feat(lib)!: use package name for css output file name (#18488)

Co-authored-by: 翠 / green <green@sapphi.red>

docs/config/build-options.md

@@ -162,10 +162,28 @@ Options to pass on to [@rollup/plugin-dynamic-import-vars](https://github.com/ro
 
 ## build.lib
 
-- **Type:** `{ entry: string | string[] | { [entryAlias: string]: string }, name?: string, formats?: ('es' | 'cjs' | 'umd' | 'iife')[], fileName?: string | ((format: ModuleFormat, entryName: string) => string) }`
+- **Type:** `{ entry: string | string[] | { [entryAlias: string]: string }, name?: string, formats?: ('es' | 'cjs' | 'umd' | 'iife')[], fileName?: string | ((format: ModuleFormat, entryName: string) => string), cssFileName?: string }`
 - **Related:** [Library Mode](/guide/build#library-mode)
 
-Build as a library. `entry` is required since the library cannot use HTML as entry. `name` is the exposed global variable and is required when `formats` includes `'umd'` or `'iife'`. Default `formats` are `['es', 'umd']`, or `['es', 'cjs']`, if multiple entries are used. `fileName` is the name of the package file output, default `fileName` is the name option of package.json, it can also be defined as function taking the `format` and `entryName` as arguments.
+Build as a library. `entry` is required since the library cannot use HTML as entry. `name` is the exposed global variable and is required when `formats` includes `'umd'` or `'iife'`. Default `formats` are `['es', 'umd']`, or `['es', 'cjs']`, if multiple entries are used.
+
+`fileName` is the name of the package file output, which defaults to the `"name"` in `package.json`. It can also be defined as a function taking the `format` and `entryName` as arguments, and returning the file name.
+
+If your package imports CSS, `cssFileName` can be used to specify the name of the CSS file output. It defaults to the same value as `fileName` if it's set a string, otherwise it also falls back to the `"name"` in `package.json`.
+
+```js twoslash [vite.config.js]
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  build: {
+    lib: {
+      entry: ['src/main.js'],
+      fileName: (format, entryName) => `my-lib-${entryName}.${format}.js`,
+      cssFileName: 'my-lib-style',
+    },
+  },
+})
+```
 
 ## build.manifest
 

docs/guide/build.md

@@ -200,7 +200,12 @@ import Bar from './Bar.vue'
 export { Foo, Bar }
 ```
 
-Running `vite build` with this config uses a Rollup preset that is oriented towards shipping libraries and produces two bundle formats: `es` and `umd` (configurable via `build.lib`):
+Running `vite build` with this config uses a Rollup preset that is oriented towards shipping libraries and produces two bundle formats:
+
+- `es` and `umd` (for single entry)
+- `es` and `cjs` (for multiple entries)
+
+The formats can be configured with the [`build.lib.formats`](/config/build-options.md#build-lib) option.
 
 ```
 $ vite build
@@ -251,6 +256,29 @@ Recommended `package.json` for your lib:
 
 :::
 
+### CSS support
+
+If your library imports any CSS, it will be bundled as a single CSS file besides the built JS files, e.g. `dist/my-lib.css`. The name defaults to `build.lib.fileName`, but can also be changed with [`build.lib.cssFileName`](/config/build-options.md#build-lib).
+
+You can export the CSS file in your `package.json` to be imported by users:
+
+```json {12}
+{
+  "name": "my-lib",
+  "type": "module",
+  "files": ["dist"],
+  "main": "./dist/my-lib.umd.cjs",
+  "module": "./dist/my-lib.js",
+  "exports": {
+    ".": {
+      "import": "./dist/my-lib.js",
+      "require": "./dist/my-lib.umd.cjs"
+    },
+    "./style.css": "./dist/my-lib.css"
+  }
+}
+```
+
 ::: tip File Extensions
 If the `package.json` does not contain `"type": "module"`, Vite will generate different file extensions for Node.js compatibility. `.js` will become `.mjs` and `.cjs` will become `.js`.
 :::

docs/guide/migration.md

@@ -32,6 +32,26 @@ From Vite 6, the modern API is used by default for Sass. If you wish to still us
 
 To migrate to the modern API, see [the Sass documentation](https://sass-lang.com/documentation/breaking-changes/legacy-js-api/).
 
+### Customize CSS output file name in library mode
+
+In Vite 5, the CSS output file name in library mode was always `style.css` and cannot be easily changed through the Vite config.
+
+From Vite 6, the default file name now uses `"name"` in `package.json` similar to the JS output files. If [`build.lib.fileName`](/config/build-options.md#build-lib) is set with a string, the value will also be used for the CSS output file name. To explicitly set a different CSS file name, you can use the new [`build.lib.cssFileName`](/config/build-options.md#build-lib) to configure it.
+
+To migrate, if you had relied on the `style.css` file name, you should update references to it to the new name based on your package name. For example:
+
+```json [package.json]
+{
+  "name": "my-lib",
+  "exports": {
+    "./style.css": "./dist/style.css" // [!code --]
+    "./style.css": "./dist/my-lib.css" // [!code ++]
+  }
+}
+```
+
+If you prefer to stick with `style.css` like in Vite 5, you can set `build.lib.cssFileName: 'style'` instead.
+
 ## Advanced
 
 There are other breaking changes which only affect few users.

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

@@ -1,4 +1,5 @@
 import path from 'node:path'
+import { fileURLToPath } from 'node:url'
 import { describe, expect, test } from 'vitest'
 import { resolveConfig } from '../../config'
 import type { InlineConfig } from '../../config'
@@ -9,9 +10,12 @@ import {
   getEmptyChunkReplacer,
   hoistAtRules,
   preprocessCSS,
+  resolveLibCssFilename,
 } from '../../plugins/css'
 import { PartialEnvironment } from '../../baseEnvironment'
 
+const __dirname = path.resolve(fileURLToPath(import.meta.url), '..')
+
 describe('search css url function', () => {
   test('some spaces before it', () => {
     expect(
@@ -369,3 +373,48 @@ describe('preprocessCSS', () => {
     `)
   })
 })
+
+describe('resolveLibCssFilename', () => {
+  test('use name from package.json', () => {
+    const filename = resolveLibCssFilename(
+      {
+        entry: 'mylib.js',
+      },
+      path.resolve(__dirname, '../packages/name'),
+    )
+    expect(filename).toBe('mylib.css')
+  })
+
+  test('set cssFileName', () => {
+    const filename = resolveLibCssFilename(
+      {
+        entry: 'mylib.js',
+        cssFileName: 'style',
+      },
+      path.resolve(__dirname, '../packages/noname'),
+    )
+    expect(filename).toBe('style.css')
+  })
+
+  test('use fileName if set', () => {
+    const filename = resolveLibCssFilename(
+      {
+        entry: 'mylib.js',
+        fileName: 'custom-name',
+      },
+      path.resolve(__dirname, '../packages/name'),
+    )
+    expect(filename).toBe('custom-name.css')
+  })
+
+  test('use fileName if set and has array entry', () => {
+    const filename = resolveLibCssFilename(
+      {
+        entry: ['mylib.js', 'mylib2.js'],
+        fileName: 'custom-name',
+      },
+      path.resolve(__dirname, '../packages/name'),
+    )
+    expect(filename).toBe('custom-name.css')
+  })
+})

packages/vite/src/node/build.ts

@@ -44,6 +44,7 @@ import {
   copyDir,
   displayTime,
   emptyDir,
+  getPkgName,
   joinUrlSegments,
   normalizePath,
   partialEncodeURIPath,
@@ -296,6 +297,12 @@ export interface LibraryOptions {
    * format as an argument.
    */
   fileName?: string | ((format: ModuleFormat, entryName: string) => string)
+  /**
+   * The name of the CSS file output if the library imports CSS. Defaults to the
+   * same value as `build.lib.fileName` if it's set a string, otherwise it falls
+   * back to the name option of the project package.json.
+   */
+  cssFileName?: string
 }
 
 export type LibraryFormats = 'es' | 'cjs' | 'umd' | 'iife' | 'system'
@@ -879,10 +886,6 @@ function prepareOutDir(
   }
 }
 
-function getPkgName(name: string) {
-  return name?.[0] === '@' ? name.split('/')[1] : name
-}
-
 type JsExt = 'js' | 'cjs' | 'mjs'
 
 function resolveOutputJsExtension(

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

@@ -41,6 +41,7 @@ import {
   toOutputFilePathInCss,
   toOutputFilePathInJS,
 } from '../build'
+import type { LibraryOptions } from '../build'
 import {
   CLIENT_PUBLIC_PATH,
   CSS_LANGS_RE,
@@ -60,6 +61,7 @@ import {
   generateCodeFrame,
   getHash,
   getPackageManagerCommand,
+  getPkgName,
   injectQuery,
   isDataUrl,
   isExternalUrl,
@@ -81,6 +83,8 @@ import { PartialEnvironment } from '../baseEnvironment'
 import type { TransformPluginContext } from '../server/pluginContainer'
 import { searchForWorkspaceRoot } from '../server/searchRoot'
 import { type DevEnvironment } from '..'
+import type { PackageCache } from '../packages'
+import { findNearestPackageData } from '../packages'
 import { addToHTMLProxyTransformResult } from './html'
 import {
   assetUrlRE,
@@ -213,7 +217,7 @@ const functionCallRE = /^[A-Z_][.\w-]*\(/i
 const transformOnlyRE = /[?&]transform-only\b/
 const nonEscapedDoubleQuoteRe = /(?<!\\)"/g
 
-const cssBundleName = 'style.css'
+const defaultCssBundleName = 'style.css'
 
 const enum PreprocessLang {
   less = 'less',
@@ -256,6 +260,9 @@ export const removedPureCssFilesCache = new WeakMap<
   Map<string, RenderedChunk>
 >()
 
+// Used only if the config doesn't code-split CSS (builds a single CSS file)
+export const cssBundleNameCache = new WeakMap<ResolvedConfig, string>()
+
 const postcssConfigCache = new WeakMap<
   ResolvedConfig,
   PostCSSConfigResult | null | Promise<PostCSSConfigResult | null>
@@ -428,6 +435,7 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
   // since output formats have no effect on the generated CSS.
   let hasEmitted = false
   let chunkCSSMap: Map<string, string>
+  let cssBundleName: string
 
   const rollupOptionsOutput = config.build.rollupOptions.output
   const assetFileNames = (
@@ -464,6 +472,14 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
       hasEmitted = false
       chunkCSSMap = new Map()
       codeSplitEmitQueue = createSerialPromiseQueue()
+      cssBundleName = config.build.lib
+        ? resolveLibCssFilename(
+            config.build.lib,
+            config.root,
+            config.packageCache,
+          )
+        : defaultCssBundleName
+      cssBundleNameCache.set(config, cssBundleName)
     },
 
     async transform(css, id) {
@@ -1851,7 +1867,9 @@ async function minifyCSS(
       ...config.css?.lightningcss,
       targets: convertTargets(config.build.cssTarget),
       cssModules: undefined,
-      filename: cssBundleName,
+      // TODO: Pass actual filename here, which can also be passed to esbuild's
+      // `sourcefile` option below to improve error messages
+      filename: defaultCssBundleName,
       code: Buffer.from(css),
       minify: true,
     })
@@ -3255,3 +3273,25 @@ export const convertTargets = (
   convertTargetsCache.set(esbuildTarget, targets)
   return targets
 }
+
+export function resolveLibCssFilename(
+  libOptions: LibraryOptions,
+  root: string,
+  packageCache?: PackageCache,
+): string {
+  if (typeof libOptions.cssFileName === 'string') {
+    return `${libOptions.cssFileName}.css`
+  } else if (typeof libOptions.fileName === 'string') {
+    return `${libOptions.fileName}.css`
+  }
+
+  const packageJson = findNearestPackageData(root, packageCache)?.data
+  const name = packageJson ? getPkgName(packageJson.name) : undefined
+
+  if (!name)
+    throw new Error(
+      'Name in package.json is required if option "build.lib.cssFileName" is not provided.',
+    )
+
+  return `${name}.css`
+}

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

@@ -39,7 +39,7 @@ import {
   publicAssetUrlRE,
   urlToBuiltUrl,
 } from './asset'
-import { isCSSRequest } from './css'
+import { cssBundleNameCache, isCSSRequest } from './css'
 import { modulePreloadPolyfillId } from './modulePreloadPolyfill'
 
 interface ScriptAssetsUrl {
@@ -909,10 +909,13 @@ export function buildHtmlPlugin(config: ResolvedConfig): Plugin {
 
         // inject css link when cssCodeSplit is false
         if (!this.environment.config.build.cssCodeSplit) {
-          const cssChunk = Object.values(bundle).find(
-            (chunk) =>
-              chunk.type === 'asset' && chunk.names.includes('style.css'),
-          ) as OutputAsset | undefined
+          const cssBundleName = cssBundleNameCache.get(config)
+          const cssChunk =
+            cssBundleName &&
+            (Object.values(bundle).find(
+              (chunk) =>
+                chunk.type === 'asset' && chunk.names.includes(cssBundleName),
+            ) as OutputAsset | undefined)
           if (cssChunk) {
             result = injectToHead(result, [
               {

packages/vite/src/node/utils.ts

@@ -1314,6 +1314,10 @@ export function getNpmPackageName(importPath: string): string | null {
   }
 }
 
+export function getPkgName(name: string): string | undefined {
+  return name?.[0] === '@' ? name.split('/')[1] : name
+}
+
 const escapeRegexRE = /[-/\\^$*+?.()|[\]{}]/g
 export function escapeRegex(str: string): string {
   return str.replace(escapeRegexRE, '\\$&')

playground/lib/__tests__/lib.spec.ts

@@ -90,6 +90,44 @@ describe.runIf(isBuild)('build', () => {
     expect(iife).toMatch('process.env.NODE_ENV')
     expect(umd).toMatch('process.env.NODE_ENV')
   })
+
+  test('single entry with css', () => {
+    const css = readFile('dist/css-single-entry/test-my-lib.css')
+    const js = readFile('dist/css-single-entry/test-my-lib.js')
+    const umd = readFile('dist/css-single-entry/test-my-lib.umd.cjs')
+    expect(css).toMatch('entry-1.css')
+    expect(js).toMatch('css-entry-1')
+    expect(umd).toContain('css-entry-1')
+  })
+
+  test('multi entry with css', () => {
+    const css = readFile('dist/css-multi-entry/test-my-lib.css')
+    const js1 = readFile('dist/css-multi-entry/css-entry-1.js')
+    const js2 = readFile('dist/css-multi-entry/css-entry-2.js')
+    const cjs1 = readFile('dist/css-multi-entry/css-entry-1.cjs')
+    const cjs2 = readFile('dist/css-multi-entry/css-entry-2.cjs')
+    expect(css).toMatch('entry-1.css')
+    expect(css).toMatch('entry-2.css')
+    expect(js1).toMatch('css-entry-1')
+    expect(js2).toMatch('css-entry-2')
+    expect(cjs1).toContain('css-entry-1')
+    expect(cjs2).toContain('css-entry-2')
+  })
+
+  test('multi entry with css and code split', () => {
+    const css1 = readFile('dist/css-code-split/css-entry-1.css')
+    const css2 = readFile('dist/css-code-split/css-entry-2.css')
+    const js1 = readFile('dist/css-code-split/css-entry-1.js')
+    const js2 = readFile('dist/css-code-split/css-entry-2.js')
+    const cjs1 = readFile('dist/css-code-split/css-entry-1.cjs')
+    const cjs2 = readFile('dist/css-code-split/css-entry-2.cjs')
+    expect(css1).toMatch('entry-1.css')
+    expect(css2).toMatch('entry-2.css')
+    expect(js1).toMatch('css-entry-1')
+    expect(js2).toMatch('css-entry-2')
+    expect(cjs1).toContain('css-entry-1')
+    expect(cjs2).toContain('css-entry-2')
+  })
 })
 
 test.runIf(isServe)('dev', async () => {

playground/lib/__tests__/serve.ts

@@ -90,6 +90,24 @@ export async function serve(): Promise<{ close(): Promise<void> }> {
       configFile: path.resolve(__dirname, '../vite.named-exports.config.js'),
     })
 
+    await build({
+      root: rootDir,
+      logLevel: 'warn', // output esbuild warns
+      configFile: path.resolve(__dirname, '../vite.css-single-entry.config.js'),
+    })
+
+    await build({
+      root: rootDir,
+      logLevel: 'warn', // output esbuild warns
+      configFile: path.resolve(__dirname, '../vite.css-multi-entry.config.js'),
+    })
+
+    await build({
+      root: rootDir,
+      logLevel: 'warn', // output esbuild warns
+      configFile: path.resolve(__dirname, '../vite.css-code-split.config.js'),
+    })
+
     // start static file server
     const serve = sirv(path.resolve(rootDir, 'dist'))
     const httpServer = http.createServer((req, res) => {

playground/lib/src/css-entry-1.js

@@ -0,0 +1,3 @@
+import './entry-1.css'
+
+export default 'css-entry-1'

playground/lib/src/css-entry-2.js

@@ -0,0 +1,3 @@
+import './entry-2.css'
+
+export default 'css-entry-2'

playground/lib/src/entry-1.css

@@ -0,0 +1,3 @@
+h1 {
+  content: 'entry-1.css';
+}

playground/lib/src/entry-2.css

@@ -0,0 +1,3 @@
+h2 {
+  content: 'entry-2.css';
+}

playground/lib/vite.css-code-split.config.js

@@ -0,0 +1,16 @@
+import { fileURLToPath } from 'node:url'
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  build: {
+    cssCodeSplit: true,
+    lib: {
+      entry: [
+        fileURLToPath(new URL('src/css-entry-1.js', import.meta.url)),
+        fileURLToPath(new URL('src/css-entry-2.js', import.meta.url)),
+      ],
+      name: 'css-code-split',
+    },
+    outDir: 'dist/css-code-split',
+  },
+})

playground/lib/vite.css-multi-entry.config.js

@@ -0,0 +1,15 @@
+import { fileURLToPath } from 'node:url'
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  build: {
+    lib: {
+      entry: [
+        fileURLToPath(new URL('src/css-entry-1.js', import.meta.url)),
+        fileURLToPath(new URL('src/css-entry-2.js', import.meta.url)),
+      ],
+      name: 'css-multi-entry',
+    },
+    outDir: 'dist/css-multi-entry',
+  },
+})

playground/lib/vite.css-single-entry.config.js

@@ -0,0 +1,12 @@
+import { fileURLToPath } from 'node:url'
+import { defineConfig } from 'vite'
+
+export default defineConfig({
+  build: {
+    lib: {
+      entry: fileURLToPath(new URL('src/css-entry-1.js', import.meta.url)),
+      name: 'css-single-entry',
+    },
+    outDir: 'dist/css-single-entry',
+  },
+})