package:build_runner v2.16.0

• New default output behavior: always fix incorrect generated files. For
  example: if you "dart run build_runner build", modify a generated file,
  then build again, it will be fixed, undoing your modifications.
• New option, --keep-modified-outputs. Use this to get the old output
  behavior: manual modifications to generated files are kept. They will be
  overwritten if a build is triggered due to an input file change, a
  configuration change or dart run build_runner clean.
• New option, --only-check, for use in continuous builds and tests. With this
  option build_runner writes nothing, but builds and compares with the files
  already on disk. If there is any difference between disk and expected output
  then the differences are logged and the build fails.
• Allow package_config 3.0.0.