[@vitejs/plugin-legacy] Why need regenerator-runtime when targeting IE11?

[l1shu]

Describe the bug

I found the docs says:

The associated issue is：#3362

But I don't understand why this is needed, because I found that regenerator-runtime will still be included in polyfills-legacy.xxx.js even if I don't add it with additionalLegacyPolyfills , I tried a minimal reproduction:

here is the main.js:

I use async in code, let babel useBuiltIns usage to import renerator-runtime/runtime.js

here is the vite.config.js:

Notice I do not manualy add regenerator-runtime by additionalLegacyPolyfills

and try debug in @vitejs/plugin-legacy source code:

Now run yarn build:

here the regenerator-runtime was auto-detection added by babel

and see the output polyfills-legacy.xxx.js:

I think the regenerator-runtime has been successfully added.

So I'm comfused about why the docs says should need regenerator-runtime when targeting IE11, is this a description error?

Thanks all

Reproduction

https://stackblitz.com/edit/vitejs-vite-zreonp?file=vite.config.js&terminal=dev

System Info

System:
    OS: macOS 12.3.1
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
    Memory: 64.06 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 16.14.2 - ~/.nvm/versions/node/v16.14.2/bin/node
    Yarn: 1.22.18 - ~/.nvm/versions/node/v16.14.2/bin/yarn
    npm: 8.5.0 - ~/.nvm/versions/node/v16.14.2/bin/npm
  Browsers:
    Chrome: 100.0.4896.127
    Safari: 15.4
  npmPackages:
    @vitejs/plugin-legacy: ^1.8.1 => 1.8.1 
    @vitejs/plugin-vue: ^2.3.1 => 2.3.1 
    vite: ^2.9.5 => 2.9.6

Used Package Manager

yarn

Logs

No response

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