feat(css): support sass modern api

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` - [Options](https://sass-lang.com/documentation/js-api/interfaces/LegacyStringOptions).
+- `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/).
 - `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.
 
@@ -243,6 +243,12 @@ export default defineConfig({
           $specialColor: new stylus.nodes.RGBA(51, 197, 255, 1),
         },
       },
+      scss: {
+        api: 'modern', // or "legacy"
+        importers: [
+          // ...
+        ],
+      },
     },
   },
 })

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

@@ -2110,7 +2110,7 @@ const makeScssWorker = (
         // eslint-disable-next-line no-restricted-globals -- this function runs inside a cjs worker
         const sass: typeof Sass = require(sassPath)
         // eslint-disable-next-line no-restricted-globals
-        const path = require('node:path')
+        const path: typeof import('node:path') = require('node:path')
 
         // NOTE: `sass` always runs it's own importer first, and only falls back to
         // the `importer` option when it can't resolve a path
@@ -2144,11 +2144,7 @@ const makeScssWorker = (
               }
             : {}),
         }
-        return new Promise<{
-          css: string
-          map?: string | undefined
-          stats: Sass.LegacyResult['stats']
-        }>((resolve, reject) => {
+        return new Promise<ScssWorkerResult>((resolve, reject) => {
           sass.render(finalOptions, (err, res) => {
             if (err) {
               reject(err)
@@ -2179,6 +2175,114 @@ const makeScssWorker = (
   return worker
 }
 
+const makeModernScssWorker = (
+  resolvers: CSSAtImportResolvers,
+  alias: Alias[],
+  maxWorkers: number | undefined,
+) => {
+  const internalCanonicalize = async (
+    url: string,
+    importer: string,
+  ): Promise<string | null> => {
+    importer = cleanScssBugUrl(importer)
+    const resolved = await resolvers.sass(url, importer)
+    return resolved ?? null
+  }
+
+  const internalLoad = async (file: string, rootFile: string) => {
+    const result = await rebaseUrls(file, rootFile, alias, '$', resolvers.sass)
+    if (result.contents) {
+      return result.contents
+    }
+    return await fsp.readFile(result.file, 'utf-8')
+  }
+
+  const worker = new WorkerWithFallback(
+    () =>
+      async (
+        sassPath: string,
+        data: string,
+        // additionalData can a function that is not cloneable but it won't be used
+        options: SassStylePreprocessorOptions & { additionalData: undefined },
+      ) => {
+        // eslint-disable-next-line no-restricted-globals -- this function runs inside a cjs worker
+        const sass: typeof Sass = require(sassPath)
+        // eslint-disable-next-line no-restricted-globals
+        const path: typeof import('node:path') = require('node:path')
+
+        const { fileURLToPath, pathToFileURL }: typeof import('node:url') =
+          // eslint-disable-next-line no-restricted-globals
+          require('node:url')
+
+        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 internalCanonicalize(url, importer)
+            return resolved ? pathToFileURL(resolved) : null
+          },
+          async load(canonicalUrl) {
+            const ext = path.extname(canonicalUrl.pathname)
+            let syntax: Sass.Syntax = 'scss'
+            if (ext === '.sass') {
+              syntax = 'indented'
+            } else if (ext === '.css') {
+              syntax = 'css'
+            }
+            const contents = await internalLoad(
+              fileURLToPath(canonicalUrl),
+              options.filename,
+            )
+            return { contents, syntax }
+          },
+        }
+        sassOptions.importers = [
+          ...(sassOptions.importers ?? []),
+          internalImporter,
+        ]
+
+        const result = await sass.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
+      },
+    {
+      parentFunctions: {
+        internalCanonicalize,
+        internalLoad,
+      },
+      shouldUseFake(_sassPath, _data, options) {
+        // functions and importer is a function and is not serializable
+        // in that case, fallback to running in main thread
+        return !!(
+          (options.functions && Object.keys(options.functions).length > 0) ||
+          (options.importers &&
+            (!Array.isArray(options.importers) || options.importers.length > 0))
+        )
+      },
+      max: maxWorkers,
+    },
+  )
+  return worker
+}
+
+type ScssWorkerResult = {
+  css: string
+  map?: string | undefined
+  stats: Pick<Sass.LegacyResult['stats'], 'includedFiles'>
+}
+
 const scssProcessor = (
   maxWorkers: number | undefined,
 ): SassStylePreprocessor => {
@@ -2196,7 +2300,9 @@ const scssProcessor = (
       if (!workerMap.has(options.alias)) {
         workerMap.set(
           options.alias,
-          makeScssWorker(resolvers, options.alias, maxWorkers),
+          options.api === 'modern'
+            ? makeModernScssWorker(resolvers, options.alias, maxWorkers)
+            : makeScssWorker(resolvers, options.alias, maxWorkers),
         )
       }
       const worker = workerMap.get(options.alias)!
@@ -2251,7 +2357,7 @@ async function rebaseUrls(
   alias: Alias[],
   variablePrefix: string,
   resolver: ResolveFn,
-): Promise<Sass.LegacyImporterResult> {
+): Promise<{ file: string; contents?: string }> {
   file = path.resolve(file) // ensure os-specific flashes
   // in the same dir, no need to rebase
   const fileDir = path.dirname(file)
@@ -2681,7 +2787,7 @@ const createPreprocessorWorkerController = (maxWorkers: number | undefined) => {
     return scss.process(
       source,
       root,
-      { ...options, indentedSyntax: true },
+      { ...options, indentedSyntax: true, syntax: 'indented' },
       resolvers,
     )
   }

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

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

playground/css/vite.config-sass-modern.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',
+        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

@@ -40,6 +40,11 @@ export async function setup({ provide }: GlobalSetupContext): Promise<void> {
         throw error
       }
     })
+  // also setup dedicated copy for "variant" tests
+  await fs.copy(
+    path.resolve(tempDir, 'css'),
+    path.resolve(tempDir, 'css__sass-modern'),
+  )
 }
 
 export async function teardown(): Promise<void> {

playground/vitestSetup.ts

@@ -136,6 +136,15 @@ beforeAll(async (s) => {
       const testCustomRoot = resolve(testDir, 'root')
       rootDir = fs.existsSync(testCustomRoot) ? testCustomRoot : testDir
 
+      // separate rootDir for variant
+      const variantName = path.basename(dirname(testPath))
+      if (variantName !== '__tests__') {
+        const variantTestDir = testDir + '__' + variantName
+        if (fs.existsSync(variantTestDir)) {
+          rootDir = testDir = variantTestDir
+        }
+      }
+
       const testCustomServe = [
         resolve(dirname(testPath), 'serve.ts'),
         resolve(dirname(testPath), 'serve.js'),