[BUGFIX] First-child and last-child selectors are broken

[oliverklee]

Fixes #286

[oliverklee]

I've used the XPath equivalents as listed on https://en.wikibooks.org/wiki/XPath/CSS_Equivalents.

@bramley: Could you please test this PR and also verify it by reading?

[bramley]

The XPaths are not correct. The first-child one is selecting all elements that are the first child of their parent. Similarly the last-child is selecting all elements that are the last child of their parent.

The Symfony css selector package generates this XPath for p:first-child

descendant-or-self::*/*[name() = 'p' and (position() = 1)]

While that could be generated by the preg_replace, the XPath expression can be more complex so I don't think it is easy (or even possible) to process a general expression with a preg_replace, e.g. p.red:first-child generates

descendant-or-self::div/*[@class and contains(concat(' ', normalize-space(@class), ' '), ' red ') and (name() = 'p') and (position() = 1)]

As there can be subtle differences between similar XPath expressions, I'm not sure it is a good idea to try to implement css to XPath conversion without having a good knowledge of both. Particularly as there is a proven package that already does that. Wouldn't it be better to treat this as "missing functionality" or as a bug and fix it by using the Symfony component?

[oliverklee]

Hi @bramley, thanks for the remarks. I've fixed the code and added some tests that fail with the old version of the patch. Could you please re-review? Thanks!

[bramley]

Yes, this looks better.
You might want to change these two test descriptions to refer to the div element, not p

        'P:first-child matches not first child with mismatching tag'
            => ['div:first-child {' . $styleRule . '} ', '#<p class="p-1">#'],

        'P:last-child not matches last child with mismatching tag'
            => ['div:last-child {' . $styleRule . '} ', '#<p class="p-3">#'],

and maybe change "matches not" to "does not match"

[oliverklee]

@bramley Good catch! Like this (re-pushed)?