flutter run failed with error "Could not resolve the package 'characters' in 'package:characters/characters.dart'."
I faced this error too while updating Flutter today to Flutter Channel beta, 1.20.0-7.2.pre for an existing project.
As mentioned in https://github.com/flutter/flutter/issues/59645#issuecomment-645236663 running: flutter clean
solved the problem.
This actually deletes the .dart_tool
plus a few other files.
I solved the the issue installing https://pub.dev/packages/characters
I faced with this Error today (when i updated to Flutter 1.20.0-7.2.pre • channel beta) and finaly i solved it with deleting the .dart_tool
(location: ../yourProject/.dart_tool
) folder in my project and run my project again.