Cannot add prefixes or suffixes to macro-generated function names

[ebkalderon]

If I write a macro intended to generate new functions at compile time, I am able to name the functions according to individual idents, but I cannot annotate or concatenate anything onto the ident if I wish.

Consider the code below:

#[macro_export]
macro_rules! components {
    ( $($cfield:ident => $component:ident),+ ) => {
        pub struct ComponentManager {
            $(pub $cfield: ComponentMap<$component>,)+
        }

        impl ComponentManager {
            pub fn new() -> ComponentManager {
                use std::collections::HashMap;
                ComponentManager {
                    $($cfield: HashMap::new(),)+
                }
            }

            // This below is the code in question!
            $(
            pub fn $cfield(&self) {
                println!("{}", self.$cfield.len()); // Placeholder
            }
            )+

            pub fn delete_all_belonging_to(&mut self, id: EntityId) {
                $(self.$cfield.remove(&id);)+
            }
        }
    };
}

Assuming that I write the following:

pub struct Position {
    pub x: f32,
    pub y: f32,
    pub z: f32
}

components! {
    positions => Position
}

then the ComponentManager now has a positions(&self) method. But if I wanted the method to be called print_positions(&self), and in the macro I were to try to implement the code in question like this:

// This below is the code in question!
$(
pub fn print_$cfield(&self) {
    println!("{}", self.$cfield.len()); // Placeholder
}
)+

then I am presented with the following error:

ecs/mod.rs:53:27: 53:34 error: expected one of `(` or `<`, found `light`
ecs/mod.rs:53             pub fn print_$cfield(&self) {
                                        ^~~~~~~
ecs/mod.rs:53:27: 53:34 error: expected one of `(` or `<`, found `light`
ecs/mod.rs:53             pub fn print_$cfield(&self) {
                                        ^~~~~~~
Build failed, waiting for other jobs to finish...
Could not compile `project`.

TL; DR: When using macros to generate function names, I am forced to use individual identifiers and cannot prefix/suffix them with other text. Is this behavior a bug in my code, a bug in rustc, or by design?

[eefriedman]

Dup of #12249.

[alexcrichton]

Indeed, thanks @eefriedman

[ebkalderon]

Whoops! Sorry for the duplicate issue. I will be following #12249 very closely; hope it gets resolved.