Private items cannot be publicly re-exported. This error indicates that you
attempted to `pub use` a type or value that was not itself public.
Erroneous code example:
```compile_fail
mod foo {
const X: u32 = 1;
}
pub use foo::X;
fn main() {}
```
The solution to this problem is to ensure that the items that you are
re-exporting are themselves marked with `pub`:
```
mod foo {
pub const X: u32 = 1;
}
pub use foo::X;
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