rustfmt removes comment in macro invocation

[tjamaan]

rustfmt will remove the comment in the following macro invocation:

macro_rules! add_my_field {
    {
        $(#[$m:meta])*
        $v:vis struct $name:ident {
            $($var_v:vis $var_name:ident: $var_ty:ty,)*
        }
    } => {
        $(#[$m])*
        $v struct $name {
            $($var_v $var_name: $var_ty,)*
            my_field: u32,
        }
    }
}

add_my_field!(
#[derive(Debug)]
struct MyStruct {
    a: u8,
    b: u16,
}
// this comment will be deleted (it doesn't matter if it's // or /* */)
);

fn main() {
    println!("{:#?}", MyStruct {
        a: 1,
        b: 2,
        my_field: 3,
    })
}

Playground link: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=c452814ae6ed3ad5042af833d1e0b359

Tested with:

• rustfmt 1.5.1-stable (fc594f15 2023-01-24)
• rustfmt 1.5.2-nightly (2023-02-16 9a7cc6c)

[ytmimi]

Thanks for reaching out!

Confirming I can reproduce this with rustfmt 1.5.2-nightly (34f9ca28 2023-02-16).

Here's a slightly smaller reproducible test case:

Input

add_my_field!(
    struct MyStruct {
        a: u8,
    }
// this comment will be deleted (it doesn't matter if it's // or /* */)
);

Output

add_my_field!(
    struct MyStruct {
        a: u8,
    }
);

[ytmimi]

Also interesting is that the comment isn't removed in this case:

Input

add_my_field!(
MyStruct // this comment will be deleted (it doesn't matter if it's // or /* */)
);

Output

add_my_field!(
    MyStruct // this comment will be deleted (it doesn't matter if it's // or /* */)
);

[ModProg]

I found a similar case where it actually breaks the code:

Input

my_macro!(
    struct Struct // comment
    ;
);

Output

my_macro!(
    struct Struct
// comment;
);