| // Copyright 2017 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| /// A macro for defining #[cfg] if-else statements. |
| /// |
| /// This is similar to the `if/elif` C preprocessor macro by allowing definition |
| /// of a cascade of `#[cfg]` cases, emitting the implementation which matches |
| /// first. |
| /// |
| /// This allows you to conveniently provide a long list #[cfg]'d blocks of code |
| /// without having to rewrite each clause multiple times. |
| macro_rules! cfg_if { |
| ($( |
| if #[cfg($($meta:meta),*)] { $($it:item)* } |
| ) else * else { |
| $($it2:item)* |
| }) => { |
| __cfg_if_items! { |
| () ; |
| $( ( ($($meta),*) ($($it)*) ), )* |
| ( () ($($it2)*) ), |
| } |
| } |
| } |
| |
| macro_rules! __cfg_if_items { |
| (($($not:meta,)*) ; ) => {}; |
| (($($not:meta,)*) ; ( ($($m:meta),*) ($($it:item)*) ), $($rest:tt)*) => { |
| __cfg_if_apply! { cfg(all(not(any($($not),*)), $($m,)*)), $($it)* } |
| __cfg_if_items! { ($($not,)* $($m,)*) ; $($rest)* } |
| } |
| } |
| |
| macro_rules! __cfg_if_apply { |
| ($m:meta, $($it:item)*) => { |
| $(#[$m] $it)* |
| } |
| } |