Re: [PATCH] rust: add C FFI types to the prelude

[Alice Ryhl]

On Mon, Apr 14, 2025 at 03:22:44PM +0200, Miguel Ojeda wrote:
> On Mon, Apr 14, 2025 at 10:47 AM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
> >
> > I wonder if it would make more sense to rephrase this section to first
> > say that rfl has type aliases for the C integer types called c_int and
> > so on, then mention that they are available in the prelude, and then
> > at the end of the section have a note that we don't use the type
> > aliases from core::ffi. I think focusing on how to use C integer
> > types, rather than technical details about how they are defined, is
> > more relevant for a reader who is just looking for coding guidelines.
> 
> Hmm... I see what you mean. In other places in the document, we start
> comparing with userspace Rust in order to establish a bit of context.
> But, more importantly, in this particular guideline I think it is
> quite important to say "do not use the usual ones", because they are
> actually different types, i.e. it is not just a style thing.
> 
> I have thought a couple times about perhaps changing the overall style
> of the document to have a 1-liner short summary on each guideline --
> some books do something like that consistently. And perhaps an
> example, before a longer description. So something like the following,
> which is closer to what you are suggesting:
> 
>     To refer to C types, use the FFI types (aliases) available from
> the `kernel` prelude, e.g. ``c_int``.
> 
>     For instance:
> 
>         ...
> 
>     Refer to them with a single segment path: e.g. ``c_char`` instead
> of ``ffi::c_char`` or ``kernel::ffi::c_char``.
> 
>     Do not use the `core::ffi::*` types -- they are different and some
> do not map to the correct C type.
> 
> But even with this style, I think it is important putting the last
> sentence in the "1-liner summary". Otherwise, someone may skip the
> guideline thinking "oh, OK, it is just a style thing about using just
> small paths, I will fix it later", without realizing they are actually
> different sets of types unless they read the entire section, no?

Hmm. Maybe, but I think having it at the end is okay. Could we catch
core::ffi with checkpath instead of clippy? Just search for core::ffi?

Alice