Pass TraversalFlags from C++ into Rust.

MozReview-Commit-ID: EVUzgnL5coN

components/style/traversal_flags.rs

@@ -0,0 +1,64 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+//! Flags that control the traversal process.
+//!
+//! We CamelCase rather than UPPER_CASING so that we can grep for the same
+//! strings across gecko and servo.
+#![allow(non_upper_case_globals)]
+
+bitflags! {
+    /// Flags that control the traversal process.
+    pub flags TraversalFlags: u32 {
+        /// Traverse only elements for animation restyles.
+        const AnimationOnly = 1 << 0,
+        /// Traverse and update all elements with CSS animations since
+        /// @keyframes rules may have changed. Triggered by CSS rule changes.
+        const ForCSSRuleChanges = 1 << 1,
+        /// Traverse only unstyled children of the root and their descendants.
+        const UnstyledChildrenOnly = 1 << 2,
+        /// FIXME(bholley): This will go away.
+        const ForReconstruct = 1 << 3,
+        /// FIXME(bholley): This will go away.
+        const ForNewlyBoundElement = 1 << 4,
+        /// FIXME(bholley): This will go away.
+        const ForThrottledAnimationFlush = 1 << 5,
+    }
+}
+
+/// Asserts that all TraversalFlags flags have a matching ServoTraversalFlags value in gecko.
+#[cfg(feature = "gecko")]
+#[inline]
+pub fn assert_traversal_flags_match() {
+    use gecko_bindings::structs;
+
+    macro_rules! check_traversal_flags {
+        ( $( $a:ident => $b:ident ),*, ) => {
+            if cfg!(debug_assertions) {
+                let mut modes = TraversalFlags::all();
+                $(
+                    assert_eq!(structs::$a as usize, $b.bits() as usize, stringify!($b));
+                    modes.remove($b);
+                )*
+                assert_eq!(modes, TraversalFlags::empty(), "all TraversalFlags bits should have an assertion");
+            }
+        }
+    }
+
+    check_traversal_flags! {
+        ServoTraversalFlags_AnimationOnly => AnimationOnly,
+        ServoTraversalFlags_ForCSSRuleChanges => ForCSSRuleChanges,
+        ServoTraversalFlags_UnstyledChildrenOnly => UnstyledChildrenOnly,
+        ServoTraversalFlags_ForReconstruct => ForReconstruct,
+        ServoTraversalFlags_ForNewlyBoundElement => ForNewlyBoundElement,
+        ServoTraversalFlags_ForThrottledAnimationFlush => ForThrottledAnimationFlush,
+    }
+}
+
+impl TraversalFlags {
+    /// Returns true if the traversal is for animation-only restyles.
+    pub fn for_animation_only(&self) -> bool {
+        self.contains(AnimationOnly)
+    }
+}