Version

3.0.0-rc.3

Reproduction link

https://github.com/cristianl/repro-vue-cli-usebuiltins

Steps to reproduce

In the repro directory, run node_modules/.bin/vue-cli-service build --modern.

The reproduction repo is a vue-cli generated project with the default settings, and only this function definition added to main.js, so Babel detects usage of Promise:

function fakePromise() {
  return Promise.all()
}

What is expected?

The vendors bundle generated for modern mode should not get polyfills of ES2015 features already supported by the browsers it targets.

What is actually happening?

Babel is automatically applying polyfills even for the modern build (in this case, polyfills for Promise, detected in main.js).

It's fixed by setting useBuiltIns: false when process.env.VUE_CLI_MODERN_BUILD is true.

It may also be a bug in babel-preset-env (when the target is esmodules, should it apply ES2015 polyfills?)