infer_clone/infer/documentation/issues/OPTIONAL_EMPTY_ACCESS.md

Optional Empty Access warnings are reported when we try to retrieve the value of a folly::Optional when it is empty (i.e. folly::none).

In the following example we get a warning as int_opt might be folly::none and its value is being accessed:

bool somef(int v);

folly::Optional<int> mightReturnNone(int v) {
   if (somef(v)) {
      return folly::Optional(v);
   }

   return folly::none;
}

int value_no_check() {
  folly::Optional<int> int_opt = mightReturnNone (4);
  return int_opt.value(); // Optional Empty Access warning
}

We do not get the warning anymore if we add a check whether int_opt is not empty:

int value_check() {
  folly::Optional<int> int_opt = mightReturnNone (4);
  if (int_opt.has_value()) {
     return int_opt.value(); // OK
  }
  return -1;
}

In some cases we know that we have a non-empty value and there is no need to have a check. Consider the following example where Infer does not warn:

bool somef(int v) {return v > 3;};

folly::Optional<int> mightReturnNone(int v) {
   if (somef(v)) {
      return folly::Optional(v);
   }

   return folly::none;
}

int value_no_check() {
  folly::Optional<int> int_opt = mightReturnNone (4); // cannot be folly::none
  return int_opt.value(); // OK
}