warning package is not compatible with webpack 5

[tomalec]

Description

@wordpress/warning and its babel-plugin rely on process.env. So for env == 'production' it's supposed not to show the warning.

The problem is webpack 5 removed process variable completely:

• https://webpack.js.org/blog/2020-10-10-webpack-5-release/#changes-to-the-structure

  Automatic polyfills for native Node.js modules were removed
  node.process removed

• https://webpack.js.org/migrate/5/#run-a-single-build-and-follow-advice

  webpack 5 does no longer include a polyfill for this Node.js variable. Avoid using it in the frontend code.
  process.env is Node.js specific and should be avoided in frontend code.

So, the typeof process !== 'undefined' && process.env !=== 'production' is always false, which prevents warning to be called for any kind of environment.

Step-by-step reproduction instructions

Follow the package's README

1. Put @wordpress/warning/babel-plugin into your babel config or use @wordpress/babel-preset-default, which already includes the babel plugin.

2. import warning from '@wordpress/warning';
   warning( 'You should see me' );

3. Build your bundle with webpack 5

Screenshots, screen recording, code snippet

No response

Environment info

   "@wordpress/warning": "2.19.0",
   "webpack": "^5.74.0",

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[tomalec]

One workaround if to add new webpack.ProvidePlugin( { process: 'process/browser' } ) to the plugins of webpack config.

However, it increases the bundle size, and @wordpress/warning/babel-plugin was meant to reduce it.

[gziolo]

What is the new pattern for marking a code block as intended only for development purposes? We could simplify the check to verify if something like SCRIPT_DEBIG (mirroring WordPress core) is set to true.

[gziolo]

I started to #50122 to see if we can fix the bug by reworking how we approach feature flagging for development-related tooling.