feat(css): support sass compiler api and sass-embedded package

docs/config/shared-options.md

@@ -225,7 +225,7 @@ Note if an inline config is provided, Vite will not search for other PostCSS con
 
 Specify options to pass to CSS pre-processors. The file extensions are used as keys for the options. The supported options for each preprocessors can be found in their respective documentation:
 
-- `sass`/`scss` - top level option `api: "legacy" | "modern"` (default `"legacy"`) allows switching which sass API to use. [Options (legacy)](https://sass-lang.com/documentation/js-api/interfaces/LegacyStringOptions), [Options (modern)](https://sass-lang.com/documentation/js-api/interfaces/stringoptions/).
+- `sass`/`scss` - top level option `api: "legacy" | "modern" | "modern-compiler"` (default `"legacy"`) allows switching which sass API to use. For the best performance, it's recommended to use `api: "modern-compiler"` with `sass-embedded` package. [Options (legacy)](https://sass-lang.com/documentation/js-api/interfaces/LegacyStringOptions), [Options (modern)](https://sass-lang.com/documentation/js-api/interfaces/stringoptions/).
 - `less` - [Options](https://lesscss.org/usage/#less-options).
 - `styl`/`stylus` - Only [`define`](https://stylus-lang.com/docs/js.html#define-name-node) is supported, which can be passed as an object.
 
@@ -244,7 +244,7 @@ export default defineConfig({
         },
       },
       scss: {
-        api: 'modern', // or "legacy"
+        api: 'modern-compiler', // or "modern", "legacy"
         importers: [
           // ...
         ],

docs/guide/features.md

@@ -257,7 +257,7 @@ That said, Vite does provide built-in support for `.scss`, `.sass`, `.less`, `.s
 
 ```bash
 # .scss and .sass
-npm add -D sass
+npm add -D sass-embedded # or sass
 
 # .less
 npm add -D less

packages/vite/package.json

@@ -142,6 +142,7 @@
     "rollup-plugin-esbuild": "^6.1.1",
     "rollup-plugin-license": "^3.5.2",
     "sass": "^1.77.8",
+    "sass-embedded": "^1.77.8",
     "sirv": "^2.0.4",
     "source-map-support": "^0.5.21",
     "strip-ansi": "^7.1.0",
@@ -157,6 +158,7 @@
     "less": "*",
     "lightningcss": "^1.21.0",
     "sass": "*",
+    "sass-embedded": "*",
     "stylus": "*",
     "sugarss": "*",
     "terser": "^5.4.0"
@@ -168,6 +170,9 @@
     "sass": {
       "optional": true
     },
+    "sass-embedded": {
+      "optional": true
+    },
     "stylus": {
       "optional": true
     },

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

@@ -2,6 +2,7 @@ import fs from 'node:fs'
 import fsp from 'node:fs/promises'
 import path from 'node:path'
 import { createRequire } from 'node:module'
+import { fileURLToPath, pathToFileURL } from 'node:url'
 import glob from 'fast-glob'
 import postcssrc from 'postcss-load-config'
 import type {
@@ -1945,7 +1946,9 @@ type StylePreprocessorOptions = {
 }
 
 type SassStylePreprocessorOptions = StylePreprocessorOptions &
-  Omit<Sass.LegacyOptions<'async'>, 'data' | 'file' | 'outFile'>
+  Omit<Sass.LegacyOptions<'async'>, 'data' | 'file' | 'outFile'> & {
+    api?: 'legacy' | 'modern' | 'modern-compiler'
+  }
 
 type StylusStylePreprocessorOptions = StylePreprocessorOptions & {
   define?: Record<string, any>
@@ -2020,6 +2023,24 @@ function loadPreprocessorPath(
   }
 }
 
+function loadSassPackage(root: string): {
+  name: 'sass' | 'sass-embedded'
+  path: string
+} {
+  // try sass-embedded before sass
+  try {
+    const path = loadPreprocessorPath('sass-embedded' as any, root)
+    return { name: 'sass-embedded', path }
+  } catch (e1) {
+    try {
+      const path = loadPreprocessorPath('sass' as any, root)
+      return { name: 'sass', path }
+    } catch (e2) {
+      throw e1
+    }
+  }
+}
+
 let cachedSss: any
 function loadSss(root: string) {
   if (cachedSss) return cachedSss
@@ -2277,6 +2298,82 @@ const makeModernScssWorker = (
   return worker
 }
 
+// this is mostly a copy&paste of makeModernScssWorker
+// however sharing code between two is hard because
+// makeModernScssWorker above needs function inlined for worker.
+const makeModernCompilerScssWorker = (
+  resolvers: CSSAtImportResolvers,
+  alias: Alias[],
+  _maxWorkers: number | undefined,
+) => {
+  let compiler: Sass.AsyncCompiler | undefined
+
+  const worker: Awaited<ReturnType<typeof makeModernScssWorker>> = {
+    async run(sassPath, data, options) {
+      // need pathToFileURL for windows since import("D:...") fails
+      // https://github.com/nodejs/node/issues/31710
+      const sass: typeof Sass = (await import(pathToFileURL(sassPath).href))
+        .default
+      compiler ??= await sass.initAsyncCompiler()
+
+      const sassOptions = { ...options } as Sass.StringOptions<'async'>
+      sassOptions.url = pathToFileURL(options.filename)
+      sassOptions.sourceMap = options.enableSourcemap
+
+      const internalImporter: Sass.Importer<'async'> = {
+        async canonicalize(url, context) {
+          const importer = context.containingUrl
+            ? fileURLToPath(context.containingUrl)
+            : options.filename
+          const resolved = await resolvers.sass(url, cleanScssBugUrl(importer))
+          return resolved ? pathToFileURL(resolved) : null
+        },
+        async load(canonicalUrl) {
+          const ext = path.extname(canonicalUrl.pathname)
+          let syntax: Sass.Syntax = 'scss'
+          if (ext && ext.toLowerCase() === '.sass') {
+            syntax = 'indented'
+          } else if (ext && ext.toLowerCase() === '.css') {
+            syntax = 'css'
+          }
+          const result = await rebaseUrls(
+            fileURLToPath(canonicalUrl),
+            options.filename,
+            alias,
+            '$',
+            resolvers.sass,
+          )
+          const contents =
+            result.contents ??
+            (await fs.promises.readFile(result.file, 'utf-8'))
+          return { contents, syntax }
+        },
+      }
+      sassOptions.importers = [
+        ...(sassOptions.importers ?? []),
+        internalImporter,
+      ]
+
+      const result = await compiler.compileStringAsync(data, sassOptions)
+      return {
+        css: result.css,
+        map: result.sourceMap ? JSON.stringify(result.sourceMap) : undefined,
+        stats: {
+          includedFiles: result.loadedUrls
+            .filter((url) => url.protocol === 'file:')
+            .map((url) => fileURLToPath(url)),
+        },
+      } satisfies ScssWorkerResult
+    },
+    async stop() {
+      compiler?.dispose()
+      compiler = undefined
+    },
+  }
+
+  return worker
+}
+
 type ScssWorkerResult = {
   css: string
   map?: string | undefined
@@ -2295,14 +2392,19 @@ const scssProcessor = (
       }
     },
     async process(source, root, options, resolvers) {
-      const sassPath = loadPreprocessorPath(PreprocessLang.sass, root)
+      const sassPackage = loadSassPackage(root)
+      // TODO: change default in v6
+      // options.api ?? sassPackage.name === "sass-embedded" ? "modern-compiler" : "modern";
+      const api = options.api ?? 'legacy'
 
       if (!workerMap.has(options.alias)) {
         workerMap.set(
           options.alias,
-          options.api === 'modern'
-            ? makeModernScssWorker(resolvers, options.alias, maxWorkers)
-            : makeScssWorker(resolvers, options.alias, maxWorkers),
+          api === 'modern-compiler'
+            ? makeModernCompilerScssWorker(resolvers, options.alias, maxWorkers)
+            : api === 'modern'
+              ? makeModernScssWorker(resolvers, options.alias, maxWorkers)
+              : makeScssWorker(resolvers, options.alias, maxWorkers),
         )
       }
       const worker = workerMap.get(options.alias)!
@@ -2320,7 +2422,7 @@ const scssProcessor = (
       }
       try {
         const result = await worker.run(
-          sassPath,
+          sassPackage.path,
           data,
           optionsWithoutAdditionalData,
         )

playground/css/__tests__/sass-modern-compiler/sass-modern-compiler.spec.ts

@@ -0,0 +1 @@
+import '../css.spec'

playground/css/vite.config-sass-modern-compiler.js

@@ -0,0 +1,31 @@
+import { defineConfig } from 'vite'
+import baseConfig from './vite.config.js'
+
+export default defineConfig({
+  ...baseConfig,
+  css: {
+    ...baseConfig.css,
+    preprocessorOptions: {
+      ...baseConfig.css.preprocessorOptions,
+      scss: {
+        api: 'modern-compiler',
+        additionalData: `$injectedColor: orange;`,
+        importers: [
+          {
+            canonicalize(url) {
+              return url === 'virtual-dep'
+                ? new URL('custom-importer:virtual-dep')
+                : null
+            },
+            load() {
+              return {
+                contents: ``,
+                syntax: 'scss',
+              }
+            },
+          },
+        ],
+      },
+    },
+  },
+})

playground/vitestGlobalSetup.ts

@@ -47,6 +47,11 @@ export async function setup({ provide }: GlobalSetupContext): Promise<void> {
     path.resolve(tempDir, 'css__sass-modern'),
     { recursive: true },
   )
+  await fs.cp(
+    path.resolve(tempDir, 'css'),
+    path.resolve(tempDir, 'css__sass-modern-compiler'),
+    { recursive: true },
+  )
 }
 
 export async function teardown(): Promise<void> {