Hello all,
I'm implementing a crate that has the purpose of wrapping some user code and make sure it is called in a certain context. I can summarize my workspace this way:
A "user_code" crate:
This contains a single "user" function, which I would have no control over. Notice that it returns a u32.
pub fn addition(a: u32, b: u32) -> u32 {
a + b
}
A "wrapper" crate:
This contains a macro_rules. This macro creates some modules and a caller function, which will call the user code seen above. This is a highly simplified version. Notice that the return value of addition is ignored.
#[macro_export]
macro_rules! macro_wrapper {
() => {
pub mod my_user_code {
use wrapper::*;
use user_code::*;
pub mod addition {
use wrapper::*;
use super::*;
pub fn caller(a: u32, b: u32) {
addition(a, b);
}
}
}
};
}
An "example" crate:
Here I simply call the wrapper macro, in order to form the modules and functions I need and then use in the main function.
#![deny(unused_results)]
use wrapper::macro_wrapper;
macro_wrapper! {
}
fn main() {
my_user_code::addition::caller(2,3);
println!("Hello, world!");
}
This might seem like super strange code (it is) but it's a very simplified example of a legit project 
My goal now is to make sure that this code doesn't compile because the return value of addition is not used - it was forgotten. The lint #![deny(unused_results)] seems to achieve exactly what I want.
However, this works only if, instead of
use wrapper::macro_wrapper;
I have the macro directly defined in the main.rs. In that case I get:
error: unused result of type `u32`
--> example\src\main.rs:14:21
|
14 | addition(a, b);
| ^^^^^^^^^^^^^^^
...
21 | / macro_wrapper! {
22 | |
23 | | }
| |_- in this macro invocation
|
note: the lint level is defined here
--> example\src\main.rs:1:9
|
1 | #![deny(unused_results)]
| ^^^^^^^^^^^^^^
= note: this error originates in the macro `macro_wrapper` (in Nightly builds, run with -Z macro-backtrace for more info)
If the macro is defined in its crate "wrapper", the code compiles and runs just fine without any error. This is not the result I expect.
What am I missing here? Thank you in advance for reading!