rust/tests/ui/eval_order_dependence.rs

#[warn(eval_order_dependence)]
#[allow(unused_assignments, unused_variables, many_single_char_names, no_effect, dead_code, blacklisted_name)]
fn main() {
    let mut x = 0;
    let a = { x = 1; 1 } + x;

    // Example from iss#277
    x += { x = 20; 2 };

    // Does it work in weird places?
    // ...in the base for a struct expression?
    struct Foo { a: i32, b: i32 };
    let base = Foo { a: 4, b: 5 };
    let foo = Foo { a: x, .. { x = 6; base } };
    // ...inside a closure?
    let closure = || {
        let mut x = 0;
        x += { x = 20; 2 };
    };
    // ...not across a closure?
    let mut y = 0;
    let b = (y, || { y = 1 });

    // && and || evaluate left-to-right.
    let a = { x = 1; true } && (x == 3);
    let a = { x = 1; true } || (x == 3);

    // Make sure we don't get confused by alpha conversion.
    let a = { let mut x = 1; x = 2; 1 } + x;

    // No warning if we don't read the variable...
    x = { x = 20; 2 };
    // ...if the assignment is in a closure...
    let b = { || { x = 1; }; 1 } + x;
    // ... or the access is under an address.
    let b = ({ let p = &x; 1 }, { x = 1; x });

    // Limitation: l-values other than simple variables don't trigger
    // the warning.
    let mut tup = (0, 0);
    let c = { tup.0 = 1; 1 } + tup.0;
    // Limitation: you can get away with a read under address-of.
    let mut z = 0;
    let b = (&{ z = x; x }, { x = 3; x });
}