Re: [PATCH 2/2] rust: pin-init: add pin projections to `#[pin_data]`

[Alice Ryhl <aliceryhl@google.com>]

On Wed, Sep 10, 2025 at 12:38 PM Benno Lossin <lossin@kernel.org> wrote:
>
> On Wed Sep 10, 2025 at 12:23 PM CEST, Alice Ryhl wrote:
> > On Fri, Sep 5, 2025 at 7:12 PM Benno Lossin <lossin@kernel.org> wrote:
> >> +    (make_pin_projections:
> >> +        @vis($vis:vis),
> >> +        @name($name:ident),
> >> +        @impl_generics($($impl_generics:tt)*),
> >> +        @ty_generics($($ty_generics:tt)*),
> >> +        @decl_generics($($decl_generics:tt)*),
> >> +        @where($($whr:tt)*),
> >> +        @pinned($($(#[$($p_attr:tt)*])* $pvis:vis $p_field:ident : $p_type:ty),* $(,)?),
> >> +        @not_pinned($($(#[$($attr:tt)*])* $fvis:vis $field:ident : $type:ty),* $(,)?),
> >> +    ) => {
> >> +        $crate::macros::paste! {
> >> +            #[doc(hidden)]
> >> +            $vis struct [< $name Projection >] <'__pin, $($decl_generics)*> {
> >
> > I'm not sure we want $vis here. That's the visibility of the original
> > struct, but I don't think we want it to be pub just because the struct
> > is.
>
> Why shouldn't it be pub if the original is pub? I don't really
> understand the concern, since the fields themselves will still have the
> correct visibility. Additionally, there is the `___pin_phantom_data`
> field that's always private, so you cannot construct this outside of the
> module.

I mean, for instance, it's going to mean that every single struct that
wraps Opaque in a private field will get a useless pub function called
project that will appear in html docs.

Pin-project limits the visibility to pub(crate) when the struct is pub.

Alice