From the ACM link someone else provided: > An area of the repository is reserved for storing open source code (developed at Google or externally). To prevent d

From the ACM link someone else provided: > An area of the repository is reserved for storing open source code (developed at Google or externally). To prevent dependency conflicts, as outlined earlier, it is important that only one version of an open source project be available at any given time. Teams that use open source software are expected to occasionally spend time upgrading their codebase to work with newer versions of open source libraries when library upgrades are performed. So if an external library has to be updated, the entire codebase must be migrated all at once. Then Rosie is used to split the change into a lot of smaller changes (to be reviewed by all affected teams). Once all the smaller changes are LGTM'ed, it's submitted all at once.