linux-kernel - Re: [PATCH v7 7/7] rust: enable `clippy::ref_as

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Message-ID: <CAJ-ks9m96vf_HxttuopuC_UfNGJbHHNdEGS2er6nZZG38pe3HQ@mail.gmail.com>
Date: Thu, 27 Mar 2025 10:15:36 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, Miguel Ojeda <ojeda@...nel.org>, 
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Subject: Re: [PATCH v7 7/7] rust: enable `clippy::ref_as_ptr` lint

On Wed, Mar 26, 2025 at 6:15 PM Benno Lossin <benno.lossin@...ton.me> wrote:
>
> On Wed Mar 26, 2025 at 11:09 PM CET, Tamir Duberstein wrote:
> > On Wed, Mar 26, 2025 at 5:09 PM Benno Lossin <benno.lossin@...ton.me> wrote:
> >> On Wed Mar 26, 2025 at 8:06 PM CET, Tamir Duberstein wrote:
> >> > On Wed, Mar 26, 2025 at 1:36 PM Benno Lossin <benno.lossin@...ton.me> wrote:
> >> >> On Wed Mar 26, 2025 at 5:57 PM CET, Tamir Duberstein wrote:
> >> >> >
> >> >> > Yeah, we should do this - but again: not relevant in this discussion.
> >> >>
> >> >> I think it's pretty relevant.
> >> >
> >> > It's not relevant because we're no longer talking about transmuting
> >> > pointer to pointer. The two options are:
> >> > 1. transmute reference to reference.
> >> > 2. coerce reference to pointer, `as` cast pointer to pointer (triggers
> >> > `ptr_as_ptr`), reborrow pointer to reference.
> >> >
> >> > If anyone can help me understand why (2) is better than (1), I'd
> >> > certainly appreciate it.
> >>
> >> I am very confident that (2) is correct. With (1) I'm not sure (see
> >> above), so that's why I mentioned it.
> >
> > Can you help me understand why you're confident about (2) but not (1)?
>
> My explanation from above explains why I'm not confident about (1):
>
>     For ptr-to-int transmutes, I know that they will probably remove
>     provenance, hence I am a bit cautious about using them for ptr-to-ptr or
>     ref-to-ref.
>
> The reason I'm confident about (2) is that that is the canonical way to
> cast the type of a reference pointing to an `!Sized` value.

Do you have a citation, other than the transmute doc?