fix(lib-mode): do not minify lib mode es output

Otherwise it breaks library tree-shaking
vuejs/core#2860 (comment)

Author: yyx990803

packages/vite/src/node/build.ts

@@ -306,9 +306,7 @@ export function resolveBuildPlugins(config: ResolvedConfig): {
     post: [
       buildImportAnalysisPlugin(config),
       buildEsbuildPlugin(config),
-      ...(options.minify === 'terser'
-        ? [terserPlugin(options.terserOptions)]
-        : []),
+      ...(options.minify === 'terser' ? [terserPlugin(config)] : []),
       ...(options.manifest ? [manifestPlugin(config)] : []),
       ...(options.ssrManifest ? [ssrManifestPlugin(config)] : []),
       buildReporterPlugin(config),

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

@@ -215,7 +215,13 @@ export const buildEsbuildPlugin = (config: ResolvedConfig): Plugin => {
       }
 
       const target = config.build.target
-      const minify = config.build.minify === 'esbuild'
+      const minify =
+        config.build.minify === 'esbuild' &&
+        // Do not minify ES lib output since that would remove pure annotations
+        // and break tree-shaking
+        // https://github.com/vuejs/vue-next/issues/2860#issuecomment-926882793
+        !(config.build.lib && opts.format === 'es')
+
       if ((!target || target === 'esnext') && !minify) {
         return null
       }

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

@@ -1,8 +1,9 @@
 import { Plugin } from '../plugin'
 import { Worker } from 'okie'
 import { Terser } from 'types/terser'
+import { ResolvedConfig } from '..'
 
-export function terserPlugin(options: Terser.MinifyOptions): Plugin {
+export function terserPlugin(config: ResolvedConfig): Plugin {
   const worker = new Worker(
     (basedir: string, code: string, options: Terser.MinifyOptions) => {
       // when vite is linked, the worker thread won't share the same resolve
@@ -20,9 +21,15 @@ export function terserPlugin(options: Terser.MinifyOptions): Plugin {
     name: 'vite:terser',
 
     async renderChunk(code, _chunk, outputOptions) {
+      // Do not minify ES lib output since that would remove pure annotations
+      // and break tree-shaking
+      if (config.build.lib && outputOptions.format === 'es') {
+        return null
+      }
+
       const res = await worker.run(__dirname, code, {
         safari10: true,
-        ...options,
+        ...config.build.terserOptions,
         sourceMap: !!outputOptions.sourcemap,
         module: outputOptions.format.startsWith('es'),
         toplevel: outputOptions.format === 'cjs'