No promotion of nullable type in "if (x?.y ?? false)"

[DanTup]

I thought there might be an existing issue fort his, but I couldn't find one. Often I find myself writing code like:

void x(List<int>? ints) {
  // Only do the thing if the list is non-null _and_ not empty
  if (ints?.isNotEmpty ?? false) {
    // Do the thing with the not-null list
    print(ints.length);
  }
}

However this reports "The property 'length' can't be unconditionally accessed because the receiver can be 'null'". My usual fix is to have an explicit null check:

  if (ints != null && ints.isNotEmpty) {

But this feels a little verbose. Maybe it'd be nice to have a .isNullOrEmpty, but that'd have to be known to the analyzer (if I implement it as an extension member, the analyzer wouldn't know it could be promoted).

[dart-github-bot]

Summary: The user is experiencing an issue where the analyzer doesn't promote a nullable type to a non-nullable type after a null-aware cascade and null coalescing operator. This results in a warning when accessing a property on the potentially null object.

[eernstg]

There is some overlap with dart-lang/language#1224. Perhaps these two issues could be combined into a request for something which is a bit more general?

[DanTup]

Thanks - looks like that issue already discusses some additional cases to the one in the title, including this one. And actually, this is an exact dupe of dart-lang/language#4006 which was closed in favour of that one.

So let's close this - it seems likely if dart-lang/language#1224 is addressed, this case would be covered because it's probably one of the simpler ones mentioned.