no type error when one side of a conditional expression is the wrong type

[skybrian]

In DartPad, there is no type error for this code, even in strong mode:

main() {
  String x1 = "x" == 3 ? true : "hello";
  String x2 = "x" == 3 ? "hi" : true;
  print(x1);
  print(x2);
}

It seems like it should be an error to assign a boolean to a string.

[a14n]

I think it's because of implicit casts. "x" == 3 ? true : "hello" has type Object that can be cast to String.

It's reported as error with :

analyzer:
  strong-mode:
    implicit-casts: false

ERROR: A value of type 'Object' cannot be assigned to a variable of type 'String' (test.dart:2)
ERROR: A value of type 'Object' cannot be assigned to a variable of type 'String' (test.dart:3)

[lrhn]

This is indeed an unfavorable interaction between finding the least upper bound of the conditional expression branches to be Object and implicit down-casts allowing Object to be assigned to anything.
It is working as the specification says it should.
I hope we'll eventually be able to do better.

[skybrian]

That's unfortunate. I wonder if we should handle this as a special case in strong mode?

[jmesserly]

@skybrian Indeed! That's covered by #25368

(edit: untagging strong mode because above issue covers that request)

[skybrian]

Okay, I guess this one is a dup then.