From 5508dbbeb05c0815758d3ae846c89e6a774a97a0 Mon Sep 17 00:00:00 2001
From: Nihal Gonsalves <nihal@nihalgonsalves.com>
Date: Mon, 17 May 2021 16:13:21 +0200
Subject: [PATCH] fix(plugin-legacy): turn off babel loose mode (#3406)

---
 packages/playground/legacy/__tests__/legacy.spec.ts | 5 +++++
 packages/playground/legacy/index.html               | 1 +
 packages/playground/legacy/main.js                  | 6 ++++++
 packages/plugin-legacy/index.js                     | 2 +-
 4 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/packages/playground/legacy/__tests__/legacy.spec.ts b/packages/playground/legacy/__tests__/legacy.spec.ts
index aff02741711964..0a9a214808c666 100644
--- a/packages/playground/legacy/__tests__/legacy.spec.ts
+++ b/packages/playground/legacy/__tests__/legacy.spec.ts
@@ -7,3 +7,8 @@ test('should work', async () => {
 test('import.meta.env.LEGACY', async () => {
   expect(await page.textContent('#env')).toMatch(isBuild ? 'true' : 'false')
 })
+
+// https://github.com/vitejs/vite/issues/3400
+test('transpiles down iterators correctly', async () => {
+  expect(await page.textContent('#iterators')).toMatch('hello')
+})
diff --git a/packages/playground/legacy/index.html b/packages/playground/legacy/index.html
index aef4bccfc61f74..b2e2c85155799f 100644
--- a/packages/playground/legacy/index.html
+++ b/packages/playground/legacy/index.html
@@ -1,3 +1,4 @@
 <h1 id="app"></h1>
 <div id="env"></div>
+<div id="iterators"></div>
 <script type="module" src="./main.js"></script>
diff --git a/packages/playground/legacy/main.js b/packages/playground/legacy/main.js
index 631f589eb541d8..18db0a9b7b84c7 100644
--- a/packages/playground/legacy/main.js
+++ b/packages/playground/legacy/main.js
@@ -15,3 +15,9 @@ if (import.meta.env.LEGACY) {
 }
 
 document.getElementById('env').textContent = `is legacy: ${isLegacy}`
+
+// Iterators
+
+document.getElementById('iterators').textContent = [...new Set(['hello'])].join(
+  ''
+)
diff --git a/packages/plugin-legacy/index.js b/packages/plugin-legacy/index.js
index 1b449c963dda4f..cb21e5f63ec42a 100644
--- a/packages/plugin-legacy/index.js
+++ b/packages/plugin-legacy/index.js
@@ -263,7 +263,7 @@ function viteLegacyPlugin(options = {}) {
               targets,
               modules: false,
               bugfixes: true,
-              loose: true,
+              loose: false,
               useBuiltIns: needPolyfills ? 'usage' : false,
               corejs: needPolyfills
                 ? { version: 3, proposals: false }