Merge pull request 'Improve :host and :host-context matching' (#2120) from FranklinDM/UXP-contrib:work_css-host-matching-fixes into master

Reviewed-on: https://repo.palemoon.org/MoonchildProductions/UXP/pulls/2120

4 files changed, 21 insertions, 6 deletions

diff --git a/layout/style/nsCSSParser.cpp b/layout/style/nsCSSParser.cpp
index c81de2d9f6..63a9bc0514 100644
--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -6547,6 +6547,11 @@ CSSParserImpl::ParsePseudoClassWithSelectorListArg(nsCSSSelector& aSelector,
     return eSelectorParsingStatus_Error; // our caller calls SkipUntil(')')
   }
 
+  if (nsCSSPseudoClasses::HasSingleSelectorArg(aType) &&
+      slist->mNext) {
+    return eSelectorParsingStatus_Error; // our caller calls SkipUntil(')')
+  }
+
   for (nsCSSSelectorList *l = slist; l; l = l->mNext) {
     nsCSSSelector *s = l->mSelectors;
     if (s == nullptr) {
diff --git a/layout/style/nsCSSPseudoClasses.cpp b/layout/style/nsCSSPseudoClasses.cpp
index a174525b1c..928326e399 100644
--- a/layout/style/nsCSSPseudoClasses.cpp
+++ b/layout/style/nsCSSPseudoClasses.cpp
@@ -102,6 +102,13 @@ nsCSSPseudoClasses::HasNthPairArg(Type aType)
          aType == Type::nthLastOfType;
 }
 
+bool
+nsCSSPseudoClasses::HasSingleSelectorArg(Type aType)
+{
+  return aType == Type::host ||
+         aType == Type::hostContext;
+}
+
 void
 nsCSSPseudoClasses::PseudoTypeToString(Type aType, nsAString& aString)
 {
diff --git a/layout/style/nsCSSPseudoClasses.h b/layout/style/nsCSSPseudoClasses.h
index 4a4bbe188c..76fcef3f78 100644
--- a/layout/style/nsCSSPseudoClasses.h
+++ b/layout/style/nsCSSPseudoClasses.h
@@ -58,6 +58,7 @@ public:
   static Type GetPseudoType(nsIAtom* aAtom, EnabledState aEnabledState);
   static bool HasStringArg(Type aType);
   static bool HasNthPairArg(Type aType);
+  static bool HasSingleSelectorArg(Type aType);
   static bool HasForgivingSelectorListArg(Type aType) {
     return aType == Type::is ||
      aType == Type::matches ||
diff --git a/layout/style/nsCSSRuleProcessor.cpp b/layout/style/nsCSSRuleProcessor.cpp
index 37d72a6037..909bfb0e81 100644
--- a/layout/style/nsCSSRuleProcessor.cpp
+++ b/layout/style/nsCSSRuleProcessor.cpp
@@ -1939,17 +1939,19 @@ static bool SelectorMatches(Element* aElement,
           // selector.
            
           // We match automatically if GetParent() and GetShadowRoot() have 
-          // the same result. Without special casing this ahead of all other 
-          // selector matching, it fails. Have not determined the cause.
-
-          if (aElement->GetParent() == aElement->GetShadowRoot()) {
+          // the same result iff our selector list is empty. Without special
+          // casing this ahead of all other selector matching, it fails.
+          // Have not determined the cause.
+          if (!pseudoClass->u.mSelectorList &&
+              aElement->GetParent() == aElement->GetShadowRoot()) {
             break;
           }
 
           // Match if any selector in the argument list matches.
-
+          // FIXME: What this effectively does is bypass the "featureless"
+          // selector check under SelectorMatches.
           NodeMatchContext nodeContext(EventStates(),
-                               nsCSSRuleProcessor::IsLink(aElement));
+                                       aNodeMatchContext.mIsRelevantLink);
           if (SelectorListMatches(aElement,
                                   pseudoClass,
                                   nodeContext,