Added assert_unsafe_precondition! check for NonZeroXxx::from_mut_unchecked

Author: SOF3

library/core/src/num/nonzero.rs

@@ -78,18 +78,6 @@ macro_rules! nonzero_integers {
                     }
                 }
 
-                /// Converts a primitive mutable reference to a non-zero mutable reference
-                /// if the referenced integer is not zero.
-                #[unstable(feature = "nonzero_from_mut", issue = "none")]
-                #[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) })
-                }
-
                 /// 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.
@@ -101,7 +89,26 @@ macro_rules! nonzero_integers {
                 #[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 { &mut *(n as *mut $Int as *mut Self) }
+                    unsafe {
+                        let n_alias = &mut *n;
+                        core::intrinsics::assert_unsafe_precondition!(
+                            concat!(stringify!($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 = "none")]
+                #[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) })
                 }