Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 1473 insertions, 0 deletions

diff --git a/mfbt/tests/TestMaybe.cpp b/mfbt/tests/TestMaybe.cpp
new file mode 100644
index 0000000000..2c56b85b6d
--- /dev/null
+++ b/mfbt/tests/TestMaybe.cpp
@@ -0,0 +1,1473 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 <type_traits>
+#include <utility>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Maybe.h"
+
+using mozilla::Maybe;
+using mozilla::Nothing;
+using mozilla::Some;
+using mozilla::SomeRef;
+using mozilla::ToMaybe;
+using mozilla::ToMaybeRef;
+
+#define RUN_TEST(t)                                                     \
+  do {                                                                  \
+    bool cond = (t());                                                  \
+    if (!cond) return 1;                                                \
+    cond = AllDestructorsWereCalled();                                  \
+    MOZ_ASSERT(cond, "Failed to destroy all objects during test: " #t); \
+    if (!cond) return 1;                                                \
+  } while (false)
+
+enum Status {
+  eWasDefaultConstructed,
+  eWasConstructed,
+  eWasCopyConstructed,
+  eWasMoveConstructed,
+  eWasConstMoveConstructed,
+  eWasAssigned,
+  eWasCopyAssigned,
+  eWasMoveAssigned,
+  eWasCopiedFrom,
+  eWasMovedFrom,
+  eWasConstMovedFrom,
+};
+
+static size_t sUndestroyedObjects = 0;
+
+static bool AllDestructorsWereCalled() { return sUndestroyedObjects == 0; }
+
+struct BasicValue {
+  BasicValue() : mStatus(eWasDefaultConstructed), mTag(0) {
+    ++sUndestroyedObjects;
+  }
+
+  explicit BasicValue(int aTag) : mStatus(eWasConstructed), mTag(aTag) {
+    ++sUndestroyedObjects;
+  }
+
+  BasicValue(const BasicValue& aOther)
+      : mStatus(eWasCopyConstructed), mTag(aOther.mTag) {
+    ++sUndestroyedObjects;
+  }
+
+  BasicValue(BasicValue&& aOther)
+      : mStatus(eWasMoveConstructed), mTag(aOther.mTag) {
+    ++sUndestroyedObjects;
+    aOther.mStatus = eWasMovedFrom;
+    aOther.mTag = 0;
+  }
+
+  BasicValue(const BasicValue&& aOther)
+      : mStatus(eWasConstMoveConstructed), mTag(aOther.mTag) {
+    ++sUndestroyedObjects;
+    aOther.mStatus = eWasConstMovedFrom;
+  }
+
+  ~BasicValue() { --sUndestroyedObjects; }
+
+  BasicValue& operator=(const BasicValue& aOther) {
+    mStatus = eWasCopyAssigned;
+    mTag = aOther.mTag;
+    return *this;
+  }
+
+  BasicValue& operator=(BasicValue&& aOther) {
+    mStatus = eWasMoveAssigned;
+    mTag = aOther.mTag;
+    aOther.mStatus = eWasMovedFrom;
+    aOther.mTag = 0;
+    return *this;
+  }
+
+  bool operator==(const BasicValue& aOther) const {
+    return mTag == aOther.mTag;
+  }
+
+  bool operator<(const BasicValue& aOther) const { return mTag < aOther.mTag; }
+
+  Status GetStatus() const { return mStatus; }
+  void SetTag(int aValue) { mTag = aValue; }
+  int GetTag() const { return mTag; }
+
+ private:
+  mutable Status mStatus;
+  int mTag;
+};
+
+struct UncopyableValue {
+  UncopyableValue() : mStatus(eWasDefaultConstructed) { ++sUndestroyedObjects; }
+
+  UncopyableValue(UncopyableValue&& aOther) : mStatus(eWasMoveConstructed) {
+    ++sUndestroyedObjects;
+    aOther.mStatus = eWasMovedFrom;
+  }
+
+  ~UncopyableValue() { --sUndestroyedObjects; }
+
+  UncopyableValue& operator=(UncopyableValue&& aOther) {
+    mStatus = eWasMoveAssigned;
+    aOther.mStatus = eWasMovedFrom;
+    return *this;
+  }
+
+  Status GetStatus() { return mStatus; }
+
+ private:
+  UncopyableValue(const UncopyableValue& aOther) = delete;
+  UncopyableValue& operator=(const UncopyableValue& aOther) = delete;
+
+  Status mStatus;
+};
+
+struct UnmovableValue {
+  UnmovableValue() : mStatus(eWasDefaultConstructed) { ++sUndestroyedObjects; }
+
+  UnmovableValue(const UnmovableValue& aOther) : mStatus(eWasCopyConstructed) {
+    ++sUndestroyedObjects;
+  }
+
+  ~UnmovableValue() { --sUndestroyedObjects; }
+
+  UnmovableValue& operator=(const UnmovableValue& aOther) {
+    mStatus = eWasCopyAssigned;
+    return *this;
+  }
+
+  Status GetStatus() { return mStatus; }
+
+  UnmovableValue(UnmovableValue&& aOther) = delete;
+  UnmovableValue& operator=(UnmovableValue&& aOther) = delete;
+
+ private:
+  Status mStatus;
+};
+
+struct UncopyableUnmovableValue {
+  UncopyableUnmovableValue() : mStatus(eWasDefaultConstructed) {
+    ++sUndestroyedObjects;
+  }
+
+  explicit UncopyableUnmovableValue(int) : mStatus(eWasConstructed) {
+    ++sUndestroyedObjects;
+  }
+
+  ~UncopyableUnmovableValue() { --sUndestroyedObjects; }
+
+  Status GetStatus() const { return mStatus; }
+
+ private:
+  UncopyableUnmovableValue(const UncopyableUnmovableValue& aOther) = delete;
+  UncopyableUnmovableValue& operator=(const UncopyableUnmovableValue& aOther) =
+      delete;
+  UncopyableUnmovableValue(UncopyableUnmovableValue&& aOther) = delete;
+  UncopyableUnmovableValue& operator=(UncopyableUnmovableValue&& aOther) =
+      delete;
+
+  Status mStatus;
+};
+
+static_assert(std::is_trivially_destructible_v<Maybe<int>>);
+static_assert(std::is_trivially_copy_constructible_v<Maybe<int>>);
+static_assert(std::is_trivially_copy_assignable_v<Maybe<int>>);
+
+static_assert(42 == Some(42).value());
+static_assert(42 == Some(42).valueOr(43));
+static_assert(42 == Maybe<int>{}.valueOr(42));
+static_assert(42 == Some(42).valueOrFrom([] { return 43; }));
+static_assert(42 == Maybe<int>{}.valueOrFrom([] { return 42; }));
+static_assert(Some(43) == [] {
+  auto val = Some(42);
+  val.apply([](int& val) { val += 1; });
+  return val;
+}());
+static_assert(Some(43) == Some(42).map([](int val) { return val + 1; }));
+static_assert(Maybe<int>(std::in_place, 43) ==
+              Maybe<int>(std::in_place, 42).map([](int val) {
+                return val + 1;
+              }));
+
+struct TriviallyDestructible {
+  TriviallyDestructible() {  // not trivially constructible
+  }
+};
+
+static_assert(std::is_trivially_destructible_v<Maybe<TriviallyDestructible>>);
+
+struct UncopyableValueLiteralType {
+  explicit constexpr UncopyableValueLiteralType(int aValue) : mValue{aValue} {}
+
+  UncopyableValueLiteralType(UncopyableValueLiteralType&&) = default;
+  UncopyableValueLiteralType& operator=(UncopyableValueLiteralType&&) = default;
+
+  int mValue;
+};
+
+static_assert(
+    std::is_trivially_destructible_v<Maybe<UncopyableValueLiteralType>>);
+static_assert(!std::is_copy_constructible_v<Maybe<UncopyableValueLiteralType>>);
+static_assert(!std::is_copy_assignable_v<Maybe<UncopyableValueLiteralType>>);
+static_assert(std::is_move_constructible_v<Maybe<UncopyableValueLiteralType>>);
+static_assert(std::is_move_assignable_v<Maybe<UncopyableValueLiteralType>>);
+
+constexpr Maybe<UncopyableValueLiteralType> someUncopyable =
+    Some(UncopyableValueLiteralType{42});
+static_assert(someUncopyable.isSome());
+static_assert(42 == someUncopyable->mValue);
+
+constexpr Maybe<UncopyableValueLiteralType> someUncopyableAssigned = [] {
+  auto res = Maybe<UncopyableValueLiteralType>{};
+  res = Some(UncopyableValueLiteralType{42});
+  return res;
+}();
+static_assert(someUncopyableAssigned.isSome());
+static_assert(42 == someUncopyableAssigned->mValue);
+
+static bool TestBasicFeatures() {
+  // Check that a Maybe<T> is initialized to Nothing.
+  Maybe<BasicValue> mayValue;
+  static_assert(std::is_same_v<BasicValue, decltype(mayValue)::ValueType>,
+                "Should have BasicValue ValueType");
+  MOZ_RELEASE_ASSERT(!mayValue);
+  MOZ_RELEASE_ASSERT(!mayValue.isSome());
+  MOZ_RELEASE_ASSERT(mayValue.isNothing());
+
+  // Check that emplace() default constructs and the accessors work.
+  mayValue.emplace();
+  MOZ_RELEASE_ASSERT(mayValue);
+  MOZ_RELEASE_ASSERT(mayValue.isSome());
+  MOZ_RELEASE_ASSERT(!mayValue.isNothing());
+  MOZ_RELEASE_ASSERT(*mayValue == BasicValue());
+  static_assert(std::is_same_v<BasicValue&, decltype(*mayValue)>,
+                "operator*() should return a BasicValue&");
+  MOZ_RELEASE_ASSERT(mayValue.value() == BasicValue());
+  static_assert(std::is_same_v<BasicValue, decltype(mayValue.value())>,
+                "value() should return a BasicValue");
+  MOZ_RELEASE_ASSERT(mayValue.ref() == BasicValue());
+  static_assert(std::is_same_v<BasicValue&, decltype(mayValue.ref())>,
+                "ref() should return a BasicValue&");
+  MOZ_RELEASE_ASSERT(mayValue.ptr() != nullptr);
+  static_assert(std::is_same_v<BasicValue*, decltype(mayValue.ptr())>,
+                "ptr() should return a BasicValue*");
+  MOZ_RELEASE_ASSERT(mayValue->GetStatus() == eWasDefaultConstructed);
+
+  // Check that reset() works.
+  mayValue.reset();
+  MOZ_RELEASE_ASSERT(!mayValue);
+  MOZ_RELEASE_ASSERT(!mayValue.isSome());
+  MOZ_RELEASE_ASSERT(mayValue.isNothing());
+
+  // Check that emplace(T1) calls the correct constructor.
+  mayValue.emplace(1);
+  MOZ_RELEASE_ASSERT(mayValue);
+  MOZ_RELEASE_ASSERT(mayValue->GetStatus() == eWasConstructed);
+  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 1);
+  mayValue.reset();
+  MOZ_RELEASE_ASSERT(!mayValue);
+
+  {
+    // Check that Maybe(std::in_place, T1) calls the correct constructor.
+    const auto mayValueConstructed = Maybe<BasicValue>(std::in_place, 1);
+    MOZ_RELEASE_ASSERT(mayValueConstructed);
+    MOZ_RELEASE_ASSERT(mayValueConstructed->GetStatus() == eWasConstructed);
+    MOZ_RELEASE_ASSERT(mayValueConstructed->GetTag() == 1);
+  }
+
+  // Check that Some() and Nothing() work.
+  mayValue = Some(BasicValue(2));
+  MOZ_RELEASE_ASSERT(mayValue);
+  MOZ_RELEASE_ASSERT(mayValue->GetStatus() == eWasMoveConstructed);
+  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 2);
+  mayValue = Nothing();
+  MOZ_RELEASE_ASSERT(!mayValue);
+
+  // Check that the accessors work through a const ref.
+  mayValue.emplace();
+  const Maybe<BasicValue>& mayValueCRef = mayValue;
+  MOZ_RELEASE_ASSERT(mayValueCRef);
+  MOZ_RELEASE_ASSERT(mayValueCRef.isSome());
+  MOZ_RELEASE_ASSERT(!mayValueCRef.isNothing());
+  MOZ_RELEASE_ASSERT(*mayValueCRef == BasicValue());
+  static_assert(std::is_same_v<const BasicValue&, decltype(*mayValueCRef)>,
+                "operator*() should return a BasicValue");
+  MOZ_RELEASE_ASSERT(mayValueCRef.value() == BasicValue());
+  static_assert(std::is_same_v<BasicValue, decltype(mayValueCRef.value())>,
+                "value() should return a BasicValue");
+  MOZ_RELEASE_ASSERT(mayValueCRef.ref() == BasicValue());
+  static_assert(std::is_same_v<const BasicValue&, decltype(mayValueCRef.ref())>,
+                "ref() should return a const BasicValue&");
+  MOZ_RELEASE_ASSERT(mayValueCRef.ptr() != nullptr);
+  static_assert(std::is_same_v<const BasicValue*, decltype(mayValueCRef.ptr())>,
+                "ptr() should return a const BasicValue*");
+  MOZ_RELEASE_ASSERT(mayValueCRef->GetStatus() == eWasDefaultConstructed);
+  mayValue.reset();
+
+  // Check that we can create and reference Maybe<const Type>.
+  Maybe<const BasicValue> mayCValue1 = Some(BasicValue(5));
+  MOZ_RELEASE_ASSERT(mayCValue1);
+  MOZ_RELEASE_ASSERT(mayCValue1.isSome());
+  MOZ_RELEASE_ASSERT(*mayCValue1 == BasicValue(5));
+  const Maybe<const BasicValue>& mayCValue1Ref = mayCValue1;
+  MOZ_RELEASE_ASSERT(mayCValue1Ref == mayCValue1);
+  MOZ_RELEASE_ASSERT(*mayCValue1Ref == BasicValue(5));
+  Maybe<const BasicValue> mayCValue2;
+  mayCValue2.emplace(6);
+  MOZ_RELEASE_ASSERT(mayCValue2);
+  MOZ_RELEASE_ASSERT(mayCValue2.isSome());
+  MOZ_RELEASE_ASSERT(*mayCValue2 == BasicValue(6));
+
+  // Check that accessors work through rvalue-references.
+  MOZ_RELEASE_ASSERT(Some(BasicValue()));
+  MOZ_RELEASE_ASSERT(Some(BasicValue()).isSome());
+  MOZ_RELEASE_ASSERT(!Some(BasicValue()).isNothing());
+  MOZ_RELEASE_ASSERT(*Some(BasicValue()) == BasicValue());
+  static_assert(std::is_same_v<BasicValue&&, decltype(*Some(BasicValue()))>,
+                "operator*() should return a BasicValue&&");
+  MOZ_RELEASE_ASSERT(Some(BasicValue()).value() == BasicValue());
+  static_assert(
+      std::is_same_v<BasicValue, decltype(Some(BasicValue()).value())>,
+      "value() should return a BasicValue");
+  MOZ_RELEASE_ASSERT(Some(BasicValue()).ref() == BasicValue());
+  static_assert(
+      std::is_same_v<BasicValue&&, decltype(Some(BasicValue()).ref())>,
+      "ref() should return a BasicValue&&");
+  MOZ_RELEASE_ASSERT(Some(BasicValue()).ptr() != nullptr);
+  static_assert(std::is_same_v<BasicValue*, decltype(Some(BasicValue()).ptr())>,
+                "ptr() should return a BasicValue*");
+  MOZ_RELEASE_ASSERT(Some(BasicValue())->GetStatus() == eWasMoveConstructed);
+
+  // Check that accessors work through const-rvalue-references.
+  auto MakeConstMaybe = []() -> const Maybe<BasicValue> {
+    return Some(BasicValue());
+  };
+  MOZ_RELEASE_ASSERT(MakeConstMaybe());
+  MOZ_RELEASE_ASSERT(MakeConstMaybe().isSome());
+  MOZ_RELEASE_ASSERT(!MakeConstMaybe().isNothing());
+  MOZ_RELEASE_ASSERT(*MakeConstMaybe() == BasicValue());
+  static_assert(std::is_same_v<const BasicValue&&, decltype(*MakeConstMaybe())>,
+                "operator*() should return a const BasicValue&&");
+  MOZ_RELEASE_ASSERT(MakeConstMaybe().value() == BasicValue());
+  static_assert(std::is_same_v<BasicValue, decltype(MakeConstMaybe().value())>,
+                "value() should return a BasicValue");
+  MOZ_RELEASE_ASSERT(MakeConstMaybe().ref() == BasicValue());
+  static_assert(
+      std::is_same_v<const BasicValue&&, decltype(MakeConstMaybe().ref())>,
+      "ref() should return a const BasicValue&&");
+  MOZ_RELEASE_ASSERT(MakeConstMaybe().ptr() != nullptr);
+  static_assert(
+      std::is_same_v<const BasicValue*, decltype(MakeConstMaybe().ptr())>,
+      "ptr() should return a const BasicValue*");
+  MOZ_RELEASE_ASSERT(MakeConstMaybe()->GetStatus() == eWasMoveConstructed);
+  MOZ_RELEASE_ASSERT(BasicValue(*MakeConstMaybe()).GetStatus() ==
+                     eWasConstMoveConstructed);
+
+  // Check that take works
+  mayValue = Some(BasicValue(6));
+  Maybe taken = mayValue.take();
+  MOZ_RELEASE_ASSERT(taken->GetStatus() == eWasMoveConstructed);
+  MOZ_RELEASE_ASSERT(taken == Some(BasicValue(6)));
+  MOZ_RELEASE_ASSERT(!mayValue.isSome());
+  MOZ_RELEASE_ASSERT(mayValue.take() == Nothing());
+
+  // Check that extract works
+  mayValue = Some(BasicValue(7));
+  BasicValue extracted = mayValue.extract();
+  MOZ_RELEASE_ASSERT(extracted.GetStatus() == eWasMoveConstructed);
+  MOZ_RELEASE_ASSERT(extracted == BasicValue(7));
+  MOZ_RELEASE_ASSERT(!mayValue.isSome());
+
+  return true;
+}
+
+template <typename T>
+static void TestCopyMaybe() {
+  {
+    MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+
+    Maybe<T> src = Some(T());
+    Maybe<T> dstCopyConstructed = src;
+
+    MOZ_RELEASE_ASSERT(2 == sUndestroyedObjects);
+    MOZ_RELEASE_ASSERT(dstCopyConstructed->GetStatus() == eWasCopyConstructed);
+  }
+
+  {
+    MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+
+    Maybe<T> src = Some(T());
+    Maybe<T> dstCopyAssigned;
+    dstCopyAssigned = src;
+
+    MOZ_RELEASE_ASSERT(2 == sUndestroyedObjects);
+    MOZ_RELEASE_ASSERT(dstCopyAssigned->GetStatus() == eWasCopyConstructed);
+  }
+}
+
+template <typename T>
+static void TestMoveMaybe() {
+  {
+    MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+
+    Maybe<T> src = Some(T());
+    Maybe<T> dstMoveConstructed = std::move(src);
+
+    MOZ_RELEASE_ASSERT(1 == sUndestroyedObjects);
+    MOZ_RELEASE_ASSERT(dstMoveConstructed->GetStatus() == eWasMoveConstructed);
+  }
+
+  {
+    MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+
+    Maybe<T> src = Some(T());
+    Maybe<T> dstMoveAssigned;
+    dstMoveAssigned = std::move(src);
+
+    MOZ_RELEASE_ASSERT(1 == sUndestroyedObjects);
+    MOZ_RELEASE_ASSERT(dstMoveAssigned->GetStatus() == eWasMoveConstructed);
+  }
+
+  {
+    MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+
+    Maybe<T> src = Some(T());
+    Maybe<T> dstMoveConstructed = src.take();
+
+    MOZ_RELEASE_ASSERT(1 == sUndestroyedObjects);
+    MOZ_RELEASE_ASSERT(dstMoveConstructed->GetStatus() == eWasMoveConstructed);
+  }
+
+  {
+    MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+
+    Maybe<T> src = Some(T());
+    T dstMoveConstructed = src.extract();
+
+    MOZ_RELEASE_ASSERT(1 == sUndestroyedObjects);
+    MOZ_RELEASE_ASSERT(dstMoveConstructed.GetStatus() == eWasMoveConstructed);
+  }
+}
+
+static bool TestCopyAndMove() {
+  MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+
+  {
+    // Check that we get moves when possible for types that can support both
+    // moves and copies.
+    {
+      Maybe<BasicValue> mayBasicValue = Some(BasicValue(1));
+      MOZ_RELEASE_ASSERT(1 == sUndestroyedObjects);
+      MOZ_RELEASE_ASSERT(mayBasicValue->GetStatus() == eWasMoveConstructed);
+      MOZ_RELEASE_ASSERT(mayBasicValue->GetTag() == 1);
+      mayBasicValue = Some(BasicValue(2));
+      MOZ_RELEASE_ASSERT(1 == sUndestroyedObjects);
+      MOZ_RELEASE_ASSERT(mayBasicValue->GetStatus() == eWasMoveAssigned);
+      MOZ_RELEASE_ASSERT(mayBasicValue->GetTag() == 2);
+      mayBasicValue.reset();
+      MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+      mayBasicValue.emplace(BasicValue(3));
+      MOZ_RELEASE_ASSERT(1 == sUndestroyedObjects);
+      MOZ_RELEASE_ASSERT(mayBasicValue->GetStatus() == eWasMoveConstructed);
+      MOZ_RELEASE_ASSERT(mayBasicValue->GetTag() == 3);
+
+      // Check that we get copies when moves aren't possible.
+      Maybe<BasicValue> mayBasicValue2 = Some(*mayBasicValue);
+      MOZ_RELEASE_ASSERT(mayBasicValue2->GetStatus() == eWasCopyConstructed);
+      MOZ_RELEASE_ASSERT(mayBasicValue2->GetTag() == 3);
+      mayBasicValue->SetTag(4);
+      mayBasicValue2 = mayBasicValue;
+      // This test should work again when we fix bug 1052940.
+      // MOZ_RELEASE_ASSERT(mayBasicValue2->GetStatus() == eWasCopyAssigned);
+      MOZ_RELEASE_ASSERT(mayBasicValue2->GetTag() == 4);
+      mayBasicValue->SetTag(5);
+      mayBasicValue2.reset();
+      mayBasicValue2.emplace(*mayBasicValue);
+      MOZ_RELEASE_ASSERT(mayBasicValue2->GetStatus() == eWasCopyConstructed);
+      MOZ_RELEASE_ASSERT(mayBasicValue2->GetTag() == 5);
+
+      // Check that std::move() works. (Another sanity check for move support.)
+      Maybe<BasicValue> mayBasicValue3 = Some(std::move(*mayBasicValue));
+      MOZ_RELEASE_ASSERT(mayBasicValue3->GetStatus() == eWasMoveConstructed);
+      MOZ_RELEASE_ASSERT(mayBasicValue3->GetTag() == 5);
+      MOZ_RELEASE_ASSERT(mayBasicValue->GetStatus() == eWasMovedFrom);
+      mayBasicValue2->SetTag(6);
+      mayBasicValue3 = Some(std::move(*mayBasicValue2));
+      MOZ_RELEASE_ASSERT(mayBasicValue3->GetStatus() == eWasMoveAssigned);
+      MOZ_RELEASE_ASSERT(mayBasicValue3->GetTag() == 6);
+      MOZ_RELEASE_ASSERT(mayBasicValue2->GetStatus() == eWasMovedFrom);
+      Maybe<BasicValue> mayBasicValue4;
+      mayBasicValue4.emplace(std::move(*mayBasicValue3));
+      MOZ_RELEASE_ASSERT(mayBasicValue4->GetStatus() == eWasMoveConstructed);
+      MOZ_RELEASE_ASSERT(mayBasicValue4->GetTag() == 6);
+      MOZ_RELEASE_ASSERT(mayBasicValue3->GetStatus() == eWasMovedFrom);
+    }
+
+    TestCopyMaybe<BasicValue>();
+    TestMoveMaybe<BasicValue>();
+  }
+
+  MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+
+  {
+    // Check that we always get copies for types that don't support moves.
+    {
+      Maybe<UnmovableValue> mayUnmovableValue = Some(UnmovableValue());
+      MOZ_RELEASE_ASSERT(mayUnmovableValue->GetStatus() == eWasCopyConstructed);
+      mayUnmovableValue = Some(UnmovableValue());
+      MOZ_RELEASE_ASSERT(mayUnmovableValue->GetStatus() == eWasCopyAssigned);
+      mayUnmovableValue.reset();
+      mayUnmovableValue.emplace(UnmovableValue());
+      MOZ_RELEASE_ASSERT(mayUnmovableValue->GetStatus() == eWasCopyConstructed);
+    }
+
+    TestCopyMaybe<UnmovableValue>();
+
+    static_assert(std::is_copy_constructible_v<Maybe<UnmovableValue>>);
+    static_assert(std::is_copy_assignable_v<Maybe<UnmovableValue>>);
+    // XXX Why do these static_asserts not hold?
+    // static_assert(!std::is_move_constructible_v<Maybe<UnmovableValue>>);
+    // static_assert(!std::is_move_assignable_v<Maybe<UnmovableValue>>);
+  }
+
+  MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+
+  {
+    // Check that types that only support moves, but not copies, work.
+    {
+      Maybe<UncopyableValue> mayUncopyableValue = Some(UncopyableValue());
+      MOZ_RELEASE_ASSERT(mayUncopyableValue->GetStatus() ==
+                         eWasMoveConstructed);
+      mayUncopyableValue = Some(UncopyableValue());
+      MOZ_RELEASE_ASSERT(mayUncopyableValue->GetStatus() == eWasMoveAssigned);
+      mayUncopyableValue.reset();
+      mayUncopyableValue.emplace(UncopyableValue());
+      MOZ_RELEASE_ASSERT(mayUncopyableValue->GetStatus() ==
+                         eWasMoveConstructed);
+      mayUncopyableValue = Nothing();
+    }
+
+    TestMoveMaybe<BasicValue>();
+
+    static_assert(!std::is_copy_constructible_v<Maybe<UncopyableValue>>);
+    static_assert(!std::is_copy_assignable_v<Maybe<UncopyableValue>>);
+    static_assert(std::is_move_constructible_v<Maybe<UncopyableValue>>);
+    static_assert(std::is_move_assignable_v<Maybe<UncopyableValue>>);
+  }
+
+  MOZ_RELEASE_ASSERT(0 == sUndestroyedObjects);
+
+  {  // Check that types that support neither moves or copies work.
+    {
+      const auto mayUncopyableUnmovableValueConstructed =
+          Maybe<UncopyableUnmovableValue>{std::in_place};
+      MOZ_RELEASE_ASSERT(mayUncopyableUnmovableValueConstructed->GetStatus() ==
+                         eWasDefaultConstructed);
+    }
+
+    Maybe<UncopyableUnmovableValue> mayUncopyableUnmovableValue;
+    mayUncopyableUnmovableValue.emplace();
+    MOZ_RELEASE_ASSERT(mayUncopyableUnmovableValue->GetStatus() ==
+                       eWasDefaultConstructed);
+    mayUncopyableUnmovableValue.reset();
+    mayUncopyableUnmovableValue.emplace(0);
+    MOZ_RELEASE_ASSERT(mayUncopyableUnmovableValue->GetStatus() ==
+                       eWasConstructed);
+    mayUncopyableUnmovableValue = Nothing();
+
+    static_assert(
+        !std::is_copy_constructible_v<Maybe<UncopyableUnmovableValue>>);
+    static_assert(!std::is_copy_assignable_v<Maybe<UncopyableUnmovableValue>>);
+    static_assert(
+        !std::is_move_constructible_v<Maybe<UncopyableUnmovableValue>>);
+    static_assert(!std::is_move_assignable_v<Maybe<UncopyableUnmovableValue>>);
+  }
+
+  {
+    // Test copy and move with a trivially copyable and trivially destructible
+    // type.
+    {
+      constexpr Maybe<int> src = Some(42);
+      constexpr Maybe<int> dstCopyConstructed = src;
+
+      static_assert(src.isSome());
+      static_assert(dstCopyConstructed.isSome());
+      static_assert(42 == *src);
+      static_assert(42 == *dstCopyConstructed);
+      static_assert(42 == dstCopyConstructed.value());
+    }
+
+    {
+      const Maybe<int> src = Some(42);
+      Maybe<int> dstCopyAssigned;
+      dstCopyAssigned = src;
+
+      MOZ_RELEASE_ASSERT(src.isSome());
+      MOZ_RELEASE_ASSERT(dstCopyAssigned.isSome());
+      MOZ_RELEASE_ASSERT(42 == *src);
+      MOZ_RELEASE_ASSERT(42 == *dstCopyAssigned);
+    }
+
+    {
+      Maybe<int> src = Some(42);
+      const Maybe<int> dstMoveConstructed = std::move(src);
+
+      MOZ_RELEASE_ASSERT(!src.isSome());
+      MOZ_RELEASE_ASSERT(dstMoveConstructed.isSome());
+      MOZ_RELEASE_ASSERT(42 == *dstMoveConstructed);
+    }
+
+    {
+      Maybe<int> src = Some(42);
+      Maybe<int> dstMoveAssigned;
+      dstMoveAssigned = std::move(src);
+
+      MOZ_RELEASE_ASSERT(!src.isSome());
+      MOZ_RELEASE_ASSERT(dstMoveAssigned.isSome());
+      MOZ_RELEASE_ASSERT(42 == *dstMoveAssigned);
+    }
+  }
+
+  return true;
+}
+
+static BasicValue* sStaticBasicValue = nullptr;
+
+static BasicValue MakeBasicValue() { return BasicValue(9); }
+
+static BasicValue& MakeBasicValueRef() { return *sStaticBasicValue; }
+
+static BasicValue* MakeBasicValuePtr() { return sStaticBasicValue; }
+
+static bool TestFunctionalAccessors() {
+  BasicValue value(9);
+  sStaticBasicValue = new BasicValue(9);
+
+  // Check that the 'some' case of functional accessors works.
+  Maybe<BasicValue> someValue = Some(BasicValue(3));
+  MOZ_RELEASE_ASSERT(someValue.valueOr(value) == BasicValue(3));
+  static_assert(std::is_same_v<BasicValue, decltype(someValue.valueOr(value))>,
+                "valueOr should return a BasicValue");
+  MOZ_RELEASE_ASSERT(someValue.valueOrFrom(&MakeBasicValue) == BasicValue(3));
+  static_assert(
+      std::is_same_v<BasicValue,
+                     decltype(someValue.valueOrFrom(&MakeBasicValue))>,
+      "valueOrFrom should return a BasicValue");
+  MOZ_RELEASE_ASSERT(someValue.ptrOr(&value) != &value);
+  static_assert(std::is_same_v<BasicValue*, decltype(someValue.ptrOr(&value))>,
+                "ptrOr should return a BasicValue*");
+  MOZ_RELEASE_ASSERT(*someValue.ptrOrFrom(&MakeBasicValuePtr) == BasicValue(3));
+  static_assert(
+      std::is_same_v<BasicValue*,
+                     decltype(someValue.ptrOrFrom(&MakeBasicValuePtr))>,
+      "ptrOrFrom should return a BasicValue*");
+  MOZ_RELEASE_ASSERT(someValue.refOr(value) == BasicValue(3));
+  static_assert(std::is_same_v<BasicValue&, decltype(someValue.refOr(value))>,
+                "refOr should return a BasicValue&");
+  MOZ_RELEASE_ASSERT(someValue.refOrFrom(&MakeBasicValueRef) == BasicValue(3));
+  static_assert(
+      std::is_same_v<BasicValue&,
+                     decltype(someValue.refOrFrom(&MakeBasicValueRef))>,
+      "refOrFrom should return a BasicValue&");
+
+  // Check that the 'some' case works through a const reference.
+  const Maybe<BasicValue>& someValueCRef = someValue;
+  MOZ_RELEASE_ASSERT(someValueCRef.valueOr(value) == BasicValue(3));
+  static_assert(
+      std::is_same_v<BasicValue, decltype(someValueCRef.valueOr(value))>,
+      "valueOr should return a BasicValue");
+  MOZ_RELEASE_ASSERT(someValueCRef.valueOrFrom(&MakeBasicValue) ==
+                     BasicValue(3));
+  static_assert(
+      std::is_same_v<BasicValue,
+                     decltype(someValueCRef.valueOrFrom(&MakeBasicValue))>,
+      "valueOrFrom should return a BasicValue");
+  MOZ_RELEASE_ASSERT(someValueCRef.ptrOr(&value) != &value);
+  static_assert(
+      std::is_same_v<const BasicValue*, decltype(someValueCRef.ptrOr(&value))>,
+      "ptrOr should return a const BasicValue*");
+  MOZ_RELEASE_ASSERT(*someValueCRef.ptrOrFrom(&MakeBasicValuePtr) ==
+                     BasicValue(3));
+  static_assert(
+      std::is_same_v<const BasicValue*,
+                     decltype(someValueCRef.ptrOrFrom(&MakeBasicValuePtr))>,
+      "ptrOrFrom should return a const BasicValue*");
+  MOZ_RELEASE_ASSERT(someValueCRef.refOr(value) == BasicValue(3));
+  static_assert(
+      std::is_same_v<const BasicValue&, decltype(someValueCRef.refOr(value))>,
+      "refOr should return a const BasicValue&");
+  MOZ_RELEASE_ASSERT(someValueCRef.refOrFrom(&MakeBasicValueRef) ==
+                     BasicValue(3));
+  static_assert(
+      std::is_same_v<const BasicValue&,
+                     decltype(someValueCRef.refOrFrom(&MakeBasicValueRef))>,
+      "refOrFrom should return a const BasicValue&");
+
+  // Check that the 'none' case of functional accessors works.
+  Maybe<BasicValue> noneValue;
+  MOZ_RELEASE_ASSERT(noneValue.valueOr(value) == BasicValue(9));
+  static_assert(std::is_same_v<BasicValue, decltype(noneValue.valueOr(value))>,
+                "valueOr should return a BasicValue");
+  MOZ_RELEASE_ASSERT(noneValue.valueOrFrom(&MakeBasicValue) == BasicValue(9));
+  static_assert(
+      std::is_same_v<BasicValue,
+                     decltype(noneValue.valueOrFrom(&MakeBasicValue))>,
+      "valueOrFrom should return a BasicValue");
+  MOZ_RELEASE_ASSERT(noneValue.ptrOr(&value) == &value);
+  static_assert(std::is_same_v<BasicValue*, decltype(noneValue.ptrOr(&value))>,
+                "ptrOr should return a BasicValue*");
+  MOZ_RELEASE_ASSERT(*noneValue.ptrOrFrom(&MakeBasicValuePtr) == BasicValue(9));
+  static_assert(
+      std::is_same_v<BasicValue*,
+                     decltype(noneValue.ptrOrFrom(&MakeBasicValuePtr))>,
+      "ptrOrFrom should return a BasicValue*");
+  MOZ_RELEASE_ASSERT(noneValue.refOr(value) == BasicValue(9));
+  static_assert(std::is_same_v<BasicValue&, decltype(noneValue.refOr(value))>,
+                "refOr should return a BasicValue&");
+  MOZ_RELEASE_ASSERT(noneValue.refOrFrom(&MakeBasicValueRef) == BasicValue(9));
+  static_assert(
+      std::is_same_v<BasicValue&,
+                     decltype(noneValue.refOrFrom(&MakeBasicValueRef))>,
+      "refOrFrom should return a BasicValue&");
+
+  // Check that the 'none' case works through a const reference.
+  const Maybe<BasicValue>& noneValueCRef = noneValue;
+  MOZ_RELEASE_ASSERT(noneValueCRef.valueOr(value) == BasicValue(9));
+  static_assert(
+      std::is_same_v<BasicValue, decltype(noneValueCRef.valueOr(value))>,
+      "valueOr should return a BasicValue");
+  MOZ_RELEASE_ASSERT(noneValueCRef.valueOrFrom(&MakeBasicValue) ==
+                     BasicValue(9));
+  static_assert(
+      std::is_same_v<BasicValue,
+                     decltype(noneValueCRef.valueOrFrom(&MakeBasicValue))>,
+      "valueOrFrom should return a BasicValue");
+  MOZ_RELEASE_ASSERT(noneValueCRef.ptrOr(&value) == &value);
+  static_assert(
+      std::is_same_v<const BasicValue*, decltype(noneValueCRef.ptrOr(&value))>,
+      "ptrOr should return a const BasicValue*");
+  MOZ_RELEASE_ASSERT(*noneValueCRef.ptrOrFrom(&MakeBasicValuePtr) ==
+                     BasicValue(9));
+  static_assert(
+      std::is_same_v<const BasicValue*,
+                     decltype(noneValueCRef.ptrOrFrom(&MakeBasicValuePtr))>,
+      "ptrOrFrom should return a const BasicValue*");
+  MOZ_RELEASE_ASSERT(noneValueCRef.refOr(value) == BasicValue(9));
+  static_assert(
+      std::is_same_v<const BasicValue&, decltype(noneValueCRef.refOr(value))>,
+      "refOr should return a const BasicValue&");
+  MOZ_RELEASE_ASSERT(noneValueCRef.refOrFrom(&MakeBasicValueRef) ==
+                     BasicValue(9));
+  static_assert(
+      std::is_same_v<const BasicValue&,
+                     decltype(noneValueCRef.refOrFrom(&MakeBasicValueRef))>,
+      "refOrFrom should return a const BasicValue&");
+
+  // Clean up so the undestroyed objects count stays accurate.
+  delete sStaticBasicValue;
+  sStaticBasicValue = nullptr;
+
+  return true;
+}
+
+static bool gFunctionWasApplied = false;
+
+static void IncrementTag(BasicValue& aValue) {
+  gFunctionWasApplied = true;
+  aValue.SetTag(aValue.GetTag() + 1);
+}
+
+static void AccessValue(const BasicValue&) { gFunctionWasApplied = true; }
+
+struct IncrementTagFunctor {
+  IncrementTagFunctor() : mBy(1) {}
+
+  void operator()(BasicValue& aValue) {
+    aValue.SetTag(aValue.GetTag() + mBy.GetTag());
+  }
+
+  BasicValue mBy;
+};
+
+static bool TestApply() {
+  // Check that apply handles the 'Nothing' case.
+  gFunctionWasApplied = false;
+  Maybe<BasicValue> mayValue;
+  mayValue.apply(&IncrementTag);
+  mayValue.apply(&AccessValue);
+  MOZ_RELEASE_ASSERT(!gFunctionWasApplied);
+
+  // Check that apply handles the 'Some' case.
+  mayValue = Some(BasicValue(1));
+  mayValue.apply(&IncrementTag);
+  MOZ_RELEASE_ASSERT(gFunctionWasApplied);
+  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 2);
+  gFunctionWasApplied = false;
+  mayValue.apply(&AccessValue);
+  MOZ_RELEASE_ASSERT(gFunctionWasApplied);
+
+  // Check that apply works with a const reference.
+  const Maybe<BasicValue>& mayValueCRef = mayValue;
+  gFunctionWasApplied = false;
+  mayValueCRef.apply(&AccessValue);
+  MOZ_RELEASE_ASSERT(gFunctionWasApplied);
+
+  // Check that apply works with functors.
+  IncrementTagFunctor tagIncrementer;
+  MOZ_RELEASE_ASSERT(tagIncrementer.mBy.GetStatus() == eWasConstructed);
+  mayValue = Some(BasicValue(1));
+  mayValue.apply(tagIncrementer);
+  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 2);
+  MOZ_RELEASE_ASSERT(tagIncrementer.mBy.GetStatus() == eWasConstructed);
+
+  // Check that apply works with lambda expressions.
+  int32_t two = 2;
+  gFunctionWasApplied = false;
+  mayValue = Some(BasicValue(2));
+  mayValue.apply([&](BasicValue& aVal) { aVal.SetTag(aVal.GetTag() * two); });
+  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 4);
+  mayValue.apply([=](BasicValue& aVal) { aVal.SetTag(aVal.GetTag() * two); });
+  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 8);
+  mayValueCRef.apply(
+      [&](const BasicValue& aVal) { gFunctionWasApplied = true; });
+  MOZ_RELEASE_ASSERT(gFunctionWasApplied == true);
+
+  return true;
+}
+
+static int TimesTwo(const BasicValue& aValue) { return aValue.GetTag() * 2; }
+
+static int TimesTwoAndResetOriginal(BasicValue& aValue) {
+  int tag = aValue.GetTag();
+  aValue.SetTag(1);
+  return tag * 2;
+}
+
+struct MultiplyTagFunctor {
+  MultiplyTagFunctor() : mBy(2) {}
+
+  int operator()(BasicValue& aValue) { return aValue.GetTag() * mBy.GetTag(); }
+
+  BasicValue mBy;
+};
+
+static bool TestMap() {
+  // Check that map handles the 'Nothing' case.
+  Maybe<BasicValue> mayValue;
+  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwo) == Nothing());
+  static_assert(std::is_same_v<Maybe<int>, decltype(mayValue.map(&TimesTwo))>,
+                "map(TimesTwo) should return a Maybe<int>");
+  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwoAndResetOriginal) == Nothing());
+
+  // Check that map handles the 'Some' case.
+  mayValue = Some(BasicValue(2));
+  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwo) == Some(4));
+  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwoAndResetOriginal) == Some(4));
+  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 1);
+  mayValue = Some(BasicValue(2));
+
+  // Check that map works with a const reference.
+  mayValue->SetTag(2);
+  const Maybe<BasicValue>& mayValueCRef = mayValue;
+  MOZ_RELEASE_ASSERT(mayValueCRef.map(&TimesTwo) == Some(4));
+  static_assert(
+      std::is_same_v<Maybe<int>, decltype(mayValueCRef.map(&TimesTwo))>,
+      "map(TimesTwo) should return a Maybe<int>");
+
+  // Check that map works with functors.
+  MultiplyTagFunctor tagMultiplier;
+  MOZ_RELEASE_ASSERT(tagMultiplier.mBy.GetStatus() == eWasConstructed);
+  MOZ_RELEASE_ASSERT(mayValue.map(tagMultiplier) == Some(4));
+  MOZ_RELEASE_ASSERT(tagMultiplier.mBy.GetStatus() == eWasConstructed);
+
+  // Check that map works with lambda expressions.
+  int two = 2;
+  mayValue = Some(BasicValue(2));
+  Maybe<int> mappedValue =
+      mayValue.map([&](const BasicValue& aVal) { return aVal.GetTag() * two; });
+  MOZ_RELEASE_ASSERT(mappedValue == Some(4));
+  mappedValue =
+      mayValue.map([=](const BasicValue& aVal) { return aVal.GetTag() * two; });
+  MOZ_RELEASE_ASSERT(mappedValue == Some(4));
+  mappedValue = mayValueCRef.map(
+      [&](const BasicValue& aVal) { return aVal.GetTag() * two; });
+  MOZ_RELEASE_ASSERT(mappedValue == Some(4));
+
+  // Check that function object qualifiers are preserved when invoked.
+  struct F {
+    std::integral_constant<int, 1> operator()(int) & { return {}; }
+    std::integral_constant<int, 2> operator()(int) const& { return {}; }
+    std::integral_constant<int, 3> operator()(int) && { return {}; }
+    std::integral_constant<int, 4> operator()(int) const&& { return {}; }
+  };
+  Maybe<int> mi = Some(0);
+  const Maybe<int> cmi = Some(0);
+  F f;
+  static_assert(std::is_same<decltype(mi.map(f)),
+                             Maybe<std::integral_constant<int, 1>>>::value,
+                "Maybe.map(&)");
+  MOZ_RELEASE_ASSERT(mi.map(f).value()() == 1);
+  static_assert(std::is_same<decltype(cmi.map(f)),
+                             Maybe<std::integral_constant<int, 1>>>::value,
+                "const Maybe.map(&)");
+  MOZ_RELEASE_ASSERT(cmi.map(f).value()() == 1);
+  const F cf;
+  static_assert(std::is_same<decltype(mi.map(cf)),
+                             Maybe<std::integral_constant<int, 2>>>::value,
+                "Maybe.map(const &)");
+  MOZ_RELEASE_ASSERT(mi.map(cf).value() == 2);
+  static_assert(std::is_same<decltype(cmi.map(cf)),
+                             Maybe<std::integral_constant<int, 2>>>::value,
+                "const Maybe.map(const &)");
+  MOZ_RELEASE_ASSERT(cmi.map(cf).value() == 2);
+  static_assert(std::is_same<decltype(mi.map(F{})),
+                             Maybe<std::integral_constant<int, 3>>>::value,
+                "Maybe.map(&&)");
+  MOZ_RELEASE_ASSERT(mi.map(F{}).value() == 3);
+  static_assert(std::is_same<decltype(cmi.map(F{})),
+                             Maybe<std::integral_constant<int, 3>>>::value,
+                "const Maybe.map(&&)");
+  MOZ_RELEASE_ASSERT(cmi.map(F{}).value() == 3);
+  using CF = const F;
+  static_assert(std::is_same<decltype(mi.map(CF{})),
+                             Maybe<std::integral_constant<int, 4>>>::value,
+                "Maybe.map(const &&)");
+  MOZ_RELEASE_ASSERT(mi.map(CF{}).value() == 4);
+  static_assert(std::is_same<decltype(cmi.map(CF{})),
+                             Maybe<std::integral_constant<int, 4>>>::value,
+                "const Maybe.map(const &&)");
+  MOZ_RELEASE_ASSERT(cmi.map(CF{}).value() == 4);
+
+  return true;
+}
+
+static bool TestToMaybe() {
+  BasicValue value(1);
+  BasicValue* nullPointer = nullptr;
+
+  // Check that a non-null pointer translates into a Some value.
+  Maybe<BasicValue> mayValue = ToMaybe(&value);
+  static_assert(std::is_same_v<Maybe<BasicValue>, decltype(ToMaybe(&value))>,
+                "ToMaybe should return a Maybe<BasicValue>");
+  MOZ_RELEASE_ASSERT(mayValue.isSome());
+  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 1);
+  MOZ_RELEASE_ASSERT(mayValue->GetStatus() == eWasCopyConstructed);
+  MOZ_RELEASE_ASSERT(value.GetStatus() != eWasMovedFrom);
+
+  // Check that a null pointer translates into a Nothing value.
+  mayValue = ToMaybe(nullPointer);
+  static_assert(
+      std::is_same_v<Maybe<BasicValue>, decltype(ToMaybe(nullPointer))>,
+      "ToMaybe should return a Maybe<BasicValue>");
+  MOZ_RELEASE_ASSERT(mayValue.isNothing());
+
+  return true;
+}
+
+static bool TestComparisonOperators() {
+  Maybe<BasicValue> nothingValue = Nothing();
+  Maybe<BasicValue> anotherNothingValue = Nothing();
+  Maybe<BasicValue> oneValue = Some(BasicValue(1));
+  Maybe<BasicValue> anotherOneValue = Some(BasicValue(1));
+  Maybe<BasicValue> twoValue = Some(BasicValue(2));
+
+  // Check equality.
+  MOZ_RELEASE_ASSERT(nothingValue == anotherNothingValue);
+  MOZ_RELEASE_ASSERT(oneValue == anotherOneValue);
+
+  // Check inequality.
+  MOZ_RELEASE_ASSERT(nothingValue != oneValue);
+  MOZ_RELEASE_ASSERT(oneValue != nothingValue);
+  MOZ_RELEASE_ASSERT(oneValue != twoValue);
+
+  // Check '<'.
+  MOZ_RELEASE_ASSERT(nothingValue < oneValue);
+  MOZ_RELEASE_ASSERT(oneValue < twoValue);
+
+  // Check '<='.
+  MOZ_RELEASE_ASSERT(nothingValue <= anotherNothingValue);
+  MOZ_RELEASE_ASSERT(nothingValue <= oneValue);
+  MOZ_RELEASE_ASSERT(oneValue <= oneValue);
+  MOZ_RELEASE_ASSERT(oneValue <= twoValue);
+
+  // Check '>'.
+  MOZ_RELEASE_ASSERT(oneValue > nothingValue);
+  MOZ_RELEASE_ASSERT(twoValue > oneValue);
+
+  // Check '>='.
+  MOZ_RELEASE_ASSERT(nothingValue >= anotherNothingValue);
+  MOZ_RELEASE_ASSERT(oneValue >= nothingValue);
+  MOZ_RELEASE_ASSERT(oneValue >= oneValue);
+  MOZ_RELEASE_ASSERT(twoValue >= oneValue);
+
+  return true;
+}
+
+// Check that Maybe<> can wrap a superclass that happens to also be a concrete
+// class (i.e. that the compiler doesn't warn when we invoke the superclass's
+// destructor explicitly in |reset()|.
+class MySuperClass {
+  virtual void VirtualMethod() { /* do nothing */
+  }
+};
+
+class MyDerivedClass : public MySuperClass {
+  void VirtualMethod() override { /* do nothing */
+  }
+};
+
+static bool TestVirtualFunction() {
+  Maybe<MySuperClass> super;
+  super.emplace();
+  super.reset();
+
+  Maybe<MyDerivedClass> derived;
+  derived.emplace();
+  derived.reset();
+
+  // If this compiles successfully, we've passed.
+  return true;
+}
+
+static Maybe<int*> ReturnSomeNullptr() { return Some(nullptr); }
+
+struct D {
+  explicit D(const Maybe<int*>&) {}
+};
+
+static bool TestSomeNullptrConversion() {
+  Maybe<int*> m1 = Some(nullptr);
+  MOZ_RELEASE_ASSERT(m1.isSome());
+  MOZ_RELEASE_ASSERT(m1);
+  MOZ_RELEASE_ASSERT(!*m1);
+
+  auto m2 = ReturnSomeNullptr();
+  MOZ_RELEASE_ASSERT(m2.isSome());
+  MOZ_RELEASE_ASSERT(m2);
+  MOZ_RELEASE_ASSERT(!*m2);
+
+  Maybe<decltype(nullptr)> m3 = Some(nullptr);
+  MOZ_RELEASE_ASSERT(m3.isSome());
+  MOZ_RELEASE_ASSERT(m3);
+  MOZ_RELEASE_ASSERT(*m3 == nullptr);
+
+  D d(Some(nullptr));
+
+  return true;
+}
+
+struct Base {};
+struct Derived : Base {};
+
+static Maybe<Base*> ReturnDerivedPointer() {
+  Derived* d = nullptr;
+  return Some(d);
+}
+
+struct ExplicitConstructorBasePointer {
+  explicit ExplicitConstructorBasePointer(const Maybe<Base*>&) {}
+};
+
+static bool TestSomePointerConversion() {
+  Base base;
+  Derived derived;
+
+  Maybe<Base*> m1 = Some(&derived);
+  MOZ_RELEASE_ASSERT(m1.isSome());
+  MOZ_RELEASE_ASSERT(m1);
+  MOZ_RELEASE_ASSERT(*m1 == &derived);
+
+  auto m2 = ReturnDerivedPointer();
+  MOZ_RELEASE_ASSERT(m2.isSome());
+  MOZ_RELEASE_ASSERT(m2);
+  MOZ_RELEASE_ASSERT(*m2 == nullptr);
+
+  Maybe<Base*> m3 = Some(&base);
+  MOZ_RELEASE_ASSERT(m3.isSome());
+  MOZ_RELEASE_ASSERT(m3);
+  MOZ_RELEASE_ASSERT(*m3 == &base);
+
+  auto s1 = Some(&derived);
+  Maybe<Base*> c1(s1);
+  MOZ_RELEASE_ASSERT(c1.isSome());
+  MOZ_RELEASE_ASSERT(c1);
+  MOZ_RELEASE_ASSERT(*c1 == &derived);
+
+  ExplicitConstructorBasePointer ecbp(Some(&derived));
+
+  return true;
+}
+
+struct SourceType1 {
+  int mTag;
+
+  operator int() const { return mTag; }
+};
+struct DestType {
+  int mTag;
+  Status mStatus;
+
+  DestType() : mTag(0), mStatus(eWasDefaultConstructed) {}
+
+  MOZ_IMPLICIT DestType(int aTag) : mTag(aTag), mStatus(eWasConstructed) {}
+
+  MOZ_IMPLICIT DestType(SourceType1&& aSrc)
+      : mTag(aSrc.mTag), mStatus(eWasMoveConstructed) {}
+
+  MOZ_IMPLICIT DestType(const SourceType1& aSrc)
+      : mTag(aSrc.mTag), mStatus(eWasCopyConstructed) {}
+
+  DestType& operator=(int aTag) {
+    mTag = aTag;
+    mStatus = eWasAssigned;
+    return *this;
+  }
+
+  DestType& operator=(SourceType1&& aSrc) {
+    mTag = aSrc.mTag;
+    mStatus = eWasMoveAssigned;
+    return *this;
+  }
+
+  DestType& operator=(const SourceType1& aSrc) {
+    mTag = aSrc.mTag;
+    mStatus = eWasCopyAssigned;
+    return *this;
+  }
+};
+struct SourceType2 {
+  int mTag;
+
+  operator DestType() const& {
+    DestType result;
+    result.mTag = mTag;
+    result.mStatus = eWasCopiedFrom;
+    return result;
+  }
+
+  operator DestType() && {
+    DestType result;
+    result.mTag = mTag;
+    result.mStatus = eWasMovedFrom;
+    return result;
+  }
+};
+
+static bool TestTypeConversion() {
+  {
+    Maybe<SourceType1> src = Some(SourceType1{1});
+    Maybe<DestType> dest = src;
+    MOZ_RELEASE_ASSERT(src.isSome() && src->mTag == 1);
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 1);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasCopyConstructed);
+
+    src = Some(SourceType1{2});
+    dest = src;
+    MOZ_RELEASE_ASSERT(src.isSome() && src->mTag == 2);
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 2);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasCopyAssigned);
+  }
+
+  {
+    Maybe<SourceType1> src = Some(SourceType1{1});
+    Maybe<DestType> dest = std::move(src);
+    MOZ_RELEASE_ASSERT(src.isNothing());
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 1);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasMoveConstructed);
+
+    src = Some(SourceType1{2});
+    dest = std::move(src);
+    MOZ_RELEASE_ASSERT(src.isNothing());
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 2);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasMoveAssigned);
+  }
+
+  {
+    Maybe<SourceType2> src = Some(SourceType2{1});
+    Maybe<DestType> dest = src;
+    MOZ_RELEASE_ASSERT(src.isSome() && src->mTag == 1);
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 1);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasCopiedFrom);
+
+    src = Some(SourceType2{2});
+    dest = src;
+    MOZ_RELEASE_ASSERT(src.isSome() && src->mTag == 2);
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 2);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasCopiedFrom);
+  }
+
+  {
+    Maybe<SourceType2> src = Some(SourceType2{1});
+    Maybe<DestType> dest = std::move(src);
+    MOZ_RELEASE_ASSERT(src.isNothing());
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 1);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasMovedFrom);
+
+    src = Some(SourceType2{2});
+    dest = std::move(src);
+    MOZ_RELEASE_ASSERT(src.isNothing());
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 2);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasMovedFrom);
+  }
+
+  {
+    Maybe<int> src = Some(1);
+    Maybe<DestType> dest = src;
+    MOZ_RELEASE_ASSERT(src.isSome() && *src == 1);
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 1);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasConstructed);
+
+    src = Some(2);
+    dest = src;
+    MOZ_RELEASE_ASSERT(src.isSome() && *src == 2);
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 2);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasAssigned);
+  }
+
+  {
+    Maybe<int> src = Some(1);
+    Maybe<DestType> dest = std::move(src);
+    MOZ_RELEASE_ASSERT(src.isNothing());
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 1);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasConstructed);
+
+    src = Some(2);
+    dest = std::move(src);
+    MOZ_RELEASE_ASSERT(src.isNothing());
+    MOZ_RELEASE_ASSERT(dest.isSome() && dest->mTag == 2);
+    MOZ_RELEASE_ASSERT(dest->mStatus == eWasAssigned);
+  }
+
+  {
+    Maybe<SourceType1> src = Some(SourceType1{1});
+    Maybe<int> dest = src;
+    MOZ_RELEASE_ASSERT(src.isSome() && src->mTag == 1);
+    MOZ_RELEASE_ASSERT(dest.isSome() && *dest == 1);
+
+    src = Some(SourceType1{2});
+    dest = src;
+    MOZ_RELEASE_ASSERT(src.isSome() && src->mTag == 2);
+    MOZ_RELEASE_ASSERT(dest.isSome() && *dest == 2);
+  }
+
+  {
+    Maybe<SourceType1> src = Some(SourceType1{1});
+    Maybe<int> dest = std::move(src);
+    MOZ_RELEASE_ASSERT(src.isNothing());
+    MOZ_RELEASE_ASSERT(dest.isSome() && *dest == 1);
+
+    src = Some(SourceType1{2});
+    dest = std::move(src);
+    MOZ_RELEASE_ASSERT(src.isNothing());
+    MOZ_RELEASE_ASSERT(dest.isSome() && *dest == 2);
+  }
+
+  {
+    Maybe<size_t> src = Some(1);
+    Maybe<char16_t> dest = src;
+    MOZ_RELEASE_ASSERT(src.isSome() && *src == 1);
+    MOZ_RELEASE_ASSERT(dest.isSome() && *dest == 1);
+
+    src = Some(2);
+    dest = src;
+    MOZ_RELEASE_ASSERT(src.isSome() && *src == 2);
+    MOZ_RELEASE_ASSERT(dest.isSome() && *dest == 2);
+  }
+
+  {
+    Maybe<size_t> src = Some(1);
+    Maybe<char16_t> dest = std::move(src);
+    MOZ_RELEASE_ASSERT(src.isNothing());
+    MOZ_RELEASE_ASSERT(dest.isSome() && *dest == 1);
+
+    src = Some(2);
+    dest = std::move(src);
+    MOZ_RELEASE_ASSERT(src.isNothing());
+    MOZ_RELEASE_ASSERT(dest.isSome() && *dest == 2);
+  }
+
+  return true;
+}
+
+static bool TestReference() {
+  static_assert(std::is_trivially_destructible_v<Maybe<int&>>);
+  static_assert(std::is_trivially_copy_constructible_v<Maybe<int&>>);
+  static_assert(std::is_trivially_copy_assignable_v<Maybe<int&>>);
+
+  static_assert(Maybe<int&>{}.isNothing());
+  static_assert(Maybe<int&>{Nothing{}}.isNothing());
+
+  {
+    Maybe<int&> defaultConstructed;
+
+    MOZ_RELEASE_ASSERT(defaultConstructed.isNothing());
+    MOZ_RELEASE_ASSERT(!defaultConstructed.isSome());
+    MOZ_RELEASE_ASSERT(!defaultConstructed);
+  }
+
+  {
+    Maybe<int&> nothing = Nothing();
+
+    MOZ_RELEASE_ASSERT(nothing.isNothing());
+    MOZ_RELEASE_ASSERT(!nothing.isSome());
+    MOZ_RELEASE_ASSERT(!nothing);
+  }
+
+  {
+    int foo = 42, bar = 42;
+    Maybe<int&> some = SomeRef(foo);
+
+    MOZ_RELEASE_ASSERT(!some.isNothing());
+    MOZ_RELEASE_ASSERT(some.isSome());
+    MOZ_RELEASE_ASSERT(some);
+    MOZ_RELEASE_ASSERT(&some.ref() == &foo);
+
+    MOZ_RELEASE_ASSERT(some.refEquals(foo));
+    MOZ_RELEASE_ASSERT(some.refEquals(SomeRef(foo)));
+    MOZ_RELEASE_ASSERT(!some.refEquals(Nothing()));
+    MOZ_RELEASE_ASSERT(!some.refEquals(bar));
+    MOZ_RELEASE_ASSERT(!some.refEquals(SomeRef(bar)));
+
+    some.ref()++;
+    MOZ_RELEASE_ASSERT(43 == foo);
+
+    (*some)++;
+    MOZ_RELEASE_ASSERT(44 == foo);
+  }
+
+  {
+    int foo = 42, bar = 42;
+    Maybe<int&> some;
+    some.emplace(foo);
+
+    MOZ_RELEASE_ASSERT(!some.isNothing());
+    MOZ_RELEASE_ASSERT(some.isSome());
+    MOZ_RELEASE_ASSERT(some);
+    MOZ_RELEASE_ASSERT(&some.ref() == &foo);
+
+    MOZ_RELEASE_ASSERT(some.refEquals(foo));
+    MOZ_RELEASE_ASSERT(some.refEquals(SomeRef(foo)));
+    MOZ_RELEASE_ASSERT(!some.refEquals(Nothing()));
+    MOZ_RELEASE_ASSERT(!some.refEquals(bar));
+    MOZ_RELEASE_ASSERT(!some.refEquals(SomeRef(bar)));
+
+    some.ref()++;
+    MOZ_RELEASE_ASSERT(43 == foo);
+  }
+
+  {
+    Maybe<int&> defaultConstructed;
+    defaultConstructed.reset();
+
+    MOZ_RELEASE_ASSERT(defaultConstructed.isNothing());
+    MOZ_RELEASE_ASSERT(!defaultConstructed.isSome());
+    MOZ_RELEASE_ASSERT(!defaultConstructed);
+  }
+
+  {
+    int foo = 42;
+    Maybe<int&> some = SomeRef(foo);
+    some.reset();
+
+    MOZ_RELEASE_ASSERT(some.isNothing());
+    MOZ_RELEASE_ASSERT(!some.isSome());
+    MOZ_RELEASE_ASSERT(!some);
+  }
+
+  {
+    int foo = 42;
+    Maybe<int&> some = SomeRef(foo);
+
+    auto& applied = some.apply([](int& ref) { ref++; });
+
+    MOZ_RELEASE_ASSERT(&some == &applied);
+    MOZ_RELEASE_ASSERT(43 == foo);
+  }
+
+  {
+    Maybe<int&> nothing;
+
+    auto& applied = nothing.apply([](int& ref) { ref++; });
+
+    MOZ_RELEASE_ASSERT(&nothing == &applied);
+  }
+
+  {
+    int foo = 42;
+    Maybe<int&> some = SomeRef(foo);
+
+    auto mapped = some.map([](int& ref) { return &ref; });
+    static_assert(std::is_same_v<decltype(mapped), Maybe<int*>>);
+
+    MOZ_RELEASE_ASSERT(&foo == *mapped);
+  }
+
+  {
+    Maybe<int&> nothing;
+
+    auto mapped = nothing.map([](int& ref) { return &ref; });
+
+    MOZ_RELEASE_ASSERT(mapped.isNothing());
+    MOZ_RELEASE_ASSERT(!mapped.isSome());
+    MOZ_RELEASE_ASSERT(!mapped);
+  }
+
+  {
+    int foo = 42;
+    auto someRef = ToMaybeRef(&foo);
+
+    static_assert(std::is_same_v<decltype(someRef), Maybe<int&>>);
+
+    MOZ_RELEASE_ASSERT(someRef.isSome());
+    MOZ_RELEASE_ASSERT(&foo == &someRef.ref());
+  }
+
+  {
+    int* fooPtr = nullptr;
+    auto someRef = ToMaybeRef(fooPtr);
+
+    static_assert(std::is_same_v<decltype(someRef), Maybe<int&>>);
+
+    MOZ_RELEASE_ASSERT(someRef.isNothing());
+  }
+
+  return true;
+}
+
+// These are quasi-implementation details, but we assert them here to prevent
+// backsliding to earlier times when Maybe<T> for smaller T took up more space
+// than T's alignment required.
+
+static_assert(sizeof(Maybe<char>) == 2 * sizeof(char),
+              "Maybe<char> shouldn't bloat at all ");
+static_assert(sizeof(Maybe<bool>) <= 2 * sizeof(bool),
+              "Maybe<bool> shouldn't bloat");
+static_assert(sizeof(Maybe<int>) <= 2 * sizeof(int),
+              "Maybe<int> shouldn't bloat");
+static_assert(sizeof(Maybe<long>) <= 2 * sizeof(long),
+              "Maybe<long> shouldn't bloat");
+static_assert(sizeof(Maybe<double>) <= 2 * sizeof(double),
+              "Maybe<double> shouldn't bloat");
+static_assert(sizeof(Maybe<int&>) == sizeof(int*));
+
+int main() {
+  RUN_TEST(TestBasicFeatures);
+  RUN_TEST(TestCopyAndMove);
+  RUN_TEST(TestFunctionalAccessors);
+  RUN_TEST(TestApply);
+  RUN_TEST(TestMap);
+  RUN_TEST(TestToMaybe);
+  RUN_TEST(TestComparisonOperators);
+  RUN_TEST(TestVirtualFunction);
+  RUN_TEST(TestSomeNullptrConversion);
+  RUN_TEST(TestSomePointerConversion);
+  RUN_TEST(TestTypeConversion);
+  RUN_TEST(TestReference);
+
+  return 0;
+}