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diff --git a/editor/libeditor/ManualNAC.h b/editor/libeditor/ManualNAC.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#ifndef mozilla_ManualNAC_h
+#define mozilla_ManualNAC_h
+
+#include "mozilla/dom/Element.h"
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+
+// 16 seems to be the maximum number of manual Native Anonymous Content (NAC)
+// nodes that editor creates for a given element.
+//
+// These need to be manually removed by the machinery that sets the NAC,
+// otherwise we'll leak.
+using ManualNACArray = AutoTArray<RefPtr<dom::Element>, 16>;
+
+/**
+ * Smart pointer class to own "manual" Native Anonymous Content, and perform
+ * the necessary registration and deregistration on the parent element.
+ */
+class ManualNACPtr final {
+ public:
+ ManualNACPtr() = default;
+ MOZ_IMPLICIT ManualNACPtr(decltype(nullptr)) {}
+ explicit ManualNACPtr(already_AddRefed<dom::Element> aNewNAC)
+ : mPtr(aNewNAC) {
+ if (!mPtr) {
+ return;
+ }
+
+ // Record the NAC on the element, so that AllChildrenIterator can find it.
+ nsIContent* parentContent = mPtr->GetParent();
+ auto nac = static_cast<ManualNACArray*>(
+ parentContent->GetProperty(nsGkAtoms::manualNACProperty));
+ if (!nac) {
+ nac = new ManualNACArray();
+ parentContent->SetProperty(nsGkAtoms::manualNACProperty, nac,
+ nsINode::DeleteProperty<ManualNACArray>);
+ }
+ nac->AppendElement(mPtr);
+ }
+
+ // We use move semantics, and delete the copy-constructor and operator=.
+ ManualNACPtr(ManualNACPtr&& aOther) : mPtr(std::move(aOther.mPtr)) {}
+ ManualNACPtr(ManualNACPtr& aOther) = delete;
+ ManualNACPtr& operator=(ManualNACPtr&& aOther) {
+ mPtr = std::move(aOther.mPtr);
+ return *this;
+ }
+ ManualNACPtr& operator=(ManualNACPtr& aOther) = delete;
+
+ ~ManualNACPtr() { Reset(); }
+
+ void Reset() {
+ if (!mPtr) {
+ return;
+ }
+
+ RefPtr<dom::Element> ptr = std::move(mPtr);
+ RemoveContentFromNACArray(ptr);
+ }
+
+ static bool IsManualNAC(nsIContent* aAnonContent) {
+ MOZ_ASSERT(aAnonContent->IsRootOfNativeAnonymousSubtree());
+ MOZ_ASSERT(aAnonContent->IsInComposedDoc());
+
+ auto* nac = static_cast<ManualNACArray*>(
+ aAnonContent->GetParent()->GetProperty(nsGkAtoms::manualNACProperty));
+ return nac && nac->Contains(aAnonContent);
+ }
+
+ static void RemoveContentFromNACArray(nsIContent* aAnonymousContent) {
+ nsIContent* parentContent = aAnonymousContent->GetParent();
+ if (!parentContent) {
+ NS_WARNING("Potentially leaking manual NAC");
+ return;
+ }
+
+ // Remove reference from the parent element.
+ auto* nac = static_cast<ManualNACArray*>(
+ parentContent->GetProperty(nsGkAtoms::manualNACProperty));
+ // Document::AdoptNode might remove all properties before destroying editor.
+ // So we have to consider that NAC could be already removed.
+ if (nac) {
+ nac->RemoveElement(aAnonymousContent);
+ if (nac->IsEmpty()) {
+ parentContent->RemoveProperty(nsGkAtoms::manualNACProperty);
+ }
+ }
+
+ aAnonymousContent->UnbindFromTree();
+ }
+
+ dom::Element* get() const { return mPtr.get(); }
+ dom::Element* operator->() const { return get(); }
+ operator dom::Element*() const& { return get(); }
+
+ private:
+ RefPtr<dom::Element> mPtr;
+};
+
+} // namespace mozilla
+
+inline void ImplCycleCollectionUnlink(mozilla::ManualNACPtr& field) {
+ field.Reset();
+}
+
+inline void ImplCycleCollectionTraverse(
+ nsCycleCollectionTraversalCallback& callback,
+ const mozilla::ManualNACPtr& field, const char* name, uint32_t flags = 0) {
+ CycleCollectionNoteChild(callback, field.get(), name, flags);
+}
+
+#endif // #ifndef mozilla_ManualNAC_h