Fix false positives for ::part in selector-pseudo-element-no-unknown

[bennypowers]

What is the problem you're trying to solve?

Using CSS Shadow Parts violates linter rules selector-pseudo-element-no-unknown for the ::part pseudo element and selector-type-no-unknown for the argument to ::part()

What solution would you like to see?

I would like to see theselector-pseudo-element-no-unknown rule updated to allow CSS Shadow Part selection.

stripe-elements::part(stripe) {
  border: none;
  box-shadow: none;
}

A plugin that scans custom-elements.json files for a all custom-elements imported by the project and validates the names of their Shadow Parts would be amazing, but is perhaps out of scope of this request.

[alexander-akait]

Feel free to send a PR with new pseudo elements, you can name then shadowTreePseudoElements https://github.com/stylelint/stylelint/blob/master/lib/reference/keywordSets.js#L205

[jeddy3]

@bennypowers Thanks for the request and for using the template.

(For anyone curious: spec for reference.)

I've labeled the issue as ready to implement. As @evilebottnawi said, please consider contributing if you have time. You can add the new set here and you'll need to unite it here.

There are steps on how to fix a bug in a rule in the Developer guide.

A plugin that scans custom-elements.json files for a all custom-elements imported by the project and validates the names of their Shadow Parts would be amazing

Yes, this is out of scope for a built-in rule but would make for an excellent plugin!