fix: do not include css string in bundle if not needed

This reduces bundle size when using esbuild as minifier.

Author: yyx990803

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

@@ -88,6 +88,7 @@ const cssModuleRE = new RegExp(`\\.module${cssLangs}`)
 const directRequestRE = /(\?|&)direct\b/
 const commonjsProxyRE = /\?commonjs-proxy/
 const inlineRE = /(\?|&)inline\b/
+const usedRE = /(\?|&)used\b/
 
 const enum PreprocessLang {
   less = 'less',
@@ -315,7 +316,11 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
       }
 
       return {
-        code: modulesCode || `export default ${JSON.stringify(css)}`,
+        code:
+          modulesCode ||
+          (usedRE.test(id)
+            ? `export default ${JSON.stringify(css)}`
+            : `export default ''`),
         map: { mappings: '' },
         // avoid the css module from being tree-shaken so that we can retrieve
         // it in renderChunk()

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

@@ -4,8 +4,13 @@ import { Plugin } from '../plugin'
 import MagicString from 'magic-string'
 import { ImportSpecifier, init, parse as parseImports } from 'es-module-lexer'
 import { OutputChunk } from 'rollup'
-import { chunkToEmittedCssFileMap, removedPureCssFilesCache } from './css'
+import {
+  chunkToEmittedCssFileMap,
+  isCSSRequest,
+  removedPureCssFilesCache
+} from './css'
 import { transformImportGlob } from '../importGlob'
+import { bareImportRE } from '../utils'
 
 /**
  * A flag for injected helpers. This flag will be set to `false` if the output
@@ -116,7 +121,7 @@ export function buildImportAnalysisPlugin(config: ResolvedConfig): Plugin {
       let imports: readonly ImportSpecifier[] = []
       try {
         imports = parseImports(source)[0]
-      } catch (e) {
+      } catch (e: any) {
         this.error(e, e.idx)
       }
 
@@ -133,15 +138,15 @@ export function buildImportAnalysisPlugin(config: ResolvedConfig): Plugin {
           s: start,
           e: end,
           ss: expStart,
+          n: specifier,
           d: dynamicIndex
         } = imports[index]
 
-        const isGlob =
+        // import.meta.glob
+        if (
           source.slice(start, end) === 'import.meta' &&
           source.slice(end, end + 5) === '.glob'
-
-        // import.meta.glob
-        if (isGlob) {
+        ) {
           const { importsString, exp, endIndex, isEager } =
             await transformImportGlob(
               source,
@@ -167,6 +172,21 @@ export function buildImportAnalysisPlugin(config: ResolvedConfig): Plugin {
           const replacement = `${preloadMethod}(() => ${original},${isModernFlag}?"${preloadMarker}":void 0)`
           str().overwrite(dynamicIndex, dynamicEnd, replacement)
         }
+
+        // Differentiate CSS imports that use the default export from those that
+        // do not by injecting a ?used query - this allows us to avoid including
+        // the CSS string when unnecessary (esbuild has trouble treeshaking
+        // them)
+        if (
+          specifier &&
+          isCSSRequest(specifier) &&
+          source.slice(expStart, start).includes('from') &&
+          // edge case for package names ending with .css (e.g normalize.css)
+          !(bareImportRE.test(specifier) && !specifier.includes('/'))
+        ) {
+          const url = specifier.replace(/\?|$/, (m) => `?used${m ? '&' : ''}`)
+          str().overwrite(start, end, dynamicIndex > -1 ? `'${url}'` : url)
+        }
       }
 
       if (
@@ -225,7 +245,7 @@ export function buildImportAnalysisPlugin(config: ResolvedConfig): Plugin {
           let imports: ImportSpecifier[]
           try {
             imports = parseImports(code)[0].filter((i) => i.d > -1)
-          } catch (e) {
+          } catch (e: any) {
             this.error(e, e.idx)
           }