Re: [PATCH] rust: alloc: allow different error types in `KBox::pin_slice`

[Alice Ryhl <aliceryhl@google.com>]

On Sat, Feb 14, 2026 at 03:56:43PM +0100, Danilo Krummrich wrote:
> On Sat Feb 14, 2026 at 3:40 PM CET, Benno Lossin wrote:
> > On Sat Feb 14, 2026 at 3:17 PM CET, Danilo Krummrich wrote:
> >> On Sat Feb 14, 2026 at 2:28 PM CET, Andreas Hindborg wrote:
> >>> @@ -333,24 +333,31 @@ pub fn pin(x: T, flags: Flags) -> Result<Pin<Box<T, A>>, AllocError>
> >>>      /// assert_eq!(s[3].d.lock().a, 20);
> >>>      /// # Ok::<(), Error>(())
> >>>      /// ```
> >>> -    pub fn pin_slice<Func, Item, E>(
> >>> +    pub fn pin_slice<Func, Item, E, E2>(
> >>>          mut init: Func,
> >>>          len: usize,
> >>>          flags: Flags,
> >>>      ) -> Result<Pin<Box<[T], A>>, E>
> >>>      where
> >>>          Func: FnMut(usize) -> Item,
> >>> -        Item: PinInit<T, E>,
> >>> -        E: From<AllocError>,
> >>
> >> I think we should keep this bound and just add:
> >
> > The `Into` trait bounds are the idiomatic ones for functions consuming
> > things. See https://doc.rust-lang.org/std/convert/trait.Into.html:
> >
> >     Prefer using Into over From when specifying trait bounds on a
> >     generic function to ensure that types that only implement Into can
> >     be used as well.
> 
> Yeah, but isn't this only because of [1], which does not apply to the kernel
> because our minimum compiler version is 1.78 anyways?
> 
> I.e. are there any cases where we can't implement From in the kernel and have to
> fall back to Into?

Probably not, but it's still best practice to use Into over From when
specifying trait bounds.

Alice