diff options
Diffstat (limited to 'library/core/src/macros/mod.rs')
| -rw-r--r-- | library/core/src/macros/mod.rs | 177 |
1 files changed, 88 insertions, 89 deletions
diff --git a/library/core/src/macros/mod.rs b/library/core/src/macros/mod.rs index c27be8d2ffd..123661b3588 100644 --- a/library/core/src/macros/mod.rs +++ b/library/core/src/macros/mod.rs @@ -168,6 +168,94 @@ pub macro assert_matches { }, } +/// A macro for defining `#[cfg]` match-like statements. +/// +/// It 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. +/// +/// Trailing `_` wildcard match arms are **optional** and they indicate a fallback branch when +/// all previous declarations do not evaluate to true. +/// +/// # Example +/// +/// ``` +/// #![feature(cfg_match)] +/// +/// cfg_match! { +/// cfg(unix) => { +/// fn foo() { /* unix specific functionality */ } +/// } +/// cfg(target_pointer_width = "32") => { +/// fn foo() { /* non-unix, 32-bit functionality */ } +/// } +/// _ => { +/// fn foo() { /* fallback implementation */ } +/// } +/// } +/// ``` +#[unstable(feature = "cfg_match", issue = "115585")] +#[rustc_diagnostic_item = "cfg_match"] +pub macro cfg_match { + // with a final wildcard + ( + $(cfg($initial_meta:meta) => { $($initial_tokens:item)* })+ + _ => { $($extra_tokens:item)* } + ) => { + cfg_match! { + @__items (); + $((($initial_meta) ($($initial_tokens)*)),)+ + (() ($($extra_tokens)*)), + } + }, + + // without a final wildcard + ( + $(cfg($extra_meta:meta) => { $($extra_tokens:item)* })* + ) => { + cfg_match! { + @__items (); + $((($extra_meta) ($($extra_tokens)*)),)* + } + }, + + // Internal and recursive macro to emit all the items + // + // Collects all the previous cfgs in a list at the beginning, so they can be + // negated. After the semicolon is all the remaining items. + (@__items ($($_:meta,)*);) => {}, + ( + @__items ($($no:meta,)*); + (($($yes:meta)?) ($($tokens:item)*)), + $($rest:tt,)* + ) => { + // Emit all items within one block, applying an appropriate #[cfg]. The + // #[cfg] will require all `$yes` matchers specified and must also negate + // all previous matchers. + #[cfg(all( + $($yes,)? + not(any($($no),*)) + ))] + cfg_match! { @__identity $($tokens)* } + + // Recurse to emit all other items in `$rest`, and when we do so add all + // our `$yes` matchers to the list of `$no` matchers as future emissions + // will have to negate everything we just matched as well. + cfg_match! { + @__items ($($no,)* $($yes,)?); + $($rest,)* + } + }, + + // Internal macro to make __apply work out right for different match types, + // because of how macros match/expand stuff. + (@__identity $($tokens:item)*) => { + $($tokens)* + } +} + /// Asserts that a boolean expression is `true` at runtime. /// /// This will invoke the [`panic!`] macro if the provided expression cannot be @@ -321,95 +409,6 @@ pub macro debug_assert_matches($($arg:tt)*) { } } -/// A macro for defining `#[cfg]` match-like statements. -/// -/// It 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. -/// -/// Trailing `_` wildcard match arms are **optional** and they indicate a fallback branch when -/// all previous declarations do not evaluate to true. -/// -/// # Example -/// -/// ``` -/// #![feature(cfg_match)] -/// -/// cfg_match! { -/// cfg(unix) => { -/// fn foo() { /* unix specific functionality */ } -/// } -/// cfg(target_pointer_width = "32") => { -/// fn foo() { /* non-unix, 32-bit functionality */ } -/// } -/// _ => { -/// fn foo() { /* fallback implementation */ } -/// } -/// } -/// ``` -#[macro_export] -#[unstable(feature = "cfg_match", issue = "115585")] -#[rustc_diagnostic_item = "cfg_match"] -macro_rules! cfg_match { - // with a final wildcard - ( - $(cfg($initial_meta:meta) => { $($initial_tokens:item)* })+ - _ => { $($extra_tokens:item)* } - ) => { - cfg_match! { - @__items (); - $((($initial_meta) ($($initial_tokens)*)),)+ - (() ($($extra_tokens)*)), - } - }; - - // without a final wildcard - ( - $(cfg($extra_meta:meta) => { $($extra_tokens:item)* })* - ) => { - cfg_match! { - @__items (); - $((($extra_meta) ($($extra_tokens)*)),)* - } - }; - - // Internal and recursive macro to emit all the items - // - // Collects all the previous cfgs in a list at the beginning, so they can be - // negated. After the semicolon is all the remaining items. - (@__items ($($_:meta,)*);) => {}; - ( - @__items ($($no:meta,)*); - (($($yes:meta)?) ($($tokens:item)*)), - $($rest:tt,)* - ) => { - // Emit all items within one block, applying an appropriate #[cfg]. The - // #[cfg] will require all `$yes` matchers specified and must also negate - // all previous matchers. - #[cfg(all( - $($yes,)? - not(any($($no),*)) - ))] - cfg_match! { @__identity $($tokens)* } - - // Recurse to emit all other items in `$rest`, and when we do so add all - // our `$yes` matchers to the list of `$no` matchers as future emissions - // will have to negate everything we just matched as well. - cfg_match! { - @__items ($($no,)* $($yes,)?); - $($rest,)* - } - }; - - // Internal macro to make __apply work out right for different match types, - // because of how macros match/expand stuff. - (@__identity $($tokens:item)*) => { - $($tokens)* - }; -} - /// Returns whether the given expression matches any of the given patterns. /// /// Like in a `match` expression, the pattern can be optionally followed by `if` |