Modules in doc-tests can not access types in super/crate module

[MauriceKayser]

I probably am just using doc-tests wrongly, but I have come across a "type not found" problem using modules in doc-tests that seems rather odd to me, because it compiles in normal code without complaining:

type MyType = u8;

// Without extra module.
fn my_func(_: MyType) {}

fn main() {
    my_func(0);
}

type MyType = u8;

// With extra module.
mod my_mod { pub(super) fn my_func(_: super::MyType) {} }

fn main() {
    my_mod::my_func(0);
}

When using the same code (without main) in doc-tests with cargo test, only the first snippet passes the test:

//! ```rust
//! type MyType = u8;
//!
//! fn my_func(_: MyType) {}
//!
//! my_func(0);
//! ```

//! ```rust
//! type MyType = u8;
//!
//! mod my_mod { pub(super) fn my_func(_: super::MyType) {} }
//!
//! my_mod::my_func(0);
//! ```

The second snippet fails with the following message:

error[E0412]: cannot find type `MyType` in module `super`
 --> src\lib.rs:4:46
  |
5 | mod my_mod { pub(super) fn my_func(_: super::MyType) {} }
  |                                              ^^^^^^ not found in `super`

I also tried to use crate::MyType instead of super::MyType but that did not work either.

Meta

rustc --version --verbose:

rustc 1.50.0-nightly (e792288df 2020-12-05)
binary: rustc
commit-hash: e792288df31636ca28108516c63a00ce4267063a
commit-date: 2020-12-05
host: x86_64-pc-windows-msvc
release: 1.50.0-nightly

[ehuss]

It doesn't work because doctests wrap the entire example in fn main() { ... }. Functions themselves don't introduce a new namespace in the module hierarchy, so the super is referring to the module scope outside of the main function. #79260 is a similar issue.

The solution is to add a main function:

//! ```rust
//! type MyType = u8;
//!
//! mod my_mod { pub(super) fn my_func(_: super::MyType) {} }
//!
//!
//! fn main() {
//!   my_mod::my_func(0);
//! }
//! ```