RFC Mentoring Opportunity: Permit `?` in `main()`

57

Right now, to write Unix CLI utilities in Rust, you wind up doing something like this:

fn inner_main() -> Result<(), HLError> {
    let args = parse_cmdline()?;
    // all the real work here
}

fn main() {
    process::exit(match inner_main() {
        Ok(_) => 0,
        Err(ref e) => {
            writeln!(io::stderr(), "{}", e).unwrap();
            1
        }
    });
}

So I like the fn main () -> something_Result_ish proposal, because it basically paves this cowpath.

However. It is very important for this use case that returning an Err from main does not trigger a panic. It normally would not represent a bug, and in some cases, it needs to produce no output other than the exit code –

$ grep -q root /etc/passwd ; echo $?
0
$ grep -q notthere /etc/passwd ; echo $?
1
$ grep -q notthere /etc/shadow ; echo $?
grep: /etc/shadow: permission denied
2
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