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/selectors/context.rs

@@ -99,6 +99,21 @@ impl QuirksMode {
     }
 }
 
+/// Whether or not this matching considered relative selector.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum RelativeSelectorMatchingState {
+    /// Was not considered for any relative selector.
+    None,
+    /// Relative selector was considered for a match, but the element to be
+    /// under matching would not anchor the relative selector. i.e. The
+    /// relative selector was not part of the first compound selector (in match
+    /// order).
+    Considered,
+    /// Same as above, but the relative selector was part of the first compound
+    /// selector (in match order).
+    ConsideredAnchor,
+}
+
 /// Data associated with the matching process for a element.  This context is
 /// used across many selectors for an element, so it's not appropriate for
 /// transient data that applies to only a single selector.
@@ -146,7 +161,7 @@ where
 
     /// The current element we're anchoring on for evaluating the relative selector.
     current_relative_selector_anchor: Option<OpaqueElement>,
-    pub considered_relative_selector: bool,
+    pub considered_relative_selector: RelativeSelectorMatchingState,
 
     quirks_mode: QuirksMode,
     needs_selector_flags: NeedsSelectorFlags,
@@ -200,7 +215,7 @@ where
             pseudo_element_matching_fn: None,
             extra_data: Default::default(),
             current_relative_selector_anchor: None,
-            considered_relative_selector: false,
+            considered_relative_selector: RelativeSelectorMatchingState::None,
             _impl: ::std::marker::PhantomData,
         }
     }
@@ -329,12 +344,14 @@ where
     where
         F: FnOnce(&mut Self) -> R,
     {
-        // TODO(dshin): Nesting should be rejected at parse time.
-        let original_relative_selector_anchor = self.current_relative_selector_anchor.take();
+        debug_assert!(
+            self.current_relative_selector_anchor.is_none(),
+            "Nesting should've been rejected at parse time"
+        );
         self.current_relative_selector_anchor = Some(anchor);
+        self.considered_relative_selector = RelativeSelectorMatchingState::Considered;
         let result = self.nest(f);
-        self.current_relative_selector_anchor = original_relative_selector_anchor;
-        self.considered_relative_selector = true;
+        self.current_relative_selector_anchor = None;
         result
     }
 

components/selectors/matching.rs

@@ -60,18 +60,13 @@ bitflags! {
         /// The element has an empty selector, so when a child is appended we
         /// might need to restyle the parent completely.
         const HAS_EMPTY_SELECTOR = 1 << 4;
-
-        /// This element has a relative selector that anchors to it, or may do so
-        /// if its descendants or its later siblings change.
-        const ANCHORS_RELATIVE_SELECTOR = 1 << 5;
     }
 }
 
 impl ElementSelectorFlags {
     /// Returns the subset of flags that apply to the element.
     pub fn for_self(self) -> ElementSelectorFlags {
-        self & (ElementSelectorFlags::HAS_EMPTY_SELECTOR |
-            ElementSelectorFlags::ANCHORS_RELATIVE_SELECTOR)
+        self & ElementSelectorFlags::HAS_EMPTY_SELECTOR
     }
 
     /// Returns the subset of flags that apply to the parent.
@@ -370,12 +365,10 @@ fn matches_relative_selectors<E: Element>(
     element: &E,
     context: &mut MatchingContext<E::Impl>,
 ) -> bool {
-    if context.needs_selector_flags() {
-        // If we've considered anchoring `:has()` selector while trying to match this element,
-        // mark it as such, as it has implications on style sharing (See style sharing
-        // code for further information).
-        element.apply_selector_flags(ElementSelectorFlags::ANCHORS_RELATIVE_SELECTOR);
-    }
+    // If we've considered anchoring `:has()` selector while trying to match this element,
+    // mark it as such, as it has implications on style sharing (See style sharing
+    // code for further information).
+    context.considered_relative_selector = RelativeSelectorMatchingState::ConsideredAnchor;
     for RelativeSelector {
         match_hint,
         selector,