missing_safety_doc warning even on functions internal to crate

[tspiteri]

Functions which are public in their module, but inside a private module, are not exposed in the API docs. In fact they do not get a warning with warn(missing_docs). They still get a warning with warn(clippy::missing_safety_doc).

[llogiq]

Oops. On one hand, the last thing I want is people to learn to delete their docs to silence the lint. On the other hand, where are you going to document the preconditions if not on the module boundary.

I guess the best solution is to split the lint by actual visibility and make the missing_private_safety_doc part lint even when there's no docs at all.

[tspiteri]

I agree that the lint should be split by visibility, not by existing docs. I mentioned the missing_docs lint to point out that missing_docs itself depends on visibility.

[RustyYato]

Was missing_private_safety_doc ever implemented? It would be very helpful to ensure that non-exposed unsafe functions and traits' preconditions are documented. If it wasn't, I think I can take a stab at implementing it.