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diff --git a/js/public/GCVector.h b/js/public/GCVector.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * 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 js_GCVector_h
+#define js_GCVector_h
+
+#include "mozilla/Assertions.h"       // MOZ_ASSERT
+#include "mozilla/Attributes.h"       // MOZ_STACK_CLASS
+#include "mozilla/MemoryReporting.h"  // MallocSizeOf
+#include "mozilla/Span.h"
+#include "mozilla/Vector.h"
+
+#include <stddef.h>  // size_t
+#include <utility>   // forward, move
+
+#include "js/AllocPolicy.h"
+#include "js/GCPolicyAPI.h"
+#include "js/RootingAPI.h"
+
+class JSTracer;
+struct JSContext;
+
+namespace JS {
+
+// A GCVector is a Vector with an additional trace method that knows how
+// to visit all of the items stored in the Vector. For vectors that contain GC
+// things, this is usually more convenient than manually iterating and marking
+// the contents.
+//
+// Most types of GC pointers as keys and values can be traced with no extra
+// infrastructure. For structs and non-gc-pointer members, ensure that there is
+// a specialization of GCPolicy<T> with an appropriate trace method available
+// to handle the custom type. Generic helpers can be found in
+// js/public/TracingAPI.h.
+//
+// Note that although this Vector's trace will deal correctly with moved items,
+// it does not itself know when to barrier or trace items. To function properly
+// it must either be used with Rooted, or barriered and traced manually.
+template <typename T, size_t MinInlineCapacity = 0,
+          typename AllocPolicy = js::TempAllocPolicy>
+class GCVector {
+  mozilla::Vector<T, MinInlineCapacity, AllocPolicy> vector;
+
+ public:
+  using ElementType = T;
+
+  explicit GCVector(AllocPolicy alloc) : vector(std::move(alloc)) {}
+  GCVector() : GCVector(AllocPolicy()) {}
+
+  GCVector(GCVector&& vec) : vector(std::move(vec.vector)) {}
+
+  GCVector& operator=(GCVector&& vec) {
+    vector = std::move(vec.vector);
+    return *this;
+  }
+
+  size_t length() const { return vector.length(); }
+  bool empty() const { return vector.empty(); }
+  size_t capacity() const { return vector.capacity(); }
+
+  T* begin() { return vector.begin(); }
+  const T* begin() const { return vector.begin(); }
+
+  T* end() { return vector.end(); }
+  const T* end() const { return vector.end(); }
+
+  T& operator[](size_t i) { return vector[i]; }
+  const T& operator[](size_t i) const { return vector[i]; }
+
+  T& back() { return vector.back(); }
+  const T& back() const { return vector.back(); }
+
+  operator mozilla::Span<T>() { return vector; }
+  operator mozilla::Span<const T>() const { return vector; }
+
+  bool initCapacity(size_t cap) { return vector.initCapacity(cap); }
+  [[nodiscard]] bool reserve(size_t req) { return vector.reserve(req); }
+  void shrinkBy(size_t amount) { return vector.shrinkBy(amount); }
+  void shrinkTo(size_t newLen) { return vector.shrinkTo(newLen); }
+  [[nodiscard]] bool growBy(size_t amount) { return vector.growBy(amount); }
+  [[nodiscard]] bool resize(size_t newLen) { return vector.resize(newLen); }
+
+  void clear() { return vector.clear(); }
+  void clearAndFree() { return vector.clearAndFree(); }
+
+  template <typename U>
+  bool append(U&& item) {
+    return vector.append(std::forward<U>(item));
+  }
+
+  void erase(T* it) { vector.erase(it); }
+  void erase(T* begin, T* end) { vector.erase(begin, end); }
+  template <typename Pred>
+  void eraseIf(Pred pred) {
+    vector.eraseIf(pred);
+  }
+  template <typename U>
+  void eraseIfEqual(const U& u) {
+    vector.eraseIfEqual(u);
+  }
+
+  template <typename... Args>
+  [[nodiscard]] bool emplaceBack(Args&&... args) {
+    return vector.emplaceBack(std::forward<Args>(args)...);
+  }
+
+  template <typename... Args>
+  void infallibleEmplaceBack(Args&&... args) {
+    vector.infallibleEmplaceBack(std::forward<Args>(args)...);
+  }
+
+  template <typename U>
+  void infallibleAppend(U&& aU) {
+    return vector.infallibleAppend(std::forward<U>(aU));
+  }
+  void infallibleAppendN(const T& aT, size_t aN) {
+    return vector.infallibleAppendN(aT, aN);
+  }
+  template <typename U>
+  void infallibleAppend(const U* aBegin, const U* aEnd) {
+    return vector.infallibleAppend(aBegin, aEnd);
+  }
+  template <typename U>
+  void infallibleAppend(const U* aBegin, size_t aLength) {
+    return vector.infallibleAppend(aBegin, aLength);
+  }
+
+  template <typename U>
+  [[nodiscard]] bool appendAll(const U& aU) {
+    return vector.append(aU.begin(), aU.end());
+  }
+  template <typename T2, size_t MinInlineCapacity2, typename AllocPolicy2>
+  [[nodiscard]] bool appendAll(
+      GCVector<T2, MinInlineCapacity2, AllocPolicy2>&& aU) {
+    return vector.appendAll(aU.begin(), aU.end());
+  }
+
+  [[nodiscard]] bool appendN(const T& val, size_t count) {
+    return vector.appendN(val, count);
+  }
+
+  template <typename U>
+  [[nodiscard]] bool append(const U* aBegin, const U* aEnd) {
+    return vector.append(aBegin, aEnd);
+  }
+  template <typename U>
+  [[nodiscard]] bool append(const U* aBegin, size_t aLength) {
+    return vector.append(aBegin, aLength);
+  }
+
+  void popBack() { return vector.popBack(); }
+  T popCopy() { return vector.popCopy(); }
+
+  size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
+    return vector.sizeOfExcludingThis(mallocSizeOf);
+  }
+
+  size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
+    return vector.sizeOfIncludingThis(mallocSizeOf);
+  }
+
+  void trace(JSTracer* trc) {
+    for (auto& elem : vector) {
+      GCPolicy<T>::trace(trc, &elem, "vector element");
+    }
+  }
+
+  bool traceWeak(JSTracer* trc) {
+    mutableEraseIf(
+        [trc](T& elem) { return !GCPolicy<T>::traceWeak(trc, &elem); });
+    return !empty();
+  }
+
+  // Like eraseIf, but may mutate the contents of the vector.
+  template <typename Pred>
+  void mutableEraseIf(Pred pred) {
+    T* src = begin();
+    T* dst = begin();
+    while (src != end()) {
+      if (!pred(*src)) {
+        if (src != dst) {
+          *dst = std::move(*src);
+        }
+        dst++;
+      }
+      src++;
+    }
+
+    MOZ_ASSERT(dst <= end());
+    shrinkBy(end() - dst);
+  }
+};
+
+// AllocPolicy is optional. It has a default value declared in TypeDecls.h
+template <typename T, typename AllocPolicy>
+class MOZ_STACK_CLASS StackGCVector : public GCVector<T, 8, AllocPolicy> {
+ public:
+  using Base = GCVector<T, 8, AllocPolicy>;
+
+ private:
+  // Inherit constructor from GCVector.
+  using Base::Base;
+};
+
+}  // namespace JS
+
+namespace js {
+
+template <typename Wrapper, typename T, size_t Capacity, typename AllocPolicy>
+class WrappedPtrOperations<JS::GCVector<T, Capacity, AllocPolicy>, Wrapper> {
+  using Vec = JS::GCVector<T, Capacity, AllocPolicy>;
+  const Vec& vec() const { return static_cast<const Wrapper*>(this)->get(); }
+
+ public:
+  const AllocPolicy& allocPolicy() const { return vec().allocPolicy(); }
+  size_t length() const { return vec().length(); }
+  bool empty() const { return vec().empty(); }
+  size_t capacity() const { return vec().capacity(); }
+  const T* begin() const { return vec().begin(); }
+  const T* end() const { return vec().end(); }
+  const T& back() const { return vec().back(); }
+
+  JS::Handle<T> operator[](size_t aIndex) const {
+    return JS::Handle<T>::fromMarkedLocation(&vec().operator[](aIndex));
+  }
+};
+
+template <typename Wrapper, typename T, size_t Capacity, typename AllocPolicy>
+class MutableWrappedPtrOperations<JS::GCVector<T, Capacity, AllocPolicy>,
+                                  Wrapper>
+    : public WrappedPtrOperations<JS::GCVector<T, Capacity, AllocPolicy>,
+                                  Wrapper> {
+  using Vec = JS::GCVector<T, Capacity, AllocPolicy>;
+  const Vec& vec() const { return static_cast<const Wrapper*>(this)->get(); }
+  Vec& vec() { return static_cast<Wrapper*>(this)->get(); }
+
+ public:
+  const AllocPolicy& allocPolicy() const { return vec().allocPolicy(); }
+  AllocPolicy& allocPolicy() { return vec().allocPolicy(); }
+  const T* begin() const { return vec().begin(); }
+  T* begin() { return vec().begin(); }
+  const T* end() const { return vec().end(); }
+  T* end() { return vec().end(); }
+  const T& back() const { return vec().back(); }
+  T& back() { return vec().back(); }
+
+  JS::Handle<T> operator[](size_t aIndex) const {
+    return JS::Handle<T>::fromMarkedLocation(&vec().operator[](aIndex));
+  }
+  JS::MutableHandle<T> operator[](size_t aIndex) {
+    return JS::MutableHandle<T>::fromMarkedLocation(&vec().operator[](aIndex));
+  }
+
+  [[nodiscard]] bool initCapacity(size_t aRequest) {
+    return vec().initCapacity(aRequest);
+  }
+  [[nodiscard]] bool reserve(size_t aRequest) {
+    return vec().reserve(aRequest);
+  }
+  void shrinkBy(size_t aIncr) { vec().shrinkBy(aIncr); }
+  [[nodiscard]] bool growBy(size_t aIncr) { return vec().growBy(aIncr); }
+  [[nodiscard]] bool resize(size_t aNewLength) {
+    return vec().resize(aNewLength);
+  }
+  void clear() { vec().clear(); }
+  void clearAndFree() { vec().clearAndFree(); }
+  template <typename U>
+  [[nodiscard]] bool append(U&& aU) {
+    return vec().append(std::forward<U>(aU));
+  }
+  template <typename... Args>
+  [[nodiscard]] bool emplaceBack(Args&&... aArgs) {
+    return vec().emplaceBack(std::forward<Args>(aArgs)...);
+  }
+  template <typename... Args>
+  void infallibleEmplaceBack(Args&&... args) {
+    vec().infallibleEmplaceBack(std::forward<Args>(args)...);
+  }
+  template <typename U>
+  [[nodiscard]] bool appendAll(U&& aU) {
+    return vec().appendAll(aU);
+  }
+  [[nodiscard]] bool appendN(const T& aT, size_t aN) {
+    return vec().appendN(aT, aN);
+  }
+  template <typename U>
+  [[nodiscard]] bool append(const U* aBegin, const U* aEnd) {
+    return vec().append(aBegin, aEnd);
+  }
+  template <typename U>
+  [[nodiscard]] bool append(const U* aBegin, size_t aLength) {
+    return vec().append(aBegin, aLength);
+  }
+  template <typename U>
+  void infallibleAppend(U&& aU) {
+    vec().infallibleAppend(std::forward<U>(aU));
+  }
+  void infallibleAppendN(const T& aT, size_t aN) {
+    vec().infallibleAppendN(aT, aN);
+  }
+  template <typename U>
+  void infallibleAppend(const U* aBegin, const U* aEnd) {
+    vec().infallibleAppend(aBegin, aEnd);
+  }
+  template <typename U>
+  void infallibleAppend(const U* aBegin, size_t aLength) {
+    vec().infallibleAppend(aBegin, aLength);
+  }
+  void popBack() { vec().popBack(); }
+  T popCopy() { return vec().popCopy(); }
+  void erase(T* aT) { vec().erase(aT); }
+  void erase(T* aBegin, T* aEnd) { vec().erase(aBegin, aEnd); }
+  template <typename Pred>
+  void eraseIf(Pred pred) {
+    vec().eraseIf(pred);
+  }
+  template <typename U>
+  void eraseIfEqual(const U& u) {
+    vec().eraseIfEqual(u);
+  }
+};
+
+template <typename Wrapper, typename T, typename AllocPolicy>
+class WrappedPtrOperations<JS::StackGCVector<T, AllocPolicy>, Wrapper>
+    : public WrappedPtrOperations<
+          typename JS::StackGCVector<T, AllocPolicy>::Base, Wrapper> {};
+
+template <typename Wrapper, typename T, typename AllocPolicy>
+class MutableWrappedPtrOperations<JS::StackGCVector<T, AllocPolicy>, Wrapper>
+    : public MutableWrappedPtrOperations<
+          typename JS::StackGCVector<T, AllocPolicy>::Base, Wrapper> {};
+
+}  // namespace js
+
+namespace JS {
+
+// An automatically rooted GCVector for stack use.
+template <typename T>
+class RootedVector : public Rooted<StackGCVector<T>> {
+  using Vec = StackGCVector<T>;
+  using Base = Rooted<Vec>;
+
+ public:
+  explicit RootedVector(JSContext* cx) : Base(cx, Vec(cx)) {}
+};
+
+// For use in rust code, an analog to RootedVector that doesn't require
+// instances to be destroyed in LIFO order.
+template <typename T>
+class PersistentRootedVector : public PersistentRooted<StackGCVector<T>> {
+  using Vec = StackGCVector<T>;
+  using Base = PersistentRooted<Vec>;
+
+ public:
+  explicit PersistentRootedVector(JSContext* cx) : Base(cx, Vec(cx)) {}
+};
+
+}  // namespace JS
+
+#endif  // js_GCVector_h