add zeroed() & Zeroable::zeroed() functions

`zeroed()` returns a zeroed out value of a sized type implementing
`Zeroable`.

The function is added as a free standing function, in addition to an
associated function on `Zeroable`, because then it can be marked `const`
(functions in traits can't be const at the moment).

Signed-off-by: Benno Lossin <lossin@kernel.org>

Author: BennoLossin

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `unsafe fn cast_[pin_]init()` functions to unsafely change the initialized type of an initializer
 - `impl<T, E> [Pin]Init<T, E> for Result<T, E>`, so results are now (pin-)initializers
 - add `Zeroable::init_zeroed()` delegating to `init_zeroed()`
+- add new `zeroed()`, a safe version of `mem::zeroed()` and also provide it via `Zeroable::zeroed()`
 
 ### Changed
 

src/lib.rs

@@ -1506,6 +1506,33 @@ pub unsafe trait Zeroable {
     {
         init_zeroed()
     }
+
+    /// Create a `Self` consisting of all zeroes.
+    ///
+    /// Whenever a type implements [`Zeroable`], this function should be preferred over
+    /// [`core::mem::zeroed()`] or using `MaybeUninit<T>::zeroed().assume_init()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use pin_init::{Zeroable, zeroed};
+    ///
+    /// #[derive(Zeroable)]
+    /// struct Point {
+    ///     x: u32,
+    ///     y: u32,
+    /// }
+    ///
+    /// let point: Point = zeroed();
+    /// assert_eq!(point.x, 0);
+    /// assert_eq!(point.y, 0);
+    /// ```
+    fn zeroed() -> Self
+    where
+        Self: Sized,
+    {
+        zeroed()
+    }
 }
 
 /// Marker trait for types that allow `Option<Self>` to be set to all zeroes in order to write
@@ -1534,6 +1561,31 @@ pub fn init_zeroed<T: Zeroable>() -> impl Init<T> {
     }
 }
 
+/// Create a `T` consisting of all zeroes.
+///
+/// Whenever a type implements [`Zeroable`], this function should be preferred over
+/// [`core::mem::zeroed()`] or using `MaybeUninit<T>::zeroed().assume_init()`.
+///
+/// # Examples
+///
+/// ```
+/// use pin_init::{Zeroable, zeroed};
+///
+/// #[derive(Zeroable)]
+/// struct Point {
+///     x: u32,
+///     y: u32,
+/// }
+///
+/// let point: Point = zeroed();
+/// assert_eq!(point.x, 0);
+/// assert_eq!(point.y, 0);
+/// ```
+pub const fn zeroed<T: Zeroable>() -> T {
+    // SAFETY:By the type invariants of `Zeroable`, all zeroes is a valid bit pattern for `T`.
+    unsafe { core::mem::zeroed() }
+}
+
 macro_rules! impl_zeroable {
     ($($({$($generics:tt)*})? $t:ty, )*) => {
         // SAFETY: Safety comments written in the macro invocation.