[Webkit-unassigned] [Bug 233283] New: [CSS Cascade Layers] [Debug] ASSERTION FAILED: m_childRules.isEmpty() when using @import with layer name

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=233283

            Bug ID: 233283
           Summary: [CSS Cascade Layers] [Debug] ASSERTION FAILED:
                    m_childRules.isEmpty() when using @import with layer
                    name
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: pangle at apple.com
                CC: koivisto at iki.fi, webkit-bug-importer at group.apple.com
            Blocks: 233208

Created attachment 444573

  --> https://bugs.webkit.org/attachment.cgi?id=444573&action=review

Reproduction Test Case

In the process of writing tests for bug 233208, I've run into this assertion in debug builds when I `@import url("./external-layers.css") layer(imported);` in a style tag. I've attached a sample page and external stylesheet the reproduce the issue. The `@import` rule behaves as expected in release builds and imports the styles scoped within the named layer.

Full crash trace:
```
ASSERTION FAILED: m_childRules.isEmpty()
./css/StyleSheetContents.cpp(146) : void WebCore::StyleSheetContents::parserAppendRule(Ref<WebCore::StyleRuleBase> &&)
1   0x4f43daf39 WTFCrash
2   0x506f89dcb WTFCrashWithInfo(int, char const*, char const*, int)
3   0x509dcb63c WebCore::StyleSheetContents::parserAppendRule(WTF::Ref<WebCore::StyleRuleBase, WTF::RawPtrTraits<WebCore::StyleRuleBase> >&&)
4   0x509e1b0f7 WebCore::CSSParserImpl::parseStyleSheet(WTF::String const&, WebCore::CSSParserContext const&, WebCore::StyleSheetContents&, WebCore::CSSParser::RuleParsing)::$_3::operator()(WTF::RefPtr<WebCore::StyleRuleBase, WTF::RawPtrTraits<WebCore::StyleRuleBase>, WTF::DefaultRefDerefTraits<WebCore::StyleRuleBase> >) const
5   0x509e0a011 bool WebCore::CSSParserImpl::consumeRuleList<WebCore::CSSParserImpl::parseStyleSheet(WTF::String const&, WebCore::CSSParserContext const&, WebCore::StyleSheetContents&, WebCore::CSSParser::RuleParsing)::$_3>(WebCore::CSSParserTokenRange, WebCore::CSSParserImpl::RuleListType, WebCore::CSSParserImpl::parseStyleSheet(WTF::String const&, WebCore::CSSParserContext const&, WebCore::StyleSheetContents&, WebCore::CSSParser::RuleParsing)::$_3)
6   0x509e004d1 WebCore::CSSParserImpl::parseStyleSheet(WTF::String const&, WebCore::CSSParserContext const&, WebCore::StyleSheetContents&, WebCore::CSSParser::RuleParsing)
7   0x509e0042b WebCore::CSSParser::parseSheet(WebCore::StyleSheetContents&, WTF::String const&, WebCore::CSSParser::RuleParsing)
8   0x509dcd72e WebCore::StyleSheetContents::parseString(WTF::String const&)
9   0x50a0d4cee WebCore::InlineStyleSheetOwner::createSheet(WebCore::Element&, WTF::String const&)
10  0x50a0d44fe WebCore::InlineStyleSheetOwner::createSheetFromTextContents(WebCore::Element&)
11  0x50a0d468b WebCore::InlineStyleSheetOwner::finishParsingChildren(WebCore::Element&)
12  0x50a4f4b13 WebCore::HTMLStyleElement::finishParsingChildren()
13  0x50a652a18 WebCore::HTMLElementStack::popCommon()
14  0x50a64de4a WebCore::HTMLElementStack::pop()
15  0x50a688f0d WebCore::HTMLTreeBuilder::processEndTag(WebCore::AtomHTMLToken&&)
16  0x50a6855f6 WebCore::HTMLTreeBuilder::processToken(WebCore::AtomHTMLToken&&)
17  0x50a684455 WebCore::HTMLTreeBuilder::constructTree(WebCore::AtomHTMLToken&&)
18  0x50a650d79 WebCore::HTMLDocumentParser::constructTreeFromHTMLToken(WebCore::HTMLTokenizer::TokenPtr&)
19  0x50a650b20 WebCore::HTMLDocumentParser::pumpTokenizerLoop(WebCore::HTMLDocumentParser::SynchronousMode, bool, WebCore::PumpSession&)
20  0x50a64fd38 WebCore::HTMLDocumentParser::pumpTokenizer(WebCore::HTMLDocumentParser::SynchronousMode)
21  0x50a64f540 WebCore::HTMLDocumentParser::pumpTokenizerIfPossible(WebCore::HTMLDocumentParser::SynchronousMode)
22  0x50a651b27 WebCore::HTMLDocumentParser::resumeParsingAfterScriptExecution()
23  0x50a651ebc WebCore::HTMLDocumentParser::notifyFinished(WebCore::PendingScript&)
24  0x50a14a8da WebCore::PendingScript::notifyClientFinished()
25  0x50a14a939 WebCore::PendingScript::notifyFinished(WebCore::LoadableScript&)
26  0x50a0f2673 WebCore::LoadableScript::notifyClientFinished()
27  0x50a0f2493 WebCore::LoadableClassicScript::notifyFinished(WebCore::CachedResource&, WebCore::NetworkLoadMetrics const&)
28  0x50ababa2f WebCore::CachedResource::checkNotify(WebCore::NetworkLoadMetrics const&)
29  0x50ab9f934 WebCore::CachedResource::finishLoading(WebCore::SharedBuffer*, WebCore::NetworkLoadMetrics const&)
30  0x50abda78c WebCore::CachedScript::finishLoading(WebCore::SharedBuffer*, WebCore::NetworkLoadMetrics const&)
31  0x50ab30112 WebCore::SubresourceLoader::didFinishLoading(WebCore::NetworkLoadMetrics const&)
```


Referenced Bugs:

https://bugs.webkit.org/show_bug.cgi?id=233208
[Bug 233208] Web Inspector: Support Cascade Layers in the Styles sidebar
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