style: Remove HasFFI as well

After the previous patches we only have one trait which we should also
tweak / rework, so let's put it all on that single trait.

Differential Revision: https://phabricator.services.mozilla.com/D177515

components/style/gecko/arc_types.rs

@@ -17,7 +17,7 @@ use crate::gecko_bindings::structs::{
     RawServoMozDocumentRule, RawServoNamespaceRule, RawServoPageRule, RawServoStyleRule,
     RawServoStyleSheetContents, RawServoSupportsRule, ServoCssRules,
 };
-use crate::gecko_bindings::sugar::ownership::{HasArcFFI, HasFFI, Strong};
+use crate::gecko_bindings::sugar::ownership::{HasArcFFI, Strong};
 use crate::media_queries::MediaList;
 use crate::properties::animated_properties::AnimationValue;
 use crate::properties::{ComputedValues, PropertyDeclarationBlock};
@@ -33,10 +33,9 @@ use std::{mem, ptr};
 
 macro_rules! impl_arc_ffi {
     ($servo_type:ty => $gecko_type:ty[$addref:ident, $release:ident]) => {
-        unsafe impl HasFFI for $servo_type {
+        unsafe impl HasArcFFI for $servo_type {
             type FFIType = $gecko_type;
         }
-        unsafe impl HasArcFFI for $servo_type {}
 
         #[no_mangle]
         pub unsafe extern "C" fn $addref(obj: &$gecko_type) {

components/style/gecko_bindings/sugar/ownership.rs

@@ -11,21 +11,18 @@ use std::mem::{forget, transmute};
 use std::ops::{Deref, DerefMut};
 use std::ptr;
 
-/// Indicates that a given Servo type has a corresponding Gecko FFI type.
-pub unsafe trait HasFFI: Sized + 'static {
-    /// The corresponding Gecko type that this rust type represents.
-    ///
-    /// See the examples in `components/style/gecko/conversions.rs`.
-    type FFIType: Sized;
-}
-
 /// Helper trait for conversions between FFI Strong/Borrowed types and Arcs
 ///
 /// Should be implemented by types which are passed over FFI as Arcs via Strong
 /// and Borrowed.
 ///
 /// In this case, the FFIType is the rough equivalent of ArcInner<Self>.
-pub unsafe trait HasArcFFI: HasFFI {
+pub unsafe trait HasArcFFI: Sized + 'static {
+    /// The corresponding Gecko type that this rust type represents.
+    ///
+    /// See the examples in `components/style/gecko/conversions.rs`.
+    type FFIType: Sized;
+
     // these methods can't be on Borrowed because it leads to an unspecified
     // impl parameter
     /// Artificially increments the refcount of a (possibly null) borrowed Arc
@@ -163,26 +160,21 @@ impl<GeckoType> Strong<GeckoType> {
 
 /// A few helpers implemented on top of Arc<ServoType> to make it more
 /// comfortable to use and write safe code with.
-pub unsafe trait FFIArcHelpers {
-    /// The Rust FFI type that we're implementing methods for.
-    type Inner: HasArcFFI;
-
+pub unsafe trait FFIArcHelpers<T: HasArcFFI> {
     /// Converts an Arc into a strong FFI reference.
     ///
     /// Arc<ServoType> -> Strong<GeckoType>
-    fn into_strong(self) -> Strong<<Self::Inner as HasFFI>::FFIType>;
+    fn into_strong(self) -> Strong<T::FFIType>;
 
     /// Produces a borrowed FFI reference by borrowing an Arc.
     ///
     /// &Arc<ServoType> -> &GeckoType
     ///
     /// Then the `arc_as_borrowed` method can go away.
-    fn as_borrowed(&self) -> &<Self::Inner as HasFFI>::FFIType;
+    fn as_borrowed(&self) -> &T::FFIType;
 }
 
-unsafe impl<T: HasArcFFI> FFIArcHelpers for RawOffsetArc<T> {
-    type Inner = T;
-
+unsafe impl<T: HasArcFFI> FFIArcHelpers<T> for RawOffsetArc<T> {
     #[inline]
     fn into_strong(self) -> Strong<T::FFIType> {
         unsafe { transmute(self) }
@@ -194,9 +186,7 @@ unsafe impl<T: HasArcFFI> FFIArcHelpers for RawOffsetArc<T> {
     }
 }
 
-unsafe impl<T: HasArcFFI> FFIArcHelpers for Arc<T> {
-    type Inner = T;
-
+unsafe impl<T: HasArcFFI> FFIArcHelpers<T> for Arc<T> {
     #[inline]
     fn into_strong(self) -> Strong<T::FFIType> {
         Arc::into_raw_offset(self).into_strong()