Re: [PATCH 03/11] rust: macros: convert `#[vtable]` macro to use `syn`

Gary Guo
2026-01-05T02:18:01Z

On Sun, 4 Jan 2026 18:44:43 -0500
Tamir Duberstein <tamird@gmail.com> wrote:

> On Thu, Dec 11, 2025 at 2:29 PM Gary Guo <gary@kernel.org> wrote:
> >
> > From: Gary Guo <gary@garyguo.net>
> >
> > `#[vtable]` is converted to use syn. This is more robust than the
> > previous heuristic-based searching of defined methods and functions.
> >
> > When doing so, the trait and impl are split into two code paths as the
> > types are distinct when parsed by `syn`.
> >
> > Signed-off-by: Gary Guo <gary@garyguo.net>
>
> Logic looks correct, but the duplication between handle_trait and
> handle_impl is unfortunate. I golfed on this a bit, see if you like
> it: https://github.com/tamird/linux/commit/8354c5a48769f5e1e52963d19ca57c31e5926b08.

I very much prefer the code to be separate. The trait and impl *should*
be different. It's just that they *look* similar.

Defining

const HAS_FOO: bool = false;

in trait is defining a new contract while providing *default* value,
while

const HAS_FOO: bool = true;

is implementing such contract with a specific value. They look the
same but I think the way `syn` treats them differently is justified.

I think the fact that existing code has a boolean and do different
things based on it is a good enough supporting reason to handle
different code path.

For some new `vtable` features that I am working on would require quite
different impl between the two.

Best,
Gary