unhygienic named labels allowed in macros

[metajack]

Hygiene currently prevents capturing variables but does not prevent you from capturing named labels.

For example:

fn main() {
    macro_rules! breakme(
        ($value: expr) => {
            break 'foo;
        }
    )
    'foo: loop { 
        breakme!("foo");
    }
}

Note, this currently causes a bus error in rustc, but probably otherwise works, and used to work before let hygiene was added.

[metajack]

cc @jbclements

[jbclements]

@metajack as I said on felix's bug, I can't reproduce this on 248765a, my last merge... maybe the next merge, cabba6b, the merge of #9136 ?

[alexcrichton]

This code compiles on today's master, and it sounds like it shouldn't.

[jbclements]

No, I think that's fine. We've never made any attempt to impose hygiene on labels. I suppose it depends on what you mean by "shouldn't." I agree that it might be nice to implement hygiene for labels ...

[edwardw]

After #12338, rustc now gives an error:

fn main() {
    macro_rules! breakme(
        ($value: expr) => {
            break 'foo;    // error: use of undeclared label `foo`
        }
    )
    'foo: loop { 
        breakme!("foo");
    }
}

So this probably could be closed.

[alexcrichton]

Hurray! Thanks @edwardw!