How to correctly import custom source generation packages - flutter

Question

I am trying to use a source generation package that I have written myself called animated_widget_generator. the annotations package is called animated_widget_annotations and the app I am trying to use it for is called example_usage.
I added the necessary packages to my dev_dependencies. here is my pubspec.yaml:
name: example_usage
description: A new Flutter project.
publish_to: 'none'
version: 1.0.0+1
environment:
sdk: ">=2.12.0 <3.0.0"
dependencies:
flutter:
sdk: flutter
cupertino_icons: ^1.0.2
dev_dependencies:
flutter_test:
sdk: flutter
animated_widget_generator:
path: ../animated_widget_generator
animated_widget_annotations:
path: ../animated_widget_annotations
build_runner: ^2.0.4
flutter:
uses-material-design: true
but when I try to run the app on my phone, it gives me the following errors:
Launching lib\main.dart on ONEPLUS A6003 in debug mode...
√ Built build\app\outputs\flutter-apk\app-debug.apk.
E/flutter (17052): [ERROR:flutter/shell/common/shell.cc(242)] Dart Error: error: import of dart:mirrors is not supported in the current Dart runtime
E/flutter (17052): [ERROR:flutter/runtime/dart_isolate.cc(169)] Could not prepare isolate.
E/flutter (17052): [ERROR:flutter/runtime/runtime_controller.cc(401)] Could not create root isolate.
E/flutter (17052): [ERROR:flutter/shell/common/shell.cc(571)] Could not launch engine with configuration.
Exited (1)
there are other questions on Stack Overflow about this error but they are always about some third party package and not about a custom source generation package and it doesn't seem like any of the answers to those questions are relevant to me
EDIT: pubspec.yaml for animated_widget_generator and animated_widget_annotations:
name: animated_widget_annotations
description: A new Flutter package project.
version: 0.0.1
author:
homepage:
environment:
sdk: ">=2.12.0 <3.0.0"
flutter: ">=1.17.0"
dependencies:
flutter:
sdk: flutter
dev_dependencies:
flutter_test:
sdk: flutter
flutter:
name: animated_widget_generator
description: A new Flutter package project.
version: 0.0.1
author:
homepage:
environment:
sdk: ">=2.12.0 <3.0.0"
flutter: ">=1.17.0"
dependencies:
flutter:
sdk: flutter
path: ^1.8.0
source_gen: ^1.0.2
json_serializable: ^4.1.3
animated_widget_annotations:
path: ../animated_widget_annotations
dev_dependencies:
flutter_test:
sdk: flutter
pedantic: ^1.11.0
build_runner: ^2.0.4
flutter:

Answer 1

You are receiving this error because the package dart:mirrors package is not available with flutter.
Do check these conversations on google groups and github for more info.
An alternative package called reflectable is available for reflection, however it has limitations at this time.

Answer 2

It is a very common problem with upcoming flutter developers. The main reason is that the flutter and dart are getting updated quickly. Sometimes after their upgradation let's say after this latest version of Flutter 2.2, you can see on their github that some packages are removed from their stable mode in order to work on them to make them more efficient. So, you can't access those packages. Make sure that you either find an alternate package for the same task or try to change the version number of the dependency to a lower number which might work because of backward compatibility. pubspec.yaml can be very difficult to understand if you have version problem because it will tell you that the dependency doesn't exist but won't tell you the reason.