No error if a non-constant is used in a constant constructor initializer list

[sgrekhov]

The code below produces an error in the analyzer but works in VM.

class A {
  int id;
  A(this.id);
  static A answer = A(42);
}

class C {
  final A a;
  const C(this.a);
  const C.fromAnswer() : a = A.answer; // Analyzer: Invalid constant value.
}

main() {
  print(C.fromAnswer().a.id); // prints 42
}

There should be an error in VM as well.

Dart SDK version: 3.7.0-274.0.dev (dev) (Thu Dec 19 20:06:50 2024 -0800) on "windows_x64"

[lrhn]

At least the front-end constant evaluator does recognize that A.answer is not valid if the constructor is invoked with const, so we won't have mutable constants. (Phew!)

It is a specified error. A.answer is a reference to a getter which isn't a constant getter, and isn't .length of a String, so it's not a potentially constant expression.

Not a big problem, you can't invoke the constructor using const. The rules are there to avoid people writing const constructors that can't actually be invoked as const, because it's not useful to allow something that the compiler can easily see will never work.
The fix here is to remove const from the C.fromAnswer constructor and then every existing successful program would still work, since there are no successful constant invocations.