fix: inject esbuild helpers in IIFE and UMD wrappers

packages/playground/lib/__tests__/lib.spec.ts

@@ -9,10 +9,22 @@ if (isBuild) {
 
   test('umd', async () => {
     expect(await page.textContent('.umd')).toBe('It works')
+    const code = fs.readFileSync(
+      path.join(testDir, 'dist/my-lib-custom-filename.umd.js'),
+      'utf-8'
+    )
+    // esbuild helpers are injected inside of the UMD wrapper
+    expect(code).toMatch(/^\(function\(/)
   })
 
   test('iife', async () => {
     expect(await page.textContent('.iife')).toBe('It works')
+    const code = fs.readFileSync(
+      path.join(testDir, 'dist/my-lib-custom-filename.iife.js'),
+      'utf-8'
+    )
+    // esbuild helpers are injected inside of the IIFE wrapper
+    expect(code).toMatch(/^var MyLib=function\(\){"use strict";/)
   })
 
   test('Library mode does not include `preload`', async () => {

packages/playground/lib/src/main.js

@@ -1,3 +1,6 @@
 export default function myLib(sel) {
+  // Force esbuild spread helpers (https://github.com/evanw/esbuild/issues/951)
+  console.log({ ...'foo' })
+
   document.querySelector(sel).textContent = 'It works'
 }

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

@@ -26,6 +26,11 @@ import { searchForWorkspaceRoot } from '..'
 
 const debug = createDebugger('vite:esbuild')
 
+const INJECT_HELPERS_IIFE_RE =
+  /(.*)(var [^\s]+=function\(.*\){"use strict";)(.*)/
+const INJECT_HELPERS_UMD_RE =
+  /(.*)(\(function\(.*\){.+amd.+function\(.*\){"use strict";)(.*)/
+
 let server: ViteDevServer
 
 export interface ESBuildOptions extends TransformOptions {
@@ -254,6 +259,26 @@ export const buildEsbuildPlugin = (config: ResolvedConfig): Plugin => {
             }
           : undefined)
       })
+
+      if (config.build.lib) {
+        // #7188, esbuild adds helpers out of the UMD and IIFE wrappers, and the
+        // names are minified potentially causing collision with other globals.
+        // We use a regex to inject the helpers inside the wrappers.
+        // We don't need to create a MagicString here because both the helpers and
+        // the headers don't modify the sourcemap
+        const injectHelpers =
+          opts.format === 'umd'
+            ? INJECT_HELPERS_UMD_RE
+            : opts.format === 'iife'
+            ? INJECT_HELPERS_IIFE_RE
+            : undefined
+        if (injectHelpers) {
+          res.code = res.code.replace(
+            injectHelpers,
+            (_, helpers, header, rest) => header + helpers + rest
+          )
+        }
+      }
       return res
     }
   }