Rename tokio::select!'s internal util module to __tokio_select_util

[WilliamVenner]

Motivation

This internal module's identifier can clash with existing identifiers in library users' code and produce confusing error messages.

mod util {
    pub fn hello_world() {
        println!("Hello, world!");
    }
}

#[tokio::main]
async fn main() {
    let f1 = async {};
    let f2 = async {};

    tokio::select! {
        _ = f1 => {
            // The following line would fix the compile error, showing that Tokio is creating an internal identifier called `util` which is clashing
            // use crate::util;

            util::hello_world();
        },

        _ = f2 => {}
    }
}

error[[E0425]](https://doc.rust-lang.org/stable/error-index.html#E0425): cannot find function `hello_world` in module `util`
  --> src/main.rs:14:19
   |
14 |             util::hello_world();
   |                   ^^^^^^^^^^^ not found in `util`
   |
help: consider importing this function
   |
1  | [use crate::util::hello_world;](https://play.rust-lang.org/#)
   |

For more information about this error, try `rustc --explain E0425`.

Solution

I have renamed the util module in tokio::select! to __tokio_util to prevent any identifier clashes.

Additionally, I also added #[doc(hidden)] to the module.

[hawkw]

thanks for the fix, this seems right to me! i had one minor suggestion.

[Darksonn]

I'm fine with renaming the module, but honestly, we should just be removing these imports and use absolute paths.

Edit: I thought this was about the hidden macro support module in Tokio.