Is this a bug report?

No

Proposal:
Support a new environment variableTERSER_CONFIG. A dev could set it to a JSON withconfig values supported by Terser and CRA would merge default this JSON with its default Terser config.

Example:

1. SetTERSER_CONFIG to{ "keep_classnames": true }
2. keep_classnames set totrue added toTerser options

Reasoning:
Certain libraries rely on class names which are minified by default by Terser. It would be nice to change that without maintaining a fork of CRA for one line of code only.
I'm pretty sure there're other cases as well. Anyway it's pretty simple to add this, it would give developers more freedom, so what's the harm, right? :)

Implementation considerations:
IfTERSER_CONFIG environment variable is present, doJSON.parse of its value and add it to Terser optionshere. AddTERSER_CONFIG tothis list.

Would you be willing to accept a PR for this functionality?