When upgrading a Flutter package for null safety I got this error when running flutter test
:
Error: A library can't opt out of null safety by default, when using sound null safety.
// @dart = 2.8
^^^^^^^^^^^^^^
Failed to load "/Users/xxxxx/test/text_test.dart":
Compilation failed
The answer was right there but I was still confused for a while, so I'm adding my answer below.
Copy: --no-sound-null-safety and add into "additional run args". Run your app with "Run/Play" Button or from "Run" Menu. In this way, you can solve "Error: Cannot run with sound null safety, because the following dependencies don't support null safety" error on Flutter project.
The problem also occurs when you have a mixed-version code i.e. the code is not fully migrated to sound null safety. To run the app:
Using IDE
Add // @dart=2.9
at the top in your main.dart
file and run the app using the Play ► icon.
// @dart=2.9
import 'package:flutter/material.dart';
void main() {
//...
}
Using command line
flutter run --no-sound-null-safety
or to be specific (say in chrome)
flutter run -d chrome --no-sound-null-safety
To solve your problem, remove the following line from text_test.dart:
// @dart = 2.8
This annotation is for opting out of sound null safety (see this and this). However, libraries (packages) are not allowed to do that if they want to be sound null safe.
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