Type promoting local variables on conditional member access

[FMorschel]

I could not find another issue related so I'll open this one but if I missed it please let me know.

When we have the following code:

void foo() {
  int? value1 = bar();
  int? value2 = bar();

  if (value1 != null && value1.isOdd) {
    value1.isOdd; // No problem
  }

  if (value2?.isOdd ?? false) {
    value2.isOdd; // This still triggers unchecked_use_of_nullable_value but we know it is not null anymore
  }
}

int? bar() => 0;

I feel like for local variables, when we have ? just after them, we could promote them to non-nulls if the following expression is constant (like true/false). I'm unsure of this when the following expression is not constant but if someone smarter than me can come up with a reasonable line of thinking to enhance this I will not complain.

[eernstg]

See dart-lang/language#1224.