rust_2021_incompatible_closure_captures suggestion expands macro

[m-ou-se]

#![warn(rust_2021_incompatible_closure_captures)]

fn main() {
    let a = ("hey".to_string(), "123".to_string());
    let _ = || dbg!(a.0);
}

produces:

help: add a dummy let to cause `a` to be fully captured
  |
29~         { let _ = &a; match $val {
29+             tmp => {
29+                 $crate::eprintln!("[{}:{}] {} = {:#?}",
30+                     $crate::file!(), $crate::line!(), $crate::stringify!($val), &tmp);
30+                 tmp
30+             }
...

It expanded the dbg!() macro. This only happens when the macro invocation is the entire body of the closure.

[m-ou-se]

cc @rust-lang/wg-rfc-2229

[m-ou-se]

Working on a fix.