Compat notifications

[Lord-KA]

Background

tarantool.compat is designed to assist with more safe deprecation of unwanted behavior. It provides several states for such behavior:

1. old behavior by default
2. new behavior by default
3. new behavior is frozen and the old behavior is removed

By the nature of compat we need to notify user about the change on every step. At this moment we print a warning in two cases, if new is default and user selects old, and if behavior is frozen and user tries to alter it.

Proposal

I think we should notify user when:

• a new behavior change is added to compat, and state that it is available and might be a better default
• default is going to shift to new behavior
• behavior is finally frozen

tt-news seems like a good way to do it.