too fast and sometimes chokidar
+        // misses change events, so enforce polling for consistency
+        usePolling: true,
+        interval: 100,
+      },
+      hmr: {
+        port: hmrPort,
+      },
+    },
+    appType: 'custom',
+  })
+  // use vite's connect instance as middleware
+  app.use(vite.middlewares)
+
+  app.use('*', async (req, res, next) => {
+    try {
+      let [url] = req.originalUrl.split('?')
+      if (url.endsWith('/')) url += 'index.html'
+
+      if (url.startsWith('/favicon.ico')) {
+        return res.status(404).end('404')
+      }
+
+      const htmlLoc = resolve(`.${url}`)
+      let template = fs.readFileSync(htmlLoc, 'utf-8')
+
+      template = template.replace('<!--[inline-css]-->', DYNAMIC_STYLES)
+
+      // Force calling transformIndexHtml with url === '/', to simulate
+      // usage by ecosystem that was recommended in the SSR documentation
+      // as `const url = req.originalUrl`
+      const html = await vite.transformIndexHtml('/', template)
+
+      res.status(200).set({ 'Content-Type': 'text/html' }).end(html)
+    } catch (e) {
+      vite && vite.ssrFixStacktrace(e)
+      console.log(e.stack)
+      res.status(500).end(e.stack)
+    }
+  })
+
+  return { app, vite }
+}
+
+if (!isTest) {
+  createServer().then(({ app }) =>
+    app.listen(5173, () => {
+      console.log('http://localhost:5173')
+    }),
+  )
+}

playground/test-utils.ts

@@ -35,6 +35,7 @@ export const ports = {
   'css/postcss-caching': 5005,
   'css/postcss-plugins-different-dir': 5006,
   'css/dynamic-import': 5007,
+  'css/lightningcss-proxy': 5008,
 }
 export const hmrPorts = {
   'optimize-missing-deps': 24680,
@@ -43,6 +44,7 @@ export const hmrPorts = {
   'ssr-html': 24683,
   'ssr-noexternal': 24684,
   'ssr-pug': 24685,
+  'css/lightningcss-proxy': 24686,
 }
 
 const hexToNameMap: Record<string, string> = {}