Add selector-pseudo-element-*list rules

[jeddy3]

Closes #3014

It’s been a while since I had the time to write some actual stylelint code, especially adding new rules.

I found myself reaching for the selector-pseudo-element-whitelist rule on my current project, so figured I’d add it.

[hudochenkov]

Good job, @jeddy3!

It’s been a while since I had the time to write some actual stylelint code, especially adding new rules.

Feels good, right? :)

Both rules checking CSS3 pseudo-elements only. CSS2 also has :before and :after pseudo-elements. I see two options: support these selectors, or add a note about this limitation to readme.

[hudochenkov]

It should also check for _.isRegExp according to readme. It would be great to have RegExp in tests as well. Both as a string and as RegExp.

The same comment applies to the second rule.

[jeddy3]

@hudochenkov Thanks for the feedback. I've made the changes.

I'm about to head out, so I've pushed up what I've got... and there's a flow error. Any flow pros know how to fix this? Setting the type to string | Class<RegExp> gives:

^^^^ property `test`. Property not found in statics of `RegExp`

[CAYdenberg]

Right, so flow doesn't understand that _.isRegExp is ensuring this is a regular expression. It thinks comparison could be a RegExp or a string, so it's warning you that .test doesn't work for strings.

Try using typeof comparison (harder for the reader, since typeof /myregexp/ === "object") or

if (comparison.test) {
    // now we know this is RegExp and we can CALL comparison.test
}

Make sense?

[jeddy3]

Make sense?

Yes, thanks very much @CAYdenberg

---

This PR is ready for review again.

[jeddy3]

@hudochenkov Restarted travis and now CI is green.

[hudochenkov]

Good job!

[jeddy3]

@stylelint/core Ready for a 2nd review

[ntwb]

LGTM

[jeddy3]

• Added: selector-pseudo-element-*list rules (#3104).