“cannot find macro” error in the macro's own doc test

Question

I am trying to add documentation tests to a Rust macro that I\'m exporting. Something like this:

/// Usage:
///
/// ```
/// let x = addone!(100);
/// ```
#[m         


        

Answer 1

Doc tests automatically wrap the code block in extern crate foo; fn main() { … } if they don’t find these elements in the code, but to get an exported macro you need the #[macro_use] attribute on the extern crate foo;.

Thus, you should write this:

/// Usage:
///
/// ```
/// # #[macro_use] extern crate foo; fn main() {
/// let x = addone!(100);
/// # }
/// ```
#[macro_export]
macro_rules! addone {
    ($x:expr) => ($x + 1)
}

(The lines prefixed with #  get hidden in the output, but included, sans the marker, in the code that gets compiled for the doc test.)

This is covered in The Rust Programming Language, first edition.

As for std, there is an implied #[macro_use] extern crate std; in all crates that lack the #![no_std] crate attribute, so its macros immediately work.