1 files changed, 27 insertions, 2 deletions
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index e5672f8542f..7c6ded08bba 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -1734,20 +1734,45 @@ impl_is_zero!(char, |x| x == '\0');
 impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
 impl_is_zero!(f64, |x: f64| x.to_bits() == 0);
 
-unsafe impl<T: ?Sized> IsZero for *const T {
+unsafe impl<T> IsZero for *const T {
     #[inline]
     fn is_zero(&self) -> bool {
         (*self).is_null()
     }
 }
 
-unsafe impl<T: ?Sized> IsZero for *mut T {
+unsafe impl<T> IsZero for *mut T {
     #[inline]
     fn is_zero(&self) -> bool {
         (*self).is_null()
     }
 }
 
+// `Option<&T>`, `Option<&mut T>` and `Option<Box<T>>` are guaranteed to represent `None` as null.
+// For fat pointers, the bytes that would be the pointer metadata in the `Some` variant
+// are padding in the `None` variant, so ignoring them and zero-initializing instead is ok.
+
+unsafe impl<T: ?Sized> IsZero for Option<&T> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.is_none()
+    }
+}
+
+unsafe impl<T: ?Sized> IsZero for Option<&mut T> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.is_none()
+    }
+}
+
+unsafe impl<T: ?Sized> IsZero for Option<Box<T>> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.is_none()
+    }
+}
+
 
 ////////////////////////////////////////////////////////////////////////////////
 // Common trait implementations for Vec