Rustc should explain that it can explain

[alexcrichton]

For example

fn main() {
    match 1i {
        1 => {}
    }
}

$ rustc foo.rs
foo.rs:2:5: 4:6 error: non-exhaustive patterns: `_` not covered [E0004]                                             
foo.rs:2     match 1i {                                                                                             
foo.rs:3         1 => {}                                                                                            
foo.rs:4     }                                                                                                      

Without prior knowledge of the --explain flag the error code listed is a little confusing here. The compiler should print a message at the end saying "pass the error code to --explain" or something like that if one is available.

Additionally, the compiler should instruct how to help contribute to documentation of error codes when documentation is not available, for example:

$ rustc --explain E0004
error: no extended information for E0004

Instead, the compiler could suggest looking at the contributing guidelines and also instruction where one would contribute if they were interested.

cc @jakub-, @brson

The compiler should print a message at the end saying "pass the error code to --explain" or something like that if one is available.

It already does that but only when one is actually available.

fn main() {
    match 1i {
        _ => {},
        _ => ()
    }
}

<anon>:4:9: 4:10 error: unreachable pattern [E0001] (pass `--explain E0001` to see a detailed explanation)
<anon>:4         _ => ()
                 ^
error: aborting due to previous error
playpen: application terminated with error code 101
Program ended.

I agree the user experience is quite far from ideal, though. I'll take a look.

[alexcrichton]

Oh I was unaware of that! This may not be as bad as I thought in that case.

[tamird]

The specific case reported here now results in:

$ rustc main.rs
main.rs:2:5: 4:6 error: non-exhaustive patterns: `_` not covered [E0004]
main.rs:2     match 1 {
main.rs:3         1 => {}
main.rs:4     }
main.rs:2:5: 4:6 help: pass `--explain E0004` to see a detailed explanation
error: aborting due to previous error

This should probably be closed?

[alexcrichton]

Yeah I think this is safe to close now.