[:is/:where] Reset tree-boundary crossing flag for each list item

Otherwise, for a selector such as ':is(:host(.a), .b) .c', the tree-
boundary crossing flag will be set when processing :host(.a), and then
incorrectly carry over to subsequent list items (i.e. .b).

Bug: 568705
Change-Id: I2a8eb5735c0fc44242d7c0e089b85814e6080b44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435190
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812691}

third_party/blink/renderer/core/css/rule_feature_set.cc

@@ -884,6 +884,11 @@ void RuleFeatureSet::AddFeaturesToInvalidationSetsForSelectorList(
            simple_selector.SelectorList()->First();
        sub_selector; sub_selector = CSSSelectorList::Next(*sub_selector)) {
     AutoRestoreMaxDirectAdjacentSelectors restore_max(sibling_features);
+    AutoRestoreTreeBoundaryCrossingFlag restore_tree_boundary(
+        descendant_features);
+
+    if (simple_selector.IsHostPseudoClass())
+      descendant_features.invalidation_flags.SetTreeBoundaryCrossing(true);
 
     descendant_features.has_features_for_rule_set_invalidation = false;
 
@@ -942,8 +947,6 @@ void RuleFeatureSet::AddFeaturesToInvalidationSetsForSimpleSelector(
     return;
   }
 
-  if (simple_selector.IsHostPseudoClass())
-    descendant_features.invalidation_flags.SetTreeBoundaryCrossing(true);
   if (simple_selector.IsV0InsertionPointCrossing())
     descendant_features.invalidation_flags.SetInsertionPointCrossing(true);
   if (simple_selector.GetPseudoType() == CSSSelector::kPseudoPart)

third_party/blink/renderer/core/css/rule_feature_set.h

@@ -324,6 +324,25 @@ class CORE_EXPORT RuleFeatureSet {
     unsigned original_value_ = 0;
   };
 
+  // For :is(:host(.a), .b) .c, the invalidation set for .a should be marked
+  // as tree-crossing, but the invalidation set for .b should not.
+  class AutoRestoreTreeBoundaryCrossingFlag {
+    STACK_ALLOCATED();
+
+   public:
+    explicit AutoRestoreTreeBoundaryCrossingFlag(
+        InvalidationSetFeatures& features)
+        : features_(features),
+          original_value_(features.invalidation_flags.TreeBoundaryCrossing()) {}
+    ~AutoRestoreTreeBoundaryCrossingFlag() {
+      features_.invalidation_flags.SetTreeBoundaryCrossing(original_value_);
+    }
+
+   private:
+    InvalidationSetFeatures& features_;
+    bool original_value_;
+  };
+
   static void ExtractInvalidationSetFeature(const CSSSelector&,
                                             InvalidationSetFeatures&);
 

third_party/blink/renderer/core/css/rule_feature_set_test.cc

@@ -1519,6 +1519,21 @@ RefTestData ref_equal_test_data[] = {
     {":is(.a, span) :is(div, .b)", ".a div, .a .b, span div, span .b"},
     {":is(.a, span) + :is(div, .b)",
      ".a + div, .a + .b, span + div, span + .b"},
+    {":is(.a, .b)::slotted(.c)", ".a::slotted(.c), .b::slotted(.c)"},
+    {".a :is(.b, .c)::slotted(.d)", ".a .b::slotted(.d), .a .c::slotted(.d)"},
+    {".a + :is(.b, .c)::slotted(.d)",
+     ".a + .b::slotted(.d), .a + .c::slotted(.d)"},
+    {":is(.a, .b)::cue(i)", ".a::cue(i), .b::cue(i)"},
+    {".a :is(.b, .c)::cue(i)", ".a .b::cue(i), .a .c::cue(i)"},
+    {".a + :is(.b, .c)::cue(i)", ".a + .b::cue(i), .a + .c::cue(i)"},
+    {":is(.a, :host + .b, .c) .d", ".a .d, :host + .b .d, .c .d"},
+    {":is(.a, :host(.b) .c, .d) div", ".a div, :host(.b) .c div, .d div"},
+    {".a :is(.b, .c)::part(foo)", ".a .b::part(foo), .a .c::part(foo)"},
+    {":is(.a, .b)::part(foo)", ".a::part(foo), .b::part(foo)"},
+    {":is(.a, .b) :is(.c, .d)::part(foo)",
+     ".a .c::part(foo), .a .d ::part(foo),"
+     ".b .c::part(foo), .b .d ::part(foo)"},
+
     // clang-format on
 };