Bug 1680724 - Add a utility function that converts a T* to a Maybe<T&>. r=jwalden

Differential Revision: https://phabricator.services.mozilla.com/D98783

mfbt/Maybe.h

@@ -880,6 +880,11 @@ constexpr Maybe<T&> SomeRef(T& aValue) {
   return value;
 }
 
+template <typename T>
+constexpr Maybe<T&> ToMaybeRef(T* const aPtr) {
+  return aPtr ? SomeRef(*aPtr) : Nothing{};
+}
+
 template <typename T>
 Maybe<std::remove_cv_t<std::remove_reference_t<T>>> ToMaybe(T* aPtr) {
   if (aPtr) {

mfbt/tests/TestMaybe.cpp

@@ -19,6 +19,7 @@ using mozilla::Nothing;
 using mozilla::Some;
 using mozilla::SomeRef;
 using mozilla::ToMaybe;
+using mozilla::ToMaybeRef;
 
 #define RUN_TEST(t)                                                     \
   do {                                                                  \
@@ -1420,6 +1421,25 @@ static bool TestReference() {
     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;
 }