Dart Static Analyzer Fails to Report Missing Constructor Parameters and Freezes on Evaluation (Occurs with Generics and Sealed Classes)

[GiancarloCante]

Hi, when using the following code snippet, I encountered a bug where the Dart static analyzer does not report an error when not all required parameters are provided to a class constructor.

Additionally, the static analysis seems to freeze when evaluating the code.

However, the error is shown when attempting to compile or run the application in the terminal.

On rare occasions, the static analyzer behaves as expected, showing the corresponding errors.

Case 1:

sealed class BaseClass<A, B, C> {
  const BaseClass({
    required this.a,
    required this.b,
    required this.c,
  });

  final A a;
  final B b;
  final C c;
}

class AClass<A, B, C> extends BaseClass<A, B, C> {
  const AClass({
    required super.a,
    required super.b,
    required super.c,
  });
}

void foo<A, B, C, T extends BaseClass<A, B, C>>(List<T Function()> list) {
  // ...
}

void main() {
  foo<int, int, int, AClass<int, int, int>>([
    () => const AClass(a: 1, b: 2, c: 3),
    () => const AClass(a: 3), // wrong
  ]);
}

Case 2:

sealed class BaseClass<A, B, C> {
  const BaseClass({
    required this.a,
    required this.b,
    required this.c,
  });

  final A a;
  final B b;
  final C c;
}

class AClass<A, B, C> extends BaseClass<A, B, C> {
  const AClass({
    required super.a,
    required super.b,
    required super.c,
  });
}

void foo<A, B, C, T extends BaseClass<A, B, C>>(List<T Function()> list) {
  // ...
}

void main() {
  foo<int, int, int, AClass<int, int, int>>([f1]);
}

AClass<int, int, int> f1() => const AClass(a: 1);

Tested On:

• Windows with Flutter 3.27.1 with Dart 3.6

• IDX Platform with the following configuration:

[✓] Flutter (Channel stable, 3.24.3, on IDX GNU/Linux 6.1.112+, locale en_US.UTF-8)
    • Flutter version 3.24.3 on channel stable at /home/user/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 2663184aa7 (3 months ago), 2024-09-11 16:27:48 -0500
    • Engine revision 36335019a8
    • Dart version 3.5.3
    • DevTools version 2.37.3

• In the DartPad it works normally.

---

From what I've noticed, the issue seems to arise when using functions that take generics as parameters in combination with sealed classes. I don't know if it occurs in other cases.

This

  foo<int, int, int, AClass<int, int, int>>([
    // () => const AClass(a: 1, b: 2, c: 3),
    // () => const AClass(a: 3),
  ]);

---

I would appreciate it if you could tell me what the reason is so I can update my code while it is being fixed.

Thanks

[julemand101]

Sounds like an issue more fitting for the implementation of Dart: https://github.com/dart-lang/sdk/issues

This repository are for discussions and issues related to the Dart Language Specification itself.

[srawlins]

CC @scheglov this might be an interesting repro of code causing the analyzer to hang.

[scheglov]

I'm not able to reproduce it, neither when I analyze these two examples as unit tests, nor when I copy / paste into a file in my IntelliJ IDE.