CFE complains of reassigned final variable when it has not been reassigned

[mateusfccp]

I am not sure, but it seems to be a regression in the CFE, as it started to happen after upgrading to the latest Flutter stable with Dart 2.15.

Consider the following code:

import 'dart:math';

void main() {
  () {
    final should = Random().nextBool() || Random().nextBool();
    final int a;

    if (should) {
      a = 1;
    } else {
      a = 2;
    }
  };
}

The following code does not compile. Instead, it generates the following errors:

line 9 - The final variable 'a' can only be set once. Try making 'a' non-final.
line 11 - The final variable 'a' can only be set once. Try making 'a' non-final.

Note that it requires this specific configuration:

• If the code is not within a nested function, it won't happen. It doesn't need to be an anonymous function, however. A named nested function will also cause this behavior;
• If the should variable has no || or &&, it won't happen. For example, final should = Random().nextBool(); won't cause this behavior;
• If the boolean expression is passed directly to the if clause (if (Random().nextBool() || Random().nextBool())), it won't happen;
• If final should = ... is moved to after final int a;, it won't happen.

[lrhn]

Definitely weird behavior.

Seems like the boolean variable somehow interferes with the definite assignment analysis of the later variable.
If you move the final should = ... to after the final a; declaration, the error also goes away.

Boolean variables carrying data sounds like something @stereotype441 might know something about.

[stereotype441]

Thanks for the bug report! I've reproduced the problem and I'll start investigating to see what's going wrong.

[stereotype441]

I've tracked down the problem to a subtle bug in flow analysis. See https://dart-review.googlesource.com/c/sdk/+/227361 for the fix, and a detailed description of what was going wrong.

[feinstein]

Excellent news!