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/// Asserts that the type has the given fields.
///
/// # Examples
///
/// One common use case is when types have fields defined multiple times as a
/// result of `#[cfg]`. This can be an issue when exposing a public API.
///
/// ```
/// # #[macro_use] extern crate static_assertions;
/// pub struct Ty {
/// #[cfg(windows)]
/// pub val1: u8,
/// #[cfg(not(windows))]
/// pub val1: usize,
///
/// #[cfg(unix)]
/// pub val2: u32,
/// #[cfg(not(unix))]
/// pub val2: usize,
/// }
///
/// // Always have `val2` regardless of OS
/// assert_fields!(Ty: val2);
/// ```
///
/// This macro even works with `enum` variants:
///
/// ```
/// # #[macro_use] extern crate static_assertions; fn main() {}
/// enum Data {
/// Val {
/// id: i32,
/// name: String,
/// bytes: [u8; 128],
/// },
/// Ptr(*const u8),
/// }
///
/// assert_fields!(Data::Val: id, bytes);
/// ```
///
/// The following example fails to compile because [`Range`] does not have a field named `middle`:
///
/// ```compile_fail
/// # #[macro_use] extern crate static_assertions; fn main() {}
/// use std::ops::Range;
///
/// assert_fields!(Range<u32>: middle);
/// ```
///
/// [`Range`]: https://doc.rust-lang.org/std/ops/struct.Range.html
#[macro_export]
macro_rules! assert_fields {
($t:ident::$v:ident: $($f:ident),+) => {
#[allow(unknown_lints, unneeded_field_pattern)]
const _: fn() = || {
#[allow(dead_code, unreachable_patterns)]
fn assert(value: $t) {
match value {
$($t::$v { $f: _, .. } => {},)+
_ => {}
}
}
};
};
($t:path: $($f:ident),+) => {
#[allow(unknown_lints, unneeded_field_pattern)]
const _: fn() = || {
$(let $t { $f: _, .. };)+
};
};
}