How to re-export Tauri command function from Rust module?

Questions
<br>
I'm new to Rust and Tauri. I'm not sure why I can't properly re-export function (pub use) and use it in tauri::generate_handler.

Code
<br>
src/main.rs

mod util;

fn main() {
    tauri::Builder::default()
        .invoke_handler(tauri::generate_handler![util::add])
        .run(tauri::generate_context!())
        .expect("error while running tauri application");
}

src/util/mod.rs

mod operation;

// pub use operation::add; // This line not work as expected
pub use operation::*; // This line no problem

src/util/operation.rs

#[tauri::command]
pub fn add(a: i32, b: i32) -> i32 {
    a + b
}

I'm not sure why pub use operation::add; not work as expect and cause

failed to resolve: could not find `__cmd__add` in `util`
could not find `__cmd__add` in `util` rustc

in tauri::generate_handler!. Where am I wrong?

The problem is that tauri::command creates a new symbol named __cmd__add and that tauri::generate_handler uses that symbol instead of (or in addition to) add itself. When you use operation::* you import everything from operation, including __cmd__add. But when you use operation::add you only import add.

A dirty workaround would be to use operation::{ add, __cmd__add }, but this is discouraged because __cmd__add is a private implementation detail, not intended to be used directly.

A full fix would require changes to Tauri, but a possible workaround for you is to wrap add in a module so that tauri::generate_handler will find __cmd__add inside that module:

• In src/util/operation.rs:

  pub mod add {
      #[tauri::command]
      pub fn add(a: i32, b: i32) -> i32 {
          a + b
      }
  }
  pub use add::add;
  

• In src/util/mod.rs:

  mod operation;
  pub use operation::add;
  

• In src/main.rs:

  mod util;
  
  fn main() {
      tauri::Builder::default()
          // Note the double `add` here:
          .invoke_handler(tauri::generate_handler![util::add::add])
          .run(tauri::generate_context!())
          .expect("error while running tauri application");
  }
  

Note that when calling tauri::generate_handler you need to refer explicitly to the add function that's inside the add module, so you need to use add::add. However when you want to call the function from your Rust code you can do it directly: let four = util::add (2, 2) will work fine.