[kristoff_it]

Yes, it can happen. In practice is not a big deal because the kind of stuff that you would want to run at comptime is pretty much all logic that manipulates its inputs without other side-effects, but one could for example add logging to a function and break its ability to be run at comptime (Zig might add in the future ways of solving this problem).

I would say that more in general the problem between public interface vs implementation details is much bigger than any type system and requires humans to negotiate what should be considered part of the public interface through other means (eg: tests, comments). Comptime is one example, another is ABI stability (eg the layout of a struct, or just its size), another could be speed or memory consumption.

Zig doesn't have an official package manager yet, we'll see what happens once we get one and people in the community have to start communicating stability guarantees to their users.