Private modules cannot be publicly re-exported. This error indicates that you
attempted to `pub use` a module that was not itself public.
Erroneous code example:
```compile_fail,E0365
mod foo {
pub const X: u32 = 1;
}
pub use foo as foo2;
fn main() {}
```
The solution to this problem is to ensure that the module that you are
re-exporting is itself marked with `pub`:
```
pub mod foo {
pub const X: u32 = 1;
}
pub use foo as foo2;
fn main() {}
```
See the 'Use Declarations' section of the reference for more information
on this topic:
https://doc.rust-lang.org/reference.html#use-declarations