RxJava 2 Migration

Proposed Plan

• Migrate independent semi-standalone services.
• Migrate UI components where possible using interop to communicate with required services.
• Migrate remaining services since consumers (UI components) will be ready for such changes at this point.
• Remove interop and RxJava 1-related dependencies.

Tips and Tricks

• Read the official documentation carefully, it contains answers to most of your questions.
• At this point RxJava 1 and RxJava 2 can be used side-by-side without any consequences. All fundamental thingies, such as Retrofit adapter and custom operators are already in place, but you may need to write your own.
• Refer to a package migrated first when in doubt. You may find it useful as a starting searching point.
• Do not forget to change (and run) unit tests, this can and will presume the correct behavior. If there is no test, prefer to write it first if possible and reasonable.
• RxJava 2 crashes on null emissions. Make sure you are not consuming such streams. The final goal is to replace Observable<T?> with either Observable<Optional<T>> or Optional<T> everywhere, no exceptions.
• Migration changes should be as isolated as possible. Change god-like services and friends, last. It is always better to migrate a single atomic thing and test it properly instead of changing basically everything.
• Create a tech task for each migration with description what to recheck. Your testing team is really good, but help them out to catch possible issues.