[CSS Nesting] Fix parsing of nested at-rules with CSSOM

https://bugs.webkit.org/show_bug.cgi?id=255530
rdar://107760234

Reviewed by Antti Koivisto.

CSS OM insertion can "bypass" the normal stack by inserting at an arbitrarily
deeply nested context.
We already have isNestedContext() function to check for this, but it was
not used here unfortunately.

* LayoutTests/imported/w3c/web-platform-tests/css/css-nesting/cssom-expected.txt:
* Source/WebCore/css/parser/CSSParserImpl.cpp:
(WebCore::CSSParserImpl::consumeQualifiedRule):
(WebCore::CSSParserImpl::consumeRegularRuleList):
(WebCore::CSSParserImpl::consumeDeclarationListOrStyleBlockHelper):

Canonical link: https://commits.webkit.org/263028@main

LayoutTests/imported/w3c/web-platform-tests/css/css-nesting/cssom-expected.txt

@@ -6,8 +6,8 @@ PASS Simple CSSOM manipulation of subrules 3
 PASS Simple CSSOM manipulation of subrules 4
 PASS Simple CSSOM manipulation of subrules 5
 PASS Simple CSSOM manipulation of subrules 6
-FAIL Simple CSSOM manipulation of subrules 7 assert_equals: @supports is added expected ".a {\n  color: red;\n  & .b { color: green; }\n  @supports selector(&) {\n  & div { font-size: 10px; }\n}\n  & .c { color: blue; }\n}" but got ".a {\n  color: red;\n  & .b { color: green; }\n  @supports selector(&) {\n}\n  & .c { color: blue; }\n}"
-FAIL Simple CSSOM manipulation of subrules 8 assert_equals: color is changed, new rule is ignored expected ".a {\n  color: olivedrab;\n  & .b { color: green; }\n  & .c { color: blue; }\n}" but got ".a {\n  color: olivedrab;\n  & .b { color: green; }\n  @supports selector(&) {\n}\n  & .c { color: blue; }\n}"
+PASS Simple CSSOM manipulation of subrules 7
+PASS Simple CSSOM manipulation of subrules 8
 PASS Simple CSSOM manipulation of subrules 9
 PASS Simple CSSOM manipulation of subrules 10
 FAIL Simple CSSOM manipulation of subrules 11 assert_equals: invalid rule containing ampersand is kept in serialization expected ".a {\n  :is(!& .foo, .b) { color: green; }\n}" but got ".a {\n  :is(.b) { color: green; }\n}"

Source/WebCore/css/parser/CSSParserImpl.cpp

@@ -416,7 +416,7 @@ RefPtr<StyleRuleBase> CSSParserImpl::consumeAtRule(CSSParserTokenRange& range, A
 // https://drafts.csswg.org/css-syntax/#consume-a-qualified-rule
 RefPtr<StyleRuleBase> CSSParserImpl::consumeQualifiedRule(CSSParserTokenRange& range, AllowedRulesType allowedRules)
 {
-    auto isNestedStyleRule = [&]() {
+    auto isNestedStyleRule = [&] {
         return isNestedContext() && allowedRules <= RegularRules;
     };
 
@@ -581,7 +581,7 @@ Vector<RefPtr<StyleRuleBase>> CSSParserImpl::consumeRegularRuleList(CSSParserTok
 {
     Vector<RefPtr<StyleRuleBase>> rules;
     if (isNestedContext()) {
-        runInNewNestingContext([&]() {
+        runInNewNestingContext([&] {
             consumeStyleBlock(block, StyleRuleType::Style, ParsingStyleDeclarationsInRuleList::Yes);
             if (!topContext().m_parsedProperties.isEmpty()) {
                 // This at-rule contains orphan declarations, we attach them to an implicit parent nesting rule. Web
@@ -1105,7 +1105,7 @@ RefPtr<StyleRuleBase> CSSParserImpl::consumeStyleRule(CSSParserTokenRange prelud
 void CSSParserImpl::consumeDeclarationListOrStyleBlockHelper(CSSParserTokenRange range, StyleRuleType ruleType, OnlyDeclarations onlyDeclarations, ParsingStyleDeclarationsInRuleList isParsingStyleDeclarationsInRuleList)
 {
     auto nestedRulesAllowed = [&]() {
-        return m_styleRuleNestingDepth && context().cssNestingEnabled && onlyDeclarations == OnlyDeclarations::No;        
+        return isNestedContext() && onlyDeclarations == OnlyDeclarations::No;        
     };
 
     ASSERT(topContext().m_parsedProperties.isEmpty());