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Rollup merge of rust-lang#120521 - reitermarkus:generic-nonzero-const…
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…ructors, r=dtolnay,oli-obk

Make `NonZero` constructors generic.

This makes `NonZero` constructors generic, so that `NonZero::new` can be used without turbofish syntax.

Tracking issue: rust-lang#120257

~~I cannot figure out how to make this work with `const` traits. Not sure if I'm using it wrong or whether there's a bug:~~

```rust
101 |         if n == T::ZERO {
    |            ^^^^^^^^^^^^ expected `host`, found `true`
    |
    = note: expected constant `host`
               found constant `true`
```

r? ``@dtolnay``
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@matthiaskrgr
matthiaskrgr authored Feb 6, 2024
2 parents 4ee56d7 + aa3f1a2 commit 3ad89af
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Showing 2 changed files with 140 additions and 84 deletions.
181 changes: 97 additions & 84 deletions library/core/src/num/nonzero.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,7 @@ mod private {
pub trait ZeroablePrimitive: Sized + Copy + private::Sealed {}

macro_rules! impl_zeroable_primitive {
($NonZero:ident ( $primitive:ty )) => {
($primitive:ty) => {
#[unstable(
feature = "nonzero_internals",
reason = "implementation detail which may disappear or be replaced at any time",
Expand All @@ -52,18 +52,18 @@ macro_rules! impl_zeroable_primitive {
};
}

impl_zeroable_primitive!(NonZeroU8(u8));
impl_zeroable_primitive!(NonZeroU16(u16));
impl_zeroable_primitive!(NonZeroU32(u32));
impl_zeroable_primitive!(NonZeroU64(u64));
impl_zeroable_primitive!(NonZeroU128(u128));
impl_zeroable_primitive!(NonZeroUsize(usize));
impl_zeroable_primitive!(NonZeroI8(i8));
impl_zeroable_primitive!(NonZeroI16(i16));
impl_zeroable_primitive!(NonZeroI32(i32));
impl_zeroable_primitive!(NonZeroI64(i64));
impl_zeroable_primitive!(NonZeroI128(i128));
impl_zeroable_primitive!(NonZeroIsize(isize));
impl_zeroable_primitive!(u8);
impl_zeroable_primitive!(u16);
impl_zeroable_primitive!(u32);
impl_zeroable_primitive!(u64);
impl_zeroable_primitive!(u128);
impl_zeroable_primitive!(usize);
impl_zeroable_primitive!(i8);
impl_zeroable_primitive!(i16);
impl_zeroable_primitive!(i32);
impl_zeroable_primitive!(i64);
impl_zeroable_primitive!(i128);
impl_zeroable_primitive!(isize);

/// A value that is known not to equal zero.
///
Expand All @@ -83,6 +83,90 @@ impl_zeroable_primitive!(NonZeroIsize(isize));
#[rustc_diagnostic_item = "NonZero"]
pub struct NonZero<T: ZeroablePrimitive>(T);

impl<T> NonZero<T>
where
T: ZeroablePrimitive,
{
/// Creates a non-zero if the given value is not zero.
#[stable(feature = "nonzero", since = "1.28.0")]
#[rustc_const_stable(feature = "const_nonzero_int_methods", since = "1.47.0")]
#[rustc_allow_const_fn_unstable(const_refs_to_cell)]
#[must_use]
#[inline]
pub const fn new(n: T) -> Option<Self> {
// SAFETY: Memory layout optimization guarantees that `Option<NonZero<T>>` has
// the same layout and size as `T`, with `0` representing `None`.
unsafe { crate::mem::transmute_copy(&n) }
}

/// Creates a non-zero without checking whether the value is non-zero.
/// This results in undefined behaviour if the value is zero.
///
/// # Safety
///
/// The value must not be zero.
#[stable(feature = "nonzero", since = "1.28.0")]
#[rustc_const_stable(feature = "nonzero", since = "1.28.0")]
#[must_use]
#[inline]
pub const unsafe fn new_unchecked(n: T) -> Self {
match Self::new(n) {
Some(n) => n,
None => {
// SAFETY: The caller guarantees that `n` is non-zero, so this is unreachable.
unsafe {
crate::intrinsics::assert_unsafe_precondition!(
"NonZero::new_unchecked requires the argument to be non-zero",
() => false
);

crate::hint::unreachable_unchecked()
}
}
}
}

/// Converts a reference to a non-zero mutable reference
/// if the referenced value is not zero.
#[unstable(feature = "nonzero_from_mut", issue = "106290")]
#[must_use]
#[inline]
pub fn from_mut(n: &mut T) -> Option<&mut Self> {
// SAFETY: Memory layout optimization guarantees that `Option<NonZero<T>>` has
// the same layout and size as `T`, with `0` representing `None`.
let opt_n = unsafe { &mut *(n as *mut T as *mut Option<Self>) };

opt_n.as_mut()
}

/// Converts a mutable reference to a non-zero mutable reference
/// without checking whether the referenced value is non-zero.
/// This results in undefined behavior if the referenced value is zero.
///
/// # Safety
///
/// The referenced value must not be zero.
#[unstable(feature = "nonzero_from_mut", issue = "106290")]
#[must_use]
#[inline]
pub unsafe fn from_mut_unchecked(n: &mut T) -> &mut Self {
match Self::from_mut(n) {
Some(n) => n,
None => {
// SAFETY: The caller guarantees that `n` references a value that is non-zero, so this is unreachable.
unsafe {
crate::intrinsics::assert_unsafe_precondition!(
"NonZero::from_mut_unchecked requires the argument to dereference as non-zero",
() => false
);

crate::hint::unreachable_unchecked()
}
}
}
}
}

macro_rules! impl_nonzero_fmt {
( #[$stability: meta] ( $( $Trait: ident ),+ ) for $Ty: ident ) => {
$(
Expand All @@ -100,7 +184,6 @@ macro_rules! impl_nonzero_fmt {
macro_rules! nonzero_integer {
(
#[$stability:meta]
#[$const_new_unchecked_stability:meta]
Self = $Ty:ident,
Primitive = $signedness:ident $Int:ident,
$(UnsignedNonZero = $UnsignedNonZero:ident,)?
Expand Down Expand Up @@ -143,74 +226,6 @@ macro_rules! nonzero_integer {
pub type $Ty = NonZero<$Int>;

impl $Ty {
/// Creates a non-zero without checking whether the value is non-zero.
/// This results in undefined behaviour if the value is zero.
///
/// # Safety
///
/// The value must not be zero.
#[$stability]
#[$const_new_unchecked_stability]
#[must_use]
#[inline]
pub const unsafe fn new_unchecked(n: $Int) -> Self {
crate::panic::debug_assert_nounwind!(
n != 0,
concat!(stringify!($Ty), "::new_unchecked requires a non-zero argument")
);
// SAFETY: this is guaranteed to be safe by the caller.
unsafe {
Self(n)
}
}

/// Creates a non-zero if the given value is not zero.
#[$stability]
#[rustc_const_stable(feature = "const_nonzero_int_methods", since = "1.47.0")]
#[must_use]
#[inline]
pub const fn new(n: $Int) -> Option<Self> {
if n != 0 {
// SAFETY: we just checked that there's no `0`
Some(unsafe { Self(n) })
} else {
None
}
}

/// Converts a primitive mutable reference to a non-zero mutable reference
/// without checking whether the referenced value is non-zero.
/// This results in undefined behavior if `*n` is zero.
///
/// # Safety
/// The referenced value must not be currently zero.
#[unstable(feature = "nonzero_from_mut", issue = "106290")]
#[must_use]
#[inline]
pub unsafe fn from_mut_unchecked(n: &mut $Int) -> &mut Self {
// SAFETY: Self is repr(transparent), and the value is assumed to be non-zero.
unsafe {
let n_alias = &mut *n;
core::intrinsics::assert_unsafe_precondition!(
concat!(stringify!($Ty), "::from_mut_unchecked requires the argument to dereference as non-zero"),
(n_alias: &mut $Int) => *n_alias != 0
);
&mut *(n as *mut $Int as *mut Self)
}
}

/// Converts a primitive mutable reference to a non-zero mutable reference
/// if the referenced integer is not zero.
#[unstable(feature = "nonzero_from_mut", issue = "106290")]
#[must_use]
#[inline]
pub fn from_mut(n: &mut $Int) -> Option<&mut Self> {
// SAFETY: Self is repr(transparent), and the value is non-zero.
// As long as the returned reference is alive,
// the user cannot `*n = 0` directly.
(*n != 0).then(|| unsafe { &mut *(n as *mut $Int as *mut Self) })
}

/// Returns the value as a primitive type.
#[$stability]
#[inline]
Expand Down Expand Up @@ -724,7 +739,6 @@ macro_rules! nonzero_integer {
(Self = $Ty:ident, Primitive = unsigned $Int:ident $(,)?) => {
nonzero_integer! {
#[stable(feature = "nonzero", since = "1.28.0")]
#[rustc_const_stable(feature = "nonzero", since = "1.28.0")]
Self = $Ty,
Primitive = unsigned $Int,
UnsignedPrimitive = $Int,
Expand All @@ -735,7 +749,6 @@ macro_rules! nonzero_integer {
(Self = $Ty:ident, Primitive = signed $Int:ident, $($rest:tt)*) => {
nonzero_integer! {
#[stable(feature = "signed_nonzero", since = "1.34.0")]
#[rustc_const_stable(feature = "signed_nonzero", since = "1.34.0")]
Self = $Ty,
Primitive = signed $Int,
$($rest)*
Expand Down
43 changes: 43 additions & 0 deletions tests/ui/print_type_sizes/niche-filling.stdout
View file
Original file line number Diff line number Diff line change
@@ -1,3 +1,30 @@
print-type-size type: `core::fmt::rt::Placeholder`: 56 bytes, alignment: 8 bytes
print-type-size field `.precision`: 16 bytes
print-type-size field `.width`: 16 bytes
print-type-size field `.position`: 8 bytes
print-type-size field `.fill`: 4 bytes
print-type-size field `.flags`: 4 bytes
print-type-size field `.align`: 1 bytes
print-type-size end padding: 7 bytes
print-type-size type: `std::fmt::Arguments<'_>`: 48 bytes, alignment: 8 bytes
print-type-size field `.pieces`: 16 bytes
print-type-size field `.args`: 16 bytes
print-type-size field `.fmt`: 16 bytes
print-type-size type: `std::panic::Location<'_>`: 24 bytes, alignment: 8 bytes
print-type-size field `.file`: 16 bytes
print-type-size field `.line`: 4 bytes
print-type-size field `.col`: 4 bytes
print-type-size type: `core::fmt::rt::Count`: 16 bytes, alignment: 8 bytes
print-type-size discriminant: 8 bytes
print-type-size variant `Is`: 8 bytes
print-type-size field `.0`: 8 bytes
print-type-size variant `Param`: 8 bytes
print-type-size field `.0`: 8 bytes
print-type-size variant `Implied`: 0 bytes
print-type-size type: `std::option::Option<&[core::fmt::rt::Placeholder]>`: 16 bytes, alignment: 8 bytes
print-type-size variant `Some`: 16 bytes
print-type-size field `.0`: 16 bytes
print-type-size variant `None`: 0 bytes
print-type-size type: `IndirectNonZero`: 12 bytes, alignment: 4 bytes
print-type-size field `.nested`: 8 bytes
print-type-size field `.post`: 2 bytes
Expand Down Expand Up @@ -68,8 +95,18 @@ print-type-size type: `Union2<std::num::NonZero<u32>, u32>`: 4 bytes, alignment:
print-type-size variant `Union2`: 4 bytes
print-type-size field `.a`: 4 bytes
print-type-size field `.b`: 4 bytes, offset: 0 bytes, alignment: 4 bytes
print-type-size type: `std::mem::ManuallyDrop<std::option::Option<std::num::NonZero<u32>>>`: 4 bytes, alignment: 4 bytes
print-type-size field `.value`: 4 bytes
print-type-size type: `std::mem::MaybeUninit<std::option::Option<std::num::NonZero<u32>>>`: 4 bytes, alignment: 4 bytes
print-type-size variant `MaybeUninit`: 4 bytes
print-type-size field `.uninit`: 0 bytes
print-type-size field `.value`: 4 bytes
print-type-size type: `std::num::NonZero<u32>`: 4 bytes, alignment: 4 bytes
print-type-size field `.0`: 4 bytes
print-type-size type: `std::option::Option<std::num::NonZero<u32>>`: 4 bytes, alignment: 4 bytes
print-type-size variant `Some`: 4 bytes
print-type-size field `.0`: 4 bytes
print-type-size variant `None`: 0 bytes
print-type-size type: `Enum4<(), (), (), MyOption<u8>>`: 2 bytes, alignment: 1 bytes
print-type-size variant `Four`: 2 bytes
print-type-size field `.0`: 2 bytes
Expand Down Expand Up @@ -105,6 +142,12 @@ print-type-size type: `MyOption<std::cmp::Ordering>`: 1 bytes, alignment: 1 byte
print-type-size variant `Some`: 1 bytes
print-type-size field `.0`: 1 bytes
print-type-size variant `None`: 0 bytes
print-type-size type: `core::fmt::rt::Alignment`: 1 bytes, alignment: 1 bytes
print-type-size discriminant: 1 bytes
print-type-size variant `Left`: 0 bytes
print-type-size variant `Right`: 0 bytes
print-type-size variant `Center`: 0 bytes
print-type-size variant `Unknown`: 0 bytes
print-type-size type: `std::cmp::Ordering`: 1 bytes, alignment: 1 bytes
print-type-size discriminant: 1 bytes
print-type-size variant `Less`: 0 bytes
Expand Down

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