@vitejs/plugin-legacy modernPolyfill is not affected by target/browserslist/source code

[kingyue737]

Describe the bug

I'm using plugin-legacy to add polyfill for modern browsers. However, the polyfills used are always the same no matter what target or browserslist I set.

Then I add structuredClone method in main.js. Unfortunately, web.structured-clone is not added by plugin. It seems that what method I use in source code does not affect modernPolyfills, either.

I tried both 1.8.2 and 2.0.0-alpha.1

Reproduction

https://stackblitz.com/edit/vitejs-vite-gsrtkm

System Info

System:
    OS: Windows 10 10.0.22000
    CPU: (20) x64 12th Gen Intel(R) Core(TM) i7-12700H
    Memory: 4.26 GB / 15.70 GB
  Binaries:
    Node: 16.15.0 - C:\Program Files\nodejs\node.EXE
    npm: 8.9.0 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Spartan (44.22000.120.0), Chromium (101.0.1210.47)
    Internet Explorer: 11.0.22000.120
  npmPackages:
    @vitejs/plugin-legacy: ^1.8.2 => 1.8.2
    vite: ^2.9.9 => 2.9.9

Used Package Manager

npm

Logs

vite v2.9.9 building for production...
✓ 4 modules transformed.
rendering chunks (1)...[@vitejs/plugin-legacy] modern polyfills: Set(4) {
  'core-js/modules/es.array.iterator.js',
  'core-js/modules/web.dom-collections.iterator.js',
  'core-js/modules/es.promise.js',
  'core-js/modules/es.regexp.exec.js'
}
dist/assets/favicon.17e50649.svg           1.49 KiB
dist/index.html                            0.53 KiB
dist/assets/index.e9192aae.js              0.91 KiB / gzip: 0.53 KiB
dist/assets/index.06d14ce2.css             0.17 KiB / gzip: 0.14 KiB
dist/assets/polyfills-modern.e9f39d78.js   34.19 KiB / gzip: 14.12 KiB

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to https://github.com/vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[sapphi-red]

About browserslist, it is tracked at #2476.
modernPolyfills not including structuredClone polyfill is a bug.

[kingyue737]

@sapphi-red Not only browserslist, even explicitly changing targets in plugin-legacy config does not affect polyfills-modern included

[sapphi-red]

That is documented here.
https://github.com/vitejs/vite/tree/main/packages/plugin-legacy#modernpolyfills:~:text=targeting%20browsers%20with%20native%20ESM%20support

For that feature request, it is tracked at #6922.

[kingyue737]

Ah I see. Currently, modernpolyfills always targets to all browsers supporting ESM, no matter what targets are set. Thank you!