Testing an assignment against null does not promote the assigned variable (unchecked_use_of_nullable_value)

[Hixie]

int? test() => null;

void main() {
  int? foo;
  while ((foo = test()) != null) {
    foo.toDouble(); // error • The method 'toDouble' can't be unconditionally invoked because the receiver can be 'null'
  }
}

[mraleph]

likely a language issue, rather then tooling issue

/cc @eernstg @stereotype441

[stereotype441]

Yeah, flow analysis doesn't handle this. It does seem like it would be good if it did.

I'm going to move this issue to the language repo and tag it as a potential future flow analysis improvement to consider.

[srawlins]

I think this is essentially #1420?

[stereotype441]

@srawlins good catch. It looks like #1420 covers multiple suggestions, and #1844 specifically covers this request, so I'll mark as a duplicate of #1844.

[stereotype441]

Duplicate of #1844.