Config json cloning is a BREAKING CHANGE!

Related: https://github.com/eslint/eslint/pull/13034#discussion_r446611500

Tell us about your environment

• ESLint Version: 7.3.1
• Node Version: v14.4.0
• npm Version: 6.14.4

What parser (default, Babel-ESLint, etc.) are you using?

eslint-mdx

Please show your full configuration:

Configuration

module.exports = {
  extends: 'plugin:unicorn/recommended',
  rules: {
    'unicorn/filename-case': [
      2,
      {
        cases: {
          kebabCase: true,
          pascalCase: true,
        },
        // ignore UPPER_CASE markdown filenames
        ignore: [/^[A-Z](([\dA-Z]+_)*[\dA-Z]+)?\.mdx?$/],
      },
    ]
  }
}

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

<!-- README.md -->

eslint README.md

What did you expect to happen? no error

What actually happened? Please include the actual, raw output from ESLint.

1:2  error  Filename is not in kebab case or pascal case. Rename it to `readme.md` or `Readme.md`  unicorn/filename-case

The error occurres because the ESLint config is json cloned since v7.3.0, and this breaks Regxp option of unicorn/filename-case, I don’t think this is an invalid usage.

[nzakas]

The discussion was to wait and see how many bug reports we received before deciding whether to revert or not. We had just one report of the use of Infinity, and given that was clearly a bug and could be easily replaced with a valid number to work the same, we decided to add a patch to allow that isolated case.

This case is more concerning because it involves encouraging end users to use regular expressions in their configs (vs one isolated instance of Infinity in one config).

With this new data, I’m in favor of reverting the change.

[anikethsaha]

similar to https://github.com/eslint/eslint/pull/13034#issuecomment-632339452 ?