After runnning build_runner build the build fails due to several messages like this from more than one builder (auto_route_generator chosen here):

[SEVERE] auto_route_generator on lib/file.dart: This builder requires
Dart inputs without syntax errors. However, package:file.dart (or an
existing part) contains the following errors.

Try fixing the errors and re-running the build.

There are no errors in the code. What’s happening and how should we fix this?