There is no such requirement. Common wisdom suggests that you should ensure zero values are useful, but that isn't about every random struct field – only the values you actually give others. Initialize your struct fields and you won't have to consider their zero state. They will never be zero.
It's funny seeing this beside the DRY thread. Seems programmers taking things a bit too literally is a common theme.
Then the zero value is their problem, not yours. You have no reason to be worried about that any more than you are worried about them not getting enough sleep, or eating unhealthy food. What are you doing to stop them from doing that? Nothing, of course. Not your problem.
Coq exists if you really feel you need a complete type system. But there is probably good reason why almost nobody uses it.
> Then the zero value is their problem, not yours.
Except for all those times you're the consumer of someone else's library and there's no way for them to indicate that creating a zero-valued struct is a bug.
Again, it's the philosophy of "Just do the right thing everywhere and you don’t have to worry!" Sometimes it's nice to work with a type system where designers of libraries can actually prevent you from writing bugs.
> Except for all those times you're the consumer of someone else's library and there's no way for them to indicate that creating a zero-valued struct is a bug.
Nonsense. Go has a built-in facility for documentation to communicate these things to other developers. Idiomatic Go strongly encourages you to use it. Consumers of the libraries expect it.
> Sometimes it's nice to work with a type system where designers of libraries can actually prevent you from writing bugs.
Well, sure. But, like I said, almost nobody uses Coq. The vast, vast, vast majority of projects – and I expect 100% of web projects – use languages with incomplete type systems, making what you seek impossible.
And there's probably a good reason for that. While complete type systems sound nice in theory, practice isn't so kind. There are tradeoffs abound. There is no free lunch in life. Sorry.