不可反驳

过程宏，将可反驳的let表达式转换为不可反驳的。

示例

panic

#![feature(proc_macro_hygiene)]

use irrefutable::irrefutable;

#[irrefutable(panic("The cause."))]
let Some((a, b)) = Some(("a", "b"));

展开为

let (a, b) = if let Some((a, b)) = Some(("a", "b")) {
    (a, b)
} else {
    panic!("The cause.");
};

return

#![feature(proc_macro_hygiene)]

use irrefutable::irrefutable;

#[irrefutable(return)]
let Some((a, b)) = Some(("a", "b"));

展开为

let (a, b) = if let Some((a, b)) = Some(("a", "b")) {
    (a, b)
} else {
    return;
};

unreachable

#![feature(proc_macro_hygiene)]

use irrefutable::irrefutable;

#[irrefutable(unreachable)]
let Some((a, b)) = Some(("a", "b"));

展开为

let (a, b) = if let Some((a, b)) = Some(("a", "b")) {
    (a, b)
} else {
    unreachable!();
};