style: Record in RestyleHints how far down the tree selector matching must be re-run.

components/style/restyle_hints.rs

@@ -37,11 +37,8 @@ use stylist::SelectorMap;
 /// unnecessary.
 #[derive(Debug, Clone, PartialEq)]
 pub struct RestyleHint {
-    /// Rerun selector matching on the element.
-    match_self: bool,
-
-    /// Rerun selector matching on all of the element's descendants.
-    match_descendants: bool,
+    /// Depths at which selector matching must be re-run.
+    match_under_self: RestyleDepths,
 
     /// Rerun selector matching on all later siblings of the element and all
     /// of their descendants.
@@ -82,6 +79,75 @@ bitflags! {
     }
 }
 
+/// Eight bit wide bitfield representing depths of a DOM subtree's descendants,
+/// used to represent which elements must have selector matching re-run on them.
+///
+/// The least significant bit indicates that selector matching must be re-run
+/// for the element itself, the second least significant bit for the element's
+/// children, the third its grandchildren, and so on.  If the most significant
+/// bit it set, it indicates that that selector matching must be re-run for
+/// elements at that depth and all of their descendants.
+#[derive(Debug, Clone, Copy, PartialEq)]
+struct RestyleDepths(u8);
+
+impl RestyleDepths {
+    /// Returns a `RestyleDepths` representing no element depths.
+    fn empty() -> Self {
+        RestyleDepths(0)
+    }
+
+    /// Returns a `RestyleDepths` representing the current element depth.
+    fn for_self() -> Self {
+        RestyleDepths(0x01)
+    }
+
+    /// Returns a `RestyleDepths` representing the depths of all descendants of
+    /// the current element.
+    fn for_descendants() -> Self {
+        RestyleDepths(0xfe)
+    }
+
+    /// Returns a `RestyleDepths` representing the current element depth and the
+    /// depths of all the current element's descendants.
+    fn for_self_and_descendants() -> Self {
+        RestyleDepths(0xff)
+    }
+
+    /// Returns whether this `RestyleDepths` represents the current element
+    /// depth and the depths of all the current element's descendants.
+    fn is_self_and_descendants(&self) -> bool {
+        self.0 == 0xff
+    }
+
+    /// Returns whether this `RestyleDepths` includes any element depth.
+    fn is_any(&self) -> bool {
+        self.0 != 0
+    }
+
+    /// Returns whether this `RestyleDepths` includes the current element depth.
+    fn has_self(&self) -> bool {
+        (self.0 & 0x01) != 0
+    }
+
+    /// Returns a new `RestyleDepths` with all depth values represented by this
+    /// `RestyleDepths` reduced by one.
+    fn propagate(&self) -> Self {
+        RestyleDepths((self.0 >> 1) | (self.0 & 0x80))
+    }
+
+    /// Returns a new `RestyleDepths` that represents the union of the depths
+    /// from `self` and `other`.
+    fn insert(&mut self, other: RestyleDepths) {
+        self.0 |= other.0;
+    }
+
+    /// Returns whether this `RestyleDepths` includes all depths represented
+    /// by `other`.
+    fn contains(&self, other: RestyleDepths) -> bool {
+        (self.0 & other.0) == other.0
+    }
+}
+
 /// Asserts that all RestyleReplacements have a matching nsRestyleHint value.
 #[cfg(feature = "gecko")]
 #[inline]
@@ -116,8 +182,7 @@ impl RestyleHint {
     #[inline]
     pub fn empty() -> Self {
         RestyleHint {
-            match_self: false,
-            match_descendants: false,
+            match_under_self: RestyleDepths::empty(),
             match_later_siblings: false,
             replacements: RestyleReplacements::empty(),
         }
@@ -128,8 +193,7 @@ impl RestyleHint {
     #[inline]
     pub fn for_self() -> Self {
         RestyleHint {
-            match_self: true,
-            match_descendants: false,
+            match_under_self: RestyleDepths::for_self(),
             match_later_siblings: false,
             replacements: RestyleReplacements::empty(),
         }
@@ -140,8 +204,7 @@ impl RestyleHint {
     #[inline]
     pub fn descendants() -> Self {
         RestyleHint {
-            match_self: false,
-            match_descendants: true,
+            match_under_self: RestyleDepths::for_descendants(),
             match_later_siblings: false,
             replacements: RestyleReplacements::empty(),
         }
@@ -152,8 +215,7 @@ impl RestyleHint {
     #[inline]
     pub fn later_siblings() -> Self {
         RestyleHint {
-            match_self: false,
-            match_descendants: false,
+            match_under_self: RestyleDepths::empty(),
             match_later_siblings: true,
             replacements: RestyleReplacements::empty(),
         }
@@ -164,8 +226,7 @@ impl RestyleHint {
     #[inline]
     pub fn subtree() -> Self {
         RestyleHint {
-            match_self: true,
-            match_descendants: true,
+            match_under_self: RestyleDepths::for_self_and_descendants(),
             match_later_siblings: false,
             replacements: RestyleReplacements::empty(),
         }
@@ -177,8 +238,7 @@ impl RestyleHint {
     #[inline]
     pub fn subtree_and_later_siblings() -> Self {
         RestyleHint {
-            match_self: true,
-            match_descendants: true,
+            match_under_self: RestyleDepths::for_self_and_descendants(),
             match_later_siblings: true,
             replacements: RestyleReplacements::empty(),
         }
@@ -189,8 +249,7 @@ impl RestyleHint {
     #[inline]
     pub fn for_replacements(replacements: RestyleReplacements) -> Self {
         RestyleHint {
-            match_self: false,
-            match_descendants: false,
+            match_under_self: RestyleDepths::empty(),
             match_later_siblings: false,
             replacements: replacements,
         }
@@ -206,14 +265,16 @@ impl RestyleHint {
     /// restyle work, and thus any `insert()` calls will have no effect.
     #[inline]
     pub fn is_maximum(&self) -> bool {
-        self.match_self && self.match_descendants && self.match_later_siblings && self.replacements.is_all()
+        self.match_under_self.is_self_and_descendants() &&
+            self.match_later_siblings &&
+            self.replacements.is_all()
     }
 
     /// Returns whether the hint specifies that some work must be performed on
     /// the current element.
     #[inline]
     pub fn affects_self(&self) -> bool {
-        self.match_self || !self.replacements.is_empty()
+        self.match_self() || !self.replacements.is_empty()
     }
 
     /// Returns whether the hint specifies that later siblings must be restyled.
@@ -233,7 +294,7 @@ impl RestyleHint {
     /// animation cascade level replacement.
     #[inline]
     pub fn has_non_animation_hint(&self) -> bool {
-        self.match_self || self.match_descendants || self.match_later_siblings ||
+        self.match_under_self.is_any() || self.match_later_siblings ||
             self.replacements.contains(RESTYLE_STYLE_ATTRIBUTE)
     }
 
@@ -241,17 +302,17 @@ impl RestyleHint {
     /// for the element.
     #[inline]
     pub fn match_self(&self) -> bool {
-        self.match_self
+        self.match_under_self.has_self()
     }
 
     /// Returns a new `RestyleHint` appropriate for children of the current
     /// element.
     #[inline]
     pub fn propagate_for_non_animation_restyle(&self) -> Self {
-        if self.match_descendants {
-            Self::subtree()
-        } else {
-            Self::empty()
+        RestyleHint {
+            match_under_self: self.match_under_self.propagate(),
+            match_later_siblings: false,
+            replacements: RestyleReplacements::empty(),
         }
     }
 
@@ -271,8 +332,7 @@ impl RestyleHint {
     /// Unions the specified `RestyleHint` into this one.
     #[inline]
     pub fn insert_from(&mut self, other: &Self) {
-        self.match_self |= other.match_self;
-        self.match_descendants |= other.match_descendants;
+        self.match_under_self.insert(other.match_under_self);
         self.match_later_siblings |= other.match_later_siblings;
         self.replacements.insert(other.replacements);
     }
@@ -289,9 +349,8 @@ impl RestyleHint {
     /// work as the specified one.
     #[inline]
     pub fn contains(&mut self, other: &Self) -> bool {
-        !(other.match_self && !self.match_self) &&
-        !(other.match_descendants && !self.match_descendants) &&
-        !(other.match_later_siblings && !self.match_later_siblings) &&
+        self.match_under_self.contains(other.match_under_self) &&
+        (self.match_later_siblings & other.match_later_siblings) == other.match_later_siblings &&
         self.replacements.contains(other.replacements)
     }
 }
@@ -319,9 +378,16 @@ impl From<nsRestyleHint> for RestyleHint {
         use gecko_bindings::structs::nsRestyleHint_eRestyle_SomeDescendants as eRestyle_SomeDescendants;
         use gecko_bindings::structs::nsRestyleHint_eRestyle_Subtree as eRestyle_Subtree;
 
+        let mut match_under_self = RestyleDepths::empty();
+        if (raw.0 & (eRestyle_Self.0 | eRestyle_Subtree.0)) != 0 {
+            match_under_self.insert(RestyleDepths::for_self());
+        }
+        if (raw.0 & (eRestyle_Subtree.0 | eRestyle_SomeDescendants.0)) != 0 {
+            match_under_self.insert(RestyleDepths::for_descendants());
+        }
+
         RestyleHint {
-            match_self: (raw.0 & (eRestyle_Self.0 | eRestyle_Subtree.0)) != 0,
-            match_descendants: (raw.0 & (eRestyle_Subtree.0 | eRestyle_SomeDescendants.0)) != 0,
+            match_under_self: match_under_self,
             match_later_siblings: (raw.0 & eRestyle_LaterSiblings.0) != 0,
             replacements: raw.into(),
         }