fix(css): preserve dynamic import css code (fix #5348)

packages/playground/css-codesplit/__tests__/css-codesplit.spec.ts

@@ -1,15 +1,31 @@
 import { findAssetFile, getColor, isBuild, readManifest } from '../../testUtils'
 
-test('should load both stylesheets', async () => {
+test('should load all stylesheets', async () => {
   expect(await getColor('h1')).toBe('red')
   expect(await getColor('h2')).toBe('blue')
+  expect(await getColor('.dynamic')).toBe('green')
+})
+
+test('should load dynamic import with inline', async () => {
+  const css = await page.textContent('.dynamic-inline')
+  expect(css).toMatch('.inline')
+
+  expect(await getColor('.inline')).not.toBe('yellow')
+})
+
+test('should load dynamic import with module', async () => {
+  const css = await page.textContent('.dynamic-module')
+  expect(css).toMatch('_mod_')
+
+  expect(await getColor('.mod')).toBe('yellow')
 })
 
 if (isBuild) {
   test('should remove empty chunk', async () => {
     expect(findAssetFile(/style.*\.js$/)).toBe('')
     expect(findAssetFile('main.*.js$')).toMatch(`/* empty css`)
     expect(findAssetFile('other.*.js$')).toMatch(`/* empty css`)
+    expect(findAssetFile(/async.*\.js$/)).toBe('')
   })
 
   test('should generate correct manifest', async () => {

packages/playground/css-codesplit/async.css

@@ -0,0 +1,3 @@
+.dynamic {
+  color: green;
+}

packages/playground/css-codesplit/index.html

@@ -1,2 +1,11 @@
+<h1>This should be red</h1>
+<h2>This should be blue</h2>
+
+<p class="dynamic">This should be green</p>
+<p class="inline">This should not be yellow</p>
+<p class="dynamic-inline"></p>
+<p class="mod">This should be yellow</p>
+<p class="dynamic-module"></p>
+
 <script type="module" src="/main.js"></script>
 <div id="app"></div>

packages/playground/css-codesplit/inline.css

@@ -0,0 +1,3 @@
+.inline {
+  color: yellow;
+}

packages/playground/css-codesplit/main.js

@@ -1,6 +1,15 @@
 import './style.css'
 import './main.css'
 
-document.getElementById(
-  'app'
-).innerHTML = `<h1>This should be red</h1><h2>This should be blue</h2>`
+import('./async.css')
+
+import('./inline.css?inline').then((css) => {
+  document.querySelector('.dynamic-inline').textContent = css.default
+})
+
+import('./mod.module.css').then((css) => {
+  document.querySelector('.dynamic-module').textContent = JSON.stringify(
+    css.default
+  )
+  document.querySelector('.mod').classList.add(css.default.mod)
+})

packages/playground/css-codesplit/mod.module.css

@@ -0,0 +1,3 @@
+.mod {
+  color: yellow;
+}

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

@@ -177,11 +177,15 @@ export function buildImportAnalysisPlugin(config: ResolvedConfig): Plugin {
           continue
         }
 
-        if (dynamicIndex > -1 && insertPreload) {
+        const isDynamic = dynamicIndex > -1
+
+        if (isDynamic && insertPreload) {
           needPreloadHelper = true
-          const original = source.slice(expStart, expEnd)
-          const replacement = `${preloadMethod}(() => ${original},${isModernFlag}?"${preloadMarker}":void 0)`
-          str().overwrite(expStart, expEnd, replacement, { contentOnly: true })
+          str().prependLeft(expStart, `${preloadMethod}(() => `)
+          str().appendRight(
+            expEnd,
+            `,${isModernFlag}?"${preloadMarker}":void 0)`
+          )
         }
 
         // Differentiate CSS imports that use the default export from those that
@@ -191,12 +195,14 @@ export function buildImportAnalysisPlugin(config: ResolvedConfig): Plugin {
         if (
           specifier &&
           isCSSRequest(specifier) &&
-          source.slice(expStart, start).includes('from') &&
+          // always inject ?used query when it is a dynamic import
+          // because there is no way to check whether the default export is used
+          (source.slice(expStart, start).includes('from') || isDynamic) &&
           // edge case for package names ending with .css (e.g normalize.css)
           !(bareImportRE.test(specifier) && !specifier.includes('/'))
         ) {
           const url = specifier.replace(/\?|$/, (m) => `?used${m ? '&' : ''}`)
-          str().overwrite(start, end, dynamicIndex > -1 ? `'${url}'` : url, {
+          str().overwrite(start, end, isDynamic ? `'${url}'` : url, {
             contentOnly: true
           })
         }