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Improve const_assert 

Now that we can panic in const context we can improve the `const_assert`
macro by adding a message string.

Original idea by Kix:

  https://github.com/rust-bitcoin/rust-bitcoin/pull/2972#discussion_r1726328228
This commit is contained in:
Tobin C. Harding 2024-08-22 17:40:27 +10:00
parent cfb53c7866
commit 3c7c8c44b6
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3 changed files with 17 additions and 7 deletions
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7
bitcoin/src/lib.rs
View File

@ -37,8 +37,6 @@
#![allow(clippy::manual_range_contains)] // More readable than clippy's format. #![allow(clippy::manual_range_contains)] // More readable than clippy's format.
#![allow(clippy::needless_borrows_for_generic_args)] // https://github.com/rust-lang/rust-clippy/issues/12454 #![allow(clippy::needless_borrows_for_generic_args)] // https://github.com/rust-lang/rust-clippy/issues/12454
use core::mem;
// We only support machines with index size of 4 bytes or more. // We only support machines with index size of 4 bytes or more.
// //
// Bitcoin consensus code relies on being able to have containers with more than 65536 (2^16) // Bitcoin consensus code relies on being able to have containers with more than 65536 (2^16)
@ -49,7 +47,10 @@ use core::mem;
// does not equal index size. // does not equal index size.
// //
// ref: https://github.com/rust-bitcoin/rust-bitcoin/pull/2929#discussion_r1661848565 // ref: https://github.com/rust-bitcoin/rust-bitcoin/pull/2929#discussion_r1661848565
internals::const_assert!(mem::size_of::<usize>() >= 4); internals::const_assert!(
core::mem::size_of::<usize>() >= 4;
"platforms that have usize less than 32 bits are not supported"
);
#[cfg(bench)] #[cfg(bench)]
extern crate test; extern crate test;

5
internals/src/lib.rs
View File

@ -63,7 +63,10 @@ impl_to_u64!(u8, u16, u32, u64);
impl ToU64 for usize { impl ToU64 for usize {
fn to_u64(self) -> u64 { fn to_u64(self) -> u64 {
crate::const_assert!(core::mem::size_of::<usize>() <= 8); crate::const_assert!(
core::mem::size_of::<usize>() <= 8;
"platforms that have usize larger than 64 bits are not supported"
);
self as u64 self as u64
} }
} }

12
internals/src/macros.rs
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@ -139,9 +139,15 @@ macro_rules! debug_from_display {
/// Asserts a boolean expression at compile time. /// Asserts a boolean expression at compile time.
#[macro_export] #[macro_export]
macro_rules! const_assert { macro_rules! const_assert {
($x:expr) => { ($x:expr $(; $message:expr)?) => {
const _: [(); 0 - !$x as usize] = []; const _: bool = {
}; if !$x {
// We can't use formatting in const, only concating literals.
panic!(concat!("assertion ", stringify!($x), " failed" $(, ": ", $message)?))
}
$x
};
}
} }
/// Derives `From<core::convert::Infallible>` for the given type. /// Derives `From<core::convert::Infallible>` for the given type.