Re: [PATCH v4 4/7] rust: alloc: add Vec::drain_all

[Danilo Krummrich <dakr@kernel.org>]

On Tue, Apr 29, 2025 at 02:44:24PM +0000, Alice Ryhl wrote:
> 
> +    /// Takes ownership of all items in this vector without consuming the allocation.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```
> +    /// let mut v = kernel::kvec![0, 1, 2, 3]?;
> +    ///
> +    /// for (i, j) in v.drain_all().enumerate() {
> +    ///     assert_eq!(i, j);
> +    /// }
> +    ///
> +    /// assert!(v.capacity() >= 4);
> +    /// # Ok::<(), Error>(())
> +    /// ```
> +    pub fn drain_all(&mut self) -> DrainAll<'_, T> {
> +        let len = self.len();
> +        // SAFETY: The length is not greater than the length.
> +        let elems = unsafe { self.dec_len(len) };

Maybe just pass self.len() directly and say that "`By the safety requirements of
`dec_len()`, self.len() is a valid argument".