[Bug]: :where is incorrectly purged when it is a child of :not

[AdrianGonz97]

Describe the bug

When the pseudo-class :where is a child of :not and the selector inside of :where is an "unused" selector, it is incorrectly purged.

I would also assume that :is is also affected by this as both pseudo-classes are treated similarly.

To Reproduce

.root :not(:where(.unused)) {
    color: purple;
}

Expected Behavior

The rule should not be purged.

Environment

purgecss@6.0.0-alpha.0

Add any other context about the problem here

n/a

Code of Conduct

• I agree to follow this project's Code of Conduct

[zokkis]

a hack is to safelist a regex like /:not.+/

[meduzen]

a hack is to safelist a regex like /:not.+/

As there’s the same issue (#978) for multiple pseudo-selectors, what I do is the following:

const purgeCssOptions = {
  safelist: [
    /:is/, // https://github.com/FullHuman/purgecss/issues/978
    /:where/, // https://github.com/FullHuman/purgecss/issues/978
    /:not/, // https://github.com/FullHuman/purgecss/issues/1197
  ],
}