Implement CSS Nesting (& selector and nested style rules)#218
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Implement CSS Nesting (& selector and nested style rules)#218jhaygood86 wants to merge 1 commit into
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Parse nested style rules and the & nesting selector (CSS Nesting 1),
resolving each nested rule at parse time into an ordinary flat rule with an
absolute selector (& -> :is(parent)), exposed on the object model via
IStyleRule.NestedRules so the parser needs no matcher/cascade awareness.
- StylesheetComposer classifies a declaration-block construct as a nested
rule vs a declaration by scanning bracket-aware for the first top-level {
(vs ;/}), with a -- custom-property guard. On the declaration branch it
rewinds the lexer (LexerBase.RewindTo, a faithful source-index restore --
not the InsertionPoint setter, whose BackNative loop mis-counts across \r\n)
and re-lexes cleanly in value mode, avoiding the hex-color value-mode
tokenization hazard a token buffer would hit.
- Nested selectors resolve against the enclosing rule's SelectorText and parse
via Parser.ParseSelector; the & substitution is string-aware so a & inside an
attribute-value string is preserved. StyleRule gains a NestedRules list.
Ported from PeachPDF, which vendors ExCSS.
jhaygood86
marked this pull request as ready for review
July 24, 2026 20:00
jhaygood86
marked this pull request as draft
July 24, 2026 20:35
jhaygood86
marked this pull request as ready for review
July 24, 2026 20:35
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Summary
Implements CSS Nesting 1: the
&nesting selector and nested style rules inside a declaration block.Nested rules are resolved at parse time into ordinary flat rules with an absolute selector (
&→:is(parent)), so the object model and any downstream matcher/cascade need no nesting awareness. Each parentStyleRuleexposes its resolved children via a newIStyleRule.NestedRules.How it works
StylesheetComposerclassifies a declaration-block construct as a nested rule vs a declaration by scanning bracket-aware for the first top-level{(vs;/}), with a--custom-property guard. Function tokens are opaque (their parens are already balanced), so only bare round/square brackets count toward depth. This resolves thediv { }(type selector, first token is an Ident) anda:hover { }(ambiguous witha: hover) cases via{-before-;.LexerBase.RewindTo, a faithful raw-source-index restore) and lets the unchanged declaration path re-lex in value mode. This is deliberately not a token pushback buffer, which would corrupt a#rrggbbvalue (the lexer tokenizes#123456differently in value vs non-value mode).&substitution is string-aware (a char scanner tracking quote state), so a&inside an attribute-value string ([data-x="a&b"]) is preserved and doesn't flip the rule off the descendant branch.Tests
CssNestingTests— 11 OM-level cases: implicit descendant,&-compound, type-selector nesting, no-&scoping, leading child combinator, hex-color regression (nested value not corrupted), top-level-unaffected, declaration-after-nested-rule, custom-property guard, multi-level nesting, and&-inside-attribute-string preservation. Full suite green.Ported from PeachPDF, which vendors ExCSS.