# macros.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/libc-0.2.95/src/macros.rs`.
Keywords: rust, rustlang, rust-lang

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    /// 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.
    #[allow(unused_macros)]
    macro_rules! cfg_if {
        // match if/else chains with a final `else`
        ($(
            if #[cfg($($meta:meta),*)] { $($it:item)* }
        ) else * else {
            $($it2:item)*
        }) => {
            cfg_if! {
                @__items
                () ;
                $( ( ($($meta),*) ($($it)*) ), )*
                ( () ($($it2)*) ),
            }
        };

        // match if/else chains lacking a final `else`
        (
            if #[cfg($($i_met:meta),*)] { $($i_it:item)* }
            $(
                else if #[cfg($($e_met:meta),*)] { $($e_it:item)* }
            )*
        ) => {
            cfg_if! {
                @__items
                () ;
                ( ($($i_met),*) ($($i_it)*) ),
                $( ( ($($e_met),*) ($($e_it)*) ), )*
                ( () () ),
            }
        };

        // Internal and recursive macro to emit all the items
        //
        // Collects all the negated `cfg`s in a list at the beginning and after the
        // semicolon is all the remaining items
        (@__items ($($not:meta,)*) ; ) => {};
        (@__items ($($not:meta,)*) ; ( ($($m:meta),*) ($($it:item)*) ),
         $($rest:tt)*) => {
            // Emit all items within one block, applying an appropriate #[cfg]. The
            // #[cfg] will require all `$m` matchers specified and must also negate
            // all previous matchers.
            cfg_if! { @__apply cfg(all($($m,)* not(any($($not),*)))), $($it)* }

            // Recurse to emit all other items in `$rest`, and when we do so add all
            // our `$m` matchers to the list of `$not` matchers as future emissions
            // will have to negate everything we just matched as well.
            cfg_if! { @__items ($($not,)* $($m,)*) ; $($rest)* }
        };

        // Internal macro to Apply a cfg attribute to a list of items
        (@__apply $m:meta, $($it:item)*) => {
            $(#[$m] $it)*
        };
    }

    #[allow(unused_macros)]
    macro_rules! s {
        ($($(#[$attr:meta])* pub $t:ident $i:ident { $($field:tt)* })*) => ($(
            s!(it: $(#[$attr])* pub $t $i { $($field)* });
        )*);
        (it: $(#[$attr:meta])* pub union $i:ident { $($field:tt)* }) => (
            compile_error!("unions cannot derive extra traits, use s_no_extra_traits instead");
        );
        (it: $(#[$attr:meta])* pub struct $i:ident { $($field:tt)* }) => (
            __item! {
                #[repr(C)]
                #[cfg_attr(feature = "extra_traits", derive(Debug, Eq, Hash, PartialEq))]
                #[allow(deprecated)]
                $(#[$attr])*
                pub struct $i { $($field)* }
            }
            #[allow(deprecated)]
            impl ::Copy for $i {}
            #[allow(deprecated)]
            impl ::Clone for $i {
                fn clone(&self) -> $i { *self }
            }
        );
    }

    #[allow(unused_macros)]
    macro_rules! s_no_extra_traits {
        ($($(#[$attr:meta])* pub $t:ident $i:ident { $($field:tt)* })*) => ($(
            s_no_extra_traits!(it: $(#[$attr])* pub $t $i { $($field)* });
        )*);
        (it: $(#[$attr:meta])* pub union $i:ident { $($field:tt)* }) => (
            cfg_if! {
                if #[cfg(libc_union)] {
                    __item! {
                        #[repr(C)]
                        $(#[$attr])*
                        pub union $i { $($field)* }
                    }

                    impl ::Copy for $i {}
                    impl ::Clone for $i {
                        fn clone(&self) -> $i { *self }
                    }
                }
            }
        );
        (it: $(#[$attr:meta])* pub struct $i:ident { $($field:tt)* }) => (
            __item! {
                #[repr(C)]
                $(#[$attr])*
                pub struct $i { $($field)* }
            }
            #[allow(deprecated)]
            impl ::Copy for $i {}
            #[allow(deprecated)]
            impl ::Clone for $i {
                fn clone(&self) -> $i { *self }
            }
        );
    }

    #[allow(unused_macros)]
    macro_rules! e {
        ($($(#[$attr:meta])* pub enum $i:ident { $($field:tt)* })*) => ($(
            __item! {
                #[cfg_attr(feature = "extra_traits", derive(Debug, Eq, Hash, PartialEq))]
                $(#[$attr])*
                pub enum $i { $($field)* }
            }
            impl ::Copy for $i {}
            impl ::Clone for $i {
                fn clone(&self) -> $i { *self }
            }
        )*);
    }

    #[allow(unused_macros)]
    macro_rules! s_paren {
        ($($(#[$attr:meta])* pub struct $i:ident ( $($field:tt)* ); )* ) => ($(
            __item! {
                #[cfg_attr(feature = "extra_traits", derive(Debug, Eq, Hash, PartialEq))]
                $(#[$attr])*
                pub struct $i ( $($field)* );
            }
            impl ::Copy for $i {}
            impl ::Clone for $i {
                fn clone(&self) -> $i { *self }
            }
        )*);
    }

    // This is a pretty horrible hack to allow us to conditionally mark
    // some functions as 'const', without requiring users of this macro
    // to care about the "const-extern-fn" feature.
    //
    // When 'const-extern-fn' is enabled, we emit the captured 'const' keyword
    // in the expanded function.
    //
    // When 'const-extern-fn' is disabled, we always emit a plain 'pub unsafe extern fn'.
    // Note that the expression matched by the macro is exactly the same - this allows
    // users of this macro to work whether or not 'const-extern-fn' is enabled
    //
    // Unfortunately, we need to duplicate most of this macro between the 'cfg_if' blocks.
    // This is because 'const unsafe extern fn' won't even parse on older compilers,
    // so we need to avoid emitting it at all of 'const-extern-fn'.
    //
    // Specifically, moving the 'cfg_if' into the macro body will *not* work.
    // Doing so would cause the '#[cfg(feature = "const-extern-fn")]' to be emitted
    // into user code. The 'cfg' gate will not stop Rust from trying to parse the
    // 'pub const unsafe extern fn', so users would get a compiler error even when
    // the 'const-extern-fn' feature is disabled
    //
    // Note that users of this macro need to place 'const' in a weird position
    // (after the closing ')' for the arguments, but before the return type).
    // This was the only way I could satisfy the following two requirements:
    // 1. Avoid ambiguity errors from 'macro_rules!' (which happen when writing '$foo:ident fn'
    // 2. Allow users of this macro to mix 'pub fn foo' and 'pub const fn bar' within the same
    // 'f!' block
    cfg_if! {
        if #[cfg(libc_const_extern_fn)] {
            #[allow(unused_macros)]
            macro_rules! f {
                ($($(#[$attr:meta])* pub $({$constness:ident})* fn $i:ident(
                            $($arg:ident: $argty:ty),*
                ) -> $ret:ty {
                    $($body:stmt);*
                })*) => ($(
                    #[inline]
                    $(#[$attr])*
                    pub $($constness)* unsafe extern fn $i($($arg: $argty),*
                    ) -> $ret {
                        $($body);*
                    }
                )*)
            }

            #[allow(unused_macros)]
            macro_rules! safe_f {
                ($($(#[$attr:meta])* pub $({$constness:ident})* fn $i:ident(
                            $($arg:ident: $argty:ty),*
                ) -> $ret:ty {
                    $($body:stmt);*
                })*) => ($(
                    #[inline]
                    $(#[$attr])*
                    pub $($constness)* extern fn $i($($arg: $argty),*
                    ) -> $ret {
                        $($body);*
                    }
                )*)
            }

            #[allow(unused_macros)]
            macro_rules! const_fn {
                ($($(#[$attr:meta])* $({$constness:ident})* fn $i:ident(
                            $($arg:ident: $argty:ty),*
                ) -> $ret:ty {
                    $($body:stmt);*
                })*) => ($(
                    #[inline]
                    $(#[$attr])*
                    $($constness)* fn $i($($arg: $argty),*
                    ) -> $ret {
                        $($body);*
                    }
                )*)
            }

        } else {
            #[allow(unused_macros)]
            macro_rules! f {
                ($($(#[$attr:meta])* pub $({$constness:ident})* fn $i:ident(
                            $($arg:ident: $argty:ty),*
                ) -> $ret:ty {
                    $($body:stmt);*
                })*) => ($(
                    #[inline]
                    $(#[$attr])*
                    pub unsafe extern fn $i($($arg: $argty),*
                    ) -> $ret {
                        $($body);*
                    }
                )*)
            }

            #[allow(unused_macros)]
            macro_rules! safe_f {
                ($($(#[$attr:meta])* pub $({$constness:ident})* fn $i:ident(
                            $($arg:ident: $argty:ty),*
                ) -> $ret:ty {
                    $($body:stmt);*
                })*) => ($(
                    #[inline]
                    $(#[$attr])*
                    pub extern fn $i($($arg: $argty),*
                    ) -> $ret {
                        $($body);*
                    }
                )*)
            }

            #[allow(unused_macros)]
            macro_rules! const_fn {
                ($($(#[$attr:meta])* $({$constness:ident})* fn $i:ident(
                            $($arg:ident: $argty:ty),*
                ) -> $ret:ty {
                    $($body:stmt);*
                })*) => ($(
                    #[inline]
                    $(#[$attr])*
                    fn $i($($arg: $argty),*
                    ) -> $ret {
                        $($body);*
                    }
                )*)
            }
        }
    }

    #[allow(unused_macros)]
    macro_rules! __item {
        ($i:item) => {
            $i
        };
    }

    #[allow(unused_macros)]
    macro_rules! align_const {
        ($($(#[$attr:meta])*
           pub const $name:ident : $t1:ty
           = $t2:ident { $($field:tt)* };)*) => ($(
            #[cfg(libc_align)]
            $(#[$attr])*
            pub const $name : $t1 = $t2 {
                $($field)*
            };
            #[cfg(not(libc_align))]
            $(#[$attr])*
            pub const $name : $t1 = $t2 {
                $($field)*
                __align: [],
            };
        )*)
    }

    // This macro is used to deprecate items that should be accessed via the mach crate
    #[allow(unused_macros)]
    macro_rules! deprecated_mach {
        (pub const $id:ident: $ty:ty = $expr:expr;) => {
            #[deprecated(
                since = "0.2.55",
                note = "Use the `mach` crate instead",
            )]
            #[allow(deprecated)]
            pub const $id: $ty = $expr;
        };
        ($(pub const $id:ident: $ty:ty = $expr:expr;)*) => {
            $(
                deprecated_mach!(
                    pub const $id: $ty = $expr;
                );
            )*
        };
        (pub type $id:ident = $ty:ty;) => {
            #[deprecated(
                since = "0.2.55",
                note = "Use the `mach` crate instead",
            )]
            #[allow(deprecated)]
            pub type $id = $ty;
        };
        ($(pub type $id:ident = $ty:ty;)*) => {
            $(
                deprecated_mach!(
                    pub type $id = $ty;
                );
            )*
        }
    }