associated function `new` is never used

a.rs

// a/mymod.rs ではなく mymod.rs をむりやり使う
#[path="./mymod.rs"]
pub mod mymod;

b.rs

// こっちも
#[path="./mymod.rs"]
pub mod mymod;

cargo build

% cargo build
   Compiling hello v0.1.0 (/home/osyoyu/Development/hello)
warning: struct `Foo` is never constructed
 --> src/./mymod.rs:1:12
  |
1 | pub struct Foo {}
  |            ^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: associated function `new` is never used
 --> src/./mymod.rs:3:12
  |
2 | impl Foo {
  | -------- associated function in this implementation
3 |     pub fn new() { }
  |            ^^^

warning: `hello` (bin "hello") generated 2 warnings
    Finished dev [unoptimized + debuginfo] target(s) in 0.07s

main.rs

mod a;
mod b;

fn main() {
    let _ = a::mymod::Foo::new();
    println!("Hello, world!");
}

mymod.rs

// a::mymod::Foo と b::mymod::Foo の両方の実装になっていて、 
// b::mymod::Foo は呼び出されていないので warning になる
pub struct Foo {}
impl Foo {
    pub fn new() { }
}