Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1029 insertions, 0 deletions

diff --git a/xpcom/ds/nsBaseHashtable.h b/xpcom/ds/nsBaseHashtable.h
new file mode 100644
index 0000000000..7b57ef4666
--- /dev/null
+++ b/xpcom/ds/nsBaseHashtable.h
@@ -0,0 +1,1029 @@
+/* -*- 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 nsBaseHashtable_h__
+#define nsBaseHashtable_h__
+
+#include <functional>
+#include <utility>
+
+#include "mozilla/dom/SafeRefPtr.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/Result.h"
+#include "mozilla/UniquePtr.h"
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsHashtablesFwd.h"
+#include "nsTHashtable.h"
+
+namespace mozilla::detail {
+
+template <typename SmartPtr>
+struct SmartPtrTraits {
+  static constexpr bool IsSmartPointer = false;
+  static constexpr bool IsRefCounted = false;
+};
+
+template <typename Pointee>
+struct SmartPtrTraits<UniquePtr<Pointee>> {
+  static constexpr bool IsSmartPointer = true;
+  static constexpr bool IsRefCounted = false;
+  using SmartPointerType = UniquePtr<Pointee>;
+  using PointeeType = Pointee;
+  using RawPointerType = Pointee*;
+  template <typename U>
+  using OtherSmartPtrType = UniquePtr<U>;
+
+  template <typename U, typename... Args>
+  static SmartPointerType NewObject(Args&&... aConstructionArgs) {
+    return mozilla::MakeUnique<U>(std::forward<Args>(aConstructionArgs)...);
+  }
+};
+
+template <typename Pointee>
+struct SmartPtrTraits<RefPtr<Pointee>> {
+  static constexpr bool IsSmartPointer = true;
+  static constexpr bool IsRefCounted = true;
+  using SmartPointerType = RefPtr<Pointee>;
+  using PointeeType = Pointee;
+  using RawPointerType = Pointee*;
+  template <typename U>
+  using OtherSmartPtrType = RefPtr<U>;
+
+  template <typename U, typename... Args>
+  static SmartPointerType NewObject(Args&&... aConstructionArgs) {
+    return MakeRefPtr<U>(std::forward<Args>(aConstructionArgs)...);
+  }
+};
+
+template <typename Pointee>
+struct SmartPtrTraits<SafeRefPtr<Pointee>> {
+  static constexpr bool IsSmartPointer = true;
+  static constexpr bool IsRefCounted = true;
+  using SmartPointerType = SafeRefPtr<Pointee>;
+  using PointeeType = Pointee;
+  using RawPointerType = Pointee*;
+  template <typename U>
+  using OtherSmartPtrType = SafeRefPtr<U>;
+
+  template <typename U, typename... Args>
+  static SmartPointerType NewObject(Args&&... aConstructionArgs) {
+    return MakeSafeRefPtr<U>(std::forward<Args>(aConstructionArgs)...);
+  }
+};
+
+template <typename Pointee>
+struct SmartPtrTraits<nsCOMPtr<Pointee>> {
+  static constexpr bool IsSmartPointer = true;
+  static constexpr bool IsRefCounted = true;
+  using SmartPointerType = nsCOMPtr<Pointee>;
+  using PointeeType = Pointee;
+  using RawPointerType = Pointee*;
+  template <typename U>
+  using OtherSmartPtrType = nsCOMPtr<U>;
+
+  template <typename U, typename... Args>
+  static SmartPointerType NewObject(Args&&... aConstructionArgs) {
+    return MakeRefPtr<U>(std::forward<Args>(aConstructionArgs)...);
+  }
+};
+
+template <class T>
+T* PtrGetWeak(T* aPtr) {
+  return aPtr;
+}
+
+template <class T>
+T* PtrGetWeak(const RefPtr<T>& aPtr) {
+  return aPtr.get();
+}
+
+template <class T>
+T* PtrGetWeak(const SafeRefPtr<T>& aPtr) {
+  return aPtr.unsafeGetRawPtr();
+}
+
+template <class T>
+T* PtrGetWeak(const nsCOMPtr<T>& aPtr) {
+  return aPtr.get();
+}
+
+template <class T>
+T* PtrGetWeak(const UniquePtr<T>& aPtr) {
+  return aPtr.get();
+}
+
+template <typename EntryType>
+class nsBaseHashtableValueIterator : public ::detail::nsTHashtableIteratorBase {
+  // friend class nsTHashtable<EntryType>;
+
+ public:
+  using iterator_category = std::forward_iterator_tag;
+  using value_type = const std::decay_t<typename EntryType::DataType>;
+  using difference_type = int32_t;
+  using pointer = value_type*;
+  using reference = value_type&;
+
+  using iterator_type = nsBaseHashtableValueIterator;
+  using const_iterator_type = nsBaseHashtableValueIterator;
+
+  using nsTHashtableIteratorBase::nsTHashtableIteratorBase;
+
+  value_type* operator->() const {
+    return &static_cast<const EntryType*>(mIterator.Get())->GetData();
+  }
+  decltype(auto) operator*() const {
+    return static_cast<const EntryType*>(mIterator.Get())->GetData();
+  }
+
+  iterator_type& operator++() {
+    mIterator.Next();
+    return *this;
+  }
+  iterator_type operator++(int) {
+    iterator_type it = *this;
+    ++*this;
+    return it;
+  }
+};
+
+template <typename EntryType>
+class nsBaseHashtableValueRange {
+ public:
+  using IteratorType = nsBaseHashtableValueIterator<EntryType>;
+  using iterator = IteratorType;
+
+  explicit nsBaseHashtableValueRange(const PLDHashTable& aHashtable)
+      : mHashtable{aHashtable} {}
+
+  auto begin() const { return IteratorType{mHashtable}; }
+  auto end() const {
+    return IteratorType{mHashtable, typename IteratorType::EndIteratorTag{}};
+  }
+  auto cbegin() const { return begin(); }
+  auto cend() const { return end(); }
+
+  uint32_t Count() const { return mHashtable.EntryCount(); }
+
+ private:
+  const PLDHashTable& mHashtable;
+};
+
+template <typename EntryType>
+auto RangeSize(const detail::nsBaseHashtableValueRange<EntryType>& aRange) {
+  return aRange.Count();
+}
+
+}  // namespace mozilla::detail
+
+/**
+ * Data type conversion helper that is used to wrap and unwrap the specified
+ * DataType.
+ */
+template <class DataType, class UserDataType>
+class nsDefaultConverter {
+ public:
+  /**
+   * Maps the storage DataType to the exposed UserDataType.
+   */
+  static UserDataType Unwrap(DataType& src) { return UserDataType(src); }
+
+  /**
+   * Const ref variant used for example with nsCOMPtr wrappers.
+   */
+  static DataType Wrap(const UserDataType& src) { return DataType(src); }
+
+  /**
+   * Generic conversion, this is useful for things like already_AddRefed.
+   */
+  template <typename U>
+  static DataType Wrap(U&& src) {
+    return std::forward<U>(src);
+  }
+
+  template <typename U>
+  static UserDataType Unwrap(U&& src) {
+    return std::forward<U>(src);
+  }
+};
+
+/**
+ * the private nsTHashtable::EntryType class used by nsBaseHashtable
+ * @see nsTHashtable for the specification of this class
+ * @see nsBaseHashtable for template parameters
+ */
+template <class KeyClass, class TDataType>
+class nsBaseHashtableET : public KeyClass {
+ public:
+  using DataType = TDataType;
+
+  const DataType& GetData() const { return mData; }
+  DataType* GetModifiableData() { return &mData; }
+  template <typename U>
+  void SetData(U&& aData) {
+    mData = std::forward<U>(aData);
+  }
+
+  decltype(auto) GetWeak() const {
+    return mozilla::detail::PtrGetWeak(GetData());
+  }
+
+ private:
+  DataType mData;
+  friend class nsTHashtable<nsBaseHashtableET<KeyClass, DataType>>;
+  template <typename KeyClassX, typename DataTypeX, typename UserDataTypeX,
+            typename ConverterX>
+  friend class nsBaseHashtable;
+  friend class ::detail::nsTHashtableKeyIterator<
+      nsBaseHashtableET<KeyClass, DataType>>;
+
+  typedef typename KeyClass::KeyType KeyType;
+  typedef typename KeyClass::KeyTypePointer KeyTypePointer;
+
+  template <typename... Args>
+  explicit nsBaseHashtableET(KeyTypePointer aKey, Args&&... aArgs);
+  nsBaseHashtableET(nsBaseHashtableET<KeyClass, DataType>&& aToMove) = default;
+  ~nsBaseHashtableET() = default;
+};
+
+/**
+ * Templated hashtable. Usually, this isn't instantiated directly but through
+ * its sub-class templates nsInterfaceHashtable, nsClassHashtable,
+ * nsRefPtrHashtable and nsTHashMap.
+ *
+ * Originally, UserDataType used to be the only type exposed to the user in the
+ * public member function signatures (hence its name), but this has proven to
+ * inadequate over time. Now, UserDataType is only exposed in by-value
+ * getter member functions that are called *Get*. Member functions that provide
+ * access to the DataType are called Lookup rather than Get. Note that this rule
+ * does not apply to nsRefPtrHashtable and nsInterfaceHashtable, as they are
+ * provide a similar interface, but are no genuine sub-classes of
+ * nsBaseHashtable.
+ *
+ * @param KeyClass a wrapper-class for the hashtable key, see nsHashKeys.h
+ *   for a complete specification.
+ * @param DataType the datatype stored in the hashtable,
+ *   for example, uint32_t or nsCOMPtr.
+ * @param UserDataType the datatype returned from the by-value getter member
+ *   functions (named *Get*), for example uint32_t or nsISupports*
+ * @param Converter that is used to map from DataType to UserDataType. A
+ *   default converter is provided that assumes implicit conversion is an
+ *   option.
+ */
+template <class KeyClass, class DataType, class UserDataType, class Converter>
+class nsBaseHashtable
+    : protected nsTHashtable<nsBaseHashtableET<KeyClass, DataType>> {
+  using Base = nsTHashtable<nsBaseHashtableET<KeyClass, DataType>>;
+  typedef mozilla::fallible_t fallible_t;
+
+ public:
+  typedef typename KeyClass::KeyType KeyType;
+  typedef nsBaseHashtableET<KeyClass, DataType> EntryType;
+
+  using nsTHashtable<EntryType>::Contains;
+  using nsTHashtable<EntryType>::GetGeneration;
+  using nsTHashtable<EntryType>::SizeOfExcludingThis;
+  using nsTHashtable<EntryType>::SizeOfIncludingThis;
+
+  nsBaseHashtable() = default;
+  explicit nsBaseHashtable(uint32_t aInitLength)
+      : nsTHashtable<EntryType>(aInitLength) {}
+
+  /**
+   * Return the number of entries in the table.
+   * @return    number of entries
+   */
+  [[nodiscard]] uint32_t Count() const {
+    return nsTHashtable<EntryType>::Count();
+  }
+
+  /**
+   * Return whether the table is empty.
+   * @return    whether empty
+   */
+  [[nodiscard]] bool IsEmpty() const {
+    return nsTHashtable<EntryType>::IsEmpty();
+  }
+
+  /**
+   * Get the value, returning a flag indicating the presence of the entry in
+   * the table.
+   *
+   * @param aKey the key to retrieve
+   * @param aData data associated with this key will be placed at this pointer.
+   *        If you only need to check if the key exists, aData may be null.
+   * @return true if the key exists. If key does not exist, aData is not
+   *   modified.
+   *
+   * @attention As opposed to Remove, this does not assign a value to *aData if
+   * no entry is present! (And also as opposed to the member function Get with
+   * the same signature that nsClassHashtable defines and hides this one.)
+   */
+  [[nodiscard]] bool Get(KeyType aKey, UserDataType* aData) const {
+    EntryType* ent = this->GetEntry(aKey);
+    if (!ent) {
+      return false;
+    }
+
+    if (aData) {
+      *aData = Converter::Unwrap(ent->mData);
+    }
+
+    return true;
+  }
+
+  /**
+   * Get the value, returning a zero-initialized POD or a default-initialized
+   * object if the entry is not present in the table.
+   *
+   * This overload can only be used if UserDataType is default-constructible.
+   * Use the double-argument Get or MaybeGet with non-default-constructible
+   * UserDataType.
+   *
+   * @param aKey the key to retrieve
+   * @return The found value, or UserDataType{} if no entry was found with the
+   *         given key.
+   * @note If zero/default-initialized values are stored in the table, it is
+   *       not possible to distinguish between such a value and a missing entry.
+   */
+  [[nodiscard]] UserDataType Get(KeyType aKey) const {
+    EntryType* ent = this->GetEntry(aKey);
+    if (!ent) {
+      return UserDataType{};
+    }
+
+    return Converter::Unwrap(ent->mData);
+  }
+
+  /**
+   * Get the value, returning Nothing if the entry is not present in the table.
+   *
+   * @param aKey the key to retrieve
+   * @return The found value wrapped in a Maybe, or Nothing if no entry was
+   *         found with the given key.
+   */
+  [[nodiscard]] mozilla::Maybe<UserDataType> MaybeGet(KeyType aKey) const {
+    EntryType* ent = this->GetEntry(aKey);
+    if (!ent) {
+      return mozilla::Nothing();
+    }
+
+    return mozilla::Some(Converter::Unwrap(ent->mData));
+  }
+
+  using SmartPtrTraits = mozilla::detail::SmartPtrTraits<DataType>;
+
+  /**
+   * Looks up aKey in the hash table. If it doesn't exist a new object of
+   * SmartPtrTraits::PointeeType will be created (using the arguments provided)
+   * and then returned.
+   *
+   * \note This can only be instantiated if DataType is a smart pointer.
+   */
+  template <typename... Args>
+  auto GetOrInsertNew(KeyType aKey, Args&&... aConstructionArgs) {
+    static_assert(
+        SmartPtrTraits::IsSmartPointer,
+        "GetOrInsertNew can only be used with smart pointer data types");
+    return mozilla::detail::PtrGetWeak(LookupOrInsertWith(std::move(aKey), [&] {
+      return SmartPtrTraits::template NewObject<
+          typename SmartPtrTraits::PointeeType>(
+          std::forward<Args>(aConstructionArgs)...);
+    }));
+  }
+
+  /**
+   * Add aKey to the table if not already present, and return a reference to its
+   * value.  If aKey is not already in the table then the a default-constructed
+   * or the provided value aData is used.
+   *
+   * If the arguments are non-trivial to provide, consider using
+   * LookupOrInsertWith instead.
+   */
+  template <typename... Args>
+  DataType& LookupOrInsert(const KeyType& aKey, Args&&... aArgs) {
+    return WithEntryHandle(aKey, [&](auto entryHandle) -> DataType& {
+      return entryHandle.OrInsert(std::forward<Args>(aArgs)...);
+    });
+  }
+
+  /**
+   * Add aKey to the table if not already present, and return a reference to its
+   * value.  If aKey is not already in the table then the value is
+   * constructed using the given factory.
+   */
+  template <typename F>
+  DataType& LookupOrInsertWith(const KeyType& aKey, F&& aFunc) {
+    return WithEntryHandle(aKey, [&aFunc](auto entryHandle) -> DataType& {
+      return entryHandle.OrInsertWith(std::forward<F>(aFunc));
+    });
+  }
+
+  /**
+   * Add aKey to the table if not already present, and return a reference to its
+   * value.  If aKey is not already in the table then the value is
+   * constructed using the given factory.
+   */
+  template <typename F>
+  [[nodiscard]] auto TryLookupOrInsertWith(const KeyType& aKey, F&& aFunc) {
+    return WithEntryHandle(
+        aKey,
+        [&aFunc](auto entryHandle)
+            -> mozilla::Result<std::reference_wrapper<DataType>,
+                               typename std::invoke_result_t<F>::err_type> {
+          if (entryHandle) {
+            return std::ref(entryHandle.Data());
+          }
+
+          // XXX Use MOZ_TRY after generalizing QM_TRY to mfbt.
+          auto res = std::forward<F>(aFunc)();
+          if (res.isErr()) {
+            return res.propagateErr();
+          }
+          return std::ref(entryHandle.Insert(res.unwrap()));
+        });
+  }
+
+  /**
+   * If it does not yet, inserts a new entry with the handle's key and the
+   * value passed to this function. Otherwise, it updates the entry by the
+   * value passed to this function.
+   *
+   * \tparam U DataType must be implicitly convertible (and assignable) from U
+   * \post HasEntry()
+   * \param aKey the key to put
+   * \param aData the new data
+   */
+  template <typename U>
+  DataType& InsertOrUpdate(KeyType aKey, U&& aData) {
+    return WithEntryHandle(aKey, [&aData](auto entryHandle) -> DataType& {
+      return entryHandle.InsertOrUpdate(std::forward<U>(aData));
+    });
+  }
+
+  template <typename U>
+  [[nodiscard]] bool InsertOrUpdate(KeyType aKey, U&& aData,
+                                    const fallible_t& aFallible) {
+    return WithEntryHandle(aKey, aFallible, [&aData](auto maybeEntryHandle) {
+      if (!maybeEntryHandle) {
+        return false;
+      }
+      maybeEntryHandle->InsertOrUpdate(std::forward<U>(aData));
+      return true;
+    });
+  }
+
+  /**
+   * Remove the entry associated with aKey (if any), _moving_ its current value
+   * into *aData.  Return true if found.
+   *
+   * This overload can only be used if DataType is default-constructible. Use
+   * the single-argument Remove or Extract with non-default-constructible
+   * DataType.
+   *
+   * @param aKey the key to remove from the hashtable
+   * @param aData where to move the value.  If an entry is not found, *aData
+   *              will be assigned a default-constructed value (i.e. reset to
+   *              zero or nullptr for primitive types).
+   * @return true if an entry for aKey was found (and removed)
+   */
+  // XXX This should also better be marked nodiscard, but due to
+  // nsClassHashtable not guaranteeing non-nullness of entries, it is usually
+  // only checked if aData is nullptr in such cases.
+  // [[nodiscard]]
+  bool Remove(KeyType aKey, DataType* aData) {
+    if (auto* ent = this->GetEntry(aKey)) {
+      if (aData) {
+        *aData = std::move(ent->mData);
+      }
+      this->RemoveEntry(ent);
+      return true;
+    }
+    if (aData) {
+      *aData = std::move(DataType());
+    }
+    return false;
+  }
+
+  /**
+   * Remove the entry associated with aKey (if any).  Return true if found.
+   *
+   * @param aKey the key to remove from the hashtable
+   * @return true if an entry for aKey was found (and removed)
+   */
+  bool Remove(KeyType aKey) {
+    if (auto* ent = this->GetEntry(aKey)) {
+      this->RemoveEntry(ent);
+      return true;
+    }
+
+    return false;
+  }
+
+  /**
+   * Retrieve the value for a key and remove the corresponding entry at
+   * the same time.
+   *
+   * @param aKey the key to retrieve and remove
+   * @return the found value, or Nothing if no entry was found with the
+   *   given key.
+   */
+  [[nodiscard]] mozilla::Maybe<DataType> Extract(KeyType aKey) {
+    mozilla::Maybe<DataType> value;
+    if (EntryType* ent = this->GetEntry(aKey)) {
+      value.emplace(std::move(ent->mData));
+      this->RemoveEntry(ent);
+    }
+    return value;
+  }
+
+  template <typename HashtableRef>
+  struct LookupResult {
+   private:
+    EntryType* mEntry;
+    HashtableRef mTable;
+#ifdef DEBUG
+    uint32_t mTableGeneration;
+#endif
+
+   public:
+    LookupResult(EntryType* aEntry, HashtableRef aTable)
+        : mEntry(aEntry),
+          mTable(aTable)
+#ifdef DEBUG
+          ,
+          mTableGeneration(aTable.GetGeneration())
+#endif
+    {
+    }
+
+    // Is there something stored in the table?
+    explicit operator bool() const {
+      MOZ_ASSERT(mTableGeneration == mTable.GetGeneration());
+      return mEntry;
+    }
+
+    void Remove() {
+      if (!*this) {
+        return;
+      }
+      mTable.RemoveEntry(mEntry);
+      mEntry = nullptr;
+    }
+
+    [[nodiscard]] DataType& Data() {
+      MOZ_ASSERT(!!*this, "must have an entry to access its value");
+      return mEntry->mData;
+    }
+
+    [[nodiscard]] const DataType& Data() const {
+      MOZ_ASSERT(!!*this, "must have an entry to access its value");
+      return mEntry->mData;
+    }
+
+    [[nodiscard]] DataType* DataPtrOrNull() {
+      return static_cast<bool>(*this) ? &mEntry->mData : nullptr;
+    }
+
+    [[nodiscard]] const DataType* DataPtrOrNull() const {
+      return static_cast<bool>(*this) ? &mEntry->mData : nullptr;
+    }
+
+    [[nodiscard]] DataType* operator->() { return &Data(); }
+    [[nodiscard]] const DataType* operator->() const { return &Data(); }
+
+    [[nodiscard]] DataType& operator*() { return Data(); }
+    [[nodiscard]] const DataType& operator*() const { return Data(); }
+  };
+
+  /**
+   * Removes all entries matching a predicate.
+   *
+   * The predicate must be compatible with signature bool (const Iterator &).
+   */
+  template <typename Pred>
+  void RemoveIf(Pred&& aPred) {
+    for (auto iter = Iter(); !iter.Done(); iter.Next()) {
+      if (aPred(const_cast<std::add_const_t<decltype(iter)>&>(iter))) {
+        iter.Remove();
+      }
+    }
+  }
+
+  /**
+   * Looks up aKey in the hashtable and returns an object that allows you to
+   * read/modify the value of the entry, or remove the entry (if found).
+   *
+   * A typical usage of this API looks like this:
+   *
+   *   if (auto entry = hashtable.Lookup(key)) {
+   *     DoSomething(entry.Data());
+   *     if (entry.Data() > 42) {
+   *       entry.Remove();
+   *     }
+   *   } // else - an entry with the given key doesn't exist
+   *
+   * This is useful for cases where you want to read/write the value of an entry
+   * and (optionally) remove the entry without having to do multiple hashtable
+   * lookups.  If you want to insert a new entry if one does not exist, then use
+   * WithEntryHandle instead, see below.
+   */
+  [[nodiscard]] auto Lookup(KeyType aKey) {
+    return LookupResult<nsBaseHashtable&>(this->GetEntry(aKey), *this);
+  }
+
+  [[nodiscard]] auto Lookup(KeyType aKey) const {
+    return LookupResult<const nsBaseHashtable&>(this->GetEntry(aKey), *this);
+  }
+
+  /**
+   * Used by WithEntryHandle as the argument type to its functor. It is
+   * associated with the Key passed to WithEntryHandle and manages only the
+   * potential entry with that key. Note that in case no modifying operations
+   * are called on the handle, the state of the hashtable remains unchanged,
+   * i.e. WithEntryHandle does not modify the hashtable itself.
+   *
+   * Provides query functions (Key, HasEntry/operator bool, Data) and
+   * modifying operations for inserting new entries (Insert), updating existing
+   * entries (Update) and removing existing entries (Remove). They have
+   * debug-only assertion that fail when the state of the entry doesn't match
+   * the expectation. There are variants prefixed with "Or" (OrInsert, OrUpdate,
+   * OrRemove) that are a no-op in case the entry does already exist resp. does
+   * not exist. There are also variants OrInsertWith and OrUpdateWith that don't
+   * accept a value, but a functor, which is only called if the operation takes
+   * place, which should be used if the provision of the value is not trivial
+   * (e.g. allocates a heap object). Finally, there's InsertOrUpdate that
+   * handles both existing and non-existing entries.
+   *
+   * Note that all functions of EntryHandle only deal with DataType, not with
+   * UserDataType.
+   */
+  class EntryHandle : protected nsTHashtable<EntryType>::EntryHandle {
+   public:
+    using Base = typename nsTHashtable<EntryType>::EntryHandle;
+
+    EntryHandle(EntryHandle&& aOther) = default;
+    ~EntryHandle() = default;
+
+    EntryHandle(const EntryHandle&) = delete;
+    EntryHandle& operator=(const EntryHandle&) = delete;
+    EntryHandle& operator=(const EntryHandle&&) = delete;
+
+    using Base::Key;
+
+    using Base::HasEntry;
+
+    using Base::operator bool;
+
+    using Base::Entry;
+
+    /**
+     * Inserts a new entry with the handle's key and the value passed to this
+     * function.
+     *
+     * \tparam Args DataType must be constructible from Args
+     * \pre !HasEntry()
+     * \post HasEntry()
+     */
+    template <typename... Args>
+    DataType& Insert(Args&&... aArgs) {
+      Base::InsertInternal(std::forward<Args>(aArgs)...);
+      return Data();
+    }
+
+    /**
+     * If it doesn't yet exist, inserts a new entry with the handle's key and
+     * the value passed to this function. The value is not consumed if no insert
+     * takes place.
+     *
+     * \tparam Args DataType must be constructible from Args
+     * \post HasEntry()
+     */
+    template <typename... Args>
+    DataType& OrInsert(Args&&... aArgs) {
+      if (!HasEntry()) {
+        return Insert(std::forward<Args>(aArgs)...);
+      }
+      return Data();
+    }
+
+    /**
+     * If it doesn't yet exist, inserts a new entry with the handle's key and
+     * the result of the functor passed to this function. The functor is not
+     * called if no insert takes place.
+     *
+     * \tparam F must return a value that is implicitly convertible to DataType
+     * \post HasEntry()
+     */
+    template <typename F>
+    DataType& OrInsertWith(F&& aFunc) {
+      if (!HasEntry()) {
+        return Insert(std::forward<F>(aFunc)());
+      }
+      return Data();
+    }
+
+    /**
+     * Updates the entry with the handle's key by the value passed to this
+     * function.
+     *
+     * \tparam U DataType must be assignable from U
+     * \pre HasEntry()
+     */
+    template <typename U>
+    DataType& Update(U&& aData) {
+      MOZ_RELEASE_ASSERT(HasEntry());
+      Data() = std::forward<U>(aData);
+      return Data();
+    }
+
+    /**
+     * If an entry with the handle's key already exists, updates its value by
+     * the value passed to this function. The value is not consumed if no update
+     * takes place.
+     *
+     * \tparam U DataType must be assignable from U
+     */
+    template <typename U>
+    void OrUpdate(U&& aData) {
+      if (HasEntry()) {
+        Update(std::forward<U>(aData));
+      }
+    }
+
+    /**
+     * If an entry with the handle's key already exists, updates its value by
+     * the the result of the functor passed to this function. The functor is not
+     * called if no update takes place.
+     *
+     * \tparam F must return a value that DataType is assignable from
+     */
+    template <typename F>
+    void OrUpdateWith(F&& aFunc) {
+      if (HasEntry()) {
+        Update(std::forward<F>(aFunc)());
+      }
+    }
+
+    /**
+     * If it does not yet, inserts a new entry with the handle's key and the
+     * value passed to this function. Otherwise, it updates the entry by the
+     * value passed to this function.
+     *
+     * \tparam U DataType must be implicitly convertible (and assignable) from U
+     * \post HasEntry()
+     */
+    template <typename U>
+    DataType& InsertOrUpdate(U&& aData) {
+      if (!HasEntry()) {
+        Insert(std::forward<U>(aData));
+      } else {
+        Update(std::forward<U>(aData));
+      }
+      return Data();
+    }
+
+    using Base::Remove;
+
+    using Base::OrRemove;
+
+    /**
+     * Returns a reference to the value of the entry.
+     *
+     * \pre HasEntry()
+     */
+    [[nodiscard]] DataType& Data() { return Entry()->mData; }
+
+    [[nodiscard]] DataType* DataPtrOrNull() {
+      return static_cast<bool>(*this) ? &Data() : nullptr;
+    }
+
+    [[nodiscard]] DataType* operator->() { return &Data(); }
+
+    [[nodiscard]] DataType& operator*() { return Data(); }
+
+   private:
+    friend class nsBaseHashtable;
+
+    explicit EntryHandle(Base&& aBase) : Base(std::move(aBase)) {}
+  };
+
+  /**
+   * Performs a scoped operation on the entry for aKey, which may or may not
+   * exist when the function is called. It calls aFunc with an EntryHandle. The
+   * result of aFunc is returned as the result of this function. Its return type
+   * may be void. See the documentation of EntryHandle for the query and
+   * modifying operations it offers.
+   *
+   * A simple use of this function is, e.g.,
+   *
+   *   hashtable.WithEntryHandle(key, [](auto&& entry) { entry.OrInsert(42); });
+   *
+   * \attention It is not safe to perform modifying operations on the hashtable
+   * other than through the EntryHandle within aFunc, and trying to do so will
+   * trigger debug assertions, and result in undefined behaviour otherwise.
+   */
+  template <class F>
+  [[nodiscard]] auto WithEntryHandle(KeyType aKey, F&& aFunc)
+      -> std::invoke_result_t<F, EntryHandle&&> {
+    return Base::WithEntryHandle(
+        aKey, [&aFunc](auto entryHandle) -> decltype(auto) {
+          return std::forward<F>(aFunc)(EntryHandle{std::move(entryHandle)});
+        });
+  }
+
+  /**
+   * Fallible variant of WithEntryHandle, with the following differences:
+   * - The functor aFunc must accept a Maybe<EntryHandle> (instead of an
+   *   EntryHandle).
+   * - In case allocation of the slot for the entry fails, Nothing is passed to
+   *   the functor.
+   *
+   * For more details, see the explanation on the non-fallible overload above.
+   */
+  template <class F>
+  [[nodiscard]] auto WithEntryHandle(KeyType aKey, const fallible_t& aFallible,
+                                     F&& aFunc)
+      -> std::invoke_result_t<F, mozilla::Maybe<EntryHandle>&&> {
+    return Base::WithEntryHandle(
+        aKey, aFallible, [&aFunc](auto maybeEntryHandle) {
+          return std::forward<F>(aFunc)(
+              maybeEntryHandle
+                  ? mozilla::Some(EntryHandle{maybeEntryHandle.extract()})
+                  : mozilla::Nothing());
+        });
+  }
+
+ public:
+  class ConstIterator {
+   public:
+    explicit ConstIterator(nsBaseHashtable* aTable)
+        : mBaseIterator(&aTable->mTable) {}
+    ~ConstIterator() = default;
+
+    KeyType Key() const {
+      return static_cast<EntryType*>(mBaseIterator.Get())->GetKey();
+    }
+    UserDataType UserData() const {
+      return Converter::Unwrap(
+          static_cast<EntryType*>(mBaseIterator.Get())->mData);
+    }
+    const DataType& Data() const {
+      return static_cast<EntryType*>(mBaseIterator.Get())->mData;
+    }
+
+    bool Done() const { return mBaseIterator.Done(); }
+    void Next() { mBaseIterator.Next(); }
+
+    ConstIterator() = delete;
+    ConstIterator(const ConstIterator&) = delete;
+    ConstIterator(ConstIterator&& aOther) = delete;
+    ConstIterator& operator=(const ConstIterator&) = delete;
+    ConstIterator& operator=(ConstIterator&&) = delete;
+
+   protected:
+    PLDHashTable::Iterator mBaseIterator;
+  };
+
+  // This is an iterator that also allows entry removal. Example usage:
+  //
+  //   for (auto iter = table.Iter(); !iter.Done(); iter.Next()) {
+  //     const KeyType key = iter.Key();
+  //     const UserDataType data = iter.UserData();
+  //     // or
+  //     const DataType& data = iter.Data();
+  //     // ... do stuff with |key| and/or |data| ...
+  //     // ... possibly call iter.Remove() once ...
+  //   }
+  //
+  class Iterator final : public ConstIterator {
+   public:
+    using ConstIterator::ConstIterator;
+
+    using ConstIterator::Data;
+    DataType& Data() {
+      return static_cast<EntryType*>(this->mBaseIterator.Get())->mData;
+    }
+
+    void Remove() { this->mBaseIterator.Remove(); }
+  };
+
+  Iterator Iter() { return Iterator(this); }
+
+  ConstIterator ConstIter() const {
+    return ConstIterator(const_cast<nsBaseHashtable*>(this));
+  }
+
+  using nsTHashtable<EntryType>::Remove;
+
+  /**
+   * Remove the entry associated with aIter.
+   *
+   * @param aIter the iterator pointing to the entry
+   * @pre !aIter.Done()
+   */
+  void Remove(ConstIterator& aIter) { aIter.mBaseIterator.Remove(); }
+
+  using typename nsTHashtable<EntryType>::iterator;
+  using typename nsTHashtable<EntryType>::const_iterator;
+
+  using nsTHashtable<EntryType>::begin;
+  using nsTHashtable<EntryType>::end;
+  using nsTHashtable<EntryType>::cbegin;
+  using nsTHashtable<EntryType>::cend;
+
+  using nsTHashtable<EntryType>::Keys;
+
+  /**
+   * Return a range of the values (of DataType). Note this range iterates over
+   * the values in place, so modifications to the nsTHashtable invalidate the
+   * range while it's iterated, except when calling Remove() with a value
+   * iterator derived from that range.
+   */
+  auto Values() const {
+    return mozilla::detail::nsBaseHashtableValueRange<EntryType>{this->mTable};
+  }
+
+  /**
+   * Remove an entry from a value range, specified via a value iterator, e.g.
+   *
+   * for (auto it = hash.Values().begin(), end = hash.Values().end();
+   *      it != end; * ++it) {
+   *   if (*it > 42) { hash.Remove(it); }
+   * }
+   *
+   * You might also consider using RemoveIf though.
+   */
+  void Remove(mozilla::detail::nsBaseHashtableValueIterator<EntryType>& aIter) {
+    aIter.mIterator.Remove();
+  }
+
+  /**
+   * reset the hashtable, removing all entries
+   */
+  void Clear() { nsTHashtable<EntryType>::Clear(); }
+
+  /**
+   * Measure the size of the table's entry storage. The size of things pointed
+   * to by entries must be measured separately; hence the "Shallow" prefix.
+   *
+   * @param   aMallocSizeOf the function used to measure heap-allocated blocks
+   * @return  the summed size of the table's storage
+   */
+  size_t ShallowSizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
+    return this->mTable.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  }
+
+  /**
+   * Like ShallowSizeOfExcludingThis, but includes sizeof(*this).
+   */
+  size_t ShallowSizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
+    return aMallocSizeOf(this) + ShallowSizeOfExcludingThis(aMallocSizeOf);
+  }
+
+  /**
+   * Swap the elements in this hashtable with the elements in aOther.
+   */
+  void SwapElements(nsBaseHashtable& aOther) {
+    nsTHashtable<EntryType>::SwapElements(aOther);
+  }
+
+  using nsTHashtable<EntryType>::MarkImmutable;
+
+  /**
+   * Makes a clone of this hashtable by copying all entries. This requires
+   * KeyType and DataType to be copy-constructible.
+   */
+  nsBaseHashtable Clone() const { return CloneAs<nsBaseHashtable>(); }
+
+ protected:
+  template <typename T>
+  T CloneAs() const {
+    static_assert(std::is_base_of_v<nsBaseHashtable, T>);
+    // XXX This can probably be optimized, see Bug 1694368.
+    T result(Count());
+    for (const auto& srcEntry : *this) {
+      result.WithEntryHandle(srcEntry.GetKey(), [&](auto&& dstEntry) {
+        dstEntry.Insert(srcEntry.GetData());
+      });
+    }
+    return result;
+  }
+};
+
+//
+// nsBaseHashtableET definitions
+//
+
+template <class KeyClass, class DataType>
+template <typename... Args>
+nsBaseHashtableET<KeyClass, DataType>::nsBaseHashtableET(KeyTypePointer aKey,
+                                                         Args&&... aArgs)
+    : KeyClass(aKey), mData(std::forward<Args>(aArgs)...) {}
+
+#endif  // nsBaseHashtable_h__