Re: [PATCH v5 6/6] rust: use strict provenance APIs

[Boqun Feng <boqun.feng@gmail.com>]

On Mon, Mar 17, 2025 at 03:05:45PM -0400, Tamir Duberstein wrote:
> On Mon, Mar 17, 2025 at 2:50 PM Tamir Duberstein <tamird@gmail.com> wrote:
> >
> > On Mon, Mar 17, 2025 at 2:17 PM Boqun Feng <boqun.feng@gmail.com> wrote:
> > >
> > > Then we should fix clippy or how we set msrv rather adding the stub.
> > > @Miguel?
> >
> > I filed https://github.com/rust-lang/rust-clippy/issues/14425.
> 
> I don't think we can wait for that to be fixed, though. Usually clippy
> is distributed with rustc via rustup, so even if this is eventually
> fixed, all versions between 1.84.0 and the fix will need this
> workaround until MSRV is >= 1.84.0.

We need to take one step back to evalute this "workaround".

First, expose_provenance() and with_exposed_provenance{,_mut}() API are
clearly defined as equavilent to `as` operation [1]. Therefore, the
changes in this patch doing the conversion with expose_provenance() and
with_exposed_provenance{,_mut}() don't change anything related to
provenance in practice.

I do agree we want to use the explicit provenance API, but I don't think
we want to introduce some API that we know we will change them latter
when we bump the rustc minimal version. So the question is: are these
stubs what we want even though in the future our minimal rustc version
stablizes provenance API? If not, then the cost of this patch cannot
justify its benefits IMO.

Now let's also look into why we choose a msrv for clippy, I would guess
it's because we need to support all the versions of rustc starting at
1.78 and we want clippy to report a problem based on 1.78 even though
we're using a higher version of rustc. But for this particular case, we
use a feature that has already been stablized in a higher version of
rustc, which means the problem reported by clippy doesn't help us, nor
does it provide better code. Frankly speaking, I think we have other
ways to ensure the support of all rustc versions without a msrv for
clippy. If I was to choose, I would simply drop the msrv. But maybe I'm
missing something.

The point is tools should help us to write good and maintainable code,
we shouldn't introduce complicated structure of code just because some
tools fail to do its job.

[1]: https://doc.rust-lang.org/std/ptr/fn.with_exposed_provenance_mut.html

Regards,
Boqun