Terser rewrites private fields instead of throwing a parser error

[TimvdLippe]

Bug report or Feature request?

Bug

Version (complete output of terser -V or specific git commit)
The version of https://try.terser.org/ (I am assuming latest, but the website doesn't show me what version it is running)

Complete CLI command or minify() options used

{
  module: true,
  compress: {},
  mangle: {},
  output: {},
  parse: {},
  rename: {},
}

terser input

export const myObject = {
  foo: 'bar',
  #something: 5,
}

terser output or error

export const myObject={foo:"bar",something:5};

Expected result
Terser should error on this, as you can't use private fields in an object. However, terser rewrites it to a regular object field which is legal syntax. So even though the input is illegal JavaScript, if users don't catch this issue, terser rewrites it to legal syntax and leading to incorrect code. Therefore, if users don't check their code in any other way, running the terser output will result in runtime errors.

[fabiosantoscode]

Usually Terser doesn't check for valid syntax on purpose, but admittedly this isn't good behaviour. It can cause confusion.