1 files changed, 187 insertions, 0 deletions
diff --git a/servo/components/style/invalidation/element/restyle_hints.rs b/servo/components/style/invalidation/element/restyle_hints.rs
new file mode 100644
index 0000000000..c0bf2424d5
--- /dev/null
+++ b/servo/components/style/invalidation/element/restyle_hints.rs
@@ -0,0 +1,187 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Restyle hints: an optimization to avoid unnecessarily matching selectors.
+
+use crate::traversal_flags::TraversalFlags;
+
+bitflags! {
+    /// The kind of restyle we need to do for a given element.
+    #[repr(C)]
+    pub struct RestyleHint: u8 {
+        /// Do a selector match of the element.
+        const RESTYLE_SELF = 1 << 0;
+
+        /// Do a selector match of the element's descendants.
+        const RESTYLE_DESCENDANTS = 1 << 1;
+
+        /// Recascade the current element.
+        const RECASCADE_SELF = 1 << 2;
+
+        /// Recascade all descendant elements.
+        const RECASCADE_DESCENDANTS = 1 << 3;
+
+        /// Replace the style data coming from CSS transitions without updating
+        /// any other style data. This hint is only processed in animation-only
+        /// traversal which is prior to normal traversal.
+        const RESTYLE_CSS_TRANSITIONS = 1 << 4;
+
+        /// Replace the style data coming from CSS animations without updating
+        /// any other style data. This hint is only processed in animation-only
+        /// traversal which is prior to normal traversal.
+        const RESTYLE_CSS_ANIMATIONS = 1 << 5;
+
+        /// Don't re-run selector-matching on the element, only the style
+        /// attribute has changed, and this change didn't have any other
+        /// dependencies.
+        const RESTYLE_STYLE_ATTRIBUTE = 1 << 6;
+
+        /// Replace the style data coming from SMIL animations without updating
+        /// any other style data. This hint is only processed in animation-only
+        /// traversal which is prior to normal traversal.
+        const RESTYLE_SMIL = 1 << 7;
+    }
+}
+
+impl RestyleHint {
+    /// Creates a new `RestyleHint` indicating that the current element and all
+    /// its descendants must be fully restyled.
+    pub fn restyle_subtree() -> Self {
+        RestyleHint::RESTYLE_SELF | RestyleHint::RESTYLE_DESCENDANTS
+    }
+
+    /// Creates a new `RestyleHint` indicating that the current element and all
+    /// its descendants must be recascaded.
+    pub fn recascade_subtree() -> Self {
+        RestyleHint::RECASCADE_SELF | RestyleHint::RECASCADE_DESCENDANTS
+    }
+
+    /// Returns whether this hint invalidates the element and all its
+    /// descendants.
+    pub fn contains_subtree(&self) -> bool {
+        self.contains(RestyleHint::RESTYLE_SELF | RestyleHint::RESTYLE_DESCENDANTS)
+    }
+
+    /// Returns whether we need to restyle this element.
+    pub fn has_non_animation_invalidations(&self) -> bool {
+        self.intersects(
+            RestyleHint::RESTYLE_SELF |
+                RestyleHint::RECASCADE_SELF |
+                (Self::replacements() & !Self::for_animations()),
+        )
+    }
+
+    /// Propagates this restyle hint to a child element.
+    pub fn propagate(&mut self, traversal_flags: &TraversalFlags) -> Self {
+        use std::mem;
+
+        // In the middle of an animation only restyle, we don't need to
+        // propagate any restyle hints, and we need to remove ourselves.
+        if traversal_flags.for_animation_only() {
+            self.remove_animation_hints();
+            return Self::empty();
+        }
+
+        debug_assert!(
+            !self.has_animation_hint(),
+            "There should not be any animation restyle hints \
+             during normal traversal"
+        );
+
+        // Else we should clear ourselves, and return the propagated hint.
+        mem::replace(self, Self::empty()).propagate_for_non_animation_restyle()
+    }
+
+    /// Returns a new `CascadeHint` appropriate for children of the current
+    /// element.
+    fn propagate_for_non_animation_restyle(&self) -> Self {
+        if self.contains(RestyleHint::RESTYLE_DESCENDANTS) {
+            return Self::restyle_subtree();
+        }
+        if self.contains(RestyleHint::RECASCADE_DESCENDANTS) {
+            return Self::recascade_subtree();
+        }
+        Self::empty()
+    }
+
+    /// Returns a hint that contains all the replacement hints.
+    pub fn replacements() -> Self {
+        RestyleHint::RESTYLE_STYLE_ATTRIBUTE | Self::for_animations()
+    }
+
+    /// The replacements for the animation cascade levels.
+    #[inline]
+    pub fn for_animations() -> Self {
+        RestyleHint::RESTYLE_SMIL |
+            RestyleHint::RESTYLE_CSS_ANIMATIONS |
+            RestyleHint::RESTYLE_CSS_TRANSITIONS
+    }
+
+    /// Returns whether the hint specifies that the currently element must be
+    /// recascaded.
+    pub fn has_recascade_self(&self) -> bool {
+        self.contains(RestyleHint::RECASCADE_SELF)
+    }
+
+    /// Returns whether the hint specifies that an animation cascade level must
+    /// be replaced.
+    #[inline]
+    pub fn has_animation_hint(&self) -> bool {
+        self.intersects(Self::for_animations())
+    }
+
+    /// Returns whether the hint specifies that an animation cascade level must
+    /// be replaced.
+    #[inline]
+    pub fn has_animation_hint_or_recascade(&self) -> bool {
+        self.intersects(Self::for_animations() | RestyleHint::RECASCADE_SELF)
+    }
+
+    /// Returns whether the hint specifies some restyle work other than an
+    /// animation cascade level replacement.
+    #[inline]
+    pub fn has_non_animation_hint(&self) -> bool {
+        !(*self & !Self::for_animations()).is_empty()
+    }
+
+    /// Returns whether the hint specifies that selector matching must be re-run
+    /// for the element.
+    #[inline]
+    pub fn match_self(&self) -> bool {
+        self.intersects(RestyleHint::RESTYLE_SELF)
+    }
+
+    /// Returns whether the hint specifies that some cascade levels must be
+    /// replaced.
+    #[inline]
+    pub fn has_replacements(&self) -> bool {
+        self.intersects(Self::replacements())
+    }
+
+    /// Removes all of the animation-related hints.
+    #[inline]
+    pub fn remove_animation_hints(&mut self) {
+        self.remove(Self::for_animations());
+
+        // While RECASCADE_SELF is not animation-specific, we only ever add and
+        // process it during traversal.  If we are here, removing animation
+        // hints, then we are in an animation-only traversal, and we know that
+        // any RECASCADE_SELF flag must have been set due to changes in
+        // inherited values after restyling for animations, and thus we want to
+        // remove it so that we don't later try to restyle the element during a
+        // normal restyle.  (We could have separate RECASCADE_SELF_NORMAL and
+        // RECASCADE_SELF_ANIMATIONS flags to make it clear, but this isn't
+        // currently necessary.)
+        self.remove(RestyleHint::RECASCADE_SELF);
+    }
+}
+
+impl Default for RestyleHint {
+    fn default() -> Self {
+        Self::empty()
+    }
+}
+
+#[cfg(feature = "servo")]
+malloc_size_of_is_0!(RestyleHint);