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diff --git a/xpcom/base/nsAutoRef.h b/xpcom/base/nsAutoRef.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/. */
+
+// NB: This code may be used from non-XPCOM code, in particular, the
+// Windows Default Browser Agent.
+
+#ifndef nsAutoRef_h_
+#define nsAutoRef_h_
+
+#include "mozilla/Attributes.h"
+
+template <class T>
+class nsSimpleRef;
+template <class T>
+class nsAutoRefBase;
+template <class T>
+class nsReturnRef;
+template <class T>
+class nsReturningRef;
+
+/**
+ * template <class T> class nsAutoRef
+ *
+ * A class that holds a handle to a resource that must be released.
+ * No reference is added on construction.
+ *
+ * No copy constructor nor copy assignment operators are available, so the
+ * resource will be held until released on destruction or explicitly
+ * |reset()| or transferred through provided methods.
+ *
+ * The publicly available methods are the public methods on this class and its
+ * public base classes |nsAutoRefBase<T>| and |nsSimpleRef<T>|.
+ *
+ * For function return values see |nsReturnRef<T>|.
+ *
+ * For each class |T|, |nsAutoRefTraits<T>| or |nsSimpleRef<T>| must be
+ * specialized to use |nsAutoRef<T>|.
+ *
+ * @param T  A class identifying the type of reference held by the
+ *           |nsAutoRef<T>| and the unique set methods for managing references
+ *           to the resource (defined by |nsAutoRefTraits<T>| or
+ *           |nsSimpleRef<T>|).
+ *
+ *           Often this is the class representing the resource.  Sometimes a
+ *           new possibly-incomplete class may need to be declared.
+ *
+ *
+ * Example:  An Automatically closing file descriptor
+ *
+ * // References that are simple integral types (as file-descriptors are)
+ * // usually need a new class to represent the resource and how to handle its
+ * // references.
+ * class nsRawFD;
+ *
+ * // Specializing nsAutoRefTraits<nsRawFD> describes how to manage file
+ * // descriptors, so that nsAutoRef<nsRawFD> provides automatic closing of
+ * // its file descriptor on destruction.
+ * template <>
+ * class nsAutoRefTraits<nsRawFD> {
+ * public:
+ *     // The file descriptor is held in an int.
+ *     typedef int RawRef;
+ *     // -1 means that there is no file associated with the handle.
+ *     static int Void() { return -1; }
+ *     // The file associated with a file descriptor is released with close().
+ *     static void Release(RawRef aFD) { close(aFD); }
+ * };
+ *
+ * // A function returning a file descriptor that must be closed.
+ * nsReturnRef<nsRawFD> get_file(const char *filename) {
+ *     // Constructing from a raw file descriptor assumes ownership.
+ *     nsAutoRef<nsRawFD> fd(open(filename, O_RDONLY));
+ *     fcntl(fd, F_SETFD, FD_CLOEXEC);
+ *     return fd.out();
+ * }
+ *
+ * void f() {
+ *     unsigned char buf[1024];
+ *
+ *     // Hold a file descriptor for /etc/hosts in fd1.
+ *     nsAutoRef<nsRawFD> fd1(get_file("/etc/hosts"));
+ *
+ *     nsAutoRef<nsRawFD> fd2;
+ *     fd2.steal(fd1); // fd2 takes the file descriptor from fd1
+ *     ssize_t count = read(fd1, buf, 1024); // error fd1 has no file
+ *     count = read(fd2, buf, 1024); // reads from /etc/hosts
+ *
+ *     // If the file descriptor is not stored then it is closed.
+ *     get_file("/etc/login.defs"); // login.defs is closed
+ *
+ *     // Now use fd1 to hold a file descriptor for /etc/passwd.
+ *     fd1 = get_file("/etc/passwd");
+ *
+ *     // The nsAutoRef<nsRawFD> can give up the file descriptor if explicitly
+ *     // instructed, but the caller must then ensure that the file is closed.
+ *     int rawfd = fd1.disown();
+ *
+ *     // Assume ownership of another file descriptor.
+ *     fd1.own(open("/proc/1/maps");
+ *
+ *     // On destruction, fd1 closes /proc/1/maps and fd2 closes /etc/hosts,
+ *     // but /etc/passwd is not closed.
+ * }
+ *
+ */
+
+template <class T>
+class nsAutoRef : public nsAutoRefBase<T> {
+ protected:
+  typedef nsAutoRef<T> ThisClass;
+  typedef nsAutoRefBase<T> BaseClass;
+  typedef nsSimpleRef<T> SimpleRef;
+  typedef typename BaseClass::RawRefOnly RawRefOnly;
+  typedef typename BaseClass::LocalSimpleRef LocalSimpleRef;
+
+ public:
+  nsAutoRef() = default;
+
+  // Explicit construction is required so as not to risk unintentionally
+  // releasing the resource associated with a raw ref.
+  explicit nsAutoRef(RawRefOnly aRefToRelease) : BaseClass(aRefToRelease) {}
+
+  // Construction from a nsReturnRef<T> function return value, which expects
+  // to give up ownership, transfers ownership.
+  // (nsReturnRef<T> is converted to const nsReturningRef<T>.)
+  explicit nsAutoRef(const nsReturningRef<T>& aReturning)
+      : BaseClass(aReturning) {}
+
+  // The only assignment operator provided is for transferring from an
+  // nsReturnRef smart reference, which expects to pass its ownership to
+  // another object.
+  //
+  // With raw references and other smart references, the type of the lhs and
+  // its taking and releasing nature is often not obvious from an assignment
+  // statement.  Assignment from a raw ptr especially is not normally
+  // expected to release the reference.
+  //
+  // Use |steal| for taking ownership from other smart refs.
+  //
+  // For raw references, use |own| to indicate intention to have the
+  // resource released.
+
+  ThisClass& operator=(const nsReturningRef<T>& aReturning) {
+    BaseClass::steal(aReturning.mReturnRef);
+    return *this;
+  }
+
+  // Conversion to a raw reference allow the nsAutoRef<T> to often be used
+  // like a raw reference.
+  operator typename SimpleRef::RawRef() const { return this->get(); }
+
+  explicit operator bool() const { return this->HaveResource(); }
+
+  // Transfer ownership from another smart reference.
+  void steal(ThisClass& aOtherRef) { BaseClass::steal(aOtherRef); }
+
+  // Assume ownership of a raw ref.
+  //
+  // |own| has similar function to |steal|, and is useful for receiving
+  // ownership from a return value of a function.  It is named differently
+  // because |own| requires more care to ensure that the function intends to
+  // give away ownership, and so that |steal| can be safely used, knowing
+  // that it won't steal ownership from any methods returning raw ptrs to
+  // data owned by a foreign object.
+  void own(RawRefOnly aRefToRelease) { BaseClass::own(aRefToRelease); }
+
+  // Exchange ownership with |aOther|
+  void swap(ThisClass& aOther) {
+    LocalSimpleRef temp;
+    temp.SimpleRef::operator=(*this);
+    SimpleRef::operator=(aOther);
+    aOther.SimpleRef::operator=(temp);
+  }
+
+  // Release the reference now.
+  void reset() {
+    this->SafeRelease();
+    LocalSimpleRef empty;
+    SimpleRef::operator=(empty);
+  }
+
+  // Pass out the reference for a function return values.
+  nsReturnRef<T> out() { return nsReturnRef<T>(this->disown()); }
+
+  // operator->() and disown() are provided by nsAutoRefBase<T>.
+  // The default nsSimpleRef<T> provides get().
+
+  // No copy constructor
+  explicit nsAutoRef(const ThisClass& aRefToSteal) = delete;
+};
+
+/**
+ * template <class T> class nsReturnRef
+ *
+ * A type for function return values that hold a reference to a resource that
+ * must be released.  See also |nsAutoRef<T>::out()|.
+ */
+
+template <class T>
+class nsReturnRef : public nsAutoRefBase<T> {
+ protected:
+  typedef nsAutoRefBase<T> BaseClass;
+  typedef typename BaseClass::RawRefOnly RawRefOnly;
+
+ public:
+  // For constructing a return value with no resource
+  nsReturnRef() = default;
+
+  // For returning a smart reference from a raw reference that must be
+  // released.  Explicit construction is required so as not to risk
+  // unintentionally releasing the resource associated with a raw ref.
+  MOZ_IMPLICIT nsReturnRef(RawRefOnly aRefToRelease)
+      : BaseClass(aRefToRelease) {}
+
+  // Move construction transfers ownership
+  nsReturnRef(nsReturnRef<T>&& aRefToSteal) = default;
+
+  MOZ_IMPLICIT nsReturnRef(const nsReturningRef<T>& aReturning)
+      : BaseClass(aReturning) {}
+
+  // Conversion to a temporary (const) object referring to this object so
+  // that the reference may be passed from a function return value
+  // (temporary) to another smart reference.  There is no need to use this
+  // explicitly.  Simply assign a nsReturnRef<T> function return value to a
+  // smart reference.
+  operator nsReturningRef<T>() { return nsReturningRef<T>(*this); }
+
+  // No conversion to RawRef operator is provided on nsReturnRef, to ensure
+  // that the return value is not carelessly assigned to a raw ptr (and the
+  // resource then released).  If passing to a function that takes a raw
+  // ptr, use get or disown as appropriate.
+};
+
+/**
+ * template <class T> class nsReturningRef
+ *
+ * A class to allow ownership to be transferred from nsReturnRef function
+ * return values.
+ *
+ * It should not be necessary for clients to reference this
+ * class directly.  Simply pass an nsReturnRef<T> to a parameter taking an
+ * |nsReturningRef<T>|.
+ *
+ * The conversion operator on nsReturnRef constructs a temporary wrapper of
+ * class nsReturningRef<T> around a non-const reference to the nsReturnRef.
+ * The wrapper can then be passed as an rvalue parameter.
+ */
+
+template <class T>
+class nsReturningRef {
+ private:
+  friend class nsReturnRef<T>;
+
+  explicit nsReturningRef(nsReturnRef<T>& aReturnRef)
+      : mReturnRef(aReturnRef) {}
+
+ public:
+  nsReturnRef<T>& mReturnRef;
+};
+
+/**
+ * template <class T> class nsAutoRefTraits
+ *
+ * A class describing traits of references managed by the default
+ * |nsSimpleRef<T>| implementation and thus |nsAutoRef<T>|.
+ * The default |nsSimpleRef<T> is suitable for resources with handles that
+ * have a void value.  (If there is no such void value for a handle,
+ * specialize |nsSimpleRef<T>|.)
+ *
+ * Specializations must be provided for each class |T| according to the
+ * following pattern:
+ *
+ * // The template parameter |T| should be a class such that the set of fields
+ * // in class nsAutoRefTraits<T> is unique for class |T|.  Usually the
+ * // resource object class is sufficient.  For handles that are simple
+ * // integral typedefs, a new unique possibly-incomplete class may need to be
+ * // declared.
+ *
+ * template <>
+ * class nsAutoRefTraits<T>
+ * {
+ *     // Specializations must provide a typedef for RawRef, describing the
+ *     // type of the handle to the resource.
+ *     typedef <handle-type> RawRef;
+ *
+ *     // Specializations should define Void(), a function returning a value
+ *     // suitable for a handle that does not have an associated resource.
+ *     //
+ *     // The return type must be a suitable as the parameter to a RawRef
+ *     // constructor and operator==.
+ *     //
+ *     // If this method is not accessible then some limited nsAutoRef
+ *     // functionality will still be available, but the default constructor,
+ *     // |reset|, and most transfer of ownership methods will not be available.
+ *     static <return-type> Void();
+ *
+ *     // Specializations must define Release() to properly finalize the
+ *     // handle to a non-void custom-deleted or reference-counted resource.
+ *     static void Release(RawRef aRawRef);
+ * };
+ *
+ * See nsPointerRefTraits for example specializations for simple pointer
+ * references.  See nsAutoRef for an example specialization for a non-pointer
+ * reference.
+ */
+
+template <class T>
+class nsAutoRefTraits;
+
+/**
+ * template <class T> class nsPointerRefTraits
+ *
+ * A convenience class useful as a base class for specializations of
+ * |nsAutoRefTraits<T>| where the handle to the resource is a pointer to |T|.
+ * By inheriting from this class, definitions of only Release(RawRef) and
+ * possibly AddRef(RawRef) need to be added.
+ *
+ * Examples of use:
+ *
+ * template <>
+ * class nsAutoRefTraits<PRFileDesc> : public nsPointerRefTraits<PRFileDesc>
+ * {
+ * public:
+ *     static void Release(PRFileDesc *ptr) { PR_Close(ptr); }
+ * };
+ *
+ * template <>
+ * class nsAutoRefTraits<FcPattern> : public nsPointerRefTraits<FcPattern>
+ * {
+ * public:
+ *     static void Release(FcPattern *ptr) { FcPatternDestroy(ptr); }
+ *     static void AddRef(FcPattern *ptr) { FcPatternReference(ptr); }
+ * };
+ */
+
+template <class T>
+class nsPointerRefTraits {
+ public:
+  // The handle is a pointer to T.
+  typedef T* RawRef;
+  // A nullptr does not have a resource.
+  static RawRef Void() { return nullptr; }
+};
+
+/**
+ * template <class T> class nsSimpleRef
+ *
+ * Constructs a non-smart reference, and provides methods to test whether
+ * there is an associated resource and (if so) get its raw handle.
+ *
+ * A default implementation is suitable for resources with handles that have a
+ * void value.  This is not intended for direct use but used by |nsAutoRef<T>|.
+ *
+ * Specialize this class if there is no particular void value for the resource
+ * handle.  A specialized implementation must also provide Release(RawRef),
+ */
+
+template <class T>
+class nsSimpleRef : protected nsAutoRefTraits<T> {
+ protected:
+  // The default implementation uses nsAutoRefTrait<T>.
+  // Specializations need not define this typedef.
+  typedef nsAutoRefTraits<T> Traits;
+  // The type of the handle to the resource.
+  // A specialization must provide a typedef for RawRef.
+  typedef typename Traits::RawRef RawRef;
+
+  // Construct with no resource.
+  //
+  // If this constructor is not accessible then some limited nsAutoRef
+  // functionality will still be available, but the default constructor,
+  // |reset|, and most transfer of ownership methods will not be available.
+  nsSimpleRef() : mRawRef(Traits::Void()) {}
+  // Construct with a handle to a resource.
+  // A specialization must provide this.
+  explicit nsSimpleRef(RawRef aRawRef) : mRawRef(aRawRef) {}
+
+  // Test whether there is an associated resource.  A specialization must
+  // provide this.  The function is permitted to always return true if the
+  // default constructor is not accessible, or if Release (and AddRef) can
+  // deal with void handles.
+  bool HaveResource() const { return mRawRef != Traits::Void(); }
+
+ public:
+  // A specialization must provide get() or loose some functionality.  This
+  // is inherited by derived classes and the specialization may choose
+  // whether it is public or protected.
+  RawRef get() const { return mRawRef; }
+
+ private:
+  RawRef mRawRef;
+};
+
+/**
+ * template <class T> class nsAutoRefBase
+ *
+ * Internal base class for |nsAutoRef<T>| and |nsReturnRef<T>|.
+ * Adds release on destruction to a |nsSimpleRef<T>|.
+ */
+
+template <class T>
+class nsAutoRefBase : public nsSimpleRef<T> {
+ protected:
+  typedef nsAutoRefBase<T> ThisClass;
+  typedef nsSimpleRef<T> SimpleRef;
+  typedef typename SimpleRef::RawRef RawRef;
+
+  nsAutoRefBase() = default;
+
+  // A type for parameters that should be passed a raw ref but should not
+  // accept implicit conversions (from another smart ref).  (The only
+  // conversion to this type is from a raw ref so only raw refs will be
+  // accepted.)
+  class RawRefOnly {
+   public:
+    MOZ_IMPLICIT RawRefOnly(RawRef aRawRef) : mRawRef(aRawRef) {}
+    operator RawRef() const { return mRawRef; }
+
+   private:
+    RawRef mRawRef;
+  };
+
+  // Construction from a raw ref assumes ownership
+  explicit nsAutoRefBase(RawRefOnly aRefToRelease) : SimpleRef(aRefToRelease) {}
+
+  // Constructors that steal ownership
+  nsAutoRefBase(ThisClass&& aRefToSteal) : SimpleRef(aRefToSteal.disown()) {}
+  explicit nsAutoRefBase(const nsReturningRef<T>& aReturning)
+      : SimpleRef(aReturning.mReturnRef.disown()) {}
+
+  ~nsAutoRefBase() { SafeRelease(); }
+
+  // An internal class providing access to protected nsSimpleRef<T>
+  // constructors for construction of temporary simple references (that are
+  // not ThisClass).
+  class LocalSimpleRef : public SimpleRef {
+   public:
+    LocalSimpleRef() = default;
+    explicit LocalSimpleRef(RawRef aRawRef) : SimpleRef(aRawRef) {}
+  };
+
+ public:
+  ThisClass& operator=(const ThisClass& aSmartRef) = delete;
+
+  RawRef operator->() const { return this->get(); }
+
+  // Transfer ownership to a raw reference.
+  //
+  // THE CALLER MUST ENSURE THAT THE REFERENCE IS EXPLICITLY RELEASED.
+  //
+  // Is this really what you want to use?  Using this removes any guarantee
+  // of release.  Use nsAutoRef<T>::out() for return values, or an
+  // nsAutoRef<T> modifiable lvalue for an out parameter.  Use disown() when
+  // the reference must be stored in a POD type object, such as may be
+  // preferred for a namespace-scope object with static storage duration,
+  // for example.
+  RawRef disown() {
+    RawRef temp = this->get();
+    LocalSimpleRef empty;
+    SimpleRef::operator=(empty);
+    return temp;
+  }
+
+ protected:
+  // steal and own are protected because they make no sense on nsReturnRef,
+  // but steal is implemented on this class for access to aOtherRef.disown()
+  // when aOtherRef is an nsReturnRef;
+
+  // Transfer ownership from another smart reference.
+  void steal(ThisClass& aOtherRef) { own(aOtherRef.disown()); }
+  // Assume ownership of a raw ref.
+  void own(RawRefOnly aRefToRelease) {
+    SafeRelease();
+    LocalSimpleRef ref(aRefToRelease);
+    SimpleRef::operator=(ref);
+  }
+
+  // Release a resource if there is one.
+  void SafeRelease() {
+    if (this->HaveResource()) {
+      this->Release(this->get());
+    }
+  }
+};
+
+#endif  // !defined(nsAutoRef_h_)