Rust macro to profile a short snippet of code and return the evaluated result. Inspired by the `dbg!` macro.

profile.rs

/// Prints and returns the value of a given expression for quick and dirty code
/// profiling.
///
/// Example usage:
///
/// ```rust
/// let s = "hello world";
/// let all_caps = profile!(s.repeat(2).to_uppercase());
///                ^-- prints: [src/main.rs:2] execution time: 2μs
///
/// println!("{}", all_caps);
/// ```
///
/// This macro works by measuring the execution time of a given expression using
/// `std::time::Instant` before returning it. The profiling information,
/// including the source file and line it originates from, is printed to
/// `stderr`.
///
/// The macro takes ownership of the expression and returns the evaluated
/// output.
///
/// Note that this macro is intended solely as a debugging or profiling tool. It
/// should therefore *not* be used in production builds and deploys.
///
/// You can aso profile multiple expressions at once:
///
/// ```rust
///     let name = "John";
///     let (msg, length) = profile!(
///         { format!("Hello {}!", name) },
///         { 7 + name.len() }
///     );
///
///     println!("{} (length: {})", msg, length);
/// ```
///
/// This prints (to stderr):
///
/// ```text,ignore
/// [src/main.rs:3] execution time: 2μs
/// [src/main.rs:4] execution time: 0μs
/// ```
///
/// The `profile!(..)` macro moves the input:
///
/// ```rust,compile_fail
/// struct NoCopy(i32);
///
/// let n = NoCopy(42);
/// let _ = profile!(n);  // <-- `n` is moved here
/// let _ = profile!(n);  // <-- `n` is moved here again; error!
/// ```
///
/// Finally, a trailing comma in the macro call will be ignored:
///
/// ```rust
/// let n = 42;
/// let _ = profile!(n,);  // <-- Trailing comma is ignored
/// let _ = profile!(n);   // <-- Same as above!
/// ```
#[macro_export]
macro_rules! profile {
    ( $x:expr ) => {{
        use std::time::Instant;
        use std::{eprintln, file, line};

        let timer = Instant::now();
        let _temp = $x;
        eprintln!(
            "[{}:{}] execution time: {}μs",
            file!(),
            line!(),
            timer.elapsed().as_micros()
        );
        _temp
    }};
    ( $val:expr, ) => { $crate::profile!($val) };
    ( $($val:expr),+ $(,)? ) => {
        ($($crate::profile!($val)),+,)
    };
}