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const: make ptr.is_null() stop execution on ambiguity
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RalfJung committed Sep 8, 2024
1 parent 55f602f commit cc4242b
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Showing 2 changed files with 7 additions and 20 deletions.
10 changes: 6 additions & 4 deletions core/src/ptr/const_ptr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -40,15 +40,17 @@ impl<T: ?Sized> *const T {

#[inline]
const fn const_impl(ptr: *const u8) -> bool {
// Compare via a cast to a thin pointer, so fat pointers are only
// considering their "data" part for null-ness.
match (ptr).guaranteed_eq(null_mut()) {
None => false,
Some(res) => res,
// To remain maximally convervative, we stop execution when we don't
// know whether the pointer is null or not.
// We can *not* return `false` here, that would be unsound in `NonNull::new`!
None => panic!("null-ness of this pointer cannot be determined in const context"),
}
}

#[allow(unused_unsafe)]
// Compare via a cast to a thin pointer, so fat pointers are only
// considering their "data" part for null-ness.
const_eval_select((self as *const u8,), const_impl, runtime_impl)
}

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17 changes: 1 addition & 16 deletions core/src/ptr/mut_ptr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -33,22 +33,7 @@ impl<T: ?Sized> *mut T {
#[rustc_diagnostic_item = "ptr_is_null"]
#[inline]
pub const fn is_null(self) -> bool {
#[inline]
fn runtime_impl(ptr: *mut u8) -> bool {
ptr.addr() == 0
}

#[inline]
const fn const_impl(ptr: *mut u8) -> bool {
// Compare via a cast to a thin pointer, so fat pointers are only
// considering their "data" part for null-ness.
match (ptr).guaranteed_eq(null_mut()) {
None => false,
Some(res) => res,
}
}

const_eval_select((self as *mut u8,), const_impl, runtime_impl)
self.cast_const().is_null()
}

/// Casts to a pointer of another type.
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