Adding upstream version 110.0.1.upstream/110.0.1upstream

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

11 files changed, 4332 insertions, 0 deletions

diff --git a/mfbt/tests/gtest/TestAlgorithm.cpp b/mfbt/tests/gtest/TestAlgorithm.cpp
new file mode 100644
index 0000000000..a01531fa77
--- /dev/null
+++ b/mfbt/tests/gtest/TestAlgorithm.cpp
@@ -0,0 +1,191 @@
+/* -*- 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/. */
+
+#include "gtest/gtest.h"
+
+#include "mozilla/Algorithm.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/ResultVariant.h"
+
+#include <iterator>
+#include <vector>
+
+using namespace mozilla;
+using std::begin;
+using std::end;
+
+namespace {
+struct MoveOnly {
+  explicit MoveOnly(int32_t aValue) : mValue{Some(aValue)} {}
+
+  MoveOnly(MoveOnly&&) = default;
+  MoveOnly& operator=(MoveOnly&&) = default;
+
+  Maybe<int32_t> mValue;
+};
+
+struct TestError {};
+
+constexpr static int32_t arr1[3] = {1, 2, 3};
+}  // namespace
+
+TEST(MFBT_Algorithm_TransformAbortOnErr, NoError)
+{
+  std::vector<int64_t> out;
+  auto res = TransformAbortOnErr(
+      begin(arr1), end(arr1), std::back_inserter(out),
+      [](const int32_t value) -> Result<int64_t, TestError> {
+        return value * 10;
+      });
+  ASSERT_TRUE(res.isOk());
+
+  const std::vector<int64_t> expected = {10, 20, 30};
+  ASSERT_EQ(expected, out);
+}
+
+TEST(MFBT_Algorithm_TransformAbortOnErr, NoError_Range)
+{
+  std::vector<int64_t> out;
+  auto res = TransformAbortOnErr(
+      arr1, std::back_inserter(out),
+      [](const int32_t value) -> Result<int64_t, TestError> {
+        return value * 10;
+      });
+  ASSERT_TRUE(res.isOk());
+
+  const std::vector<int64_t> expected = {10, 20, 30};
+  ASSERT_EQ(expected, out);
+}
+
+TEST(MFBT_Algorithm_TransformAbortOnErr, ErrorOnFirst)
+{
+  std::vector<int64_t> out;
+  auto res = TransformAbortOnErr(
+      begin(arr1), end(arr1), std::back_inserter(out),
+      [](const int32_t value) -> Result<int64_t, TestError> {
+        return Err(TestError{});
+      });
+  ASSERT_TRUE(res.isErr());
+  ASSERT_TRUE(out.empty());
+}
+
+TEST(MFBT_Algorithm_TransformAbortOnErr, ErrorOnOther)
+{
+  std::vector<int64_t> out;
+  auto res = TransformAbortOnErr(
+      begin(arr1), end(arr1), std::back_inserter(out),
+      [](const int32_t value) -> Result<int64_t, TestError> {
+        if (value > 2) {
+          return Err(TestError{});
+        }
+        return value * 10;
+      });
+  ASSERT_TRUE(res.isErr());
+
+  // XXX Should we assert on this, or is the content of out an implementation
+  // detail?
+  const std::vector<int64_t> expected = {10, 20};
+  ASSERT_EQ(expected, out);
+}
+
+TEST(MFBT_Algorithm_TransformAbortOnErr, ErrorOnOther_Move)
+{
+  MoveOnly in[3] = {MoveOnly{1}, MoveOnly{2}, MoveOnly{3}};
+  std::vector<int64_t> out;
+  auto res = TransformAbortOnErr(
+      std::make_move_iterator(begin(in)), std::make_move_iterator(end(in)),
+      std::back_inserter(out),
+      [](MoveOnly value) -> Result<int64_t, TestError> {
+        if (*value.mValue > 1) {
+          return Err(TestError{});
+        }
+        return *value.mValue * 10;
+      });
+  ASSERT_TRUE(res.isErr());
+
+  ASSERT_FALSE(in[0].mValue);
+  ASSERT_FALSE(in[1].mValue);
+  ASSERT_TRUE(in[2].mValue);
+
+  // XXX Should we assert on this, or is the content of out an implementation
+  // detail?
+  const std::vector<int64_t> expected = {10};
+  ASSERT_EQ(expected, out);
+}
+
+TEST(MFBT_Algorithm_TransformIfAbortOnErr, NoError)
+{
+  std::vector<int64_t> out;
+  auto res = TransformIfAbortOnErr(
+      begin(arr1), end(arr1), std::back_inserter(out),
+      [](const int32_t value) { return value % 2 == 1; },
+      [](const int32_t value) -> Result<int64_t, TestError> {
+        return value * 10;
+      });
+  ASSERT_TRUE(res.isOk());
+
+  const std::vector<int64_t> expected = {10, 30};
+  ASSERT_EQ(expected, out);
+}
+
+TEST(MFBT_Algorithm_TransformIfAbortOnErr, NoError_Range)
+{
+  std::vector<int64_t> out;
+  auto res = TransformIfAbortOnErr(
+      arr1, std::back_inserter(out),
+      [](const int32_t value) { return value % 2 == 1; },
+      [](const int32_t value) -> Result<int64_t, TestError> {
+        return value * 10;
+      });
+  ASSERT_TRUE(res.isOk());
+
+  const std::vector<int64_t> expected = {10, 30};
+  ASSERT_EQ(expected, out);
+}
+
+TEST(MFBT_Algorithm_TransformIfAbortOnErr, ErrorOnOther)
+{
+  std::vector<int64_t> out;
+  auto res = TransformIfAbortOnErr(
+      begin(arr1), end(arr1), std::back_inserter(out),
+      [](const int32_t value) { return value % 2 == 1; },
+      [](const int32_t value) -> Result<int64_t, TestError> {
+        if (value > 2) {
+          return Err(TestError{});
+        }
+        return value * 10;
+      });
+  ASSERT_TRUE(res.isErr());
+
+  const std::vector<int64_t> expected = {10};
+  ASSERT_EQ(expected, out);
+}
+
+TEST(MFBT_Algorithm_TransformIfAbortOnErr, ErrorOnOther_Move)
+{
+  MoveOnly in[3] = {MoveOnly{1}, MoveOnly{2}, MoveOnly{3}};
+  std::vector<int64_t> out;
+  auto res = TransformIfAbortOnErr(
+      std::make_move_iterator(begin(in)), std::make_move_iterator(end(in)),
+      std::back_inserter(out),
+      [](const MoveOnly& value) { return *value.mValue % 2 == 1; },
+      [](MoveOnly value) -> Result<int64_t, TestError> {
+        if (*value.mValue > 1) {
+          return Err(TestError{});
+        }
+        return *value.mValue * 10;
+      });
+  ASSERT_TRUE(res.isErr());
+
+  ASSERT_FALSE(in[0].mValue);
+  ASSERT_TRUE(in[1].mValue);
+  ASSERT_FALSE(in[2].mValue);
+
+  // XXX Should we assert on this, or is the content of out an implementation
+  // detail?
+  const std::vector<int64_t> expected = {10};
+  ASSERT_EQ(expected, out);
+}
diff --git a/mfbt/tests/gtest/TestBuffer.cpp b/mfbt/tests/gtest/TestBuffer.cpp
new file mode 100644
index 0000000000..df36282be1
--- /dev/null
+++ b/mfbt/tests/gtest/TestBuffer.cpp
@@ -0,0 +1,96 @@
+/* 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/. */
+
+#include "gtest/gtest.h"
+
+#include "mozilla/Buffer.h"
+#include "mozilla/Array.h"
+
+using namespace mozilla;
+
+TEST(Buffer, TestBufferInfallible)
+{
+  const size_t LEN = 8;
+  Array<int32_t, LEN> arr = {1, 2, 3, 4, 5, 6, 7, 8};
+  Buffer<int32_t> buf(arr);
+
+  for (size_t i = 0; i < LEN; i++) {
+    ASSERT_EQ(buf[i], arr[i]);
+  }
+
+  auto iter = buf.begin();
+  auto end = buf.end();
+  for (size_t i = 0; i < LEN; i++) {
+    ASSERT_EQ(*iter, arr[i]);
+    iter++;
+  }
+  ASSERT_EQ(iter, end);
+
+  Span<int32_t> span = buf;
+  for (size_t i = 0; i < LEN; i++) {
+    ASSERT_EQ(span[i], arr[i]);
+  }
+
+  auto spanIter = span.begin();
+  auto spanEnd = span.end();
+  for (size_t i = 0; i < LEN; i++) {
+    ASSERT_EQ(*spanIter, arr[i]);
+    spanIter++;
+  }
+  ASSERT_EQ(spanIter, spanEnd);
+
+  span[3] = 42;
+  ASSERT_EQ(buf[3], 42);
+
+  Buffer<int32_t> another(std::move(buf));
+  ASSERT_EQ(another[3], 42);
+  ASSERT_EQ(buf.Length(), 0U);
+}
+
+TEST(Buffer, TestBufferFallible)
+{
+  const size_t LEN = 8;
+  Array<int32_t, LEN> arr = {1, 2, 3, 4, 5, 6, 7, 8};
+  auto maybe = Buffer<int32_t>::CopyFrom(arr);
+  ASSERT_TRUE(maybe.isSome());
+  Buffer<int32_t> buf(std::move(*maybe));
+
+  for (size_t i = 0; i < LEN; i++) {
+    ASSERT_EQ(buf[i], arr[i]);
+  }
+
+  auto iter = buf.begin();
+  auto end = buf.end();
+  for (size_t i = 0; i < LEN; i++) {
+    ASSERT_EQ(*iter, arr[i]);
+    iter++;
+  }
+  ASSERT_EQ(iter, end);
+
+  Span<int32_t> span = buf;
+  for (size_t i = 0; i < LEN; i++) {
+    ASSERT_EQ(span[i], arr[i]);
+  }
+
+  auto spanIter = span.begin();
+  auto spanEnd = span.end();
+  for (size_t i = 0; i < LEN; i++) {
+    ASSERT_EQ(*spanIter, arr[i]);
+    spanIter++;
+  }
+  ASSERT_EQ(spanIter, spanEnd);
+
+  span[3] = 42;
+  ASSERT_EQ(buf[3], 42);
+
+  Buffer<int32_t> another(std::move(buf));
+  ASSERT_EQ(another[3], 42);
+  ASSERT_EQ(buf.Length(), 0U);
+}
+
+TEST(Buffer, TestBufferElements)
+{
+  ASSERT_EQ(Buffer<int32_t>().Elements(),
+            reinterpret_cast<int32_t*>(alignof(int32_t)));
+}
diff --git a/mfbt/tests/gtest/TestInitializedOnce.cpp b/mfbt/tests/gtest/TestInitializedOnce.cpp
new file mode 100644
index 0000000000..a043013451
--- /dev/null
+++ b/mfbt/tests/gtest/TestInitializedOnce.cpp
@@ -0,0 +1,200 @@
+/* -*- 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/. */
+
+#include "gtest/gtest.h"
+
+#include "mozilla/InitializedOnce.h"
+
+#include <type_traits>
+
+using namespace mozilla;
+
+namespace {
+template <typename T>
+void AssertIsSome(const T& aVal) {
+  ASSERT_TRUE(aVal);
+  ASSERT_TRUE(aVal.isSome());
+  ASSERT_FALSE(aVal.isNothing());
+}
+
+template <typename T>
+void AssertIsNothing(const T& aVal) {
+  ASSERT_FALSE(aVal);
+  ASSERT_FALSE(aVal.isSome());
+  ASSERT_TRUE(aVal.isNothing());
+}
+
+static_assert(std::is_trivially_destructible_v<InitializedOnce<const int>>);
+static_assert(std::is_trivially_destructible_v<LazyInitializedOnce<const int>>);
+
+static_assert(!std::is_copy_constructible_v<InitializedOnce<const int>>);
+static_assert(!std::is_copy_assignable_v<InitializedOnce<const int>>);
+
+static_assert(!std::is_default_constructible_v<InitializedOnce<const int>>);
+static_assert(std::is_default_constructible_v<LazyInitializedOnce<const int>>);
+static_assert(std::is_default_constructible_v<
+              LazyInitializedOnceEarlyDestructible<const int>>);
+
+// XXX We cannot test for move-constructability/move-assignability at the
+// moment, since the operations are always defined, but trigger static_assert's
+// if they should not be used. This is not too bad, since we are never copyable.
+
+constexpr InitializedOnce<const int>* kPtrInitializedOnceIntLazyInitForbid =
+    nullptr;
+constexpr LazyInitializedOnce<const int>* kPtrInitializedOnceIntLazyInitAllow =
+    nullptr;
+constexpr LazyInitializedOnceEarlyDestructible<const int>*
+    kPtrInitializedOnceIntLazyInitAllowResettable = nullptr;
+
+template <class T, typename = decltype(std::declval<T*>()->destroy())>
+constexpr bool test_has_destroy_method(const T*) {
+  return true;
+}
+constexpr bool test_has_destroy_method(...) { return false; }
+
+static_assert(test_has_destroy_method(kPtrInitializedOnceIntLazyInitForbid));
+static_assert(!test_has_destroy_method(kPtrInitializedOnceIntLazyInitAllow));
+static_assert(
+    test_has_destroy_method(kPtrInitializedOnceIntLazyInitAllowResettable));
+
+template <class T,
+          typename = decltype(std::declval<T*>()->init(std::declval<int>()))>
+constexpr bool test_has_init_method(const T*) {
+  return true;
+}
+constexpr bool test_has_init_method(...) { return false; }
+
+static_assert(!test_has_init_method(kPtrInitializedOnceIntLazyInitForbid));
+static_assert(test_has_init_method(kPtrInitializedOnceIntLazyInitAllow));
+static_assert(
+    test_has_init_method(kPtrInitializedOnceIntLazyInitAllowResettable));
+
+struct MoveOnly {
+  explicit constexpr MoveOnly(int aValue) : mValue{aValue} {}
+
+  MoveOnly(MoveOnly&&) = default;
+  MoveOnly& operator=(MoveOnly&&) = default;
+
+  int mValue;
+};
+
+}  // namespace
+
+constexpr int testValue = 32;
+
+TEST(InitializedOnce, ImmediateInit)
+{
+  constexpr InitializedOnce<const MoveOnly> val{testValue};
+
+  // compile-time assertions
+  static_assert(val);
+  static_assert(val.isSome());
+  static_assert(!val.isNothing());
+  static_assert(testValue == (*val).mValue);
+  static_assert(testValue == val->mValue);
+  static_assert(testValue == val.ref().mValue);
+
+  // run-time assertions
+  AssertIsSome(val);
+  ASSERT_EQ(testValue, (*val).mValue);
+  ASSERT_EQ(testValue, val->mValue);
+  ASSERT_EQ(testValue, val.ref().mValue);
+}
+
+TEST(InitializedOnce, ImmediateInitReset)
+{
+  InitializedOnce<const MoveOnly> val{testValue};
+  val.destroy();
+
+  AssertIsNothing(val);
+}
+
+TEST(InitializedOnce, MoveConstruct)
+{
+  InitializedOnce<const MoveOnly> oldVal{testValue};
+  InitializedOnce<const MoveOnly> val{std::move(oldVal)};
+
+  AssertIsNothing(oldVal);
+  AssertIsSome(val);
+}
+
+TEST(InitializedOnceAllowLazy, DefaultCtor)
+{
+  LazyInitializedOnce<const MoveOnly> val;
+
+  AssertIsNothing(val);
+}
+
+TEST(InitializedOnceAllowLazy, Init)
+{
+  LazyInitializedOnce<const MoveOnly> val;
+  val.init(testValue);
+
+  AssertIsSome(val);
+  ASSERT_EQ(testValue, (*val).mValue);
+  ASSERT_EQ(testValue, val->mValue);
+  ASSERT_EQ(testValue, val.ref().mValue);
+}
+
+TEST(InitializedOnceAllowLazy, do_Init)
+{
+  LazyInitializedOnce<const MoveOnly> val;
+  do_Init(val) = MoveOnly{testValue};
+
+  AssertIsSome(val);
+  ASSERT_EQ(testValue, (*val).mValue);
+  ASSERT_EQ(testValue, val->mValue);
+  ASSERT_EQ(testValue, val.ref().mValue);
+}
+
+TEST(InitializedOnceAllowLazyResettable, DefaultCtor)
+{
+  LazyInitializedOnceEarlyDestructible<const MoveOnly> val;
+
+  AssertIsNothing(val);
+}
+
+TEST(InitializedOnceAllowLazyResettable, Init)
+{
+  LazyInitializedOnceEarlyDestructible<const MoveOnly> val;
+  val.init(testValue);
+
+  AssertIsSome(val);
+  ASSERT_EQ(testValue, (*val).mValue);
+  ASSERT_EQ(testValue, val->mValue);
+  ASSERT_EQ(testValue, val.ref().mValue);
+}
+
+TEST(InitializedOnceAllowLazyResettable, InitReset)
+{
+  LazyInitializedOnceEarlyDestructible<const MoveOnly> val;
+  val.init(testValue);
+  val.destroy();
+
+  AssertIsNothing(val);
+}
+
+TEST(InitializedOnceAllowLazyResettable, MoveConstruct)
+{
+  LazyInitializedOnceEarlyDestructible<const MoveOnly> oldVal{testValue};
+  LazyInitializedOnceEarlyDestructible<const MoveOnly> val{std::move(oldVal)};
+
+  AssertIsNothing(oldVal);
+  AssertIsSome(val);
+}
+
+TEST(InitializedOnceAllowLazyResettable, MoveAssign)
+{
+  LazyInitializedOnceEarlyDestructible<const MoveOnly> oldVal{testValue};
+  LazyInitializedOnceEarlyDestructible<const MoveOnly> val;
+
+  val = std::move(oldVal);
+
+  AssertIsNothing(oldVal);
+  AssertIsSome(val);
+}
+
+// XXX How do we test for assertions to be hit?
diff --git a/mfbt/tests/gtest/TestLinkedList.cpp b/mfbt/tests/gtest/TestLinkedList.cpp
new file mode 100644
index 0000000000..d53cba5920
--- /dev/null
+++ b/mfbt/tests/gtest/TestLinkedList.cpp
@@ -0,0 +1,78 @@
+/* -*- 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/. */
+
+#include "gtest/gtest.h"
+
+#include "mozilla/LinkedList.h"
+#include "mozilla/RefPtr.h"
+
+using mozilla::AutoCleanLinkedList;
+using mozilla::LinkedList;
+using mozilla::LinkedListElement;
+
+class PtrClass : public LinkedListElement<PtrClass> {
+ public:
+  bool* mResult;
+
+  explicit PtrClass(bool* result) : mResult(result) { EXPECT_TRUE(!*mResult); }
+
+  virtual ~PtrClass() { *mResult = true; }
+};
+
+class InheritedPtrClass : public PtrClass {
+ public:
+  bool* mInheritedResult;
+
+  InheritedPtrClass(bool* result, bool* inheritedResult)
+      : PtrClass(result), mInheritedResult(inheritedResult) {
+    EXPECT_TRUE(!*mInheritedResult);
+  }
+
+  virtual ~InheritedPtrClass() { *mInheritedResult = true; }
+};
+
+TEST(LinkedList, AutoCleanLinkedList)
+{
+  bool rv1 = false;
+  bool rv2 = false;
+  bool rv3 = false;
+  {
+    AutoCleanLinkedList<PtrClass> list;
+    list.insertBack(new PtrClass(&rv1));
+    list.insertBack(new InheritedPtrClass(&rv2, &rv3));
+  }
+
+  EXPECT_TRUE(rv1);
+  EXPECT_TRUE(rv2);
+  EXPECT_TRUE(rv3);
+}
+
+class CountedClass final : public LinkedListElement<RefPtr<CountedClass>> {
+ public:
+  int mCount;
+  void AddRef() { mCount++; }
+  void Release() { mCount--; }
+
+  CountedClass() : mCount(0) {}
+  ~CountedClass() { EXPECT_TRUE(mCount == 0); }
+};
+
+TEST(LinkedList, AutoCleanLinkedListRefPtr)
+{
+  RefPtr<CountedClass> elt1 = new CountedClass;
+  CountedClass* elt2 = new CountedClass;
+  {
+    AutoCleanLinkedList<RefPtr<CountedClass>> list;
+    list.insertBack(elt1);
+    list.insertBack(elt2);
+
+    EXPECT_TRUE(elt1->mCount == 2);
+    EXPECT_TRUE(elt2->mCount == 1);
+  }
+
+  EXPECT_TRUE(elt1->mCount == 1);
+  EXPECT_TRUE(elt2->mCount == 0);
+}
diff --git a/mfbt/tests/gtest/TestMainThreadWeakPtr.cpp b/mfbt/tests/gtest/TestMainThreadWeakPtr.cpp
new file mode 100644
index 0000000000..1722ade8c1
--- /dev/null
+++ b/mfbt/tests/gtest/TestMainThreadWeakPtr.cpp
@@ -0,0 +1,42 @@
+/* -*- 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/. */
+
+#include "gtest/gtest.h"
+
+#include "mozilla/WeakPtr.h"
+#include "mozilla/UniquePtr.h"
+#include <thread>
+
+using namespace mozilla;
+
+struct C : public SupportsWeakPtr {
+  int mNum{0};
+};
+
+struct HasWeakPtrToC {
+  explicit HasWeakPtrToC(C* c) : mPtr(c) {}
+
+  MainThreadWeakPtr<C> mPtr;
+
+  ~HasWeakPtrToC() {
+    MOZ_RELEASE_ASSERT(!NS_IsMainThread(), "Should be released OMT");
+  }
+};
+
+TEST(MFBT_MainThreadWeakPtr, Basic)
+{
+  auto c = MakeUnique<C>();
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  auto weakRef = MakeUnique<HasWeakPtrToC>(c.get());
+
+  std::thread t([weakRef = std::move(weakRef)] {});
+
+  MOZ_RELEASE_ASSERT(!weakRef);
+  c = nullptr;
+
+  t.join();
+}
diff --git a/mfbt/tests/gtest/TestMozDbg.cpp b/mfbt/tests/gtest/TestMozDbg.cpp
new file mode 100644
index 0000000000..24ccd8ed37
--- /dev/null
+++ b/mfbt/tests/gtest/TestMozDbg.cpp
@@ -0,0 +1,170 @@
+/* -*- 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/. */
+
+#include <iostream>
+#include <type_traits>
+
+#include "gtest/gtest.h"
+#include "mozilla/DbgMacro.h"
+#include "mozilla/Unused.h"
+
+using namespace mozilla;
+
+#define TEST_MOZ_DBG_TYPE_IS(type_, expression_...)                    \
+  static_assert(std::is_same_v<type_, decltype(MOZ_DBG(expression_))>, \
+                "MOZ_DBG should return the indicated type")
+
+#define TEST_MOZ_DBG_TYPE_SAME(expression_...)                                 \
+  static_assert(                                                               \
+      std::is_same_v<decltype((expression_)), decltype(MOZ_DBG(expression_))>, \
+      "MOZ_DBG should return the same type")
+
+struct Number {
+  explicit Number(int aValue) : mValue(aValue) {}
+
+  Number(const Number& aOther) = default;
+
+  Number(Number&& aOther) : mValue(aOther.mValue) { aOther.mValue = 0; }
+
+  Number& operator=(const Number& aOther) = default;
+
+  Number& operator=(Number&& aOther) {
+    mValue = aOther.mValue;
+    aOther.mValue = 0;
+    return *this;
+  }
+
+  ~Number() { mValue = -999; }
+
+  int mValue;
+
+  MOZ_DEFINE_DBG(Number, mValue)
+};
+
+struct MoveOnly {
+  explicit MoveOnly(int aValue) : mValue(aValue) {}
+
+  MoveOnly(const MoveOnly& aOther) = delete;
+
+  MoveOnly(MoveOnly&& aOther) : mValue(aOther.mValue) { aOther.mValue = 0; }
+
+  MoveOnly& operator=(MoveOnly& aOther) = default;
+
+  MoveOnly& operator=(MoveOnly&& aOther) {
+    mValue = aOther.mValue;
+    aOther.mValue = 0;
+    return *this;
+  }
+
+  int mValue;
+
+  MOZ_DEFINE_DBG(MoveOnly)
+};
+
+void StaticAssertions() {
+  int x = 123;
+  Number y(123);
+  Number z(234);
+  MoveOnly w(456);
+
+  // Static assertions.
+
+  // lvalues
+  TEST_MOZ_DBG_TYPE_SAME(x);        // int&
+  TEST_MOZ_DBG_TYPE_SAME(y);        // Number&
+  TEST_MOZ_DBG_TYPE_SAME(x = 234);  // int&
+  TEST_MOZ_DBG_TYPE_SAME(y = z);    // Number&
+  TEST_MOZ_DBG_TYPE_SAME(w);        // MoveOnly&
+
+  // prvalues (which MOZ_DBG turns into xvalues by creating objects for them)
+  TEST_MOZ_DBG_TYPE_IS(int&&, 123);
+  TEST_MOZ_DBG_TYPE_IS(int&&, 1 + 2);
+  TEST_MOZ_DBG_TYPE_IS(int*&&, &x);
+  TEST_MOZ_DBG_TYPE_IS(int&&, x++);
+  TEST_MOZ_DBG_TYPE_IS(Number&&, Number(123));
+  TEST_MOZ_DBG_TYPE_IS(MoveOnly&&, MoveOnly(123));
+
+  // xvalues
+  TEST_MOZ_DBG_TYPE_SAME(std::move(y));  // int&&
+  TEST_MOZ_DBG_TYPE_SAME(std::move(y));  // Number&&
+  TEST_MOZ_DBG_TYPE_SAME(std::move(w));  // MoveOnly&
+
+  Unused << x;
+  Unused << y;
+  Unused << z;
+}
+
+TEST(MozDbg, ObjectValues)
+{
+  // Test that moves and assignments all operate correctly with MOZ_DBG wrapped
+  // around various parts of the expression.
+
+  Number a(1);
+  Number b(4);
+
+  ASSERT_EQ(a.mValue, 1);
+
+  MOZ_DBG(a.mValue);
+  ASSERT_EQ(a.mValue, 1);
+
+  MOZ_DBG(a.mValue + 1);
+  ASSERT_EQ(a.mValue, 1);
+
+  MOZ_DBG(a.mValue = 2);
+  ASSERT_EQ(a.mValue, 2);
+
+  MOZ_DBG(a).mValue = 3;
+  ASSERT_EQ(a.mValue, 3);
+
+  MOZ_DBG(a = b);
+  ASSERT_EQ(a.mValue, 4);
+  ASSERT_EQ(b.mValue, 4);
+
+  b.mValue = 5;
+  MOZ_DBG(a) = b;
+  ASSERT_EQ(a.mValue, 5);
+  ASSERT_EQ(b.mValue, 5);
+
+  b.mValue = 6;
+  MOZ_DBG(a = std::move(b));
+  ASSERT_EQ(a.mValue, 6);
+  ASSERT_EQ(b.mValue, 0);
+
+  b.mValue = 7;
+  MOZ_DBG(a) = std::move(b);
+  ASSERT_EQ(a.mValue, 7);
+  ASSERT_EQ(b.mValue, 0);
+
+  b.mValue = 8;
+  a = std::move(MOZ_DBG(b));
+  ASSERT_EQ(a.mValue, 8);
+  ASSERT_EQ(b.mValue, 0);
+
+  a = MOZ_DBG(Number(9));
+  ASSERT_EQ(a.mValue, 9);
+
+  MoveOnly c(1);
+  MoveOnly d(2);
+
+  c = std::move(MOZ_DBG(d));
+  ASSERT_EQ(c.mValue, 2);
+  ASSERT_EQ(d.mValue, 0);
+
+  c.mValue = 3;
+  d.mValue = 4;
+  c = MOZ_DBG(std::move(d));
+  ASSERT_EQ(c.mValue, 4);
+  ASSERT_EQ(d.mValue, 0);
+
+  c.mValue = 5;
+  d.mValue = 6;
+  MOZ_DBG(c = std::move(d));
+  ASSERT_EQ(c.mValue, 6);
+  ASSERT_EQ(d.mValue, 0);
+
+  c = MOZ_DBG(MoveOnly(7));
+  ASSERT_EQ(c.mValue, 7);
+}
diff --git a/mfbt/tests/gtest/TestResultExtensions.cpp b/mfbt/tests/gtest/TestResultExtensions.cpp
new file mode 100644
index 0000000000..711e4f33e4
--- /dev/null
+++ b/mfbt/tests/gtest/TestResultExtensions.cpp
@@ -0,0 +1,579 @@
+/* -*- 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/. */
+
+#include "gtest/gtest.h"
+
+#include "mozilla/ResultExtensions.h"
+#include "nsLocalFile.h"
+
+#include <functional>
+
+using namespace mozilla;
+
+namespace {
+class TestClass {
+ public:
+  static constexpr int kTestValue = 42;
+
+  nsresult NonOverloadedNoInput(int* aOut) {
+    *aOut = kTestValue;
+    return NS_OK;
+  }
+  nsresult NonOverloadedNoInputFails(int* aOut) { return NS_ERROR_FAILURE; }
+
+  nsresult NonOverloadedNoInputConst(int* aOut) const {
+    *aOut = kTestValue;
+    return NS_OK;
+  }
+  nsresult NonOverloadedNoInputFailsConst(int* aOut) const {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsresult NonOverloadedNoInputRef(int& aOut) {
+    aOut = kTestValue;
+    return NS_OK;
+  }
+  nsresult NonOverloadedNoInputFailsRef(int& aOut) { return NS_ERROR_FAILURE; }
+
+  nsresult NonOverloadedNoInputComplex(std::pair<int, int>* aOut) {
+    *aOut = std::pair{kTestValue, kTestValue};
+    return NS_OK;
+  }
+  nsresult NonOverloadedNoInputFailsComplex(std::pair<int, int>* aOut) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsresult NonOverloadedWithInput(int aIn, int* aOut) {
+    *aOut = aIn;
+    return NS_OK;
+  }
+  nsresult NonOverloadedWithInputFails(int aIn, int* aOut) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsresult NonOverloadedNoOutput(int aIn) { return NS_OK; }
+  nsresult NonOverloadedNoOutputFails(int aIn) { return NS_ERROR_FAILURE; }
+
+  nsresult PolymorphicNoInput(nsIFile** aOut) {
+    *aOut = MakeAndAddRef<nsLocalFile>().take();
+    return NS_OK;
+  }
+  nsresult PolymorphicNoInputFails(nsIFile** aOut) { return NS_ERROR_FAILURE; }
+};
+
+class RefCountedTestClass {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(RefCountedTestClass);
+
+  static constexpr int kTestValue = 42;
+
+  nsresult NonOverloadedNoInput(int* aOut) {
+    *aOut = kTestValue;
+    return NS_OK;
+  }
+  nsresult NonOverloadedNoInputFails(int* aOut) { return NS_ERROR_FAILURE; }
+
+ private:
+  ~RefCountedTestClass() = default;
+};
+
+// Check that DerefedType deduces the types as expected
+static_assert(std::is_same_v<mozilla::detail::DerefedType<RefCountedTestClass&>,
+                             RefCountedTestClass>);
+static_assert(std::is_same_v<mozilla::detail::DerefedType<RefCountedTestClass*>,
+                             RefCountedTestClass>);
+static_assert(
+    std::is_same_v<mozilla::detail::DerefedType<RefPtr<RefCountedTestClass>>,
+                   RefCountedTestClass>);
+
+static_assert(std::is_same_v<mozilla::detail::DerefedType<nsIFile&>, nsIFile>);
+static_assert(std::is_same_v<mozilla::detail::DerefedType<nsIFile*>, nsIFile>);
+static_assert(
+    std::is_same_v<mozilla::detail::DerefedType<nsCOMPtr<nsIFile>>, nsIFile>);
+}  // namespace
+
+TEST(ResultExtensions_ToResultInvoke, Lambda_NoInput)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = ToResultInvoke<int>(
+        [&foo](int* out) { return foo.NonOverloadedNoInput(out); });
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr = ToResultInvoke<int>(
+        [&foo](int* out) { return foo.NonOverloadedNoInputFails(out); });
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvoke, MemFn_NoInput)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr =
+        ToResultInvoke<int>(std::mem_fn(&TestClass::NonOverloadedNoInput), foo);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr = ToResultInvoke<int>(
+        std::mem_fn(&TestClass::NonOverloadedNoInputFails), foo);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvoke, MemFn_Polymorphic_NoInput)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = ToResultInvoke<nsCOMPtr<nsIFile>>(
+        std::mem_fn(&TestClass::PolymorphicNoInput), foo);
+    static_assert(std::is_same_v<decltype(valOrErr),
+                                 Result<nsCOMPtr<nsIFile>, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_NE(nullptr, valOrErr.inspect());
+
+    ASSERT_EQ(ToResultInvoke<nsString>(std::mem_fn(&nsIFile::GetPath),
+                                       *MakeRefPtr<nsLocalFile>())
+                  .inspect(),
+              ToResultInvoke<nsString>(std::mem_fn(&nsIFile::GetPath),
+                                       valOrErr.inspect())
+                  .inspect());
+  }
+
+  // failure
+  {
+    auto valOrErr = ToResultInvoke<nsCOMPtr<nsIFile>>(
+        std::mem_fn(&TestClass::PolymorphicNoInputFails), foo);
+    static_assert(std::is_same_v<decltype(valOrErr),
+                                 Result<nsCOMPtr<nsIFile>, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoInput)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = ToResultInvokeMember(foo, &TestClass::NonOverloadedNoInput);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr =
+        ToResultInvokeMember(foo, &TestClass::NonOverloadedNoInputFails);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoInput_Const)
+{
+  const TestClass foo;
+
+  // success
+  {
+    auto valOrErr =
+        ToResultInvokeMember(foo, &TestClass::NonOverloadedNoInputConst);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr =
+        ToResultInvokeMember(foo, &TestClass::NonOverloadedNoInputFailsConst);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoInput_Ref)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr =
+        ToResultInvokeMember(foo, &TestClass::NonOverloadedNoInputRef);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr =
+        ToResultInvokeMember(foo, &TestClass::NonOverloadedNoInputFailsRef);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoInput_Complex)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr =
+        ToResultInvokeMember(foo, &TestClass::NonOverloadedNoInputComplex);
+    static_assert(std::is_same_v<decltype(valOrErr),
+                                 Result<std::pair<int, int>, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ((std::pair{TestClass::kTestValue, TestClass::kTestValue}),
+              valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr =
+        ToResultInvokeMember(foo, &TestClass::NonOverloadedNoInputFailsComplex);
+    static_assert(std::is_same_v<decltype(valOrErr),
+                                 Result<std::pair<int, int>, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, WithInput)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = ToResultInvokeMember(
+        foo, &TestClass::NonOverloadedWithInput, -TestClass::kTestValue);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(-TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr = ToResultInvokeMember(
+        foo, &TestClass::NonOverloadedWithInputFails, -TestClass::kTestValue);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoOutput)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = ToResultInvokeMember(foo, &TestClass::NonOverloadedNoOutput,
+                                         -TestClass::kTestValue);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<Ok, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+  }
+
+  // failure
+  {
+    auto valOrErr = ToResultInvokeMember(
+        foo, &TestClass::NonOverloadedNoOutputFails, -TestClass::kTestValue);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<Ok, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoInput_Macro)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoInput);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoInputFails);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoInput_Const_Macro)
+{
+  const TestClass foo;
+
+  // success
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoInputConst);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr =
+        MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoInputFailsConst);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoInput_Ref_Macro)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoInputRef);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr =
+        MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoInputFailsRef);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoInput_Complex_Macro)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr =
+        MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoInputComplex);
+    static_assert(std::is_same_v<decltype(valOrErr),
+                                 Result<std::pair<int, int>, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ((std::pair{TestClass::kTestValue, TestClass::kTestValue}),
+              valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr =
+        MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoInputFailsComplex);
+
+    static_assert(std::is_same_v<decltype(valOrErr),
+                                 Result<std::pair<int, int>, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, WithInput_Macro)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedWithInput,
+                                                -TestClass::kTestValue);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(-TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(
+        foo, NonOverloadedWithInputFails, -TestClass::kTestValue);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoOutput_Macro)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoOutput,
+                                                -TestClass::kTestValue);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<Ok, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+  }
+
+  // failure
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoOutputFails,
+                                                -TestClass::kTestValue);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<Ok, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, NoInput_Complex_Macro_Typed)
+{
+  TestClass foo;
+
+  // success
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER_TYPED(
+        (std::pair<int, int>), foo, NonOverloadedNoInputComplex);
+    static_assert(std::is_same_v<decltype(valOrErr),
+                                 Result<std::pair<int, int>, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ((std::pair{TestClass::kTestValue, TestClass::kTestValue}),
+              valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER_TYPED(
+        (std::pair<int, int>), foo, NonOverloadedNoInputFailsComplex);
+    static_assert(std::is_same_v<decltype(valOrErr),
+                                 Result<std::pair<int, int>, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, RefPtr_NoInput)
+{
+  auto foo = MakeRefPtr<RefCountedTestClass>();
+
+  // success
+  {
+    auto valOrErr =
+        ToResultInvokeMember(foo, &RefCountedTestClass::NonOverloadedNoInput);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr = ToResultInvokeMember(
+        foo, &RefCountedTestClass::NonOverloadedNoInputFails);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, RefPtr_NoInput_Macro)
+{
+  auto foo = MakeRefPtr<RefCountedTestClass>();
+
+  // success
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoInput);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(foo, NonOverloadedNoInputFails);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, RawPtr_NoInput_Macro)
+{
+  auto foo = MakeRefPtr<RefCountedTestClass>();
+  auto* fooPtr = foo.get();
+
+  // success
+  {
+    auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(fooPtr, NonOverloadedNoInput);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isOk());
+    ASSERT_EQ(TestClass::kTestValue, valOrErr.unwrap());
+  }
+
+  // failure
+  {
+    auto valOrErr =
+        MOZ_TO_RESULT_INVOKE_MEMBER(fooPtr, NonOverloadedNoInputFails);
+    static_assert(std::is_same_v<decltype(valOrErr), Result<int, nsresult>>);
+    ASSERT_TRUE(valOrErr.isErr());
+    ASSERT_EQ(NS_ERROR_FAILURE, valOrErr.unwrapErr());
+  }
+}
+
+TEST(ResultExtensions_ToResultInvokeMember, nsCOMPtr_AbstractClass_WithInput)
+{
+  nsCOMPtr<nsIFile> file = MakeAndAddRef<nsLocalFile>();
+
+  auto valOrErr = ToResultInvokeMember(file, &nsIFile::Equals, file);
+  static_assert(std::is_same_v<decltype(valOrErr), Result<bool, nsresult>>);
+  ASSERT_TRUE(valOrErr.isOk());
+  ASSERT_EQ(true, valOrErr.unwrap());
+}
+
+TEST(ResultExtensions_ToResultInvokeMember,
+     RawPtr_AbstractClass_WithInput_Macro)
+{
+  nsCOMPtr<nsIFile> file = MakeAndAddRef<nsLocalFile>();
+  auto* filePtr = file.get();
+
+  auto valOrErr = MOZ_TO_RESULT_INVOKE_MEMBER(filePtr, Equals, file);
+  static_assert(std::is_same_v<decltype(valOrErr), Result<bool, nsresult>>);
+  ASSERT_TRUE(valOrErr.isOk());
+  ASSERT_EQ(true, valOrErr.unwrap());
+}
+
+TEST(ResultExtensions_ToResultInvokeMember,
+     RawPtr_AbstractClass_NoInput_Macro_Typed)
+{
+  nsCOMPtr<nsIFile> file = MakeAndAddRef<nsLocalFile>();
+  auto* filePtr = file.get();
+
+  auto valOrErr =
+      MOZ_TO_RESULT_INVOKE_MEMBER_TYPED(nsCOMPtr<nsIFile>, filePtr, Clone);
+  static_assert(
+      std::is_same_v<decltype(valOrErr), Result<nsCOMPtr<nsIFile>, nsresult>>);
+  ASSERT_TRUE(valOrErr.isOk());
+  ASSERT_NE(nullptr, valOrErr.unwrap());
+}
diff --git a/mfbt/tests/gtest/TestReverseIterator.cpp b/mfbt/tests/gtest/TestReverseIterator.cpp
new file mode 100644
index 0000000000..a1ba019aa1
--- /dev/null
+++ b/mfbt/tests/gtest/TestReverseIterator.cpp
@@ -0,0 +1,104 @@
+/* -*- 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/. */
+
+#include "gtest/gtest.h"
+
+#include "mozilla/ReverseIterator.h"
+
+using namespace mozilla;
+
+TEST(ReverseIterator, Const_RangeBasedFor)
+{
+  const std::vector<int> in = {1, 2, 3, 4};
+  const auto reversedRange =
+      detail::IteratorRange<ReverseIterator<std::vector<int>::const_iterator>>{
+          ReverseIterator{in.end()}, ReverseIterator{in.begin()}};
+
+  const std::vector<int> expected = {4, 3, 2, 1};
+  std::vector<int> out;
+  for (auto i : reversedRange) {
+    out.emplace_back(i);
+  }
+
+  EXPECT_EQ(expected, out);
+}
+
+TEST(ReverseIterator, NonConst_RangeBasedFor)
+{
+  std::vector<int> in = {1, 2, 3, 4};
+  auto reversedRange =
+      detail::IteratorRange<ReverseIterator<std::vector<int>::iterator>>{
+          ReverseIterator{in.end()}, ReverseIterator{in.begin()}};
+
+  const std::vector<int> expected = {-1, -2, -3, -4};
+  for (auto& i : reversedRange) {
+    i = -i;
+  }
+
+  EXPECT_EQ(expected, in);
+}
+
+TEST(ReverseIterator, Difference)
+{
+  const std::vector<int> in = {1, 2, 3, 4};
+  using reverse_iterator = ReverseIterator<std::vector<int>::const_iterator>;
+
+  reverse_iterator rbegin = reverse_iterator{in.end()},
+                   rend = reverse_iterator{in.begin()};
+  EXPECT_EQ(4, rend - rbegin);
+  EXPECT_EQ(0, rend - rend);
+  EXPECT_EQ(0, rbegin - rbegin);
+
+  --rend;
+  EXPECT_EQ(3, rend - rbegin);
+
+  ++rbegin;
+  EXPECT_EQ(2, rend - rbegin);
+
+  rend--;
+  EXPECT_EQ(1, rend - rbegin);
+
+  rbegin++;
+  EXPECT_EQ(0, rend - rbegin);
+}
+
+TEST(ReverseIterator, Comparison)
+{
+  const std::vector<int> in = {1, 2, 3, 4};
+  using reverse_iterator = ReverseIterator<std::vector<int>::const_iterator>;
+
+  reverse_iterator rbegin = reverse_iterator{in.end()},
+                   rend = reverse_iterator{in.begin()};
+  EXPECT_TRUE(rbegin < rend);
+  EXPECT_FALSE(rend < rbegin);
+  EXPECT_FALSE(rend < rend);
+  EXPECT_FALSE(rbegin < rbegin);
+
+  EXPECT_TRUE(rend > rbegin);
+  EXPECT_FALSE(rbegin > rend);
+  EXPECT_FALSE(rend > rend);
+  EXPECT_FALSE(rbegin > rbegin);
+
+  EXPECT_TRUE(rbegin <= rend);
+  EXPECT_FALSE(rend <= rbegin);
+  EXPECT_TRUE(rend <= rend);
+  EXPECT_TRUE(rbegin <= rbegin);
+
+  EXPECT_TRUE(rend >= rbegin);
+  EXPECT_FALSE(rbegin >= rend);
+  EXPECT_TRUE(rend >= rend);
+  EXPECT_TRUE(rbegin >= rbegin);
+
+  EXPECT_FALSE(rend == rbegin);
+  EXPECT_FALSE(rbegin == rend);
+  EXPECT_TRUE(rend == rend);
+  EXPECT_TRUE(rbegin == rbegin);
+
+  EXPECT_TRUE(rend != rbegin);
+  EXPECT_TRUE(rbegin != rend);
+  EXPECT_FALSE(rend != rend);
+  EXPECT_FALSE(rbegin != rbegin);
+}
diff --git a/mfbt/tests/gtest/TestSpan.cpp b/mfbt/tests/gtest/TestSpan.cpp
new file mode 100644
index 0000000000..405a87ee2c
--- /dev/null
+++ b/mfbt/tests/gtest/TestSpan.cpp
@@ -0,0 +1,2354 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+// Adapted from
+// https://github.com/Microsoft/GSL/blob/3819df6e378ffccf0e29465afe99c3b324c2aa70/tests/Span_tests.cpp
+
+#include "gtest/gtest.h"
+
+#include "mozilla/Span.h"
+
+#include "nsString.h"
+#include "nsTArray.h"
+#include "mozilla/Range.h"
+
+#include <type_traits>
+
+#define SPAN_TEST(name) TEST(SpanTest, name)
+#define CHECK_THROW(a, b)
+
+using namespace mozilla;
+
+static_assert(std::is_convertible_v<Range<int>, Span<const int>>,
+              "Range should convert into const");
+static_assert(std::is_convertible_v<Range<const int>, Span<const int>>,
+              "const Range should convert into const");
+static_assert(!std::is_convertible_v<Range<const int>, Span<int>>,
+              "Range should not drop const in conversion");
+static_assert(std::is_convertible_v<Span<int>, Range<const int>>,
+              "Span should convert into const");
+static_assert(std::is_convertible_v<Span<const int>, Range<const int>>,
+              "const Span should convert into const");
+static_assert(!std::is_convertible_v<Span<const int>, Range<int>>,
+              "Span should not drop const in conversion");
+static_assert(std::is_convertible_v<Span<const int>, Span<const int>>,
+              "const Span should convert into const");
+static_assert(std::is_convertible_v<Span<int>, Span<const int>>,
+              "Span should convert into const");
+static_assert(!std::is_convertible_v<Span<const int>, Span<int>>,
+              "Span should not drop const in conversion");
+static_assert(std::is_convertible_v<const nsTArray<int>, Span<const int>>,
+              "const nsTArray should convert into const");
+static_assert(std::is_convertible_v<nsTArray<int>, Span<const int>>,
+              "nsTArray should convert into const");
+static_assert(!std::is_convertible_v<const nsTArray<int>, Span<int>>,
+              "nsTArray should not drop const in conversion");
+static_assert(std::is_convertible_v<nsTArray<const int>, Span<const int>>,
+              "nsTArray should convert into const");
+static_assert(!std::is_convertible_v<nsTArray<const int>, Span<int>>,
+              "nsTArray should not drop const in conversion");
+
+static_assert(std::is_convertible_v<const std::vector<int>, Span<const int>>,
+              "const std::vector should convert into const");
+static_assert(std::is_convertible_v<std::vector<int>, Span<const int>>,
+              "std::vector should convert into const");
+static_assert(!std::is_convertible_v<const std::vector<int>, Span<int>>,
+              "std::vector should not drop const in conversion");
+
+/**
+ * Rust slice-compatible nullptr replacement value.
+ */
+#define SLICE_CONST_INT_PTR reinterpret_cast<const int*>(alignof(const int))
+
+/**
+ * Rust slice-compatible nullptr replacement value.
+ */
+#define SLICE_INT_PTR reinterpret_cast<int*>(alignof(int))
+
+/**
+ * Rust slice-compatible nullptr replacement value.
+ */
+#define SLICE_CONST_INT_PTR_PTR \
+  reinterpret_cast<const int**>(alignof(const int*))
+
+/**
+ * Rust slice-compatible nullptr replacement value.
+ */
+#define SLICE_INT_PTR_PTR reinterpret_cast<int**>(alignof(int*))
+
+namespace {
+struct BaseClass {};
+struct DerivedClass : BaseClass {};
+}  // namespace
+
+void AssertSpanOfThreeInts(Span<const int> s) {
+  ASSERT_EQ(s.size(), 3U);
+  ASSERT_EQ(s[0], 1);
+  ASSERT_EQ(s[1], 2);
+  ASSERT_EQ(s[2], 3);
+}
+
+void AssertSpanOfThreeChars(Span<const char> s) {
+  ASSERT_EQ(s.size(), 3U);
+  ASSERT_EQ(s[0], 'a');
+  ASSERT_EQ(s[1], 'b');
+  ASSERT_EQ(s[2], 'c');
+}
+
+void AssertSpanOfThreeChar16s(Span<const char16_t> s) {
+  ASSERT_EQ(s.size(), 3U);
+  ASSERT_EQ(s[0], 'a');
+  ASSERT_EQ(s[1], 'b');
+  ASSERT_EQ(s[2], 'c');
+}
+
+void AssertSpanOfThreeCharsViaString(const nsACString& aStr) {
+  AssertSpanOfThreeChars(aStr);
+}
+
+void AssertSpanOfThreeChar16sViaString(const nsAString& aStr) {
+  AssertSpanOfThreeChar16s(aStr);
+}
+
+SPAN_TEST(default_constructor) {
+  {
+    Span<int> s;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int> cs;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+    Span<int, 0> s;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int, 0> cs;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<int, 1> s;
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);  // explains why it can't compile
+#endif
+  }
+
+  {
+    Span<int> s{};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int> cs{};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+}
+
+SPAN_TEST(size_optimization) {
+  {
+    Span<int> s;
+    ASSERT_EQ(sizeof(s), sizeof(int*) + sizeof(size_t));
+  }
+
+  {
+    Span<int, 0> s;
+    ASSERT_EQ(sizeof(s), sizeof(int*));
+  }
+}
+
+SPAN_TEST(from_nullptr_constructor) {
+  {
+    Span<int> s = nullptr;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int> cs = nullptr;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+    Span<int, 0> s = nullptr;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int, 0> cs = nullptr;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<int, 1> s = nullptr;
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);  // explains why it can't compile
+#endif
+  }
+
+  {
+    Span<int> s{nullptr};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int> cs{nullptr};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+    Span<int*> s{nullptr};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR_PTR);
+
+    Span<const int*> cs{nullptr};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR_PTR);
+  }
+}
+
+SPAN_TEST(from_nullptr_length_constructor) {
+  {
+    Span<int> s{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int> cs{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+  {
+    Span<int, 0> s{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+
+    Span<const int, 0> cs{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR);
+  }
+
+#if 0
+        {
+            auto workaround_macro = []() { Span<int, 1> s{ nullptr, static_cast<Span<int>::index_type>(0) }; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        {
+            auto workaround_macro = []() { Span<int> s{nullptr, 1}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+
+            auto const_workaround_macro = []() { Span<const int> cs{nullptr, 1}; };
+            CHECK_THROW(const_workaround_macro(), fail_fast);
+        }
+
+        {
+            auto workaround_macro = []() { Span<int, 0> s{nullptr, 1}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+
+            auto const_workaround_macro = []() { Span<const int, 0> s{nullptr, 1}; };
+            CHECK_THROW(const_workaround_macro(), fail_fast);
+        }
+#endif
+  {
+    Span<int*> s{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR_PTR);
+
+    Span<const int*> cs{nullptr, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), SLICE_CONST_INT_PTR_PTR);
+  }
+}
+
+SPAN_TEST(from_pointer_length_constructor) {
+  int arr[4] = {1, 2, 3, 4};
+
+  {
+    Span<int> s{&arr[0], 2};
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    Span<int, 2> s{&arr[0], 2};
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    int* p = nullptr;
+    Span<int> s{p, static_cast<Span<int>::index_type>(0)};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+  }
+
+#if 0
+        {
+            int* p = nullptr;
+            auto workaround_macro = [=]() { Span<int> s{p, 2}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+#endif
+
+  {
+    auto s = Span(&arr[0], 2);
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    int* p = nullptr;
+    auto s = Span(p, static_cast<Span<int>::index_type>(0));
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+  }
+
+#if 0
+        {
+            int* p = nullptr;
+            auto workaround_macro = [=]() { Span(p, 2); };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+#endif
+}
+
+SPAN_TEST(from_pointer_pointer_constructor) {
+  int arr[4] = {1, 2, 3, 4};
+
+  {
+    Span<int> s{&arr[0], &arr[2]};
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    Span<int, 2> s{&arr[0], &arr[2]};
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    Span<int> s{&arr[0], &arr[0]};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 0> s{&arr[0], &arr[0]};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  // this will fail the std::distance() precondition, which asserts on MSVC
+  // debug builds
+  //{
+  //    auto workaround_macro = [&]() { Span<int> s{&arr[1], &arr[0]}; };
+  //    CHECK_THROW(workaround_macro(), fail_fast);
+  //}
+
+  // this will fail the std::distance() precondition, which asserts on MSVC
+  // debug builds
+  //{
+  //    int* p = nullptr;
+  //    auto workaround_macro = [&]() { Span<int> s{&arr[0], p}; };
+  //    CHECK_THROW(workaround_macro(), fail_fast);
+  //}
+
+  {
+    int* p = nullptr;
+    Span<int> s{p, p};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+  }
+
+  {
+    int* p = nullptr;
+    Span<int, 0> s{p, p};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+  }
+
+  // this will fail the std::distance() precondition, which asserts on MSVC
+  // debug builds
+  //{
+  //    int* p = nullptr;
+  //    auto workaround_macro = [&]() { Span<int> s{&arr[0], p}; };
+  //    CHECK_THROW(workaround_macro(), fail_fast);
+  //}
+
+  {
+    auto s = Span(&arr[0], &arr[2]);
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    auto s = Span(&arr[0], &arr[0]);
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    int* p = nullptr;
+    auto s = Span(p, p);
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), SLICE_INT_PTR);
+  }
+}
+
+SPAN_TEST(from_array_constructor) {
+  int arr[5] = {1, 2, 3, 4, 5};
+
+  {
+    Span<int> s{arr};
+    ASSERT_EQ(s.Length(), 5U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 5> s{arr};
+    ASSERT_EQ(s.Length(), 5U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  int arr2d[2][3] = {{1, 2, 3}, {4, 5, 6}};
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  { Span<int, 6> s{arr}; }
+
+  {
+    Span<int, 0> s{arr};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<int> s{arr2d};
+    ASSERT_EQ(s.Length(), 6U);
+    ASSERT_EQ(s.data(), &arr2d[0][0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[5], 6);
+  }
+
+  {
+    Span<int, 0> s{arr2d};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr2d[0][0]);
+  }
+
+  { Span<int, 6> s{arr2d}; }
+#endif
+  {
+    Span<int[3]> s{&(arr2d[0]), 1};
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr2d[0]);
+  }
+
+  int arr3d[2][3][2] = {{{1, 2}, {3, 4}, {5, 6}}, {{7, 8}, {9, 10}, {11, 12}}};
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int> s{arr3d};
+    ASSERT_EQ(s.Length(), 12U);
+    ASSERT_EQ(s.data(), &arr3d[0][0][0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[11], 12);
+  }
+
+  {
+    Span<int, 0> s{arr3d};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr3d[0][0][0]);
+  }
+
+  { Span<int, 11> s{arr3d}; }
+
+  {
+    Span<int, 12> s{arr3d};
+    ASSERT_EQ(s.Length(), 12U);
+    ASSERT_EQ(s.data(), &arr3d[0][0][0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[5], 6);
+  }
+#endif
+  {
+    Span<int[3][2]> s{&arr3d[0], 1};
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr3d[0]);
+  }
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.Length(), 5U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    auto s = Span(&(arr2d[0]), 1);
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr2d[0]);
+  }
+
+  {
+    auto s = Span(&arr3d[0], 1);
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr3d[0]);
+  }
+}
+
+SPAN_TEST(from_dynamic_array_constructor) {
+  double(*arr)[3][4] = new double[100][3][4];
+
+  {
+    Span<double> s(&arr[0][0][0], 10);
+    ASSERT_EQ(s.Length(), 10U);
+    ASSERT_EQ(s.data(), &arr[0][0][0]);
+  }
+
+  {
+    auto s = Span(&arr[0][0][0], 10);
+    ASSERT_EQ(s.Length(), 10U);
+    ASSERT_EQ(s.data(), &arr[0][0][0]);
+  }
+
+  delete[] arr;
+}
+
+SPAN_TEST(from_std_array_constructor) {
+  std::array<int, 4> arr = {{1, 2, 3, 4}};
+
+  {
+    Span<int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int> cs{arr};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+  {
+    Span<int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int, 4> cs{arr};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int, 2> cs{arr};
+    ASSERT_EQ(cs.size(), 2U);
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+  {
+    Span<int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int, 0> cs{arr};
+    ASSERT_EQ(cs.size(), 0U);
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+  { Span<int, 5> s{arr}; }
+
+  {
+    auto get_an_array = []() -> std::array<int, 4> { return {1, 2, 3, 4}; };
+    auto take_a_Span = [](Span<int> s) { static_cast<void>(s); };
+    // try to take a temporary std::array
+    take_a_Span(get_an_array());
+  }
+#endif
+
+  {
+    auto get_an_array = []() -> std::array<int, 4> { return {{1, 2, 3, 4}}; };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary std::array
+    take_a_Span(get_an_array());
+  }
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+}
+
+SPAN_TEST(from_const_std_array_constructor) {
+  const std::array<int, 4> arr = {{1, 2, 3, 4}};
+
+  {
+    Span<const int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  { Span<const int, 5> s{arr}; }
+#endif
+
+  {
+    auto get_an_array = []() -> const std::array<int, 4> {
+      return {{1, 2, 3, 4}};
+    };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary std::array
+    take_a_Span(get_an_array());
+  }
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+}
+
+SPAN_TEST(from_std_array_const_constructor) {
+  std::array<const int, 4> arr = {{1, 2, 3, 4}};
+
+  {
+    Span<const int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  { Span<const int, 5> s{arr}; }
+
+  { Span<int, 4> s{arr}; }
+#endif
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+}
+
+SPAN_TEST(from_mozilla_array_constructor) {
+  mozilla::Array<int, 4> arr(1, 2, 3, 4);
+
+  {
+    Span<int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int> cs{arr};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int, 4> cs{arr};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int, 2> cs{arr};
+    ASSERT_EQ(cs.size(), 2U);
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int, 0> cs{arr};
+    ASSERT_EQ(cs.size(), 0U);
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+  { Span<int, 5> s{arr}; }
+
+  {
+    auto get_an_array = []() -> mozilla::Array<int, 4> { return {1, 2, 3, 4}; };
+    auto take_a_Span = [](Span<int> s) { static_cast<void>(s); };
+    // try to take a temporary mozilla::Array
+    take_a_Span(get_an_array());
+  }
+#endif
+
+  {
+    auto get_an_array = []() -> mozilla::Array<int, 4> { return {1, 2, 3, 4}; };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary mozilla::Array
+    take_a_Span(get_an_array());
+  }
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+}
+
+SPAN_TEST(from_const_mozilla_array_constructor) {
+  const mozilla::Array<int, 4> arr(1, 2, 3, 4);
+
+  {
+    Span<const int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  { Span<const int, 5> s{arr}; }
+#endif
+
+#if 0
+  {
+    auto get_an_array = []() -> const mozilla::Array<int, 4> {
+      return { 1, 2, 3, 4 };
+    };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary mozilla::Array
+    take_a_Span(get_an_array());
+  }
+#endif
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+}
+
+SPAN_TEST(from_mozilla_array_const_constructor) {
+  mozilla::Array<const int, 4> arr(1, 2, 3, 4);
+
+  {
+    Span<const int> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 4> s{arr};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{arr};
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 0> s{arr};
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  { Span<const int, 5> s{arr}; }
+
+  { Span<int, 4> s{arr}; }
+#endif
+
+  {
+    auto s = Span(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+}
+
+SPAN_TEST(from_container_constructor) {
+  std::vector<int> v = {1, 2, 3};
+  const std::vector<int> cv = v;
+
+  {
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{v};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.size()));
+    ASSERT_EQ(s.data(), v.data());
+
+    Span<const int> cs{v};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.size()));
+    ASSERT_EQ(cs.data(), v.data());
+  }
+
+  std::string str = "hello";
+  const std::string cstr = "hello";
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<char> s{str};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.size()));
+    ASSERT_EQ(s.data(), str.data());
+#endif
+    Span<const char> cs{str};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(str.size()));
+    ASSERT_EQ(cs.data(), str.data());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<char> s{cstr};
+#endif
+    Span<const char> cs{cstr};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(cstr.size()));
+    ASSERT_EQ(cs.data(), cstr.data());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    auto get_temp_vector = []() -> std::vector<int> { return {}; };
+    auto use_Span = [](Span<int> s) { static_cast<void>(s); };
+    use_Span(get_temp_vector());
+#endif
+  }
+
+  {
+    auto get_temp_vector = []() -> std::vector<int> { return {}; };
+    auto use_Span = [](Span<const int> s) { static_cast<void>(s); };
+    use_Span(get_temp_vector());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    auto get_temp_string = []() -> std::string { return {}; };
+    auto use_Span = [](Span<char> s) { static_cast<void>(s); };
+    use_Span(get_temp_string());
+#endif
+  }
+
+  {
+    auto get_temp_string = []() -> std::string { return {}; };
+    auto use_Span = [](Span<const char> s) { static_cast<void>(s); };
+    use_Span(get_temp_string());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    auto get_temp_vector = []() -> const std::vector<int> { return {}; };
+    auto use_Span = [](Span<const char> s) { static_cast<void>(s); };
+    use_Span(get_temp_vector());
+#endif
+  }
+
+  {
+    auto get_temp_string = []() -> const std::string { return {}; };
+    auto use_Span = [](Span<const char> s) { static_cast<void>(s); };
+    use_Span(get_temp_string());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    std::map<int, int> m;
+    Span<int> s{m};
+#endif
+  }
+
+  {
+    auto s = Span(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.size()));
+    ASSERT_EQ(s.data(), v.data());
+
+    auto cs = Span(cv);
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(cv.size()));
+    ASSERT_EQ(cs.data(), cv.data());
+  }
+}
+
+SPAN_TEST(from_xpcom_collections) {
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{v};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{v};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    auto s = Span(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+  {
+    AutoTArray<int, 5> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{v};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{v};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    AutoTArray<int, 5> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    auto s = Span(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+  {
+    FallibleTArray<int> v;
+    *(v.AppendElement(fallible)) = 1;
+    *(v.AppendElement(fallible)) = 2;
+    *(v.AppendElement(fallible)) = 3;
+
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{v};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{v};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    FallibleTArray<int> v;
+    *(v.AppendElement(fallible)) = 1;
+    *(v.AppendElement(fallible)) = 2;
+    *(v.AppendElement(fallible)) = 3;
+
+    AssertSpanOfThreeInts(v);
+
+    auto s = Span(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+  {
+    nsAutoString str;
+    str.AssignLiteral(u"abc");
+
+    AssertSpanOfThreeChar16s(str);
+    AssertSpanOfThreeChar16sViaString(str);
+
+    Span<char16_t> s{str.GetMutableData()};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(s.data(), str.BeginWriting());
+    ASSERT_EQ(s[2], 'c');
+
+    Span<const char16_t> cs{str};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(cs.data(), str.BeginReading());
+    ASSERT_EQ(cs[2], 'c');
+  }
+  {
+    nsAutoString str;
+    str.AssignLiteral(u"abc");
+
+    AssertSpanOfThreeChar16s(str);
+    AssertSpanOfThreeChar16sViaString(str);
+
+    auto s = Span(str);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(s.data(), str.BeginReading());
+    ASSERT_EQ(s[2], 'c');
+  }
+  {
+    nsAutoCString str;
+    str.AssignLiteral("abc");
+
+    AssertSpanOfThreeChars(str);
+    AssertSpanOfThreeCharsViaString(str);
+
+    Span<const uint8_t> cs{str};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(cs.data(), reinterpret_cast<const uint8_t*>(str.BeginReading()));
+    ASSERT_EQ(cs[2], 'c');
+  }
+  {
+    nsAutoCString str;
+    str.AssignLiteral("abc");
+
+    AssertSpanOfThreeChars(str);
+    AssertSpanOfThreeCharsViaString(str);
+
+    auto s = Span(str);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(s.data(), str.BeginReading());
+    ASSERT_EQ(s[2], 'c');
+  }
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    Range<int> r(v.Elements(), v.Length());
+
+    AssertSpanOfThreeInts(r);
+
+    Span<int> s{r};
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{r};
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    Range<int> r(v.Elements(), v.Length());
+
+    AssertSpanOfThreeInts(r);
+
+    auto s = Span(r);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+}
+
+SPAN_TEST(from_cstring) {
+  {
+    const char* str = nullptr;
+    auto cs = MakeStringSpan(str);
+    ASSERT_EQ(cs.size(), 0U);
+  }
+  {
+    const char* str = "abc";
+
+    auto cs = MakeStringSpan(str);
+    ASSERT_EQ(cs.size(), 3U);
+    ASSERT_EQ(cs.data(), str);
+    ASSERT_EQ(cs[2], 'c');
+
+    static_assert(MakeStringSpan("abc").size() == 3U);
+    static_assert(MakeStringSpan("abc")[2] == 'c');
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<const char> scccl("literal");  // error
+
+    Span<const char> sccel;
+    sccel = "literal";  // error
+
+    cs = Span("literal");  // error
+#endif
+  }
+  {
+    char arr[4] = {'a', 'b', 'c', 0};
+
+    auto cs = MakeStringSpan(arr);
+    ASSERT_EQ(cs.size(), 3U);
+    ASSERT_EQ(cs.data(), arr);
+    ASSERT_EQ(cs[2], 'c');
+
+    cs = Span(arr);
+    ASSERT_EQ(cs.size(), 4U);  // zero terminator is part of the array span.
+    ASSERT_EQ(cs.data(), arr);
+    ASSERT_EQ(cs[2], 'c');
+    ASSERT_EQ(cs[3], '\0');  // zero terminator is part of the array span.
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<char> scca(arr);         // error
+    Span<const char> sccca(arr);  // error
+
+    Span<const char> scccea;
+    scccea = arr;  // error
+#endif
+  }
+  {
+    const char16_t* str = nullptr;
+    auto cs = MakeStringSpan(str);
+    ASSERT_EQ(cs.size(), 0U);
+  }
+  {
+    char16_t arr[4] = {'a', 'b', 'c', 0};
+    const char16_t* str = arr;
+
+    auto cs = MakeStringSpan(str);
+    ASSERT_EQ(cs.size(), 3U);
+    ASSERT_EQ(cs.data(), str);
+    ASSERT_EQ(cs[2], 'c');
+
+    static_assert(MakeStringSpan(u"abc").size() == 3U);
+    static_assert(MakeStringSpan(u"abc")[2] == u'c');
+
+    cs = MakeStringSpan(arr);
+    ASSERT_EQ(cs.size(), 3U);
+    ASSERT_EQ(cs.data(), str);
+    ASSERT_EQ(cs[2], 'c');
+
+    cs = Span(arr);
+    ASSERT_EQ(cs.size(), 4U);  // zero terminator is part of the array span.
+    ASSERT_EQ(cs.data(), str);
+    ASSERT_EQ(cs[2], 'c');
+    ASSERT_EQ(cs[3], '\0');  // zero terminator is part of the array span.
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<char16_t> scca(arr);  // error
+
+    Span<const char16_t> scccea;
+    scccea = arr;  // error
+
+    Span<const char16_t> scccl(u"literal");  // error
+
+    Span<const char16_t>* sccel;
+    *sccel = u"literal";  // error
+
+    cs = Span(u"literal");  // error
+#endif
+  }
+}
+
+SPAN_TEST(from_convertible_Span_constructor){{Span<DerivedClass> avd;
+Span<const DerivedClass> avcd = avd;
+static_cast<void>(avcd);
+}
+
+{
+#ifdef CONFIRM_COMPILATION_ERRORS
+  Span<DerivedClass> avd;
+  Span<BaseClass> avb = avd;
+  static_cast<void>(avb);
+#endif
+}
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+{
+  Span<int> s;
+  Span<unsigned int> s2 = s;
+  static_cast<void>(s2);
+}
+
+{
+  Span<int> s;
+  Span<const unsigned int> s2 = s;
+  static_cast<void>(s2);
+}
+
+{
+  Span<int> s;
+  Span<short> s2 = s;
+  static_cast<void>(s2);
+}
+#endif
+}
+
+SPAN_TEST(copy_move_and_assignment) {
+  Span<int> s1;
+  ASSERT_TRUE(s1.empty());
+
+  int arr[] = {3, 4, 5};
+
+  Span<const int> s2 = arr;
+  ASSERT_EQ(s2.Length(), 3U);
+  ASSERT_EQ(s2.data(), &arr[0]);
+
+  s2 = s1;
+  ASSERT_TRUE(s2.empty());
+
+  auto get_temp_Span = [&]() -> Span<int> { return {&arr[1], 2}; };
+  auto use_Span = [&](Span<const int> s) {
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[1]);
+  };
+  use_Span(get_temp_Span());
+
+  s1 = get_temp_Span();
+  ASSERT_EQ(s1.Length(), 2U);
+  ASSERT_EQ(s1.data(), &arr[1]);
+}
+
+SPAN_TEST(first) {
+  int arr[5] = {1, 2, 3, 4, 5};
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.First<2>().Length(), 2U);
+    ASSERT_EQ(av.First(2).Length(), 2U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.First<0>().Length(), 0U);
+    ASSERT_EQ(av.First(0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.First<5>().Length(), 5U);
+    ASSERT_EQ(av.First(5).Length(), 5U);
+  }
+
+#if 0
+        {
+            Span<int, 5> av = arr;
+#  ifdef CONFIRM_COMPILATION_ERRORS
+            ASSERT_EQ(av.First<6>().Length() , 6U);
+            ASSERT_EQ(av.First<-1>().Length() , -1);
+#  endif
+            CHECK_THROW(av.First(6).Length(), fail_fast);
+        }
+#endif
+
+  {
+    Span<int> av;
+    ASSERT_EQ(av.First<0>().Length(), 0U);
+    ASSERT_EQ(av.First(0).Length(), 0U);
+  }
+}
+
+SPAN_TEST(last) {
+  int arr[5] = {1, 2, 3, 4, 5};
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Last<2>().Length(), 2U);
+    ASSERT_EQ(av.Last(2).Length(), 2U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Last<0>().Length(), 0U);
+    ASSERT_EQ(av.Last(0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Last<5>().Length(), 5U);
+    ASSERT_EQ(av.Last(5).Length(), 5U);
+  }
+
+#if 0
+        {
+            Span<int, 5> av = arr;
+#  ifdef CONFIRM_COMPILATION_ERRORS
+            ASSERT_EQ(av.Last<6>().Length() , 6U);
+#  endif
+            CHECK_THROW(av.Last(6).Length(), fail_fast);
+        }
+#endif
+
+  {
+    Span<int> av;
+    ASSERT_EQ(av.Last<0>().Length(), 0U);
+    ASSERT_EQ(av.Last(0).Length(), 0U);
+  }
+}
+
+SPAN_TEST(from_to) {
+  int arr[5] = {1, 2, 3, 4, 5};
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.From(3).Length(), 2U);
+    ASSERT_EQ(av.From(2)[1], 4);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.From(5).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.From(0).Length(), 5U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.To(3).Length(), 3U);
+    ASSERT_EQ(av.To(3)[1], 2);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.To(0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.To(5).Length(), 5U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.FromTo(1, 4).Length(), 3U);
+    ASSERT_EQ(av.FromTo(1, 4)[1], 3);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.FromTo(2, 2).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.FromTo(0, 5).Length(), 5U);
+  }
+}
+
+SPAN_TEST(Subspan) {
+  int arr[5] = {1, 2, 3, 4, 5};
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<2, 2>().Length()), 2U);
+    ASSERT_EQ(av.Subspan(2, 2).Length(), 2U);
+    ASSERT_EQ(av.Subspan(2, 3).Length(), 3U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<0, 0>().Length()), 0U);
+    ASSERT_EQ(av.Subspan(0, 0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<0, 5>().Length()), 5U);
+    ASSERT_EQ(av.Subspan(0, 5).Length(), 5U);
+    CHECK_THROW(av.Subspan(0, 6).Length(), fail_fast);
+    CHECK_THROW(av.Subspan(1, 5).Length(), fail_fast);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<4, 0>().Length()), 0U);
+    ASSERT_EQ(av.Subspan(4, 0).Length(), 0U);
+    ASSERT_EQ(av.Subspan(5, 0).Length(), 0U);
+    CHECK_THROW(av.Subspan(6, 0).Length(), fail_fast);
+  }
+
+  {
+    Span<int> av;
+    ASSERT_EQ((av.Subspan<0, 0>().Length()), 0U);
+    ASSERT_EQ(av.Subspan(0, 0).Length(), 0U);
+    CHECK_THROW((av.Subspan<1, 0>().Length()), fail_fast);
+  }
+
+  {
+    Span<int> av;
+    ASSERT_EQ(av.Subspan(0).Length(), 0U);
+    CHECK_THROW(av.Subspan(1).Length(), fail_fast);
+  }
+
+  {
+    Span<int> av = arr;
+    ASSERT_EQ(av.Subspan(0).Length(), 5U);
+    ASSERT_EQ(av.Subspan(1).Length(), 4U);
+    ASSERT_EQ(av.Subspan(4).Length(), 1U);
+    ASSERT_EQ(av.Subspan(5).Length(), 0U);
+    CHECK_THROW(av.Subspan(6).Length(), fail_fast);
+    auto av2 = av.Subspan(1);
+    for (int i = 0; i < 4; ++i) ASSERT_EQ(av2[i], i + 2);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Subspan(0).Length(), 5U);
+    ASSERT_EQ(av.Subspan(1).Length(), 4U);
+    ASSERT_EQ(av.Subspan(4).Length(), 1U);
+    ASSERT_EQ(av.Subspan(5).Length(), 0U);
+    CHECK_THROW(av.Subspan(6).Length(), fail_fast);
+    auto av2 = av.Subspan(1);
+    for (int i = 0; i < 4; ++i) ASSERT_EQ(av2[i], i + 2);
+  }
+}
+
+SPAN_TEST(at_call) {
+  int arr[4] = {1, 2, 3, 4};
+
+  {
+    Span<int> s = arr;
+    ASSERT_EQ(s.at(0), 1);
+    CHECK_THROW(s.at(5), fail_fast);
+  }
+
+  {
+    int arr2d[2] = {1, 6};
+    Span<int, 2> s = arr2d;
+    ASSERT_EQ(s.at(0), 1);
+    ASSERT_EQ(s.at(1), 6);
+    CHECK_THROW(s.at(2), fail_fast);
+  }
+}
+
+SPAN_TEST(operator_function_call) {
+  int arr[4] = {1, 2, 3, 4};
+
+  {
+    Span<int> s = arr;
+    ASSERT_EQ(s(0), 1);
+    CHECK_THROW(s(5), fail_fast);
+  }
+
+  {
+    int arr2d[2] = {1, 6};
+    Span<int, 2> s = arr2d;
+    ASSERT_EQ(s(0), 1);
+    ASSERT_EQ(s(1), 6);
+    CHECK_THROW(s(2), fail_fast);
+  }
+}
+
+SPAN_TEST(iterator_default_init) {
+  Span<int>::iterator it1;
+  Span<int>::iterator it2;
+  ASSERT_EQ(it1, it2);
+}
+
+SPAN_TEST(const_iterator_default_init) {
+  Span<int>::const_iterator it1;
+  Span<int>::const_iterator it2;
+  ASSERT_EQ(it1, it2);
+}
+
+SPAN_TEST(iterator_conversions) {
+  Span<int>::iterator badIt;
+  Span<int>::const_iterator badConstIt;
+  ASSERT_EQ(badIt, badConstIt);
+
+  int a[] = {1, 2, 3, 4};
+  Span<int> s = a;
+
+  auto it = s.begin();
+  auto cit = s.cbegin();
+
+  ASSERT_EQ(it, cit);
+  ASSERT_EQ(cit, it);
+
+  Span<int>::const_iterator cit2 = it;
+  ASSERT_EQ(cit2, cit);
+
+  Span<int>::const_iterator cit3 = it + 4;
+  ASSERT_EQ(cit3, s.cend());
+}
+
+SPAN_TEST(iterator_comparisons) {
+  int a[] = {1, 2, 3, 4};
+  {
+    Span<int> s = a;
+    Span<int>::iterator it = s.begin();
+    auto it2 = it + 1;
+    Span<int>::const_iterator cit = s.cbegin();
+
+    ASSERT_EQ(it, cit);
+    ASSERT_EQ(cit, it);
+    ASSERT_EQ(it, it);
+    ASSERT_EQ(cit, cit);
+    ASSERT_EQ(cit, s.begin());
+    ASSERT_EQ(s.begin(), cit);
+    ASSERT_EQ(s.cbegin(), cit);
+    ASSERT_EQ(it, s.begin());
+    ASSERT_EQ(s.begin(), it);
+
+    ASSERT_NE(it, it2);
+    ASSERT_NE(it2, it);
+    ASSERT_NE(it, s.end());
+    ASSERT_NE(it2, s.end());
+    ASSERT_NE(s.end(), it);
+    ASSERT_NE(it2, cit);
+    ASSERT_NE(cit, it2);
+
+    ASSERT_LT(it, it2);
+    ASSERT_LE(it, it2);
+    ASSERT_LE(it2, s.end());
+    ASSERT_LT(it, s.end());
+    ASSERT_LE(it, cit);
+    ASSERT_LE(cit, it);
+    ASSERT_LT(cit, it2);
+    ASSERT_LE(cit, it2);
+    ASSERT_LT(cit, s.end());
+    ASSERT_LE(cit, s.end());
+
+    ASSERT_GT(it2, it);
+    ASSERT_GE(it2, it);
+    ASSERT_GT(s.end(), it2);
+    ASSERT_GE(s.end(), it2);
+    ASSERT_GT(it2, cit);
+    ASSERT_GE(it2, cit);
+  }
+}
+
+SPAN_TEST(begin_end) {
+  {
+    int a[] = {1, 2, 3, 4};
+    Span<int> s = a;
+
+    Span<int>::iterator it = s.begin();
+    Span<int>::iterator it2 = std::begin(s);
+    ASSERT_EQ(it, it2);
+
+    it = s.end();
+    it2 = std::end(s);
+    ASSERT_EQ(it, it2);
+  }
+
+  {
+    int a[] = {1, 2, 3, 4};
+    Span<int> s = a;
+
+    auto it = s.begin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 1);
+
+    auto beyond = s.end();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4U);
+    ASSERT_EQ(first - first, 0U);
+    ASSERT_EQ(beyond - beyond, 0U);
+
+    ++it;
+    ASSERT_EQ(it - first, 1U);
+    ASSERT_EQ(*it, 2);
+    *it = 22;
+    ASSERT_EQ(*it, 22);
+    ASSERT_EQ(beyond - it, 3U);
+
+    it = first;
+    ASSERT_EQ(it, first);
+    while (it != s.end()) {
+      *it = 5;
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0U);
+
+    for (auto& n : s) {
+      ASSERT_EQ(n, 5);
+    }
+  }
+}
+
+SPAN_TEST(cbegin_cend) {
+#if 0
+          {
+              int a[] = { 1, 2, 3, 4 };
+              Span<int> s = a;
+
+              Span<int>::const_iterator cit = s.cbegin();
+              Span<int>::const_iterator cit2 = std::cbegin(s);
+              ASSERT_EQ(cit , cit2);
+
+              cit = s.cend();
+              cit2 = std::cend(s);
+              ASSERT_EQ(cit , cit2);
+          }
+#endif
+  {
+    int a[] = {1, 2, 3, 4};
+    Span<int> s = a;
+
+    auto it = s.cbegin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 1);
+
+    auto beyond = s.cend();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4U);
+    ASSERT_EQ(first - first, 0U);
+    ASSERT_EQ(beyond - beyond, 0U);
+
+    ++it;
+    ASSERT_EQ(it - first, 1U);
+    ASSERT_EQ(*it, 2);
+    ASSERT_EQ(beyond - it, 3U);
+
+    int last = 0;
+    it = first;
+    ASSERT_EQ(it, first);
+    while (it != s.cend()) {
+      ASSERT_EQ(*it, last + 1);
+
+      last = *it;
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0U);
+  }
+}
+
+SPAN_TEST(rbegin_rend) {
+  {
+    int a[] = {1, 2, 3, 4};
+    Span<int> s = a;
+
+    auto it = s.rbegin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 4);
+
+    auto beyond = s.rend();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4U);
+    ASSERT_EQ(first - first, 0U);
+    ASSERT_EQ(beyond - beyond, 0U);
+
+    ++it;
+    ASSERT_EQ(it - first, 1U);
+    ASSERT_EQ(*it, 3);
+    *it = 22;
+    ASSERT_EQ(*it, 22);
+    ASSERT_EQ(beyond - it, 3U);
+
+    it = first;
+    ASSERT_EQ(it, first);
+    while (it != s.rend()) {
+      *it = 5;
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0U);
+
+    for (auto& n : s) {
+      ASSERT_EQ(n, 5);
+    }
+  }
+}
+
+SPAN_TEST(crbegin_crend) {
+  {
+    int a[] = {1, 2, 3, 4};
+    Span<int> s = a;
+
+    auto it = s.crbegin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 4);
+
+    auto beyond = s.crend();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4U);
+    ASSERT_EQ(first - first, 0U);
+    ASSERT_EQ(beyond - beyond, 0U);
+
+    ++it;
+    ASSERT_EQ(it - first, 1U);
+    ASSERT_EQ(*it, 3);
+    ASSERT_EQ(beyond - it, 3U);
+
+    it = first;
+    ASSERT_EQ(it, first);
+    int last = 5;
+    while (it != s.crend()) {
+      ASSERT_EQ(*it, last - 1);
+      last = *it;
+
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0U);
+  }
+}
+
+SPAN_TEST(comparison_operators) {
+  {
+    Span<int> s1 = nullptr;
+    Span<int> s2 = nullptr;
+    ASSERT_EQ(s1, s2);
+    ASSERT_FALSE(s1 != s2);
+    ASSERT_FALSE(s1 < s2);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s1, s2);
+    ASSERT_EQ(s2, s1);
+    ASSERT_FALSE(s2 != s1);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s2, s1);
+    ASSERT_FALSE(s2 > s1);
+    ASSERT_GE(s2, s1);
+  }
+
+  {
+    int arr[] = {2, 1};
+    Span<int> s1 = arr;
+    Span<int> s2 = arr;
+
+    ASSERT_EQ(s1, s2);
+    ASSERT_FALSE(s1 != s2);
+    ASSERT_FALSE(s1 < s2);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s1, s2);
+    ASSERT_EQ(s2, s1);
+    ASSERT_FALSE(s2 != s1);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s2, s1);
+    ASSERT_FALSE(s2 > s1);
+    ASSERT_GE(s2, s1);
+  }
+
+  {
+    int arr[] = {2, 1};  // bigger
+
+    Span<int> s1 = nullptr;
+    Span<int> s2 = arr;
+
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_LT(s1, s2);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s2 <= s1);
+    ASSERT_GT(s2, s1);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s2, s1);
+    ASSERT_FALSE(s1 >= s2);
+  }
+
+  {
+    int arr1[] = {1, 2};
+    int arr2[] = {1, 2};
+    Span<int> s1 = arr1;
+    Span<int> s2 = arr2;
+
+    ASSERT_EQ(s1, s2);
+    ASSERT_FALSE(s1 != s2);
+    ASSERT_FALSE(s1 < s2);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s1, s2);
+    ASSERT_EQ(s2, s1);
+    ASSERT_FALSE(s2 != s1);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s2, s1);
+    ASSERT_FALSE(s2 > s1);
+    ASSERT_GE(s2, s1);
+  }
+
+  {
+    int arr[] = {1, 2, 3};
+
+    AssertSpanOfThreeInts(arr);
+
+    Span<int> s1 = {&arr[0], 2};  // shorter
+    Span<int> s2 = arr;           // longer
+
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_LT(s1, s2);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s2 <= s1);
+    ASSERT_GT(s2, s1);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s2, s1);
+    ASSERT_FALSE(s1 >= s2);
+  }
+
+  {
+    int arr1[] = {1, 2};  // smaller
+    int arr2[] = {2, 1};  // bigger
+
+    Span<int> s1 = arr1;
+    Span<int> s2 = arr2;
+
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_LT(s1, s2);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s2 <= s1);
+    ASSERT_GT(s2, s1);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s2, s1);
+    ASSERT_FALSE(s1 >= s2);
+  }
+}
+
+SPAN_TEST(as_bytes) {
+  int a[] = {1, 2, 3, 4};
+
+  {
+    Span<const int> s = a;
+    ASSERT_EQ(s.Length(), 4U);
+    Span<const uint8_t> bs = AsBytes(s);
+    ASSERT_EQ(static_cast<const void*>(bs.data()),
+              static_cast<const void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+  }
+
+  {
+    Span<int> s;
+    auto bs = AsBytes(s);
+    ASSERT_EQ(bs.Length(), s.Length());
+    ASSERT_EQ(bs.Length(), 0U);
+    ASSERT_EQ(bs.size_bytes(), 0U);
+    ASSERT_EQ(static_cast<const void*>(bs.data()),
+              static_cast<const void*>(s.data()));
+    ASSERT_EQ(bs.data(), reinterpret_cast<const uint8_t*>(SLICE_INT_PTR));
+  }
+
+  {
+    Span<int> s = a;
+    auto bs = AsBytes(s);
+    ASSERT_EQ(static_cast<const void*>(bs.data()),
+              static_cast<const void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+  }
+}
+
+SPAN_TEST(as_writable_bytes) {
+  int a[] = {1, 2, 3, 4};
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    // you should not be able to get writeable bytes for const objects
+    Span<const int> s = a;
+    ASSERT_EQ(s.Length(), 4U);
+    Span<const byte> bs = AsWritableBytes(s);
+    ASSERT_EQ(static_cast<void*>(bs.data()), static_cast<void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+#endif
+  }
+
+  {
+    Span<int> s;
+    auto bs = AsWritableBytes(s);
+    ASSERT_EQ(bs.Length(), s.Length());
+    ASSERT_EQ(bs.Length(), 0U);
+    ASSERT_EQ(bs.size_bytes(), 0U);
+    ASSERT_EQ(static_cast<void*>(bs.data()), static_cast<void*>(s.data()));
+    ASSERT_EQ(bs.data(), reinterpret_cast<uint8_t*>(SLICE_INT_PTR));
+  }
+
+  {
+    Span<int> s = a;
+    auto bs = AsWritableBytes(s);
+    ASSERT_EQ(static_cast<void*>(bs.data()), static_cast<void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+  }
+}
+
+SPAN_TEST(as_chars) {
+  const uint8_t a[] = {1, 2, 3, 4};
+  Span<const uint8_t> u = Span(a);
+  Span<const char> c = AsChars(u);
+  ASSERT_EQ(static_cast<const void*>(u.data()),
+            static_cast<const void*>(c.data()));
+  ASSERT_EQ(u.size(), c.size());
+}
+
+SPAN_TEST(as_writable_chars) {
+  uint8_t a[] = {1, 2, 3, 4};
+  Span<uint8_t> u = Span(a);
+  Span<char> c = AsWritableChars(u);
+  ASSERT_EQ(static_cast<void*>(u.data()), static_cast<void*>(c.data()));
+  ASSERT_EQ(u.size(), c.size());
+}
+
+SPAN_TEST(fixed_size_conversions) {
+  int arr[] = {1, 2, 3, 4};
+
+  // converting to an Span from an equal size array is ok
+  Span<int, 4> s4 = arr;
+  ASSERT_EQ(s4.Length(), 4U);
+
+  // converting to dynamic_range is always ok
+  {
+    Span<int> s = s4;
+    ASSERT_EQ(s.Length(), s4.Length());
+    static_cast<void>(s);
+  }
+
+// initialization or assignment to static Span that REDUCES size is NOT ok
+#ifdef CONFIRM_COMPILATION_ERRORS
+  { Span<int, 2> s = arr; }
+  {
+    Span<int, 2> s2 = s4;
+    static_cast<void>(s2);
+  }
+#endif
+
+#if 0
+        // even when done dynamically
+        {
+            Span<int> s = arr;
+            auto f = [&]() {
+                Span<int, 2> s2 = s;
+                static_cast<void>(s2);
+            };
+            CHECK_THROW(f(), fail_fast);
+        }
+#endif
+
+  // but doing so explicitly is ok
+
+  // you can convert statically
+  {
+    Span<int, 2> s2 = {arr, 2};
+    static_cast<void>(s2);
+  }
+  {
+    Span<int, 1> s1 = s4.First<1>();
+    static_cast<void>(s1);
+  }
+
+  // ...or dynamically
+  {
+    // NB: implicit conversion to Span<int,1> from Span<int>
+    Span<int, 1> s1 = s4.First(1);
+    static_cast<void>(s1);
+  }
+
+#if 0
+        // initialization or assignment to static Span that requires size INCREASE is not ok.
+        int arr2[2] = {1, 2};
+#endif
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  { Span<int, 4> s3 = arr2; }
+  {
+    Span<int, 2> s2 = arr2;
+    Span<int, 4> s4a = s2;
+  }
+#endif
+
+#if 0
+        {
+            auto f = [&]() {
+                Span<int, 4> _s4 = {arr2, 2};
+                static_cast<void>(_s4);
+            };
+            CHECK_THROW(f(), fail_fast);
+        }
+
+        // this should fail - we are trying to assign a small dynamic Span to a fixed_size larger one
+        Span<int> av = arr2;
+        auto f = [&]() {
+            Span<int, 4> _s4 = av;
+            static_cast<void>(_s4);
+        };
+        CHECK_THROW(f(), fail_fast);
+#endif
+}
+
+#if 0
+    SPAN_TEST(interop_with_std_regex)
+    {
+        char lat[] = { '1', '2', '3', '4', '5', '6', 'E', 'F', 'G' };
+        Span<char> s = lat;
+        auto f_it = s.begin() + 7;
+
+        std::match_results<Span<char>::iterator> match;
+
+        std::regex_match(s.begin(), s.end(), match, std::regex(".*"));
+        ASSERT_EQ(match.ready());
+        ASSERT_TRUE(!match.empty());
+        ASSERT_TRUE(match[0].matched);
+        ASSERT_TRUE(match[0].first , s.begin());
+        ASSERT_EQ(match[0].second , s.end());
+
+        std::regex_search(s.begin(), s.end(), match, std::regex("F"));
+        ASSERT_TRUE(match.ready());
+        ASSERT_TRUE(!match.empty());
+        ASSERT_TRUE(match[0].matched);
+        ASSERT_EQ(match[0].first , f_it);
+        ASSERT_EQ(match[0].second , (f_it + 1));
+    }
+
+SPAN_TEST(interop_with_gsl_at)
+{
+  int arr[5] = { 1, 2, 3, 4, 5 };
+  Span<int> s{ arr };
+  ASSERT_EQ(at(s, 0) , 1 );
+ASSERT_EQ(at(s, 1) , 2U);
+}
+#endif
+
+SPAN_TEST(default_constructible) {
+  ASSERT_TRUE((std::is_default_constructible<Span<int>>::value));
+  ASSERT_TRUE((std::is_default_constructible<Span<int, 0>>::value));
+  ASSERT_TRUE((!std::is_default_constructible<Span<int, 42>>::value));
+}
+
+SPAN_TEST(type_inference) {
+  static constexpr int arr[5] = {1, 2, 3, 4, 5};
+  constexpr auto s = Span{arr};
+  static_assert(std::is_same_v<const Span<const int, 5>, decltype(s)>);
+  static_assert(arr == s.Elements());
+}
+
+SPAN_TEST(split_at_dynamic_with_dynamic_extent) {
+  static constexpr int arr[5] = {1, 2, 3, 4, 5};
+  constexpr Span<const int> s = Span{arr};
+
+  {  // Split at begin.
+    constexpr auto splitAt0Result = s.SplitAt(0);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt0Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt0Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt0Result.second.Elements());
+    ASSERT_EQ(0u, splitAt0Result.first.Length());
+    ASSERT_EQ(5u, splitAt0Result.second.Length());
+  }
+
+  {  // Split at end.
+    constexpr auto splitAt5Result = s.SplitAt(s.Length());
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt5Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt5Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt5Result.first.Elements());
+    ASSERT_EQ(5u, splitAt5Result.first.Length());
+    ASSERT_EQ(0u, splitAt5Result.second.Length());
+  }
+
+  {
+    // Split inside.
+    constexpr auto splitAt3Result = s.SplitAt(3);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt3Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt3Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt3Result.first.Elements());
+    ASSERT_EQ(s.Elements() + 3, splitAt3Result.second.Elements());
+    ASSERT_EQ(3u, splitAt3Result.first.Length());
+    ASSERT_EQ(2u, splitAt3Result.second.Length());
+  }
+}
+
+SPAN_TEST(split_at_dynamic_with_static_extent) {
+  static constexpr int arr[5] = {1, 2, 3, 4, 5};
+  constexpr auto s = Span{arr};
+
+  {
+    // Split at begin.
+    constexpr auto splitAt0Result = s.SplitAt(0);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt0Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt0Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt0Result.second.Elements());
+  }
+
+  {
+    // Split at end.
+    constexpr auto splitAt5Result = s.SplitAt(s.Length());
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt5Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt5Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt5Result.first.Elements());
+  }
+
+  {
+    // Split inside.
+    constexpr auto splitAt3Result = s.SplitAt(3);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt3Result.first)>);
+    static_assert(
+        std::is_same_v<Span<const int>, decltype(splitAt3Result.second)>);
+    ASSERT_EQ(s.Elements(), splitAt3Result.first.Elements());
+    ASSERT_EQ(s.Elements() + 3, splitAt3Result.second.Elements());
+  }
+}
+
+SPAN_TEST(split_at_static) {
+  static constexpr int arr[5] = {1, 2, 3, 4, 5};
+  constexpr auto s = Span{arr};
+
+  // Split at begin.
+  constexpr auto splitAt0Result = s.SplitAt<0>();
+  static_assert(
+      std::is_same_v<Span<const int, 0>, decltype(splitAt0Result.first)>);
+  static_assert(
+      std::is_same_v<Span<const int, 5>, decltype(splitAt0Result.second)>);
+  static_assert(splitAt0Result.second.Elements() == s.Elements());
+
+  // Split at end.
+  constexpr auto splitAt5Result = s.SplitAt<s.Length()>();
+  static_assert(std::is_same_v<Span<const int, s.Length()>,
+                               decltype(splitAt5Result.first)>);
+  static_assert(
+      std::is_same_v<Span<const int, 0>, decltype(splitAt5Result.second)>);
+  static_assert(splitAt5Result.first.Elements() == s.Elements());
+
+  // Split inside.
+  constexpr auto splitAt3Result = s.SplitAt<3>();
+  static_assert(
+      std::is_same_v<Span<const int, 3>, decltype(splitAt3Result.first)>);
+  static_assert(
+      std::is_same_v<Span<const int, 2>, decltype(splitAt3Result.second)>);
+  static_assert(splitAt3Result.first.Elements() == s.Elements());
+  static_assert(splitAt3Result.second.Elements() == s.Elements() + 3);
+}
+
+SPAN_TEST(as_const_dynamic) {
+  static int arr[5] = {1, 2, 3, 4, 5};
+  auto span = Span{arr, 5};
+  auto constSpan = span.AsConst();
+  static_assert(std::is_same_v<Span<const int>, decltype(constSpan)>);
+}
+
+SPAN_TEST(as_const_static) {
+  {
+    static constexpr int constArr[5] = {1, 2, 3, 4, 5};
+    constexpr auto span = Span{constArr};  // is already a Span<const int>
+    constexpr auto constSpan = span.AsConst();
+
+    static_assert(
+        std::is_same_v<const Span<const int, 5>, decltype(constSpan)>);
+  }
+
+  {
+    static int arr[5] = {1, 2, 3, 4, 5};
+    auto span = Span{arr};
+    auto constSpan = span.AsConst();
+    static_assert(std::is_same_v<Span<const int, 5>, decltype(constSpan)>);
+  }
+}
+
+SPAN_TEST(construct_from_iterators_dynamic) {
+  const int constArr[5] = {1, 2, 3, 4, 5};
+  auto constSpan = Span{constArr};
+
+  // const from const
+  {
+    const auto wholeSpan = Span{constSpan.cbegin(), constSpan.cend()};
+    static_assert(std::is_same_v<decltype(wholeSpan), const Span<const int>>);
+    ASSERT_TRUE(constSpan == wholeSpan);
+
+    const auto emptyBeginSpan = Span{constSpan.cbegin(), constSpan.cbegin()};
+    ASSERT_TRUE(emptyBeginSpan.IsEmpty());
+
+    const auto emptyEndSpan = Span{constSpan.cend(), constSpan.cend()};
+    ASSERT_TRUE(emptyEndSpan.IsEmpty());
+
+    const auto subSpan = Span{constSpan.cbegin() + 1, constSpan.cend() - 1};
+    ASSERT_EQ(constSpan.Length() - 2, subSpan.Length());
+    ASSERT_EQ(constSpan.Elements() + 1, subSpan.Elements());
+  }
+
+  int arr[5] = {1, 2, 3, 4, 5};
+  auto span = Span{arr};
+
+  // const from non-const
+  {
+    const auto wholeSpan = Span{span.cbegin(), span.cend()};
+    static_assert(std::is_same_v<decltype(wholeSpan), const Span<const int>>);
+    // XXX Can't use span == wholeSpan because of difference in constness.
+    ASSERT_EQ(span.Elements(), wholeSpan.Elements());
+    ASSERT_EQ(span.Length(), wholeSpan.Length());
+
+    const auto emptyBeginSpan = Span{span.cbegin(), span.cbegin()};
+    ASSERT_TRUE(emptyBeginSpan.IsEmpty());
+
+    const auto emptyEndSpan = Span{span.cend(), span.cend()};
+    ASSERT_TRUE(emptyEndSpan.IsEmpty());
+
+    const auto subSpan = Span{span.cbegin() + 1, span.cend() - 1};
+    ASSERT_EQ(span.Length() - 2, subSpan.Length());
+    ASSERT_EQ(span.Elements() + 1, subSpan.Elements());
+  }
+
+  // non-const from non-const
+  {
+    const auto wholeSpan = Span{span.begin(), span.end()};
+    static_assert(std::is_same_v<decltype(wholeSpan), const Span<int>>);
+    ASSERT_TRUE(span == wholeSpan);
+
+    const auto emptyBeginSpan = Span{span.begin(), span.begin()};
+    ASSERT_TRUE(emptyBeginSpan.IsEmpty());
+
+    const auto emptyEndSpan = Span{span.end(), span.end()};
+    ASSERT_TRUE(emptyEndSpan.IsEmpty());
+
+    const auto subSpan = Span{span.begin() + 1, span.end() - 1};
+    ASSERT_EQ(span.Length() - 2, subSpan.Length());
+  }
+}
+
+SPAN_TEST(construct_from_iterators_static) {
+  static constexpr int arr[5] = {1, 2, 3, 4, 5};
+  constexpr auto constSpan = Span{arr};
+
+  // const
+  {
+    const auto wholeSpan = Span{constSpan.cbegin(), constSpan.cend()};
+    static_assert(std::is_same_v<decltype(wholeSpan), const Span<const int>>);
+    ASSERT_TRUE(constSpan == wholeSpan);
+
+    const auto emptyBeginSpan = Span{constSpan.cbegin(), constSpan.cbegin()};
+    ASSERT_TRUE(emptyBeginSpan.IsEmpty());
+
+    const auto emptyEndSpan = Span{constSpan.cend(), constSpan.cend()};
+    ASSERT_TRUE(emptyEndSpan.IsEmpty());
+
+    const auto subSpan = Span{constSpan.cbegin() + 1, constSpan.cend() - 1};
+    ASSERT_EQ(constSpan.Length() - 2, subSpan.Length());
+    ASSERT_EQ(constSpan.Elements() + 1, subSpan.Elements());
+  }
+}
+
+SPAN_TEST(construct_from_container_with_type_deduction) {
+  std::vector<int> vec = {1, 2, 3, 4, 5};
+
+  // from const
+  {
+    const auto& constVecRef = vec;
+
+    auto span = Span{constVecRef};
+    static_assert(std::is_same_v<decltype(span), Span<const int>>);
+  }
+
+  // from non-const
+  {
+    auto span = Span{vec};
+    static_assert(std::is_same_v<decltype(span), Span<int>>);
+  }
+}
diff --git a/mfbt/tests/gtest/TestTainting.cpp b/mfbt/tests/gtest/TestTainting.cpp
new file mode 100644
index 0000000000..ed9ba1e160
--- /dev/null
+++ b/mfbt/tests/gtest/TestTainting.cpp
@@ -0,0 +1,484 @@
+/* -*- 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/. */
+
+#include "gtest/gtest.h"
+#include <math.h>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Range.h"
+#include "mozilla/Tainting.h"
+#include "nsTHashtable.h"
+#include "nsHashKeys.h"
+#include "nsTArray.h"
+#include <array>
+#include <deque>
+#include <forward_list>
+#include <list>
+#include <map>
+#include <set>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+using mozilla::Tainted;
+
+#define EXPECTED_INT 10
+#define EXPECTED_CHAR 'z'
+
+static bool externalFunction(int arg) { return arg > 2; }
+
+// ==================================================================
+// MOZ_VALIDATE_AND_GET =============================================
+TEST(Tainting, moz_validate_and_get)
+{
+  int bar;
+  int comparisonVariable = 20;
+  Tainted<int> foo = Tainted<int>(EXPECTED_INT);
+
+  bar = MOZ_VALIDATE_AND_GET(foo, foo < 20);
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // This test is for comparison to an external variable, testing the
+  // default capture mode of the lambda used inside the macro.
+  bar = MOZ_VALIDATE_AND_GET(foo, foo < comparisonVariable);
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  bar = MOZ_VALIDATE_AND_GET(
+      foo, foo < 20,
+      "foo must be less than 20 because higher values represent decibel"
+      "levels greater than a a jet engine inside your ear.");
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // Test an external variable with a comment.
+  bar = MOZ_VALIDATE_AND_GET(foo, foo < comparisonVariable, "Test comment");
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // Test an external function with a comment.
+  bar = MOZ_VALIDATE_AND_GET(foo, externalFunction(foo), "Test comment");
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // Lambda Tests
+  bar =
+      MOZ_VALIDATE_AND_GET(foo, ([&foo]() { return externalFunction(foo); }()));
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // This test is for the lambda variant with a supplied assertion
+  // string.
+  bar =
+      MOZ_VALIDATE_AND_GET(foo, ([&foo]() { return externalFunction(foo); }()),
+                           "This tests a comment");
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // This test is for the lambda variant with a captured variable
+  bar = MOZ_VALIDATE_AND_GET(foo, ([&foo, &comparisonVariable] {
+                               bool intermediateResult = externalFunction(foo);
+                               return intermediateResult ||
+                                      comparisonVariable < 4;
+                             }()),
+                             "This tests a comment");
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // This test is for the lambda variant with full capture mode
+  bar = MOZ_VALIDATE_AND_GET(foo, ([&] {
+                               bool intermediateResult = externalFunction(foo);
+                               return intermediateResult ||
+                                      comparisonVariable < 4;
+                             }()),
+                             "This tests a comment");
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // External lambdas
+  auto lambda1 = [](int foo) { return externalFunction(foo); };
+
+  auto lambda2 = [&](int foo) {
+    bool intermediateResult = externalFunction(foo);
+    return intermediateResult || comparisonVariable < 4;
+  };
+
+  // Test with an explicit capture
+  auto lambda3 = [&comparisonVariable](int foo) {
+    bool intermediateResult = externalFunction(foo);
+    return intermediateResult || comparisonVariable < 4;
+  };
+
+  bar = MOZ_VALIDATE_AND_GET(foo, lambda1(foo));
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // Test with a comment
+  bar = MOZ_VALIDATE_AND_GET(foo, lambda1(foo), "Test comment.");
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // Test with a default capture mode
+  bar = MOZ_VALIDATE_AND_GET(foo, lambda2(foo), "Test comment.");
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  bar = MOZ_VALIDATE_AND_GET(foo, lambda3(foo), "Test comment.");
+  ASSERT_EQ(bar, EXPECTED_INT);
+
+  // We can't test MOZ_VALIDATE_AND_GET failing, because that triggers
+  // a release assert.
+}
+
+// ==================================================================
+// MOZ_IS_VALID =====================================================
+TEST(Tainting, moz_is_valid)
+{
+  int comparisonVariable = 20;
+  Tainted<int> foo = Tainted<int>(EXPECTED_INT);
+
+  ASSERT_TRUE(MOZ_IS_VALID(foo, foo < 20));
+
+  ASSERT_FALSE(MOZ_IS_VALID(foo, foo > 20));
+
+  ASSERT_TRUE(MOZ_IS_VALID(foo, foo < comparisonVariable));
+
+  ASSERT_TRUE(
+      MOZ_IS_VALID(foo, ([&foo]() { return externalFunction(foo); }())));
+
+  ASSERT_TRUE(MOZ_IS_VALID(foo, ([&foo, &comparisonVariable]() {
+                             bool intermediateResult = externalFunction(foo);
+                             return intermediateResult ||
+                                    comparisonVariable < 4;
+                           }())));
+
+  // External lambdas
+  auto lambda1 = [](int foo) { return externalFunction(foo); };
+
+  auto lambda2 = [&](int foo) {
+    bool intermediateResult = externalFunction(foo);
+    return intermediateResult || comparisonVariable < 4;
+  };
+
+  // Test with an explicit capture
+  auto lambda3 = [&comparisonVariable](int foo) {
+    bool intermediateResult = externalFunction(foo);
+    return intermediateResult || comparisonVariable < 4;
+  };
+
+  ASSERT_TRUE(MOZ_IS_VALID(foo, lambda1(foo)));
+
+  ASSERT_TRUE(MOZ_IS_VALID(foo, lambda2(foo)));
+
+  ASSERT_TRUE(MOZ_IS_VALID(foo, lambda3(foo)));
+}
+
+// ==================================================================
+// MOZ_VALIDATE_OR ==================================================
+TEST(Tainting, moz_validate_or)
+{
+  int result;
+  int comparisonVariable = 20;
+  Tainted<int> foo = Tainted<int>(EXPECTED_INT);
+
+  result = MOZ_VALIDATE_OR(foo, foo < 20, 100);
+  ASSERT_EQ(result, EXPECTED_INT);
+
+  result = MOZ_VALIDATE_OR(foo, foo > 20, 100);
+  ASSERT_EQ(result, 100);
+
+  result = MOZ_VALIDATE_OR(foo, foo < comparisonVariable, 100);
+  ASSERT_EQ(result, EXPECTED_INT);
+
+  // External lambdas
+  auto lambda1 = [](int foo) { return externalFunction(foo); };
+
+  auto lambda2 = [&](int foo) {
+    bool intermediateResult = externalFunction(foo);
+    return intermediateResult || comparisonVariable < 4;
+  };
+
+  // Test with an explicit capture
+  auto lambda3 = [&comparisonVariable](int foo) {
+    bool intermediateResult = externalFunction(foo);
+    return intermediateResult || comparisonVariable < 4;
+  };
+
+  result = MOZ_VALIDATE_OR(foo, lambda1(foo), 100);
+  ASSERT_EQ(result, EXPECTED_INT);
+
+  result = MOZ_VALIDATE_OR(foo, lambda2(foo), 100);
+  ASSERT_EQ(result, EXPECTED_INT);
+
+  result = MOZ_VALIDATE_OR(foo, lambda3(foo), 100);
+  ASSERT_EQ(result, EXPECTED_INT);
+
+  result =
+      MOZ_VALIDATE_OR(foo, ([&foo]() { return externalFunction(foo); }()), 100);
+  ASSERT_EQ(result, EXPECTED_INT);
+
+  // This test is for the lambda variant with a supplied assertion
+  // string.
+  result =
+      MOZ_VALIDATE_OR(foo, ([&foo] { return externalFunction(foo); }()), 100);
+  ASSERT_EQ(result, EXPECTED_INT);
+
+  // This test is for the lambda variant with a captured variable
+  result =
+      MOZ_VALIDATE_OR(foo, ([&foo, &comparisonVariable] {
+                        bool intermediateResult = externalFunction(foo);
+                        return intermediateResult || comparisonVariable < 4;
+                      }()),
+                      100);
+  ASSERT_EQ(result, EXPECTED_INT);
+
+  // This test is for the lambda variant with full capture mode
+  result =
+      MOZ_VALIDATE_OR(foo, ([&] {
+                        bool intermediateResult = externalFunction(foo);
+                        return intermediateResult || comparisonVariable < 4;
+                      }()),
+                      100);
+  ASSERT_EQ(result, EXPECTED_INT);
+}
+
+// ==================================================================
+// MOZ_FIND_AND_VALIDATE ============================================
+TEST(Tainting, moz_find_and_validate)
+{
+  Tainted<int> foo = Tainted<int>(EXPECTED_INT);
+  Tainted<char> baz = Tainted<char>(EXPECTED_CHAR);
+
+  //-------------------------------
+  const mozilla::Array<int, 6> mozarrayWithFoo(0, 5, EXPECTED_INT, 15, 20, 25);
+  const mozilla::Array<int, 5> mozarrayWithoutFoo(0, 5, 15, 20, 25);
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(foo, list_item == foo, mozarrayWithFoo) ==
+              mozarrayWithFoo[2]);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item == foo,
+                                    mozarrayWithoutFoo) == nullptr);
+
+  //-------------------------------
+  class TestClass {
+   public:
+    int a;
+    int b;
+
+    TestClass(int a, int b) {
+      this->a = a;
+      this->b = b;
+    }
+
+    bool operator==(const TestClass& other) const {
+      return this->a == other.a && this->b == other.b;
+    }
+  };
+
+  const mozilla::Array<TestClass, 5> mozarrayOfClassesWithFoo(
+      TestClass(0, 1), TestClass(2, 3), TestClass(EXPECTED_INT, EXPECTED_INT),
+      TestClass(4, 5), TestClass(6, 7));
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(
+                  foo, foo == list_item.a && foo == list_item.b,
+                  mozarrayOfClassesWithFoo) == mozarrayOfClassesWithFoo[2]);
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(
+                  foo, (foo == list_item.a && foo == list_item.b),
+                  mozarrayOfClassesWithFoo) == mozarrayOfClassesWithFoo[2]);
+
+  ASSERT_TRUE(
+      *MOZ_FIND_AND_VALIDATE(
+          foo,
+          (foo == list_item.a && foo == list_item.b && externalFunction(foo)),
+          mozarrayOfClassesWithFoo) == mozarrayOfClassesWithFoo[2]);
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(
+                  foo, ([](int tainted_val, TestClass list_item) {
+                    return tainted_val == list_item.a &&
+                           tainted_val == list_item.b;
+                  }(foo, list_item)),
+                  mozarrayOfClassesWithFoo) == mozarrayOfClassesWithFoo[2]);
+
+  auto lambda4 = [](int tainted_val, TestClass list_item) {
+    return tainted_val == list_item.a && tainted_val == list_item.b;
+  };
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(foo, lambda4(foo, list_item),
+                                     mozarrayOfClassesWithFoo) ==
+              mozarrayOfClassesWithFoo[2]);
+
+  //-------------------------------
+  const char m[] = "m";
+  const char o[] = "o";
+  const char z[] = {EXPECTED_CHAR, '\0'};
+  const char l[] = "l";
+  const char a[] = "a";
+
+  nsTHashtable<nsCharPtrHashKey> hashtableWithBaz;
+  hashtableWithBaz.PutEntry(m);
+  hashtableWithBaz.PutEntry(o);
+  hashtableWithBaz.PutEntry(z);
+  hashtableWithBaz.PutEntry(l);
+  hashtableWithBaz.PutEntry(a);
+  nsTHashtable<nsCharPtrHashKey> hashtableWithoutBaz;
+  hashtableWithoutBaz.PutEntry(m);
+  hashtableWithoutBaz.PutEntry(o);
+  hashtableWithoutBaz.PutEntry(l);
+  hashtableWithoutBaz.PutEntry(a);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(baz, *list_item.GetKey() == baz,
+                                    hashtableWithBaz) ==
+              hashtableWithBaz.GetEntry(z));
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(baz, *list_item.GetKey() == baz,
+                                    hashtableWithoutBaz) == nullptr);
+
+  //-------------------------------
+  const nsTArray<int> nsTArrayWithFoo = {0, 5, EXPECTED_INT, 15, 20, 25};
+  const nsTArray<int> nsTArrayWithoutFoo = {0, 5, 15, 20, 25};
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(foo, list_item == foo, nsTArrayWithFoo) ==
+              nsTArrayWithFoo[2]);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item == foo,
+                                    nsTArrayWithoutFoo) == nullptr);
+
+  //-------------------------------
+  const std::array<int, 6> arrayWithFoo{0, 5, EXPECTED_INT, 15, 20, 25};
+  const std::array<int, 5> arrayWithoutFoo{0, 5, 15, 20, 25};
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(foo, list_item == foo, arrayWithFoo) ==
+              arrayWithFoo[2]);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item == foo, arrayWithoutFoo) ==
+              nullptr);
+
+  //-------------------------------
+  const std::deque<int> dequeWithFoo{0, 5, EXPECTED_INT, 15, 20, 25};
+  const std::deque<int> dequeWithoutFoo{0, 5, 15, 20, 25};
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(foo, list_item == foo, dequeWithFoo) ==
+              dequeWithFoo[2]);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item == foo, dequeWithoutFoo) ==
+              nullptr);
+
+  //-------------------------------
+  const std::forward_list<int> forwardWithFoo{0, 5, EXPECTED_INT, 15, 20, 25};
+  const std::forward_list<int> forwardWithoutFoo{0, 5, 15, 20, 25};
+
+  auto forwardListIt = forwardWithFoo.begin();
+  std::advance(forwardListIt, 2);
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(foo, list_item == foo, forwardWithFoo) ==
+              *forwardListIt);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item == foo, forwardWithoutFoo) ==
+              nullptr);
+
+  //-------------------------------
+  const std::list<int> listWithFoo{0, 5, EXPECTED_INT, 15, 20, 25};
+  const std::list<int> listWithoutFoo{0, 5, 15, 20, 25};
+
+  auto listIt = listWithFoo.begin();
+  std::advance(listIt, 2);
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(foo, list_item == foo, listWithFoo) ==
+              *listIt);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item == foo, listWithoutFoo) ==
+              nullptr);
+
+  //-------------------------------
+  const std::map<std::string, int> mapWithFoo{{
+      {"zero", 0},
+      {"five", 5},
+      {"ten", EXPECTED_INT},
+      {"fifteen", 15},
+      {"twenty", 20},
+      {"twenty-five", 25},
+  }};
+  const std::map<std::string, int> mapWithoutFoo{{
+      {"zero", 0},
+      {"five", 5},
+      {"fifteen", 15},
+      {"twenty", 20},
+      {"twenty-five", 25},
+  }};
+
+  const auto map_it = mapWithFoo.find("ten");
+
+  ASSERT_TRUE(
+      MOZ_FIND_AND_VALIDATE(foo, list_item.second == foo, mapWithFoo)->second ==
+      map_it->second);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item.second == foo,
+                                    mapWithoutFoo) == nullptr);
+
+  //-------------------------------
+  const std::set<int> setWithFoo{0, 5, EXPECTED_INT, 15, 20, 25};
+  const std::set<int> setWithoutFoo{0, 5, 15, 20, 25};
+
+  auto setIt = setWithFoo.find(EXPECTED_INT);
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(foo, list_item == foo, setWithFoo) ==
+              *setIt);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item == foo, setWithoutFoo) ==
+              nullptr);
+
+  //-------------------------------
+  const std::unordered_map<std::string, int> unordermapWithFoo = {
+      {"zero", 0},     {"five", 5},    {"ten", EXPECTED_INT},
+      {"fifteen", 15}, {"twenty", 20}, {"twenty-five", 25},
+  };
+  const std::unordered_map<std::string, int> unordermapWithoutFoo{{
+      {"zero", 0},
+      {"five", 5},
+      {"fifteen", 15},
+      {"twenty", 20},
+      {"twenty-five", 25},
+  }};
+
+  auto unorderedMapIt = unordermapWithFoo.find("ten");
+
+  ASSERT_TRUE(
+      MOZ_FIND_AND_VALIDATE(foo, list_item.second == foo, unordermapWithFoo)
+          ->second == unorderedMapIt->second);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item.second == foo,
+                                    unordermapWithoutFoo) == nullptr);
+
+  //-------------------------------
+  const std::unordered_set<int> unorderedsetWithFoo{0,  5,  EXPECTED_INT,
+                                                    15, 20, 25};
+  const std::unordered_set<int> unorderedsetWithoutFoo{0, 5, 15, 20, 25};
+
+  auto unorderedSetIt = unorderedsetWithFoo.find(EXPECTED_INT);
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(foo, list_item == foo,
+                                     unorderedsetWithFoo) == *unorderedSetIt);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item == foo,
+                                    unorderedsetWithoutFoo) == nullptr);
+
+  //-------------------------------
+  const std::vector<int> vectorWithFoo{0, 5, EXPECTED_INT, 15, 20, 25};
+  const std::vector<int> vectorWithoutFoo{0, 5, 15, 20, 25};
+
+  ASSERT_TRUE(*MOZ_FIND_AND_VALIDATE(foo, list_item == foo, vectorWithFoo) ==
+              vectorWithFoo[2]);
+
+  ASSERT_TRUE(MOZ_FIND_AND_VALIDATE(foo, list_item == foo, vectorWithoutFoo) ==
+              nullptr);
+}
+
+// ==================================================================
+// MOZ_NO_VALIDATE ==================================================
+TEST(Tainting, moz_no_validate)
+{
+  int result;
+  Tainted<int> foo = Tainted<int>(EXPECTED_INT);
+
+  result = MOZ_NO_VALIDATE(
+      foo,
+      "Value is used to match against a dictionary key in the parent."
+      "If there's no key present, there won't be a match."
+      "There is no risk of grabbing a cross-origin value from the dictionary,"
+      "because the IPC actor is instatiated per-content-process and the "
+      "dictionary is not shared between actors.");
+  ASSERT_TRUE(result == EXPECTED_INT);
+}
diff --git a/mfbt/tests/gtest/moz.build b/mfbt/tests/gtest/moz.build
new file mode 100644
index 0000000000..5ded0f4391
--- /dev/null
+++ b/mfbt/tests/gtest/moz.build
@@ -0,0 +1,34 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+UNIFIED_SOURCES += [
+    "TestBuffer.cpp",
+    "TestLinkedList.cpp",
+    "TestReverseIterator.cpp",
+    "TestSpan.cpp",
+    "TestTainting.cpp",
+]
+
+SOURCES += [
+    "TestAlgorithm.cpp",
+    "TestInitializedOnce.cpp",
+    "TestMainThreadWeakPtr.cpp",
+    "TestResultExtensions.cpp",
+]
+
+if not CONFIG["MOZILLA_OFFICIAL"]:
+    UNIFIED_SOURCES += [
+        # MOZ_DBG is not defined in MOZILLA_OFFICIAL builds.
+        "TestMozDbg.cpp",
+    ]
+
+# LOCAL_INCLUDES += [
+#    "../../base",
+# ]
+
+FINAL_LIBRARY = "xul-gtest"
+
+REQUIRES_UNIFIED_BUILD = True