lambda-var hygiene

[jbclements]

lambda vars and function arguments should be treated hygienically. This is a placeholder bug to attach to some xfailed tests. FWIW, I think this is not a huge amount of work.

[edwardw]

What exactly does this ticket ask? The following already works out-of-box:

#[feature(macro_rules)];

macro_rules! macro_invoke (($ex:expr) => ({let _x = 9; $ex()}))
pub fn main() {
    let _x = 8;
    assert_eq!(macro_invoke!(|| _x),8)
}

[flaper87]

@jbclements I couldn't find any test with #9383 in it. Does @edwardw comment address what you meant? If so, we can mark this issue as needtest.

[huonw]

No, it's still wrong. This is referring to function/lambda arguments. The following compiles and prints 1:

#[feature(macro_rules)];

macro_rules! wrong {
    ($e: expr) => {
        (|x| { $e })(1)
    }
}

macro_rules! right {
    ($e: expr) => {
        { let x = 1; $e }
    }
}

fn main() {
    println!("{}", wrong!(x));
    // println!("{}", right!(x));
}

(Uncommenting the right! invocation gives "unresolved name x", which the wrong! one should too.)

[jbclements]

Oops, yes, closed by #15425 .