Bug 1372061 - Change StyleChildrenIterator FFI functions to use placement new/delete. r=bholley

MozReview-Commit-ID: BEWvJcaJxA

--HG--
extra : rebase_source : 48b4982001a305b95a88578cb278c3c6e4beac70

dom/base/ChildIterator.h

@@ -264,8 +264,11 @@ private:
  *
  * Note: it assumes that no mutation of the DOM or frame tree takes place during
  * iteration, and will break horribly if that is not true.
+ *
+ * We require this to be memmovable since Rust code can create and move
+ * StyleChildrenIterators.
  */
-class StyleChildrenIterator : private AllChildrenIterator
+class MOZ_NEEDS_MEMMOVABLE_MEMBERS StyleChildrenIterator : private AllChildrenIterator
 {
 public:
   explicit StyleChildrenIterator(const nsIContent* aContent)

layout/style/ServoBindingTypes.h

@@ -68,6 +68,7 @@ typedef mozilla::ComputedTiming RawGeckoComputedTiming;
 typedef nsTArray<const RawServoStyleRule*> RawGeckoServoStyleRuleList;
 typedef nsTArray<nsCSSPropertyID> RawGeckoCSSPropertyIDList;
 typedef mozilla::gfx::Float RawGeckoGfxMatrix4x4[16];
+typedef mozilla::dom::StyleChildrenIterator RawGeckoStyleChildrenIterator;
 
 // We have these helper types so that we can directly generate
 // things like &T or Borrowed<T> on the Rust side in the function, providing
@@ -156,6 +157,7 @@ DECL_BORROWED_MUT_REF_TYPE_FOR(RawGeckoServoStyleRuleList)
 DECL_BORROWED_MUT_REF_TYPE_FOR(nsCSSPropertyIDSet)
 DECL_BORROWED_REF_TYPE_FOR(RawGeckoCSSPropertyIDList)
 DECL_BORROWED_REF_TYPE_FOR(nsXBLBinding)
+DECL_BORROWED_MUT_REF_TYPE_FOR(RawGeckoStyleChildrenIterator)
 
 #undef DECL_ARC_REF_TYPE_FOR
 #undef DECL_OWNED_REF_TYPE_FOR

layout/style/ServoBindings.cpp

@@ -204,23 +204,23 @@ Gecko_DestroyAnonymousContentList(nsTArray<nsIContent*>* aAnonContent)
   delete aAnonContent;
 }
 
-StyleChildrenIteratorOwnedOrNull
-Gecko_MaybeCreateStyleChildrenIterator(RawGeckoNodeBorrowed aNode)
+void
+Gecko_ConstructStyleChildrenIterator(
+  RawGeckoElementBorrowed aElement,
+  RawGeckoStyleChildrenIteratorBorrowedMut aIterator)
 {
-  if (!aNode->IsElement()) {
-    return nullptr;
-  }
-
-  const Element* el = aNode->AsElement();
-  return StyleChildrenIterator::IsNeeded(el) ? new StyleChildrenIterator(el)
-                                             : nullptr;
+  MOZ_ASSERT(aElement);
+  MOZ_ASSERT(aIterator);
+  new (aIterator) StyleChildrenIterator(aElement);
 }
 
 void
-Gecko_DropStyleChildrenIterator(StyleChildrenIteratorOwned aIterator)
+Gecko_DestroyStyleChildrenIterator(
+  RawGeckoStyleChildrenIteratorBorrowedMut aIterator)
 {
   MOZ_ASSERT(aIterator);
-  delete aIterator;
+
+  aIterator->~StyleChildrenIterator();
 }
 
 nsIContent*
@@ -235,7 +235,7 @@ Gecko_ElementBindingAnonymousContent(RawGeckoElementBorrowed aElement)
 }
 
 RawGeckoNodeBorrowed
-Gecko_GetNextStyleChild(StyleChildrenIteratorBorrowedMut aIterator)
+Gecko_GetNextStyleChild(RawGeckoStyleChildrenIteratorBorrowedMut aIterator)
 {
   MOZ_ASSERT(aIterator);
   return aIterator->GetNextChild();

layout/style/ServoBindings.h

@@ -137,12 +137,11 @@ void Gecko_DestroyAnonymousContentList(nsTArray<nsIContent*>* anon_content);
 // By default, Servo walks the DOM by traversing the siblings of the DOM-view
 // first child. This generally works, but misses anonymous children, which we
 // want to traverse during styling. To support these cases, we create an
-// optional heap-allocated iterator for nodes that need it. If the creation
-// method returns null, Servo falls back to the aforementioned simpler (and
-// faster) sibling traversal.
-StyleChildrenIteratorOwnedOrNull Gecko_MaybeCreateStyleChildrenIterator(RawGeckoNodeBorrowed node);
-void Gecko_DropStyleChildrenIterator(StyleChildrenIteratorOwned it);
-RawGeckoNodeBorrowedOrNull Gecko_GetNextStyleChild(StyleChildrenIteratorBorrowedMut it);
+// optional stack-allocated iterator in aIterator for nodes that need it.
+void Gecko_ConstructStyleChildrenIterator(RawGeckoElementBorrowed aElement,
+                                          RawGeckoStyleChildrenIteratorBorrowedMut aIterator);
+void Gecko_DestroyStyleChildrenIterator(RawGeckoStyleChildrenIteratorBorrowedMut aIterator);
+RawGeckoNodeBorrowedOrNull Gecko_GetNextStyleChild(RawGeckoStyleChildrenIteratorBorrowedMut it);
 
 void Gecko_LoadStyleSheet(mozilla::css::Loader* loader,
                           mozilla::ServoStyleSheet* parent,

layout/style/ServoBindings.toml

@@ -57,6 +57,7 @@ headers = [
     "mozilla/ServoElementSnapshot.h",
     "mozilla/ServoElementSnapshotTable.h",
     "mozilla/dom/Element.h",
+    "mozilla/dom/ChildIterator.h",
     "mozilla/dom/NameSpaceConstants.h",
     "mozilla/LookAndFeel.h",
     "mozilla/ServoBindings.h",
@@ -123,6 +124,7 @@ whitelist-types = [
     "mozilla::css::SheetParsingMode",
     "mozilla::css::URLMatchingFunction",
     "mozilla::dom::IterationCompositeOperation",
+    "mozilla::dom::StyleChildrenIterator",
     "mozilla::HalfCorner",
     "mozilla::PropertyStyleAnimationValuePair",
     "mozilla::TraversalRestyleBehavior",
@@ -348,6 +350,7 @@ structs-types = [
     "RawGeckoPresContext",
     "RawGeckoPresContextOwned",
     "RawGeckoStyleAnimationList",
+    "RawGeckoStyleChildrenIteratorBorrowedMut",
     "RawGeckoServoStyleRuleList",
     "RawGeckoURLExtraData",
     "RawGeckoXBLBinding",
@@ -453,7 +456,6 @@ array-types = [
 ]
 servo-owned-types = [
     { name = "RawServoStyleSet", opaque = true },
-    { name = "StyleChildrenIterator", opaque = true },
     { name = "ServoElementSnapshot", opaque = false },
     { name = "RawServoAnimationValueMap", opaque = true },
 ]