non-nullable promotion on assignment not working

[mit-mit]

main.dart:

void main() {
  int? a;
  a = 42;
  int b = a;
  print(b);
}

$ ./dart-sdk7/bin/dartanalyzer --enable-experiment=non-nullable main.dart
Analyzing main.dart...
  error • A value of type 'int?' can't be assigned to a variable of type 'int'. • main.dart:4:11 • invalid_assignment
1 error found.
| ~/tmp @ mit-macbookpro3 (mit)
$ ./dart-sdk7/bin/dartanalyzer --version
dartanalyzer version 2.7.0-dev.1.0
| ~/tmp @ mit-macbookpro3 (mit)

[mit-mit]

cc @lrhn this is expected to work, right?

[lrhn]

I expect it to work, and I'm hitting it now while migrating dart:_http.

Being nullable is always "interesting". A lot of code paths have a shape like:

Foo? something;
if (somethingElse) {
  something = computeFoo();
  bar = something.whatnot();
}

It's too annoying to have to introduce a new variable when you already have a local variable.

[mit-mit]

cc @johnniwinther @stereotype441

[stereotype441]

Agreed. The non-nullable analogue of the declared type needs to be a type of interest. This is on my list to work on.

[sortie]

This pattern came up a bunch when migrating dart:io and the code could be made nicer once this feature is implemented.

[scheglov]

https://dart-review.googlesource.com/c/sdk/+/144040