Parse CSS Nesting's leading-combinator shorthand in nested rules

[davesnx]

A nested rule whose prelude starts with a combinator (.parent { > .child {} }, + .sib {}, ~ .sib {}) failed with Parse error while reading token '>', although CSS Nesting defines it as & > .child; only a :has(> img) payload accepted a leading combinator. Rules inside another rule's block, or an at-rule's block, now parse their prelude with parse_nested_selector_list, which reads an item starting with a combinator as a RelativeSelector. Selector_nesting.compute_new_prefix rewrites it into the explicit-& shape before substitution, so both spellings produce the same AST, the same class and the same CSS. The root of [%css], [%styled.global] and a raw stylesheet keeps rejecting a leading combinator, because there is no parent to resolve against.

.parent { > .child { color: red } }   -> .parent > .child{color:red;}   (same class as `& > .child`)
.parent { + .sib { color: red } }     -> .parent + .sib{color:red;}
> .a { color: red }                   -> parse error at the root, unchanged

[%styled.global] also rejects a leading combinator inside an at-rule block with no enclosing style rule (@media print { > .a {} }) with the same "no parent selector to resolve against" error a parentless & gives. Before, that input compiled and shipped a literal unresolved & in the extracted CSS.

Evidence at b3ba860:

• Parser_test.re: 8 shorthand cases red before and green after; 2 cases guard the root-level rejection.
• New cram test packages/ppx/test/css-support/nested-relative-selectors.t: each shorthand form and its & spelling render to an identical class and CSS.
• New snapshot reason-styled-global2-top-level-relative-selector-error.t: the at-rule case errors with the caret on > .a; it compiled silently before.
• make format-check, make build, make test: all exit 0.

Risk: two-way door. Only previously failing inputs parse, plus the new rejection of a [%styled.global] input that was silently broken; a revert restores both.

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1 Skipped Deployment

Project	Deployment	Actions	Updated
styled-ppx	Ignored	Preview	Sep 23, 2026 6:41am UTC