Handling process.env.SOME_UNDEFINED_KEY as undefined with DefinePlugin

[whatasoda]

Bug report

What is the current behavior?
If I configure DefinePlugin with 'process.env': {...} format, some env variables which is not specified to the plugin is replaced with { /* full content of process.env I specified */ }.SOME_UNDEFINED_KEY, though the evaluated value is obviously undefined.
It'll affect bundle file size if I forget specifying some env variables, or if dependencies of my project use their custom env variables like SC_ATTR of styled-components.
I know 'process.env.SOME_ENV_VAR_NAME': ... format is recommended. But I sometimes use destructuring assignment with process.env and I don't want to give up doing that because of its convenience.

If the current behavior is a bug, please provide the steps to reproduce.

Here is the repo to reproduce the issue.
https://github.com/whatasoda/webpack-define-plugin-report

webpack.config.js

const TerserPlugin = require('terser-webpack-plugin');
const webpack = require('webpack');
const path = require('path');

module.exports = {
  mode: 'production',
  entry: path.resolve(__dirname, 'index.js'),
  output: {
    path: path.resolve(__dirname, 'dist'),
  },
  optimization: {
    minimize: true,
    minimizer: [new TerserPlugin({})],
  },
  plugins: [
    new webpack.DefinePlugin({
      'process.env': {
        BROWSER: JSON.stringify(true),
        UNRELATED_ENV_VAR: JSON.stringify('hello'),
      },
    }),
  ],
};

index.js

if (process.env.BROWSER) {
  console.log('Hello, browser!');
}

if (process.env.SERVER) {
  console.log('Hello, server!');
}

Then the output file is like:

console.log("Hello, browser!"),{BROWSER:!0,UNRELATED_ENV_VAR:"hello"}.SERVER&&console.log("Hello, server!");

What is the expected behavior?

I'm happy if the output file becomes the same as when I specify undefined to SERVER, like:

console.log("Hello, browser!");

I saw a similar is reported at #10425, but it seems not to be fixed yet.
Thank you in advance.

Other relevant information:
webpack version: 5.15.0
Node.js version: 10.15.3
Operating System: macOS Catalina Version 10.15.7
Additional tools:
terser-webpack-plugin: 5.1.1

[alexander-akait]

To be honestly I think it is not bug, change logic will break other cases... We have note about this:
https://webpack.js.org/plugins/define-plugin/

When defining values for process prefer 'process.env.NODE_ENV': JSON.stringify('production') over process: { env: { NODE_ENV: JSON.stringify('production') } }. Using the latter will overwrite the process object which can break compatibility with some modules that expect other values on the process object to be defined.

[whatasoda]

I know the note. But as I mentioned, I wanted to use destructuring assignment with process.env 😭 I hope there will be some update on #5392. Perhaps it'll help me.

change logic will break other cases

Anyway, this comment is enough for me to close this issue. Thank you for your support!