inconceivable/
lib.rs

1/*
2 * Copyright (c) 2020 William Cody Laeder
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a copy
5 * of this software and associated documentation files (the "Software"), to deal
6 * in the Software without restriction, including without limitation the rights
7 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
8 * copies of the Software, and to permit persons to whom the Software is
9 * furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice shall be included in all
12 * copies or substantial portions of the Software.
13 *
14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
15 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
16 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
17 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
18 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
19 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
20 * SOFTWARE.
21 *
22 */
23#![cfg_attr(not(feature = "std"), no_std)]
24
25/// inconceivable is a macro which closely parallels `std::unreachable`, or `std::panic`.
26///
27/// The primary difference is that when this crate is
28/// configured with the `ub_inconceivable` option it will emit
29/// the `core::hint::unreachable_unchecked` to hint
30/// for the compiler to understand a condition should
31/// never occur.
32///
33/// Generally compilers assume UB won't happen. This macro
34/// offers the "best of both worlds", it provides a solid
35/// way of asserting/testing behavior in debug builds, and
36/// no cost in properly configured release builds.
37#[macro_export]
38macro_rules! inconceivable {
39    () => {
40        {
41        #[cfg(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27", not(feature = "std")))]
42        {
43            unsafe{ core::hint::unreachable_unchecked() }
44        }
45
46        #[cfg(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27", feature = "std"))]
47        {
48            unsafe{ std::hint::unreachable_unchecked() }
49        }
50
51
52        #[cfg(not(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27")))]
53        {
54            unreachable!()
55        }
56        }
57    };
58    ($msg: expr) => {
59        {
60        #[cfg(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27", not(feature = "std")))]
61        {
62            unsafe{ core::hint::unreachable_unchecked() }
63        }
64
65        #[cfg(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27", feature = "std"))]
66        {
67            unsafe{ std::hint::unreachable_unchecked() }
68        }
69
70
71        #[cfg(not(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27")))]
72        {
73            unreachable!($msg)
74        }
75        }
76    };
77    ($msg: expr,) => {
78        {
79        #[cfg(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27", not(feature = "std")))]
80        {
81            unsafe{ core::hint::unreachable_unchecked() }
82        }
83
84        #[cfg(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27", feature = "std"))]
85        {
86            unsafe{ std::hint::unreachable_unchecked() }
87        }
88
89
90        #[cfg(not(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27")))]
91        {
92            unreachable!($msg)
93        }
94        }
95    };
96    ($fmt: expr, $($arg:tt)*) => {
97        {
98        #[cfg(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27", not(feature = "std")))]
99        {
100            unsafe{ core::hint::unreachable_unchecked() }
101        }
102
103        #[cfg(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27", feature = "std"))]
104        {
105            unsafe{ std::hint::unreachable_unchecked() }
106        }
107
108        #[cfg(not(all(feature = "ub_inconceivable", feature = "RUSTC_VERSION_GE_1_27")))]
109        {
110            unreachable!($fmt, $($arg)*)
111        }
112        }
113    };
114}
115
116#[cfg(test)]
117mod test {
118
119    #[cfg(not(feature = "ub_inconceivable"))]
120    #[test]
121    #[should_panic]
122    fn test_expansion() {
123        match 10usize {
124            1 => {}
125            _ => inconceivable!(),
126        };
127    }
128}
inconceivable/lib.rs

inconceivable/
lib.rs
