feat(css): support resolving stylesheets via export conditions

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

@@ -695,8 +695,10 @@ function createCSSResolvers(config: ResolvedConfig): CSSAtImportResolvers {
         (cssResolve = config.createResolver({
           extensions: ['.css'],
           mainFields: ['style'],
+          conditions: ['style'],
           tryIndex: false,
-          preferRelative: true
+          preferRelative: true,
+          isUnsafeExport: true
         }))
       )
     },
@@ -707,9 +709,11 @@ function createCSSResolvers(config: ResolvedConfig): CSSAtImportResolvers {
         (sassResolve = config.createResolver({
           extensions: ['.scss', '.sass', '.css'],
           mainFields: ['sass', 'style'],
+          conditions: ['sass', 'style'],
           tryIndex: true,
           tryPrefix: '_',
-          preferRelative: true
+          preferRelative: true,
+          isUnsafeExport: true
         }))
       )
     },
@@ -720,8 +724,10 @@ function createCSSResolvers(config: ResolvedConfig): CSSAtImportResolvers {
         (lessResolve = config.createResolver({
           extensions: ['.less', '.css'],
           mainFields: ['less', 'style'],
+          conditions: ['less', 'style'],
           tryIndex: false,
-          preferRelative: true
+          preferRelative: true,
+          isUnsafeExport: true
         }))
       )
     }

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

@@ -92,6 +92,8 @@ export interface InternalResolveOptions extends Required<ResolveOptions> {
   skipPackageJson?: boolean
   preferRelative?: boolean
   isRequire?: boolean
+  // When true, the export resolver should opt out of Node's default resolution conditions
+  isUnsafeExport?: boolean
   // #3040
   // when the importer is a ts module,
   // if the specifier requests a non-existent `.js/jsx/mjs/cjs` file,
@@ -1014,7 +1016,7 @@ function resolveExports(
   targetWeb: boolean
 ) {
   const conditions = [options.isProduction ? 'production' : 'development']
-  if (!options.isRequire) {
+  if (!options.isRequire && !options.isUnsafeExport) {
     conditions.push('module')
   }
   if (options.conditions.length > 0) {
@@ -1024,6 +1026,7 @@ function resolveExports(
   return _resolveExports(pkg, key, {
     browser: targetWeb && !conditions.includes('node'),
     require: options.isRequire && !conditions.includes('import'),
+    unsafe: options.isUnsafeExport,
     conditions
   })
 }

playground/css/__tests__/css.spec.ts

@@ -277,6 +277,14 @@ test('@import dependency w/ stylus entry', async () => {
   expect(await getColor('.css-dep-stylus')).toBe('red')
 })
 
+test('@import dependency w/ style export mapping', async () => {
+  expect(await getColor('.css-dep-exports')).toBe('purple')
+})
+
+test('@import dependency w/ sass export mapping', async () => {
+  expect(await getColor('.css-dep-exports-sass')).toBe('orange')
+})
+
 test('@import dependency w/out package scss', async () => {
   expect(await getColor('.sass-dep')).toBe('lavender')
 })

playground/css/css-dep-exports/index.js

@@ -0,0 +1 @@
+throw new Error('should not be imported')

playground/css/css-dep-exports/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "css-dep-exports",
+  "private": true,
+  "version": "1.0.0",
+  "exports": {
+    ".": {
+      "import": "./index.js",
+      "sass": "./style.scss",
+      "style": "./style.css"
+    },
+    "./package.json": "./package.json"
+  }
+}

playground/css/css-dep-exports/style.css

@@ -0,0 +1,3 @@
+.css-dep-exports {
+  color: purple;
+}

playground/css/css-dep-exports/style.scss

@@ -0,0 +1,3 @@
+.css-dep-exports-sass {
+  color: orange;
+}

playground/css/dep.css

@@ -1 +1,2 @@
 @import 'css-dep';
+@import 'css-dep-exports';

playground/css/index.html

@@ -126,6 +126,13 @@ <h1>CSS</h1>
     @import dependency w/ styl entrypoints: this should be red
   </p>
 
+  <p class="css-dep-exports">
+    @import dependency w/ style export mapping: this should be purple
+  </p>
+  <p class="css-dep-exports-sass">
+    @import dependency w/ sass export mapping: this should be orange
+  </p>
+
   <p class="dir-dep">PostCSS dir-dependency: this should be grey</p>
   <p class="dir-dep-2">
     PostCSS dir-dependency (file 2): this should be grey too

playground/css/sass.scss

@@ -1,6 +1,7 @@
 @import '@/nested'; // alias + custom index resolving -> /nested/_index.scss
 @import '@/nested/partial'; // sass convention: omitting leading _ for partials
 @import 'css-dep'; // package w/ sass entry points
+@import 'css-dep-exports'; // package with a sass export mapping
 @import 'virtual-dep'; // virtual file added through importer
 @import '@/pkg-dep'; // package w/out sass field
 @import '@/weapp.wxss'; // wxss file