Missing docs lint ineffectual in test builds

[fenhl]

The missing_docs lint does not do anything in test builds. Minimal code example:

#![cfg_attr(test, deny(missing_docs))]

To reproduce, make a new crate, replace src/lib.rs with the above code, and run cargo test. The command will run successfully. I would expect the command to report a “missing documentation for crate” compile error.

As for the cause, my wild guess is some sort of interaction between cfg(test) and which items are detected as public.

[steveklabnik]

Triage: as a slightly more full example, this crate will compile with --test, but not compile without it:

#![deny(missing_docs)]

#[test]
fn foo() {}

fn lol() {}

fn main() {}

[steveklabnik]

Triage: no change

[ehuss]

This is also an issue for editors that use cargo check --profile=test in order to include tests in the check. This means the lint doesn't ever fire in the editor.

It looks like the check was added in 4a5d887. I suspect the reasoning is that code inside a cfg(test) block should not be checked for missing docs, which makes sense. I think it would be nicer to allow missing_docs to run with --test, but to not check any block/module/item that is marked with cfg(test). Unfortunately, I think that is very difficult or impossible to do. 😦