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/// Declare a new const array without specify length.
/// It helps when apply conditional compilation to part of a const array.
///
/// # Syntax
/// The macro wraps any number of const array declarations(with length `_`).
///
/// ```
/// use crate::auto_const_array;
/// auto_const_array! {
///     pub const FOO: [u8; _] = [1, 2, 3];
///
///     #[allow(unused)]
///     const BAR: [u32; _] = [1];
/// }
/// ```
#[macro_export]
macro_rules! auto_const_array {
    () => {};
    ($(#[$attr:meta])* $vis:vis const $name:ident: [$t:ty; _] = [$($inner:expr,)*]; $($rest:tt)*) => {
        $(#[$attr])* $vis const $name: [$t; const_array![; $($inner)*]] = [$($inner,)*];
        $crate::auto_const_array!($($rest)*)
    };
    ($(#[$attr:meta])* $vis:vis const $name:ident: [$t:ty; _] = [$($inner:expr),*]; $($rest:tt)*) => {
        $(#[$attr])* $vis const $name: [$t; const_array![; $($inner)*]] = [$($inner,)*];
        $crate::auto_const_array!($($rest)*)
    };
    ($(#[$attr:meta])* $vis:vis const $name:ident: [$t:ty; _] = [$($inner:expr,)*]) => {
        $(#[$attr])* $vis const $name: [$t; const_array![; $($inner)*]] = [$($inner,)*];
    };
    ($(#[$attr:meta])* $vis:vis const $name:ident: [$t:ty; _] = [$($inner:expr),*]) => {
        $(#[$attr])* $vis const $name: [$t; const_array![; $($inner)*]] = [$($inner,)*];
    };
}