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