> We use the version number to run a series of steps on each proto to upgrade old fields to new ones

It sounds like you've built your own back-compat functionality on top of protobuf?

The only functionality protobuf is giving you here is optional-by-default (and mandatory version numbers, but most wire formats require that)

Yeah, I’d probably say something more like, “we leverage protobuf built ins to make a slightly more advanced back compat system”

We do rename deprecated fields and often give new fields their names. We rely on the field number to make that work.

> We do rename deprecated fields and often give new fields their names. We rely on the field number to make that work.

Why share names? Wouldn't it be safer to, well, not?

The code becomes hard to read. You might need to change int health to float health. In that case “health” properly describes the idea. We’d change this to int DEPRECATED_health and float health.

Folks can argue that’s ugly but I’ve not seen one instance of someone confused.