Add support for pseudo class :has

[tornqvist]

A naive implementation of the :has (aka. parent) selector. It only supports selecting children but not any of the more complex and interesting uses of the selector. It does however avoid crashing on unrecognized new syntax, see leeoniya#55 (comment).

div:has(span) { … } /* will match <div><span></span><div> */
span:has(+ span) { … } /* will not match <div><span></span><span></span><div> */

I also noticed that pseudo class selectors don't support multiple selectors, e.g. :not(span, div) but that is a different matter.

[leeoniya]

@tornqvist did you mean to open this against the main repo?

It only supports selecting children

any barriers to just doing this recursively?

[tornqvist]

This change is very similar to leeoniya#59 so I opened it here to avoid merge conflicts. If both are accepted I could merge this before you accept the other one but if you prefer, I could open a PR against the main repo.

any barriers to just doing this recursively?

My specific use case is for selecting an element preceding a specific sibling, e.g. .foo:has(+ .bar), and this doesn't support that. I can't see how that could be achieved with recursive :has(…):has(…). Or maybe that's not what you meant? But this does fix the crash, which is enough for me for the time being.

[tornqvist]

I take it you're not opposed to this fix, @leeoniya? Should I go ahead and merge it into the :is branch and we can then merge that into the main repo, given that you're okay with these two changes?

[leeoniya]

sorry, i will take a closer look at both of your PRs over the weekend. been a bit busy past week.