Ok, TIL there’s a thing called Required, but otherwise, one way to do this is to rename the other part/field/key(s), so that old code reveals itself in much the same way as using a deleted field (because it does, actually)
Another way is explicitly have a separate type for records with/without the feature. (if one is a strict subset, you can have a downgrade/slice method on the more capable class.
Lastly, I would say that you need static typing, testing, both. People from static-land get vertigo without types, and it does give good night sleep, but it’s no substitute for testing. Testing can be a substitute for static typing in combination with coverage requirements, but at that point you’re doing so much more work that the static typing straight jacket seems pretty chill.
Backstage has become quite misaligned to what we were originally trying to do. Originally, we were trying to inventory and map the service eco-system, to deal with a few concrete problems. For example, when developing new things, you had to go through the village elders and the grape vine to find out what everyone else was doing. Another serious problem was not knowing / forgetting that we had some tool that would’ve been very useful when the on-call pager went off at fuck you dark thirty.
A reason we could build that map in System-Z (the predecessor of Backstage) is that our (sort of) HTTP/2 had a feature to tell us who had called methods on a service. (you could get the same from munging access logs, if you have them)
Anyway, the key features were that you could see what services your service was calling, who was calling you, and how those other systems were doing, and that you could see all the tools (e.g. build, logs, monitoring) your service was connected to. (for the ops / on-call use case)
A lot of those tool integrations were just links to “blahchat/#team”, “themonitoring/theservice?alerts=all” or whatever, to hotlink directly into the right place.
It was built on an opt-in philosophy, where “blahchat/#team” was the default, but if (you’re John-John and) you insist that the channel for ALF has to be #melmac, you can have that, but you have to add it yourself.
More recently, I’ve seen swagger/openapi used to great effect. I still want the map of who’s calling who and I strongly recommend mechanicanizing how that’s made. (extract it from logs or something, don’t rely on hand-drawn maps) I want to like C4, but I haven’t managed to get any use out of it. Just throw it in graphviz dot-file.
Oh, one trick that’s useful there: local maps. For each service S, get the list of everything that connects to it. Make a subset graph of those services, but make sure to include the other connections between those, the ones that don’t involve S. (“oh, so that’s why…”)