Problem with pub keyword in macros

[GuillaumeGomez]

Hey,

I have an issue on my macros use. The source code of my macro is here. I can't put the pub keyword and if I call my macro like this :

pub impl_GObjectFunctions!(t1, t2)

The methods aren't public. Am I doing something wrong or is it a compiler's bug ?

Thanks in advance.

[GuillaumeGomez]

Any news on it ?

[kmcallister]

Related? #14660

[GuillaumeGomez]

I think.

[hugoduncan]

I just encountered this. I can reproduce it with:

macro_rules! defn {
    ($n:ident) => (
        fn $n (&self) -> i32 {
            println!("{}", stringify!($n));
            1
        }
        )
}

#[derive(Copy)]
pub struct S;

impl S {
    // Attempt to define a public method via a macro.
    // The resulting method ends up being non-public.
    pub defn!(f);
}

[GuillaumeGomez]

Now let's just hope it'll be fixed sooner or later !

[kmcallister]

Hm, what should pub item_macro!(); actually mean? A macro in item position can expand to zero or more items. Should the pub qualifier apply to all of them, or should it be an error to use it with a multi-item macro?

We might want to forbid pub in this position for 1.0, and come back to the issue later. I had a design for item macro sugar that I think would be rather nice.

The current workaround is to write

item_macro!(pub thing ...);

The precise syntax is up to the macro author and can accommodate multiple items.

This workaround would be less annoying if we had a "0 or 1" repeat operator in macros.

[hugoduncan]

@kmcallister Could you be a little more explicit about the workaround - I can't seem to get it to work.

[kmcallister]

@hugoduncan: Here's an example from the compiler itself.

This approach from lazy-static looks better, with less duplicated code.

[hugoduncan]

@kmcallister Thanks for the examples. If I understand them correctly (neither of which generate fn forms, iiuc), I should be matching on pub and inserting a literal pub in the expansion, but this does not seem to work :

macro_rules! defn {
    (pub $n:ident) => (
        pub fn $n (&self) -> i32 { 1 } )
}

#[derive(Copy)]
pub struct S;

impl S {
    defn!(pub f);
}


#[cfg(test)]
mod tests {
    use super::S;

    #[test]
    fn test_f() {
        let s=S;
        assert_eq!(1, s.f());
    }
}

[kmcallister]

It works for me on rustc 1.0.0-dev (e4e7aa2 2015-02-16). The playpen is just too old to have my fix for #17436.

[hugoduncan]

Thanks for the confirmation. I'll be looking forward to a new nightly for once :)