rust/tests/ui/hygiene/hygienic-labels.rs

// run-pass
#![allow(unreachable_code)]
#![allow(unused_labels)]
// Test that labels injected by macros do not break hygiene.

// Issue #24278: The label/lifetime shadowing checker from #24162
// conservatively ignores hygiene, and thus issues warnings that are
// both true- and false-positives for this test.

macro_rules! loop_x {
    ($e: expr) => {
        // $e shouldn't be able to interact with this 'x
        'x: loop {
            $e
        }
    };
}

macro_rules! run_once {
    ($e: expr) => {
        // ditto
        'x: for _ in 0..1 {
            $e
        }
    };
}

macro_rules! while_x {
    ($e: expr) => {
        // ditto
        'x: while 1 + 1 == 2 {
            $e
        }
    };
}

pub fn main() {
    'x: for _ in 0..1 {
        // this 'x should refer to the outer loop, lexically
        loop_x!(break 'x);
        panic!("break doesn't act hygienically inside for loop");
    }

    'x: loop {
        // ditto
        loop_x!(break 'x);
        panic!("break doesn't act hygienically inside infinite loop");
    }

    'x: while 1 + 1 == 2 {
        while_x!(break 'x);
        panic!("break doesn't act hygienically inside infinite while loop");
    }

    'x: for _ in 0..1 {
        // ditto
        run_once!(continue 'x);
        panic!("continue doesn't act hygienically inside for loop");
    }
}