#[tokio::main] usage messes up error lines

[yageek]

I'm using some async main function using the #[tokio::main] macro.

When I make some code error (which happens quite often) inside the main function, all errors are referencing the line of the macro instead of pointing to the lines inside my own code.

This makes a pain to find the reason of the bug. Is there any tool or trick to solve this?

[carllerche]

Do you have an example / repro?

[yageek]

You can use this repo and branch : https://github.com/yageek/tilleuls-web/tree/error/main_macro.

All errors are referencing the same line

EDIT: The repository was private. I added a new post below with more information.

[yageek]

I may complete my previous comment with some additional information.

I have a buggy main function annotated with the #[tokio::main].
The errors are reported as following:

error[E0502]: cannot borrow `*app_data` as mutable because it is also borrowed as immutable
   --> src/main.rs:115:1
    |
115 | #[tokio::main]
    | ^^^^^^^^^^^^^^
    | |
    | mutable borrow occurs here
    | immutable borrow occurs here
    | has type `std::sync::Arc<std::sync::RwLock<AppData<'1>>>`
    | argument requires that `app_data` is borrowed for `'1`

error[E0716]: temporary value dropped while borrowed
   --> src/main.rs:115:1
    |
115 | #[tokio::main]
    | ^^^^^^^^^^^^^-
    | |            |
    | |            temporary value is freed at the end of this statement
    | creates a temporary which is freed while still in use
    | has type `std::sync::Arc<std::sync::RwLock<AppData<'1>>>`
    | argument requires that borrow lasts for `'1`

error[E0597]: `app_data` does not live long enough
   --> src/main.rs:115:1
    |
115 | #[tokio::main]
    | ^^^^^^^^^^^^^-
    | |            |
    | |            `app_data` dropped here while still borrowed
    | borrowed value does not live long enough
    | has type `std::sync::Arc<std::sync::RwLock<AppData<'1>>>`
    | argument requires that `app_data` is borrowed for `'1`

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0502, E0597, E0716.
For more information about an error, try `rustc --explain E0502`.
error: could not compile `tilleuls-webapp`.

However, if I move it into a non annotated function and call it from main, I have the expected output:

error[E0597]: `app_data` does not live long enough
   --> src/main.rs:236:42
    |
235 |                   app_data: Arc<RwLock<AppData>>| {
    |                   -------- has type `std::sync::Arc<std::sync::RwLock<AppData<'1>>>`
236 |                 let mut app_data = &mut *app_data.write().unwrap(); // --
    |                                          ^^^^^^^^--------
    |                                          |
    |                                          borrowed value does not live long enough
    |                                          argument requires that `app_data` is borrowed for `'1`
...
247 |             },
    |             - `app_data` dropped here while still borrowed

error[E0716]: temporary value dropped while borrowed
   --> src/main.rs:236:42
    |
235 |                   app_data: Arc<RwLock<AppData>>| {
    |                   -------- has type `std::sync::Arc<std::sync::RwLock<AppData<'1>>>`
236 |                 let mut app_data = &mut *app_data.write().unwrap(); // --
    |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
...
239 |                 let items = render_order_preview(&app_data, form);
    |                             ------------------------------------- argument requires that borrow lasts for `'1`
...
247 |             },
    |             - temporary value is freed at the end of this statement

error[E0597]: `app_data` does not live long enough
   --> src/main.rs:239:50
    |
235 |                   app_data: Arc<RwLock<AppData>>| {
    |                   -------- has type `std::sync::Arc<std::sync::RwLock<AppData<'1>>>`
...
239 |                 let items = render_order_preview(&app_data, form);
    |                             ---------------------^^^^^^^^^-------
    |                             |                    |
    |                             |                    borrowed value does not live long enough
    |                             argument requires that `app_data` is borrowed for `'1`
...
247 |             },
    |             - `app_data` dropped here while still borrowed

error[E0502]: cannot borrow `*app_data` as mutable because it is also borrowed as immutable
   --> src/main.rs:245:17
    |
235 |                   app_data: Arc<RwLock<AppData>>| {
    |                   -------- has type `std::sync::Arc<std::sync::RwLock<AppData<'1>>>`
...
239 |                 let items = render_order_preview(&app_data, form);
    |                             -------------------------------------
    |                             |                    |
    |                             |                    immutable borrow occurs here
    |                             argument requires that `app_data` is borrowed for `'1`
...
245 |                 app_data.new_session(cart);
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^ mutable borrow occurs here

error: aborting due to 4 previous errors

Some errors have detailed explanations: E0502, E0597, E0716.
For more information about an error, try `rustc --explain E0502`.
error: could not compile `tilleuls-webapp`.

Is there something to configure to have a proper output without defining a new function?

[Darksonn]

There's something weird going on here. Errors are usually displayed correctly, but I can reproduce your issue. It may be some syntax issue confusing the compiler, or some sort of bug in displaying that error in that specific situation.

[Matthias247]

I had the same issue with the tokio::test macro, which also showed all errors on the macro. Now later on I can't reproduce it. Definitely seems weird.