Rollup merge of rust-lang#68976 - ecstatic-morse:const-non-zero, r=dtolnay

Make `num::NonZeroX::new` an unstable `const fn`

cc rust-lang#53718

These require `#[feature(const_if_match)]`, meaning they must remain unstable for the time being.

Author: Dylan-DPC

src/libcore/num/mod.rs

@@ -69,8 +69,9 @@ assert_eq!(size_of::<Option<core::num::", stringify!($Ty), ">>(), size_of::<", s
 
                 /// Creates a non-zero if the given value is not zero.
                 #[$stability]
+                #[rustc_const_unstable(feature = "const_nonzero_int_methods", issue = "53718")]
                 #[inline]
-                pub fn new(n: $Int) -> Option<Self> {
+                pub const fn new(n: $Int) -> Option<Self> {
                     if n != 0 {
                         // SAFETY: we just checked that there's no `0`
                         Some(unsafe { Self(n) })

src/test/ui/consts/const-nonzero.rs

@@ -1,9 +1,18 @@
-// build-pass (FIXME(62277): could be check-pass?)
+// run-pass
+
+#![feature(const_nonzero_int_methods)]
 
 use std::num::NonZeroU8;
 
 const X: NonZeroU8 = unsafe { NonZeroU8::new_unchecked(5) };
 const Y: u8 = X.get();
 
+const ZERO: Option<NonZeroU8> = NonZeroU8::new(0);
+const ONE: Option<NonZeroU8> = NonZeroU8::new(1);
+
 fn main() {
+    assert_eq!(Y, 5);
+
+    assert!(ZERO.is_none());
+    assert_eq!(ONE.unwrap().get(), 1);
 }