fix(css): avoid generating empty JS files when JS files becomes empty…

… but has CSS files imported (#16078)

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

@@ -549,6 +549,8 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
 
     async renderChunk(code, chunk, opts) {
       let chunkCSS = ''
+      // the chunk is empty if it's a dynamic entry chunk that only contains a CSS import
+      const isJsChunkEmpty = code === '' && !chunk.isEntry
       let isPureCssChunk = true
       const ids = Object.keys(chunk.modules)
       for (const id of ids) {
@@ -561,7 +563,7 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
               isPureCssChunk = false
             }
           }
-        } else {
+        } else if (!isJsChunkEmpty) {
           // if the module does not have a style, then it's not a pure css chunk.
           // this is true because in the `transform` hook above, only modules
           // that are css gets added to the `styles` map.
@@ -723,13 +725,13 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
       }
 
       if (chunkCSS) {
+        if (isPureCssChunk && (opts.format === 'es' || opts.format === 'cjs')) {
+          // this is a shared CSS-only chunk that is empty.
+          pureCssChunks.add(chunk)
+        }
+
         if (config.build.cssCodeSplit) {
           if (opts.format === 'es' || opts.format === 'cjs') {
-            if (isPureCssChunk) {
-              // this is a shared CSS-only chunk that is empty.
-              pureCssChunks.add(chunk)
-            }
-
             const isEntry = chunk.isEntry && isPureCssChunk
             const cssFullAssetName = ensureFileExt(chunk.name, '.css')
             // if facadeModuleId doesn't exist or doesn't have a CSS extension,
@@ -837,6 +839,40 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
         return
       }
 
+      function extractCss() {
+        let css = ''
+        const collected = new Set<OutputChunk>()
+        const prelimaryNameToChunkMap = new Map(
+          Object.values(bundle)
+            .filter((chunk): chunk is OutputChunk => chunk.type === 'chunk')
+            .map((chunk) => [chunk.preliminaryFileName, chunk]),
+        )
+
+        function collect(fileName: string) {
+          const chunk = bundle[fileName]
+          if (!chunk || chunk.type !== 'chunk' || collected.has(chunk)) return
+          collected.add(chunk)
+
+          chunk.imports.forEach(collect)
+          css += chunkCSSMap.get(chunk.preliminaryFileName) ?? ''
+        }
+
+        for (const chunkName of chunkCSSMap.keys())
+          collect(prelimaryNameToChunkMap.get(chunkName)?.fileName ?? '')
+
+        return css
+      }
+      let extractedCss = !hasEmitted && extractCss()
+      if (extractedCss) {
+        hasEmitted = true
+        extractedCss = await finalizeCss(extractedCss, true, config)
+        this.emitFile({
+          name: cssBundleName,
+          type: 'asset',
+          source: extractedCss,
+        })
+      }
+
       // remove empty css chunks and their imports
       if (pureCssChunks.size) {
         // map each pure css chunk (rendered chunk) to it's corresponding bundle
@@ -893,40 +929,6 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
           delete bundle[`${fileName}.map`]
         })
       }
-
-      function extractCss() {
-        let css = ''
-        const collected = new Set<OutputChunk>()
-        const prelimaryNameToChunkMap = new Map(
-          Object.values(bundle)
-            .filter((chunk): chunk is OutputChunk => chunk.type === 'chunk')
-            .map((chunk) => [chunk.preliminaryFileName, chunk]),
-        )
-
-        function collect(fileName: string) {
-          const chunk = bundle[fileName]
-          if (!chunk || chunk.type !== 'chunk' || collected.has(chunk)) return
-          collected.add(chunk)
-
-          chunk.imports.forEach(collect)
-          css += chunkCSSMap.get(chunk.preliminaryFileName) ?? ''
-        }
-
-        for (const chunkName of chunkCSSMap.keys())
-          collect(prelimaryNameToChunkMap.get(chunkName)?.fileName ?? '')
-
-        return css
-      }
-      let extractedCss = !hasEmitted && extractCss()
-      if (extractedCss) {
-        hasEmitted = true
-        extractedCss = await finalizeCss(extractedCss, true, config)
-        this.emitFile({
-          name: cssBundleName,
-          type: 'asset',
-          source: extractedCss,
-        })
-      }
     },
   }
 }

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

@@ -3,6 +3,7 @@ import {
   findAssetFile,
   getColor,
   isBuild,
+  listAssets,
   page,
   readManifest,
   untilUpdated,
@@ -12,6 +13,7 @@ test('should load all stylesheets', async () => {
   expect(await getColor('h1')).toBe('red')
   expect(await getColor('h2')).toBe('blue')
   expect(await getColor('.dynamic')).toBe('green')
+  expect(await getColor('.async-js')).toBe('blue')
   expect(await getColor('.chunk')).toBe('magenta')
 })
 
@@ -40,7 +42,12 @@ describe.runIf(isBuild)('build', () => {
     expect(findAssetFile(/style-.*\.js$/)).toBe('')
     expect(findAssetFile('main.*.js$')).toMatch(`/* empty css`)
     expect(findAssetFile('other.*.js$')).toMatch(`/* empty css`)
-    expect(findAssetFile(/async.*\.js$/)).toBe('')
+    expect(findAssetFile(/async-[-\w]{8}\.js$/)).toBe('')
+
+    const assets = listAssets()
+    expect(assets).not.toContainEqual(
+      expect.stringMatching(/async-js-[-\w]{8}\.js$/),
+    )
   })
 
   test('should remove empty chunk, HTML without JS', async () => {

playground/css-codesplit/async-js.css

@@ -0,0 +1,3 @@
+.async-js {
+  color: blue;
+}

playground/css-codesplit/async-js.js

@@ -0,0 +1,2 @@
+// a JS file that becomes an empty file but imports CSS files
+import './async-js.css'

playground/css-codesplit/index.html

@@ -2,6 +2,7 @@ <h1>This should be red</h1>
 <h2>This should be blue</h2>
 
 <p class="dynamic">This should be green</p>
+<p class="async-js">This should be blue</p>
 <p class="inline">This should not be yellow</p>
 <p class="dynamic-inline"></p>
 <p class="mod">This should be yellow</p>

playground/css-codesplit/main.js

@@ -9,6 +9,7 @@ import chunkCssUrl from './chunk.css?url'
 globalThis.__test_chunkCssUrl = chunkCssUrl
 
 import('./async.css')
+import('./async-js')
 
 import('./inline.css?inline').then((css) => {
   document.querySelector('.dynamic-inline').textContent = css.default

playground/css-no-codesplit/__tests__/css-no-codesplit.spec.ts

@@ -0,0 +1,17 @@
+import { describe, expect, test } from 'vitest'
+import { expectWithRetry, getColor, isBuild, listAssets } from '~utils'
+
+test('should load all stylesheets', async () => {
+  expect(await getColor('.shared-linked')).toBe('blue')
+  await expectWithRetry(() => getColor('.async-js')).toBe('blue')
+})
+
+describe.runIf(isBuild)('build', () => {
+  test('should remove empty chunk', async () => {
+    const assets = listAssets()
+    expect(assets).not.toContainEqual(
+      expect.stringMatching(/shared-linked-.*\.js$/),
+    )
+    expect(assets).not.toContainEqual(expect.stringMatching(/async-js-.*\.js$/))
+  })
+})

playground/css-no-codesplit/async-js.css

@@ -0,0 +1,3 @@
+.async-js {
+  color: blue;
+}

playground/css-no-codesplit/async-js.js

@@ -0,0 +1,2 @@
+// a JS file that becomes an empty file but imports CSS files
+import './async-js.css'

playground/css-no-codesplit/index.html

@@ -0,0 +1,5 @@
+<link rel="stylesheet" href="./shared-linked.css" />
+<script type="module" src="./index.js"></script>
+
+<p class="shared-linked">shared linked: this should be blue</p>
+<p class="async-js">async JS importing CSS: this should be blue</p>

playground/css-no-codesplit/index.js

@@ -0,0 +1 @@
+import('./async-js')

playground/css-no-codesplit/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "@vitejs/test-css-no-codesplit",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vite build",
+    "debug": "node --inspect-brk ../../packages/vite/bin/vite",
+    "preview": "vite preview"
+  }
+}

playground/css-no-codesplit/shared-linked.css

@@ -0,0 +1,3 @@
+.shared-linked {
+  color: blue;
+}

playground/css-no-codesplit/sub.html

@@ -0,0 +1 @@
+<link rel="stylesheet" href="./shared-linked.css" />

playground/css-no-codesplit/vite.config.js

@@ -0,0 +1,14 @@
+import { resolve } from 'node:path'
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  build: {
+    cssCodeSplit: false,
+    rollupOptions: {
+      input: {
+        index: resolve(__dirname, './index.html'),
+        sub: resolve(__dirname, './sub.html'),
+      },
+    },
+  },
+})