1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
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!();
}
}
}
}
}
|
