a missing semicolon can mess up the whole diagnostics

[0x8f701]

The following example has a missing semicolon, this semicolon has broken the whole diagnostic, The Butterfly Effect makes it hard to understand what's exactly happening and give a really bad develop experience.

Code:

use std::sync::{Arc, RwLock};

async fn test(data: Arc<RwLock<usize>>) -> usize {
    *data.write().unwrap() += 2;
    *data.write().unwrap()
}

#[async_std::main]
async fn main() -> Result<(), ()> {
    let data = Arc::new(RwLock::new(1)) // missing semicolon :)
    println!("{}", test(data).await);
    println!("Hello, world!");
    Ok(())
}

What's showing as diagnostics:

[bjorn3]

The main function not found are coming from rustc. They are caused by the fact that #[async_std::main] can't be expanded due to the syntax error, which means that rustc will just completely ignore the function.

[0x8f701]

@bjorn3 great thanks on your quick reply~ I'm wondering what can be done on this? As an user it's frustrating to see this kind of meaningless information

[bjorn3]

As an heuristic if a function is called main and couldn't be parsed, then a dummy fn main() {} could be inserted by rustc without any attributes.

[jonas-schievink]

Also rustc's "main not found" diagnostic encompasses the entire source file for some reason

[lnicola]

I think this is an upstream issue and we shouldn't try to do anything about it.

I filed rust-lang/rust#77968 upstream (maybe someone can add the A-diagnostics label).