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Diffstat (limited to '')
| -rw-r--r-- | third_party/rust/cfg-if/src/lib.rs | 176 |
1 files changed, 176 insertions, 0 deletions
diff --git a/third_party/rust/cfg-if/src/lib.rs b/third_party/rust/cfg-if/src/lib.rs new file mode 100644 index 0000000000..52bbbe0f37 --- /dev/null +++ b/third_party/rust/cfg-if/src/lib.rs @@ -0,0 +1,176 @@ +//! A macro for defining `#[cfg]` if-else statements. +//! +//! The macro provided by this crate, `cfg_if`, 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. +//! +//! # Example +//! +//! ``` +//! cfg_if::cfg_if! { +//! if #[cfg(unix)] { +//! fn foo() { /* unix specific functionality */ } +//! } else if #[cfg(target_pointer_width = "32")] { +//! fn foo() { /* non-unix, 32-bit functionality */ } +//! } else { +//! fn foo() { /* fallback implementation */ } +//! } +//! } +//! +//! # fn main() {} +//! ``` + +#![no_std] +#![doc(html_root_url = "https://docs.rs/cfg-if")] +#![deny(missing_docs)] +#![cfg_attr(test, deny(warnings))] + +/// The main macro provided by this crate. See crate documentation for more +/// information. +#[macro_export] +macro_rules! cfg_if { + // match if/else chains with a final `else` + ($( + if #[cfg($meta:meta)] { $($tokens:tt)* } + ) else * else { + $($tokens2:tt)* + }) => { + $crate::cfg_if! { + @__items + () ; + $( ( ($meta) ($($tokens)*) ), )* + ( () ($($tokens2)*) ), + } + }; + + // match if/else chains lacking a final `else` + ( + if #[cfg($i_met:meta)] { $($i_tokens:tt)* } + $( + else if #[cfg($e_met:meta)] { $($e_tokens:tt)* } + )* + ) => { + $crate::cfg_if! { + @__items + () ; + ( ($i_met) ($($i_tokens)*) ), + $( ( ($e_met) ($($e_tokens)*) ), )* + ( () () ), + } + }; + + // Internal and recursive macro to emit all the items + // + // Collects all the negated cfgs in a list at the beginning and after the + // semicolon is all the remaining items + (@__items ($($not:meta,)*) ; ) => {}; + (@__items ($($not:meta,)*) ; ( ($($m:meta),*) ($($tokens:tt)*) ), $($rest:tt)*) => { + // Emit all items within one block, applying an appropriate #[cfg]. The + // #[cfg] will require all `$m` matchers specified and must also negate + // all previous matchers. + #[cfg(all($($m,)* not(any($($not),*))))] $crate::cfg_if! { @__identity $($tokens)* } + + // Recurse to emit all other items in `$rest`, and when we do so add all + // our `$m` matchers to the list of `$not` matchers as future emissions + // will have to negate everything we just matched as well. + $crate::cfg_if! { @__items ($($not,)* $($m,)*) ; $($rest)* } + }; + + // Internal macro to make __apply work out right for different match types, + // because of how macros matching/expand stuff. + (@__identity $($tokens:tt)*) => { + $($tokens)* + }; +} + +#[cfg(test)] +mod tests { + cfg_if! { + if #[cfg(test)] { + use core::option::Option as Option2; + fn works1() -> Option2<u32> { Some(1) } + } else { + fn works1() -> Option<u32> { None } + } + } + + cfg_if! { + if #[cfg(foo)] { + fn works2() -> bool { false } + } else if #[cfg(test)] { + fn works2() -> bool { true } + } else { + fn works2() -> bool { false } + } + } + + cfg_if! { + if #[cfg(foo)] { + fn works3() -> bool { false } + } else { + fn works3() -> bool { true } + } + } + + cfg_if! { + if #[cfg(test)] { + use core::option::Option as Option3; + fn works4() -> Option3<u32> { Some(1) } + } + } + + cfg_if! { + if #[cfg(foo)] { + fn works5() -> bool { false } + } else if #[cfg(test)] { + fn works5() -> bool { true } + } + } + + #[test] + fn it_works() { + assert!(works1().is_some()); + assert!(works2()); + assert!(works3()); + assert!(works4().is_some()); + assert!(works5()); + } + + #[test] + #[allow(clippy::assertions_on_constants)] + fn test_usage_within_a_function() { + cfg_if! {if #[cfg(debug_assertions)] { + // we want to put more than one thing here to make sure that they + // all get configured properly. + assert!(cfg!(debug_assertions)); + assert_eq!(4, 2+2); + } else { + assert!(works1().is_some()); + assert_eq!(10, 5+5); + }} + } + + trait Trait { + fn blah(&self); + } + + #[allow(dead_code)] + struct Struct; + + impl Trait for Struct { + cfg_if! { + if #[cfg(feature = "blah")] { + fn blah(&self) { + unimplemented!(); + } + } else { + fn blah(&self) { + unimplemented!(); + } + } + } + } +} |