Rollup merge of #119990 - reitermarkus:nonzero-type-alias, r=dtolnay

Add private `NonZero<T>` type alias.

According to step 2 suggested in #100428 (review).

This adds a private type alias for `NonZero<T>` so that some parts of the code can already start using `NonZero<T>` syntax.

Using `NonZero<T>` for `convert` and other parts which implement `From` doesn't work while it is a type alias, since this results in conflicting implementations.

library/core/src/num/mod.rs

@@ -59,6 +59,8 @@ pub use dec2flt::ParseFloatError;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use error::ParseIntError;
 
+pub(crate) use nonzero::NonZero;
+
 #[stable(feature = "nonzero", since = "1.28.0")]
 pub use nonzero::{NonZeroU128, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize};
 
@@ -482,7 +484,7 @@ impl u8 {
         Self = u8,
         ActualT = u8,
         SignedT = i8,
-        NonZeroT = NonZeroU8,
+        NonZeroT = NonZero<u8>,
         BITS = 8,
         MAX = 255,
         rot = 2,
@@ -1097,7 +1099,7 @@ impl u16 {
         Self = u16,
         ActualT = u16,
         SignedT = i16,
-        NonZeroT = NonZeroU16,
+        NonZeroT = NonZero<u16>,
         BITS = 16,
         MAX = 65535,
         rot = 4,
@@ -1146,7 +1148,7 @@ impl u32 {
         Self = u32,
         ActualT = u32,
         SignedT = i32,
-        NonZeroT = NonZeroU32,
+        NonZeroT = NonZero<u32>,
         BITS = 32,
         MAX = 4294967295,
         rot = 8,
@@ -1170,7 +1172,7 @@ impl u64 {
         Self = u64,
         ActualT = u64,
         SignedT = i64,
-        NonZeroT = NonZeroU64,
+        NonZeroT = NonZero<u64>,
         BITS = 64,
         MAX = 18446744073709551615,
         rot = 12,
@@ -1194,7 +1196,7 @@ impl u128 {
         Self = u128,
         ActualT = u128,
         SignedT = i128,
-        NonZeroT = NonZeroU128,
+        NonZeroT = NonZero<u128>,
         BITS = 128,
         MAX = 340282366920938463463374607431768211455,
         rot = 16,
@@ -1220,7 +1222,7 @@ impl usize {
         Self = usize,
         ActualT = u16,
         SignedT = isize,
-        NonZeroT = NonZeroUsize,
+        NonZeroT = NonZero<usize>,
         BITS = 16,
         MAX = 65535,
         rot = 4,
@@ -1245,7 +1247,7 @@ impl usize {
         Self = usize,
         ActualT = u32,
         SignedT = isize,
-        NonZeroT = NonZeroUsize,
+        NonZeroT = NonZero<usize>,
         BITS = 32,
         MAX = 4294967295,
         rot = 8,
@@ -1270,7 +1272,7 @@ impl usize {
         Self = usize,
         ActualT = u64,
         SignedT = isize,
-        NonZeroT = NonZeroUsize,
+        NonZeroT = NonZero<usize>,
         BITS = 64,
         MAX = 18446744073709551615,
         rot = 12,

library/core/src/num/nonzero.rs

@@ -8,6 +8,69 @@ use super::from_str_radix;
 use super::{IntErrorKind, ParseIntError};
 use crate::intrinsics;
 
+mod private {
+    #[unstable(
+        feature = "nonzero_internals",
+        reason = "implementation detail which may disappear or be replaced at any time",
+        issue = "none"
+    )]
+    #[const_trait]
+    pub trait Sealed {}
+}
+
+/// A marker trait for primitive types which can be zero.
+///
+/// This is an implementation detail for [`NonZero<T>`](NonZero) which may disappear or be replaced at any time.
+#[unstable(
+    feature = "nonzero_internals",
+    reason = "implementation detail which may disappear or be replaced at any time",
+    issue = "none"
+)]
+#[const_trait]
+pub trait ZeroablePrimitive: Sized + Copy + private::Sealed {
+    type NonZero;
+}
+
+#[unstable(
+    feature = "nonzero_internals",
+    reason = "implementation detail which may disappear or be replaced at any time",
+    issue = "none"
+)]
+pub(crate) type NonZero<T> = <T as ZeroablePrimitive>::NonZero;
+
+macro_rules! impl_zeroable_primitive {
+    ($NonZero:ident ( $primitive:ty )) => {
+        #[unstable(
+            feature = "nonzero_internals",
+            reason = "implementation detail which may disappear or be replaced at any time",
+            issue = "none"
+        )]
+        impl const private::Sealed for $primitive {}
+
+        #[unstable(
+            feature = "nonzero_internals",
+            reason = "implementation detail which may disappear or be replaced at any time",
+            issue = "none"
+        )]
+        impl const ZeroablePrimitive for $primitive {
+            type NonZero = $NonZero;
+        }
+    };
+}
+
+impl_zeroable_primitive!(NonZeroU8(u8));
+impl_zeroable_primitive!(NonZeroU16(u16));
+impl_zeroable_primitive!(NonZeroU32(u32));
+impl_zeroable_primitive!(NonZeroU64(u64));
+impl_zeroable_primitive!(NonZeroU128(u128));
+impl_zeroable_primitive!(NonZeroUsize(usize));
+impl_zeroable_primitive!(NonZeroI8(i8));
+impl_zeroable_primitive!(NonZeroI16(i16));
+impl_zeroable_primitive!(NonZeroI32(i32));
+impl_zeroable_primitive!(NonZeroI64(i64));
+impl_zeroable_primitive!(NonZeroI128(i128));
+impl_zeroable_primitive!(NonZeroIsize(isize));
+
 macro_rules! impl_nonzero_fmt {
     ( #[$stability: meta] ( $( $Trait: ident ),+ ) for $Ty: ident ) => {
         $(

library/core/src/num/uint_macros.rs

@@ -3,7 +3,7 @@ macro_rules! uint_impl {
         Self = $SelfT:ty,
         ActualT = $ActualT:ident,
         SignedT = $SignedT:ident,
-        NonZeroT = $NonZeroT:ident,
+        NonZeroT = $NonZeroT:ty,
 
         // There are all for use *only* in doc comments.
         // As such, they're all passed as literals -- passing them as a string
@@ -842,6 +842,7 @@ macro_rules! uint_impl {
                       without modifying the original"]
         #[inline]
         pub const fn checked_ilog2(self) -> Option<u32> {
+            // FIXME: Simply use `NonZero::new` once it is actually generic.
             if let Some(x) = <$NonZeroT>::new(self) {
                 Some(x.ilog2())
             } else {
@@ -864,6 +865,7 @@ macro_rules! uint_impl {
                       without modifying the original"]
         #[inline]
         pub const fn checked_ilog10(self) -> Option<u32> {
+            // FIXME: Simply use `NonZero::new` once it is actually generic.
             if let Some(x) = <$NonZeroT>::new(self) {
                 Some(x.ilog10())
             } else {

library/core/src/slice/iter.rs

@@ -12,7 +12,7 @@ use crate::iter::{
 };
 use crate::marker::PhantomData;
 use crate::mem::{self, SizedTypeProperties};
-use crate::num::NonZeroUsize;
+use crate::num::{NonZero, NonZeroUsize};
 use crate::ptr::{self, invalid, invalid_mut, NonNull};
 
 use super::{from_raw_parts, from_raw_parts_mut};
@@ -1305,12 +1305,12 @@ forward_iterator! { RSplitNMut: T, &'a mut [T] }
 #[must_use = "iterators are lazy and do nothing unless consumed"]
 pub struct Windows<'a, T: 'a> {
     v: &'a [T],
-    size: NonZeroUsize,
+    size: NonZero<usize>,
 }
 
 impl<'a, T: 'a> Windows<'a, T> {
     #[inline]
-    pub(super) fn new(slice: &'a [T], size: NonZeroUsize) -> Self {
+    pub(super) fn new(slice: &'a [T], size: NonZero<usize>) -> Self {
         Self { v: slice, size }
     }
 }