Add key to constructor fix generates new diagnostic

[FMorschel]

Consider (enable use_key_in_widget_constructors lint):

import 'package:flutter/widgets.dart';

class Foo extends StatelessWidget {
  final String txt = getNonConstString();

  static String getNonConstString() => 'Hello World';

  @override
  Widget build(BuildContext context) {
    return const Placeholder();
  }
}

It would generate:

class Foo extends StatelessWidget {
  final String txt = getNonConstString();
//                   ^^^^^^^^^^^^^^^^^ const_eval_method_invocation

  const Foo({super.key});
//^^^^^ const_constructor_with_field_initialized_by_non_const

  static String getNonConstString() => 'Hello World';

  @override
  Widget build(BuildContext context) {
    return const Placeholder();
  }
}

We should be able to detect that the const version would be invalid and omit the const then.

CC @bwilkerson @srawlins

[bwilkerson]

I agree. If we can detect when to omit const we should do so.

We might want to talk to the Flutter team first, though, to find out whether we should just drop the const always. I don't think there's as much benefit to const as there was when we first started encouraging users to use it, and I think we've stopped trying to encourage its use.