Support nesting pseudo-classes like ":not" or ":is" (Less.js 4.2)

[stell]

Less.php 5.4 does not seem to process the following selector correctly:

.uk-form-small:is(.uk-input, .uk-search-input, .uk-select:not([multiple]):not([size])) {
    height: 42px;
}

The parser aborts with an error during compilation.

Expected behavior

The selector should be parsed correctly and compiled without errors.

Actual behavior

A parse error occurs although the CSS syntax is valid.

[Krinkle]

Thanks for the report.

I've confirmed this bug is not a regression in Less.php 5.4, as the same error happens Less.php 4.x and 3.x.

Less.php 5.4 aims for upstream parity with Less.js 3.13, and I've confirmed the same bug happens there (Playground preview). This means right now, we are on parity with upstream and passing their spec in this regard. But we don't mind backport bug fixes ahead of semver-major changes, so we can definitely fix this soon.

Upstream has fixed this bug in Less.js 4.2 (Playground preview). Based on upstream changelog, my guess is less/less.js#4268 and less/less.js#4290.

[helmutkaufmann]

Is there any chance this gets addressed/implemented in less.php in the near future?

[Krinkle]

Our current target is Less.js 3.13, not Less.js 4.x. So we are not likely to prioritise this ourselves right now. But, patches are welcome will be reviewed and released in a timely fashion.