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diff --git a/mfbt/EnumeratedRange.h b/mfbt/EnumeratedRange.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/. */
+
+/* Iterator over contiguous enum values */
+
+/*
+ * Implements generator functions that create a range to iterate over the values
+ * of a scoped or unscoped enum. Unlike IntegerRange, which can only function on
+ * the underlying integral type, the elements of the generated sequence will
+ * have the type of the enum in question.
+ *
+ * Note that the enum values should be contiguous in the iterated range;
+ * unfortunately there exists no way for EnumeratedRange to enforce this
+ * either dynamically or at compile time.
+ */
+
+#ifndef mozilla_EnumeratedRange_h
+#define mozilla_EnumeratedRange_h
+
+#include <limits>
+#include <type_traits>
+
+#include "mozilla/ReverseIterator.h"
+
+namespace mozilla {
+
+namespace detail {
+
+template <typename EnumTypeT>
+class EnumeratedIterator {
+ public:
+  typedef typename std::underlying_type<EnumTypeT>::type IntTypeT;
+
+  template <typename EnumType>
+  constexpr explicit EnumeratedIterator(EnumType aCurrent)
+      : mCurrent(aCurrent) {}
+
+  template <typename EnumType>
+  explicit EnumeratedIterator(const EnumeratedIterator<EnumType>& aOther)
+      : mCurrent(aOther.mCurrent) {}
+
+  EnumTypeT operator*() const { return mCurrent; }
+
+  /* Increment and decrement operators */
+
+  EnumeratedIterator& operator++() {
+    mCurrent = EnumTypeT(IntTypeT(mCurrent) + IntTypeT(1));
+    return *this;
+  }
+  EnumeratedIterator& operator--() {
+    mCurrent = EnumTypeT(IntTypeT(mCurrent) - IntTypeT(1));
+    return *this;
+  }
+  EnumeratedIterator operator++(int) {
+    auto ret = *this;
+    mCurrent = EnumTypeT(IntTypeT(mCurrent) + IntTypeT(1));
+    return ret;
+  }
+  EnumeratedIterator operator--(int) {
+    auto ret = *this;
+    mCurrent = EnumTypeT(IntTypeT(mCurrent) - IntTypeT(1));
+    return ret;
+  }
+
+  /* Comparison operators */
+
+  template <typename EnumType>
+  friend bool operator==(const EnumeratedIterator<EnumType>& aIter1,
+                         const EnumeratedIterator<EnumType>& aIter2);
+  template <typename EnumType>
+  friend bool operator!=(const EnumeratedIterator<EnumType>& aIter1,
+                         const EnumeratedIterator<EnumType>& aIter2);
+  template <typename EnumType>
+  friend bool operator<(const EnumeratedIterator<EnumType>& aIter1,
+                        const EnumeratedIterator<EnumType>& aIter2);
+  template <typename EnumType>
+  friend bool operator<=(const EnumeratedIterator<EnumType>& aIter1,
+                         const EnumeratedIterator<EnumType>& aIter2);
+  template <typename EnumType>
+  friend bool operator>(const EnumeratedIterator<EnumType>& aIter1,
+                        const EnumeratedIterator<EnumType>& aIter2);
+  template <typename EnumType>
+  friend bool operator>=(const EnumeratedIterator<EnumType>& aIter1,
+                         const EnumeratedIterator<EnumType>& aIter2);
+
+ private:
+  EnumTypeT mCurrent;
+};
+
+template <typename EnumType>
+bool operator==(const EnumeratedIterator<EnumType>& aIter1,
+                const EnumeratedIterator<EnumType>& aIter2) {
+  return aIter1.mCurrent == aIter2.mCurrent;
+}
+
+template <typename EnumType>
+bool operator!=(const EnumeratedIterator<EnumType>& aIter1,
+                const EnumeratedIterator<EnumType>& aIter2) {
+  return aIter1.mCurrent != aIter2.mCurrent;
+}
+
+template <typename EnumType>
+bool operator<(const EnumeratedIterator<EnumType>& aIter1,
+               const EnumeratedIterator<EnumType>& aIter2) {
+  return aIter1.mCurrent < aIter2.mCurrent;
+}
+
+template <typename EnumType>
+bool operator<=(const EnumeratedIterator<EnumType>& aIter1,
+                const EnumeratedIterator<EnumType>& aIter2) {
+  return aIter1.mCurrent <= aIter2.mCurrent;
+}
+
+template <typename EnumType>
+bool operator>(const EnumeratedIterator<EnumType>& aIter1,
+               const EnumeratedIterator<EnumType>& aIter2) {
+  return aIter1.mCurrent > aIter2.mCurrent;
+}
+
+template <typename EnumType>
+bool operator>=(const EnumeratedIterator<EnumType>& aIter1,
+                const EnumeratedIterator<EnumType>& aIter2) {
+  return aIter1.mCurrent >= aIter2.mCurrent;
+}
+
+template <typename EnumTypeT>
+class EnumeratedRange {
+ public:
+  typedef EnumeratedIterator<EnumTypeT> iterator;
+  typedef EnumeratedIterator<EnumTypeT> const_iterator;
+  typedef ReverseIterator<iterator> reverse_iterator;
+  typedef ReverseIterator<const_iterator> const_reverse_iterator;
+
+  template <typename EnumType>
+  constexpr EnumeratedRange(EnumType aBegin, EnumType aEnd)
+      : mBegin(aBegin), mEnd(aEnd) {}
+
+  iterator begin() const { return iterator(mBegin); }
+  const_iterator cbegin() const { return begin(); }
+  iterator end() const { return iterator(mEnd); }
+  const_iterator cend() const { return end(); }
+  reverse_iterator rbegin() const { return reverse_iterator(mEnd); }
+  const_reverse_iterator crbegin() const { return rbegin(); }
+  reverse_iterator rend() const { return reverse_iterator(mBegin); }
+  const_reverse_iterator crend() const { return rend(); }
+
+ private:
+  EnumTypeT mBegin;
+  EnumTypeT mEnd;
+};
+
+}  // namespace detail
+
+#ifdef __GNUC__
+// Enums can have an unsigned underlying type, which makes some of the
+// comparisons below always true or always false. Temporarily disable
+// -Wtype-limits to avoid breaking -Werror builds.
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wtype-limits"
+#endif
+
+// Create a range to iterate from aBegin to aEnd, exclusive.
+template <typename EnumType>
+constexpr detail::EnumeratedRange<EnumType> MakeEnumeratedRange(EnumType aBegin,
+                                                                EnumType aEnd) {
+  MOZ_ASSERT(aBegin <= aEnd, "Cannot generate invalid, unbounded range!");
+  return detail::EnumeratedRange<EnumType>(aBegin, aEnd);
+}
+
+// Create a range to iterate from EnumType(0) to aEnd, exclusive. EnumType(0)
+// should exist, but note that there is no way for us to ensure that it does!
+template <typename EnumType>
+constexpr detail::EnumeratedRange<EnumType> MakeEnumeratedRange(EnumType aEnd) {
+  return MakeEnumeratedRange(EnumType(0), aEnd);
+}
+
+// Create a range to iterate from aBegin to aEnd, inclusive.
+//
+// NOTE: This internally constructs a value that is one past `aEnd`, so the
+// enumeration needs to either have a fixed underlying type, or `aEnd + 1` must
+// be inside the range of the enumeration, in order to not be undefined
+// behavior.
+//
+// See bug 1614512.
+template <typename EnumType>
+constexpr detail::EnumeratedRange<EnumType> MakeInclusiveEnumeratedRange(
+    EnumType aBegin, EnumType aEnd) {
+  using EnumUnderlyingType = typename std::underlying_type_t<EnumType>;
+  const auto end = static_cast<EnumUnderlyingType>(aEnd);
+
+  MOZ_ASSERT(end != std::numeric_limits<EnumUnderlyingType>::max(),
+             "aEnd shouldn't overflow!");
+  return MakeEnumeratedRange(aBegin, static_cast<EnumType>(end + 1));
+}
+
+#ifdef __GNUC__
+#  pragma GCC diagnostic pop
+#endif
+
+}  // namespace mozilla
+
+#endif  // mozilla_EnumeratedRange_h