hashbrown/macros.rs
1// See the cfg-if crate.
2#[allow(unused_macro_rules)]
3macro_rules! cfg_if {
4 // match if/else chains with a final `else`
5 ($(
6 if #[cfg($($meta:meta),*)] { $($it:item)* }
7 ) else * else {
8 $($it2:item)*
9 }) => {
10 cfg_if! {
11 @__items
12 () ;
13 $( ( ($($meta),*) ($($it)*) ), )*
14 ( () ($($it2)*) ),
15 }
16 };
17
18 // match if/else chains lacking a final `else`
19 (
20 if #[cfg($($i_met:meta),*)] { $($i_it:item)* }
21 $(
22 else if #[cfg($($e_met:meta),*)] { $($e_it:item)* }
23 )*
24 ) => {
25 cfg_if! {
26 @__items
27 () ;
28 ( ($($i_met),*) ($($i_it)*) ),
29 $( ( ($($e_met),*) ($($e_it)*) ), )*
30 ( () () ),
31 }
32 };
33
34 // Internal and recursive macro to emit all the items
35 //
36 // Collects all the negated cfgs in a list at the beginning and after the
37 // semicolon is all the remaining items
38 (@__items ($($not:meta,)*) ; ) => {};
39 (@__items ($($not:meta,)*) ; ( ($($m:meta),*) ($($it:item)*) ), $($rest:tt)*) => {
40 // Emit all items within one block, applying an appropriate #[cfg]. The
41 // #[cfg] will require all `$m` matchers specified and must also negate
42 // all previous matchers.
43 cfg_if! { @__apply cfg(all($($m,)* not(any($($not),*)))), $($it)* }
44
45 // Recurse to emit all other items in `$rest`, and when we do so add all
46 // our `$m` matchers to the list of `$not` matchers as future emissions
47 // will have to negate everything we just matched as well.
48 cfg_if! { @__items ($($not,)* $($m,)*) ; $($rest)* }
49 };
50
51 // Internal macro to Apply a cfg attribute to a list of items
52 (@__apply $m:meta, $($it:item)*) => {
53 $(#[$m] $it)*
54 };
55}
56
57// Helper macro for specialization. This also helps avoid parse errors if the
58// default fn syntax for specialization changes in the future.
59#[cfg(feature = "nightly")]
60macro_rules! default_fn {
61 (#[$($a:tt)*] $($tt:tt)*) => {
62 #[$($a)*] default $($tt)*
63 }
64}
65#[cfg(not(feature = "nightly"))]
66macro_rules! default_fn {
67 ($($tt:tt)*) => {
68 $($tt)*
69 }
70}