style: Move ANCHORS_RELATIVE_SELECTOR out of nsINode flags

Move the flag to ComputedValueFlags, like `CONSIDERED_RELATIVE_SELECTOR`.

Differential Revision: https://phabricator.services.mozilla.com/D180726

components/style/dom.rs

@@ -900,10 +900,6 @@ pub trait TElement:
         &self,
         display: &Display,
     ) -> euclid::default::Size2D<Option<app_units::Au>>;
-
-    /// Returns true if this element anchors a relative selector, now or after
-    /// a DOM mutation.
-    fn anchors_relative_selector(&self) -> bool;
 }
 
 /// TNode and TElement aren't Send because we want to be careful and explicit

components/style/gecko/wrapper.rs

@@ -894,9 +894,6 @@ fn selector_flags_to_node_flags(flags: ElementSelectorFlags) -> u32 {
     if flags.contains(ElementSelectorFlags::HAS_EMPTY_SELECTOR) {
         gecko_flags |= NODE_HAS_EMPTY_SELECTOR;
     }
-    if flags.contains(ElementSelectorFlags::ANCHORS_RELATIVE_SELECTOR) {
-        gecko_flags |= NODE_ANCHORS_RELATIVE_SELECTOR;
-    }
 
     gecko_flags
 }
@@ -1730,11 +1727,6 @@ impl<'le> TElement for GeckoElement<'le> {
             }
         }
     }
-
-    fn anchors_relative_selector(&self) -> bool {
-        use crate::gecko_bindings::structs::NODE_ANCHORS_RELATIVE_SELECTOR;
-        self.flags() & NODE_ANCHORS_RELATIVE_SELECTOR != 0
-    }
 }
 
 impl<'le> PartialEq for GeckoElement<'le> {

components/style/properties/computed_value_flags.rs

@@ -121,6 +121,10 @@ bitflags! {
 
         /// Whether the style evaluated any relative selector.
         const CONSIDERED_RELATIVE_SELECTOR = 1 << 24;
+
+        /// Whether the style evaluated the matched element to be an anchor of
+        /// a relative selector.
+        const ANCHORS_RELATIVE_SELECTOR = 1 << 25;
     }
 }
 
@@ -153,7 +157,9 @@ impl ComputedValueFlags {
     /// Flags that are an input to the cascade.
     #[inline]
     fn cascade_input_flags() -> Self {
-        Self::USES_VIEWPORT_UNITS_ON_CONTAINER_QUERIES | Self::CONSIDERED_RELATIVE_SELECTOR
+        Self::USES_VIEWPORT_UNITS_ON_CONTAINER_QUERIES |
+            Self::CONSIDERED_RELATIVE_SELECTOR |
+            Self::ANCHORS_RELATIVE_SELECTOR
     }
 
     /// Returns the flags that are always propagated to descendants.

components/style/sharing/mod.rs

@@ -632,7 +632,11 @@ impl<E: TElement> StyleSharingCache<E> {
         //   matching `.foo`, even if `:has()` may not even be used. Ideally we'd
         //   have something like `RelativeSelectorConsidered::RightMost`, but the
         //   element flag is required for invalidation, and this reduces more tracking.
-        if element.anchors_relative_selector() {
+        if style
+            .style
+            .0
+            .flags
+            .intersects(ComputedValueFlags::ANCHORS_RELATIVE_SELECTOR) {
             debug!("Failing to insert to the cache: may anchor relative selector");
             return;
         }

components/style/style_resolver.rs

@@ -16,7 +16,7 @@ use crate::rule_tree::StrongRuleNode;
 use crate::selector_parser::{PseudoElement, SelectorImpl};
 use crate::stylist::RuleInclusion;
 use log::Level::Trace;
-use selectors::matching::{MatchingContext, NeedsSelectorFlags};
+use selectors::matching::{MatchingContext, NeedsSelectorFlags, RelativeSelectorMatchingState};
 use selectors::matching::{MatchingMode, VisitedHandlingMode};
 use servo_arc::Arc;
 
@@ -503,16 +503,24 @@ where
                 }
             }
         }
-
-        if matching_context.considered_relative_selector {
-            // This is a bit awkward - ideally, the flag is set directly where `considered_relative_selector`
-            // is; however, in that context, the implementation detail of `extra_data` is not visible, so
-            // it's done here. A trait for manipulating the flags is an option, but not worth it for a single flag.
-            matching_context
-                .extra_data
-                .cascade_input_flags
-                .insert(ComputedValueFlags::CONSIDERED_RELATIVE_SELECTOR);
-        }
+        // This is a bit awkward - ideally, the flag is set directly where `considered_relative_selector`
+        // is; however, in that context, the implementation detail of `extra_data` is not visible, so
+        // it's done here. A trait for manipulating the flags is an option, but not worth it for a single flag.
+        match matching_context.considered_relative_selector {
+            RelativeSelectorMatchingState::None => (),
+            RelativeSelectorMatchingState::Considered => {
+                matching_context
+                    .extra_data
+                    .cascade_input_flags
+                    .insert(ComputedValueFlags::CONSIDERED_RELATIVE_SELECTOR);
+            },
+            RelativeSelectorMatchingState::ConsideredAnchor => {
+                matching_context.extra_data.cascade_input_flags.insert(
+                    ComputedValueFlags::ANCHORS_RELATIVE_SELECTOR |
+                        ComputedValueFlags::CONSIDERED_RELATIVE_SELECTOR,
+                );
+            },
+        };
 
         MatchingResults {
             rule_node,