Add support for new CSS ::slotted() pseudo element

third_party/WebKit/Source/core/css/SelectorChecker.cpp

Index: third_party/WebKit/Source/core/css/SelectorChecker.cpp
diff --git a/third_party/WebKit/Source/core/css/SelectorChecker.cpp b/third_party/WebKit/Source/core/css/SelectorChecker.cpp
index 059d75bd91d9fbce37afaef90ba93f758c1e3973..de08250631e660f87318c7750ed1c9ad1872233f 100644
--- a/third_party/WebKit/Source/core/css/SelectorChecker.cpp
+++ b/third_party/WebKit/Source/core/css/SelectorChecker.cpp
@@ -47,6 +47,7 @@
 #include "core/html/HTMLInputElement.h"
 #include "core/html/HTMLOptionElement.h"
 #include "core/html/HTMLSelectElement.h"
+#include "core/html/HTMLSlotElement.h"
 #include "core/html/parser/HTMLParserIdioms.h"
 #include "core/html/track/vtt/VTTElement.h"
 #include "core/inspector/InspectorInstrumentation.h"
@@ -113,6 +114,20 @@ static Element* parentElement(const SelectorChecker::SelectorCheckingContext& co
     return context.element->parentElement();
 }
 
+static const HTMLSlotElement* findSlotElementInScope(const SelectorChecker::SelectorCheckingContext& context)
+{
+    if (!context.scope)
+        return nullptr;
+
+    const HTMLSlotElement* slot = context.element->assignedSlot();
+    while (slot) {
+        if (slot->treeScope() == context.scope->treeScope())
+            return slot;
+        slot = slot->assignedSlot();
+    }
+    return nullptr;
+}
+
 static bool scopeContainsLastMatchedElement(const SelectorChecker::SelectorCheckingContext& context)
 {
     // If this context isn't scoped, skip checking.
@@ -452,6 +467,16 @@ SelectorChecker::Match SelectorChecker::matchForRelation(const SelectorCheckingC
             return SelectorFailsCompletely;
         }
 
+    case CSSSelector::ShadowSlot:

[rune, 2016/01/11 10:07:23]

It's possible to implement this without this combinator and add the code below
to the PseudoSlotted handling instead. You only need to make sure PseudoSlotted
is listed first in the compound (which we already do in the parser to make sure
it ends up in a separate right-most compound) to make sure we match .slot for
the slot, not the slotted element, in .slot::slotted(.slotted).

+        {
+            const HTMLSlotElement* slot = findSlotElementInScope(context);
+            if (!slot)
+                return SelectorFailsCompletely;
+
+            nextContext.element = const_cast<HTMLSlotElement*>(slot);
+            return matchSelector(nextContext, result);
+        }
+
     case CSSSelector::SubSelector:
         ASSERT_NOT_REACHED();
     }
@@ -1023,6 +1048,19 @@ bool SelectorChecker::checkPseudoElement(const SelectorCheckingContext& context,
                 return root->type() == ShadowRootType::UserAgent && element.shadowPseudoId() == selector.value();
             return false;
         }
+    case CSSSelector::PseudoSlotted:
+        {
+            SelectorCheckingContext subContext(context);
+            subContext.isSubSelector = true;
+            subContext.scope = nullptr;
+            subContext.treatShadowHostAsNormalScope = false;
+
+            // ::slotted() only allows one compound selector.
+            ASSERT(selector.selectorList()->first());
+            ASSERT(!CSSSelectorList::next(*selector.selectorList()->first()));
+            subContext.selector = selector.selectorList()->first();
+            return match(subContext);
+        }
     case CSSSelector::PseudoContent:
         return element.isInShadowTree() && element.isInsertionPoint();
     case CSSSelector::PseudoShadow: