It will just cause a `pub get` fail (Package foo requires SDK version >=1.5.0 but the current SDK is x.x.x), but it won't prevent the application from running.

It will just cause a `pub get` fail (Package foo requires SDK version >=1.5.0 but the current SDK is x.x.x), but it won't prevent the application from running. Only `pub` cares about that pubspec.yaml file.