Re: [PATCH v4 3/7] rust: alloc: add Vec::push_within_capacity

[Danilo Krummrich <dakr@kernel.org>]

On Tue, Apr 29, 2025 at 02:44:23PM +0000, Alice Ryhl wrote:
> 
> +    /// Appends an element to the back of the [`Vec`] instance without reallocating.
> +    ///
> +    /// Fails if the vector does not have capacity for the new element.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```
> +    /// let mut v = KVec::with_capacity(10, GFP_KERNEL)?;
> +    /// for i in 0..10 {
> +    ///     v.push_within_capacity(i).unwrap();

I'd prefer to make this

	v.push_within_capacity(i).map_err(|_| ENOMEM)?;

instead.

> +    /// }
> +    ///
> +    /// assert!(v.push_within_capacity(10).is_err());
> +    /// # Ok::<(), Error>(())
> +    /// ```
> +    pub fn push_within_capacity(&mut self, v: T) -> Result<(), T> {
> +        if self.len() < self.capacity() {
> +            // SAFETY: The length is less than the capacity.
> +            unsafe { self.push_within_capacity_unchecked(v) };
> +            Ok(())
> +        } else {
> +            Err(v)
> +        }
> +    }
>  
> +    /// Appends an element to the back of the [`Vec`] instance without reallocating.
> +    ///
> +    /// # Safety
> +    ///
> +    /// The length must be less than the capacity.

NIT: Maybe be more specific and say:

"`self.len()` must be less than `self.capacity()`."