1 files changed, 121 insertions, 0 deletions
diff --git a/servo/components/style/gecko/restyle_damage.rs b/servo/components/style/gecko/restyle_damage.rs
new file mode 100644
index 0000000000..4749daea18
--- /dev/null
+++ b/servo/components/style/gecko/restyle_damage.rs
@@ -0,0 +1,121 @@
+/* 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/. */
+
+//! Gecko's restyle damage computation (aka change hints, aka `nsChangeHint`).
+
+use crate::gecko_bindings::bindings;
+use crate::gecko_bindings::structs;
+use crate::gecko_bindings::structs::nsChangeHint;
+use crate::matching::{StyleChange, StyleDifference};
+use crate::properties::ComputedValues;
+use std::ops::{BitAnd, BitOr, BitOrAssign, Not};
+
+/// The representation of Gecko's restyle damage is just a wrapper over
+/// `nsChangeHint`.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct GeckoRestyleDamage(nsChangeHint);
+
+impl GeckoRestyleDamage {
+    /// Trivially construct a new `GeckoRestyleDamage`.
+    #[inline]
+    pub fn new(raw: nsChangeHint) -> Self {
+        GeckoRestyleDamage(raw)
+    }
+
+    /// Get the inner change hint for this damage.
+    #[inline]
+    pub fn as_change_hint(&self) -> nsChangeHint {
+        self.0
+    }
+
+    /// Get an empty change hint, that is (`nsChangeHint(0)`).
+    #[inline]
+    pub fn empty() -> Self {
+        GeckoRestyleDamage(nsChangeHint(0))
+    }
+
+    /// Returns whether this restyle damage represents the empty damage.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.0 == nsChangeHint(0)
+    }
+
+    /// Computes the `StyleDifference` (including the appropriate change hint)
+    /// given an old and a new style.
+    pub fn compute_style_difference(
+        old_style: &ComputedValues,
+        new_style: &ComputedValues,
+    ) -> StyleDifference {
+        let mut any_style_changed = false;
+        let mut reset_only = false;
+        let hint = unsafe {
+            bindings::Gecko_CalcStyleDifference(
+                old_style.as_gecko_computed_style(),
+                new_style.as_gecko_computed_style(),
+                &mut any_style_changed,
+                &mut reset_only,
+            )
+        };
+        if reset_only && !old_style.custom_properties_equal(new_style) {
+            // The Gecko_CalcStyleDifference call only checks the non-custom
+            // property structs, so we check the custom properties here. Since
+            // they generate no damage themselves, we can skip this check if we
+            // already know we had some inherited (regular) property
+            // differences.
+            any_style_changed = true;
+            reset_only = false;
+        }
+        let change = if any_style_changed {
+            StyleChange::Changed { reset_only }
+        } else {
+            StyleChange::Unchanged
+        };
+        let damage = GeckoRestyleDamage(nsChangeHint(hint));
+        StyleDifference { damage, change }
+    }
+
+    /// Returns true if this restyle damage contains all the damage of |other|.
+    pub fn contains(self, other: Self) -> bool {
+        self & other == other
+    }
+
+    /// Gets restyle damage to reconstruct the entire frame, subsuming all
+    /// other damage.
+    pub fn reconstruct() -> Self {
+        GeckoRestyleDamage(structs::nsChangeHint::nsChangeHint_ReconstructFrame)
+    }
+}
+
+impl Default for GeckoRestyleDamage {
+    fn default() -> Self {
+        Self::empty()
+    }
+}
+
+impl BitOr for GeckoRestyleDamage {
+    type Output = Self;
+    fn bitor(self, other: Self) -> Self {
+        GeckoRestyleDamage(self.0 | other.0)
+    }
+}
+
+impl BitOrAssign for GeckoRestyleDamage {
+    fn bitor_assign(&mut self, other: Self) {
+        *self = *self | other;
+    }
+}
+
+impl BitAnd for GeckoRestyleDamage {
+    type Output = Self;
+    fn bitand(self, other: Self) -> Self {
+        GeckoRestyleDamage(nsChangeHint((self.0).0 & (other.0).0))
+    }
+}
+
+impl Not for GeckoRestyleDamage {
+    type Output = Self;
+    fn not(self) -> Self {
+        GeckoRestyleDamage(nsChangeHint(!(self.0).0))
+    }
+}