stylo: Remove usage of ServoComputedValues from binding functions

components/servo_arc/lib.rs

@@ -889,6 +889,12 @@ impl<'a, T> ArcBorrow<'a, T> {
         arc
     }
 
+    /// For constructing from a reference known to be Arc-backed,
+    /// e.g. if we obtain such a reference over FFI
+    pub unsafe fn from_ref(r: &'a T) -> Self {
+        ArcBorrow(r)
+    }
+
     pub fn with_arc<F, U>(&self, f: F) -> U where F: FnOnce(&Arc<T>) -> U, T: 'static {
         // Synthesize transient Arc, which never touches the refcount.
         let transient = unsafe { NoDrop::new(Arc::from_raw(self.0)) };

components/style/gecko/arc_types.rs

@@ -13,13 +13,14 @@ use gecko_bindings::bindings::{RawServoKeyframe, RawServoKeyframesRule};
 use gecko_bindings::bindings::{RawServoMediaRule, RawServoNamespaceRule, RawServoPageRule};
 use gecko_bindings::bindings::{RawServoRuleNode, RawServoRuleNodeStrong, RawServoDocumentRule};
 use gecko_bindings::bindings::ServoCssRules;
-use gecko_bindings::structs::{RawServoAnimationValue, RawServoDeclarationBlock, RawServoStyleRule, RawServoMediaList};
-use gecko_bindings::structs::{RawServoStyleSheetContents, ServoStyleContext};
-use gecko_bindings::sugar::ownership::{HasArcFFI, HasFFI};
+use gecko_bindings::structs::{RawServoAnimationValue, RawServoDeclarationBlock, RawServoStyleRule};
+use gecko_bindings::structs::{RawServoMediaList, RawServoStyleSheetContents};
+use gecko_bindings::sugar::ownership::{HasArcFFI, HasFFI, Strong};
 use media_queries::MediaList;
 use properties::{ComputedValues, PropertyDeclarationBlock};
 use properties::animated_properties::AnimationValue;
 use rule_tree::StrongRuleNode;
+use servo_arc::{Arc, ArcBorrow};
 use shared_lock::Locked;
 use std::{mem, ptr};
 use stylesheets::{CssRules, StylesheetContents, StyleRule, ImportRule, KeyframesRule, MediaRule};
@@ -51,9 +52,6 @@ impl_arc_ffi!(Locked<CssRules> => ServoCssRules
 impl_arc_ffi!(StylesheetContents => RawServoStyleSheetContents
               [Servo_StyleSheetContents_AddRef, Servo_StyleSheetContents_Release]);
 
-impl_arc_ffi!(ComputedValues => ServoStyleContext
-              [Servo_StyleContext_AddRef, Servo_StyleContext_Release]);
-
 impl_arc_ffi!(Locked<PropertyDeclarationBlock> => RawServoDeclarationBlock
               [Servo_DeclarationBlock_AddRef, Servo_DeclarationBlock_Release]);
 
@@ -114,3 +112,28 @@ pub unsafe extern "C" fn Servo_RuleNode_Release(obj: &RawServoRuleNode) {
     let ptr = StrongRuleNode::from_ffi(&obj);
     ptr::read(ptr as *const StrongRuleNode);
 }
+
+// ServoStyleContext is not an opaque type on any side of FFI.
+// This means that doing the HasArcFFI type trick is actually unsound,
+// since it gives us a way to construct an Arc<ServoStyleContext> from
+// an &ServoStyleContext, which in general is not allowed. So we
+// implement the restricted set of arc type functionality we need.
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleContext_AddRef(obj: &ComputedValues) {
+    mem::forget(ArcBorrow::from_ref(obj).clone_arc());
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleContext_Release(obj: &ComputedValues) {
+    ArcBorrow::from_ref(obj).with_arc(|a: &Arc<ComputedValues>| {
+        let _: Arc<ComputedValues> = ptr::read(a);
+    });
+}
+
+
+impl From<Arc<ComputedValues>> for Strong<ComputedValues> {
+    fn from(arc: Arc<ComputedValues>) -> Self {
+        unsafe { mem::transmute(Arc::into_raw_offset(arc)) }
+    }
+}

components/style/gecko/generated/bindings.rs

@@ -5,7 +5,7 @@ use gecko_bindings::structs::nsStyleTransformMatrix;
 use gecko_bindings::structs::nsTArray;
 type nsACString_internal = nsACString;
 type nsAString_internal = nsAString;
-pub type ServoStyleContextBorrowed<'a> = &'a ServoStyleContext;
+pub type ServoStyleContextBorrowed<'a> = &'a ::properties::ComputedValues;
 pub type ServoStyleContextBorrowedOrNull<'a> = Option<&'a ::properties::ComputedValues>;
 pub type ServoComputedValuesBorrowed<'a> = &'a ServoComputedValues;
 pub type ServoComputedValuesBorrowedOrNull<'a> = Option<&'a ServoComputedValues>;
@@ -2322,7 +2322,7 @@ extern "C" {
 }
 extern "C" {
     pub fn Servo_ComputedValues_SpecifiesAnimationsOrTransitions(computed_values:
-                                                                     ServoComputedValuesBorrowed)
+                                                                     ServoStyleContextBorrowed)
      -> bool;
 }
 extern "C" {
@@ -2705,7 +2705,7 @@ extern "C" {
 }
 extern "C" {
     pub fn Servo_ComputedValues_GetStyleBits(values:
-                                                 ServoComputedValuesBorrowed)
+                                                 ServoStyleContextBorrowed)
      -> u64;
 }
 extern "C" {
@@ -2717,7 +2717,7 @@ extern "C" {
 }
 extern "C" {
     pub fn Servo_ComputedValues_GetStyleRuleList(values:
-                                                     ServoComputedValuesBorrowed,
+                                                     ServoStyleContextBorrowed,
                                                  rules:
                                                      RawGeckoServoStyleRuleListBorrowedMut);
 }
@@ -2804,17 +2804,17 @@ extern "C" {
 }
 extern "C" {
     pub fn Servo_GetCustomPropertyValue(computed_values:
-                                            ServoComputedValuesBorrowed,
+                                            ServoStyleContextBorrowed,
                                         name: *const nsAString,
                                         value: *mut nsAString) -> bool;
 }
 extern "C" {
     pub fn Servo_GetCustomPropertiesCount(computed_values:
-                                              ServoComputedValuesBorrowed)
+                                              ServoStyleContextBorrowed)
      -> u32;
 }
 extern "C" {
-    pub fn Servo_GetCustomPropertyNameAt(arg1: ServoComputedValuesBorrowed,
+    pub fn Servo_GetCustomPropertyNameAt(arg1: ServoStyleContextBorrowed,
                                          index: u32, name: *mut nsAString)
      -> bool;
 }

components/style/gecko/generated/structs_debug.rs

@@ -16,7 +16,7 @@ pub type ServoRuleNode = Option<::rule_tree::StrongRuleNode>;
 pub type ServoVisitedStyle = Option<::servo_arc::RawOffsetArc<::properties::ComputedValues>>;
 pub type ServoComputedValueFlags = ::properties::computed_value_flags::ComputedValueFlags;
 pub type ServoRawOffsetArc<T> = ::servo_arc::RawOffsetArc<T>;
-pub type ServoStyleContextStrong = ::gecko_bindings::sugar::ownership::Strong<ServoStyleContext>;
+pub type ServoStyleContextStrong = ::gecko_bindings::sugar::ownership::Strong<::properties::ComputedValues>;
 
 #[allow(non_snake_case, non_camel_case_types, non_upper_case_globals)]
 pub mod root {

components/style/gecko/generated/structs_release.rs

@@ -16,7 +16,7 @@ pub type ServoRuleNode = Option<::rule_tree::StrongRuleNode>;
 pub type ServoVisitedStyle = Option<::servo_arc::RawOffsetArc<::properties::ComputedValues>>;
 pub type ServoComputedValueFlags = ::properties::computed_value_flags::ComputedValueFlags;
 pub type ServoRawOffsetArc<T> = ::servo_arc::RawOffsetArc<T>;
-pub type ServoStyleContextStrong = ::gecko_bindings::sugar::ownership::Strong<ServoStyleContext>;
+pub type ServoStyleContextStrong = ::gecko_bindings::sugar::ownership::Strong<::properties::ComputedValues>;
 
 #[allow(non_snake_case, non_camel_case_types, non_upper_case_globals)]
 pub mod root {

components/style/properties/gecko.mako.rs

@@ -227,7 +227,8 @@ impl ComputedValuesInner {
     ) -> Arc<ComputedValues> {
         let arc = unsafe {
             let arc: Arc<ComputedValues> = Arc::new(uninitialized());
-            bindings::Gecko_ServoStyleContext_Init(&arc.0 as *const _ as *mut _, parent, pres_context,
+            bindings::Gecko_ServoStyleContext_Init(&arc.0 as *const _ as *mut _,
+                                                   parent, pres_context,
                                                    &self, pseudo_ty, pseudo_tag);
             // We're simulating a move by having C++ do a memcpy and then forgetting
             // it on this end.