fix(css): missing css in lib mode (#10185)

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

@@ -563,7 +563,7 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
           // the legacy build should avoid inserting entry CSS modules here, they
           // will be collected into `chunk.viteMetadata.importedCss` and injected
           // later by the `'vite:build-html'` plugin into the `index.html`
-          if (chunk.isEntry) {
+          if (chunk.isEntry && !config.build.lib) {
             return null
           }
           chunkCSS = await finalizeCss(chunkCSS, true, config)

playground/vue-lib/__tests__/vue-lib.spec.ts

@@ -22,4 +22,15 @@ describe('vue component library', () => {
     expect(code).toContain('styleA') // styleA is used by CompA
     expect(code).not.toContain('styleB') // styleB is not used
   })
+
+  test('should inject css when cssCodeSplit = true', async () => {
+    // Build lib
+    const { output } = (
+      await build({
+        logLevel: 'silent',
+        configFile: path.resolve(__dirname, '../vite.config.lib-css.ts')
+      })
+    )[0]
+    expect(output[0].code).toContain('.card{padding:4rem}')
+  })
 })

playground/vue-lib/package.json

@@ -5,6 +5,7 @@
   "scripts": {
     "dev-consumer": "vite --config ./vite.config.consumer.ts",
     "build-lib": "vite build --config ./vite.config.lib.ts",
+    "build-lib-css": "vite build --config ./vite.config.lib-css.ts",
     "build-consumer": "vite build --config ./vite.config.consumer.ts"
   },
   "dependencies": {

playground/vue-lib/src-lib-css/index.css

@@ -0,0 +1,3 @@
+.card {
+  padding: 4rem;
+}

playground/vue-lib/src-lib-css/index.ts

@@ -0,0 +1,3 @@
+import './index.css'
+
+export function setup() {}

playground/vue-lib/vite.config.lib-css.ts

@@ -0,0 +1,16 @@
+import path from 'node:path'
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  root: __dirname,
+  build: {
+    outDir: 'dist/lib',
+    cssCodeSplit: true,
+    lib: {
+      entry: path.resolve(__dirname, 'src-lib-css/index.ts'),
+      name: 'index',
+      formats: ['umd'],
+      fileName: 'index.js'
+    }
+  }
+})