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assert_unsafe_precondition!: assume() the expression #106220

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assert_unsafe_precondition!: assume() the expression #106220

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19 changes: 12 additions & 7 deletions library/core/src/intrinsics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2274,22 +2274,27 @@ extern "rust-intrinsic" {
#[allow_internal_unstable(const_eval_select)] // permit this to be called in stably-const fn
macro_rules! assert_unsafe_precondition {
($name:expr, $([$($tt:tt)*])?($($i:ident:$ty:ty),*$(,)?) => $e:expr) => {
if cfg!(debug_assertions) {
{
// allow non_snake_case to allow capturing const generics
#[allow(non_snake_case)]
#[inline(always)]
fn runtime$(<$($tt)*>)?($($i:$ty),*) {
if !$e {
// don't unwind to reduce impact on code size
::core::panicking::panic_nounwind(
concat!("unsafe precondition(s) violated: ", $name)
);
if cfg!(debug_assertions) {
if !$e {
// don't unwind to reduce impact on code size
$crate::panicking::panic_nounwind(
concat!("unsafe precondition(s) violated: ", $name)
);
}
} else {
// SAFETY: the caller must ensure this
unsafe { $crate::intrinsics::assume($e) };
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The macro should only be invoked from unsafe contexts, so this explicit unsafe block is superfluous (and indeed potentially harmful, as it could introduce UB if the macro is accidentally invoked from a safe context).

Suggested change
unsafe { $crate::intrinsics::assume($e) };
$crate::intrinsics::assume($e);

}
}
#[allow(non_snake_case)]
const fn comptime$(<$($tt)*>)?($(_:$ty),*) {}

::core::intrinsics::const_eval_select(($($i,)*), comptime, runtime);
$crate::intrinsics::const_eval_select(($($i,)*), comptime, runtime);
}
};
}
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