rust: pin-init: replace clippy `expect` with `allow`

[PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Benno Lossin 1 month, 2 weeks ago

`clippy` has changed behavior in [1] (Rust 1.95) where it no longer
warns about the `let_and_return` lint when a comment is placed between
the let binding and the return expression. Nightly thus fails to build,
because the expectation is no longer fulfilled.

Thus replace the expectation with an `allow`.

Link: https://github.com/rust-lang/rust-clippy/pull/16461 [1]
Signed-off-by: Benno Lossin <lossin@kernel.org>
---
 rust/pin-init/src/lib.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/pin-init/src/lib.rs b/rust/pin-init/src/lib.rs
index 49945fc07f25..fe4c85ae3f02 100644
--- a/rust/pin-init/src/lib.rs
+++ b/rust/pin-init/src/lib.rs
@@ -1143,13 +1143,13 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
 ///
 /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
 ///   pointer must result in a valid `U`.
-#[expect(clippy::let_and_return)]
 pub const unsafe fn cast_pin_init<T, U, E>(init: impl PinInit<T, E>) -> impl PinInit<U, E> {
     // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
     // requirements.
     let res = unsafe { pin_init_from_closure(|ptr: *mut U| init.__pinned_init(ptr.cast::<T>())) };
     // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
     // cycle when computing the type returned by this function)
+    #[allow(clippy::let_and_return)]
     res
 }
 
@@ -1159,13 +1159,13 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
 ///
 /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
 ///   pointer must result in a valid `U`.
-#[expect(clippy::let_and_return)]
 pub const unsafe fn cast_init<T, U, E>(init: impl Init<T, E>) -> impl Init<U, E> {
     // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
     // requirements.
     let res = unsafe { init_from_closure(|ptr: *mut U| init.__init(ptr.cast::<T>())) };
     // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
     // cycle when computing the type returned by this function)
+    #[allow(clippy::let_and_return)]
     res
 }
 

base-commit: ca4ee40bf13dbd3a4be3b40a00c33a1153d487e5
-- 
2.52.0

Re: [PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Miguel Ojeda 1 month, 1 week ago

On Sun, Feb 15, 2026 at 2:22 PM Benno Lossin <lossin@kernel.org> wrote:
>
> `clippy` has changed behavior in [1] (Rust 1.95) where it no longer
> warns about the `let_and_return` lint when a comment is placed between
> the let binding and the return expression. Nightly thus fails to build,
> because the expectation is no longer fulfilled.
>
> Thus replace the expectation with an `allow`.
>
> Link: https://github.com/rust-lang/rust-clippy/pull/16461 [1]
> Signed-off-by: Benno Lossin <lossin@kernel.org>

Applied to `rust-fixes` -- thanks everyone!

Gary: I wasn't sure if you would have wanted me to pick your tag,
since it was conditional to adding the message, but we agreed to add
it later on. Just in case, I didn't add it to be on the safe side, but
I can add it.

By the way, I added:

  Cc: stable@vger.kernel.org # Needed in 6.18.y and later.

    [ The errors were:

          error: this lint expectation is unfulfilled
              --> rust/pin-init/src/lib.rs:1279:10
               |
          1279 | #[expect(clippy::let_and_return)]
               |          ^^^^^^^^^^^^^^^^^^^^^^
               |
               = note: `-D unfulfilled-lint-expectations` implied by
`-D warnings`
               = help: to override `-D warnings` add
`#[allow(unfulfilled_lint_expectations)]`

          error: this lint expectation is unfulfilled
              --> rust/pin-init/src/lib.rs:1295:10
               |
          1295 | #[expect(clippy::let_and_return)]
               |          ^^^^^^^^^^^^^^^^^^^^^^

        - Miguel ]

Cheers,
Miguel

Re: [PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Miguel Ojeda 1 month, 2 weeks ago

As we discaOn Sun, Feb 15, 2026 at 2:22 PM Benno Lossin
<lossin@kernel.org> wrote:
>
> `clippy` has changed behavior in [1] (Rust 1.95) where it no longer
> warns about the `let_and_return` lint when a comment is placed between
> the let binding and the return expression. Nightly thus fails to build,
> because the expectation is no longer fulfilled.
>
> Thus replace the expectation with an `allow`.
>
> Link: https://github.com/rust-lang/rust-clippy/pull/16461 [1]
> Signed-off-by: Benno Lossin <lossin@kernel.org>

Thanks for figuring out the PR upstream, that is always helpful -- I
also noticed it in the 2026-02-13 nightly, so this saved me having to
dig into it.

If you want, when you decide it is ready, I can take it into rust-fixes.

By the way, if you send a new version, please include the error -- it
makes it easier for others to find it later in lore.kernel.org. In
case you don't have it around, this is what I got in that run from a
few days ago:

    error: this lint expectation is unfulfilled
        --> rust/pin-init/src/lib.rs:1279:10
         |
    1279 | #[expect(clippy::let_and_return)]
         |          ^^^^^^^^^^^^^^^^^^^^^^
         |
         = note: `-D unfulfilled-lint-expectations` implied by `-D warnings`
         = help: to override `-D warnings` add
`#[allow(unfulfilled_lint_expectations)]`

    error: this lint expectation is unfulfilled
        --> rust/pin-init/src/lib.rs:1295:10
         |
    1295 | #[expect(clippy::let_and_return)]
         |          ^^^^^^^^^^^^^^^^^^^^^^

Cheers,
Miguel

Re: [PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Gary Guo 1 month, 2 weeks ago

On 2026-02-15 13:22, Benno Lossin wrote:
> `clippy` has changed behavior in [1] (Rust 1.95) where it no longer
> warns about the `let_and_return` lint when a comment is placed between
> the let binding and the return expression. Nightly thus fails to build,
> because the expectation is no longer fulfilled.
> 
> Thus replace the expectation with an `allow`.
> 
> Link: https://github.com/rust-lang/rust-clippy/pull/16461 [1]
> Signed-off-by: Benno Lossin <lossin@kernel.org>

I think it's worth adding a comment (or reason) that this is no longer needed after 1.95.

With that:

Reviewed-by: Gary Guo <gary@garyguo.net>

> ---
>  rust/pin-init/src/lib.rs | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/rust/pin-init/src/lib.rs b/rust/pin-init/src/lib.rs
> index 49945fc07f25..fe4c85ae3f02 100644
> --- a/rust/pin-init/src/lib.rs
> +++ b/rust/pin-init/src/lib.rs
> @@ -1143,13 +1143,13 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
>  ///
>  /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
>  ///   pointer must result in a valid `U`.
> -#[expect(clippy::let_and_return)]
>  pub const unsafe fn cast_pin_init<T, U, E>(init: impl PinInit<T, E>) -> impl PinInit<U, E> {
>      // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
>      // requirements.
>      let res = unsafe { pin_init_from_closure(|ptr: *mut U| init.__pinned_init(ptr.cast::<T>())) };
>      // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
>      // cycle when computing the type returned by this function)
> +    #[allow(clippy::let_and_return)]
>      res
>  }
>  
> @@ -1159,13 +1159,13 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
>  ///
>  /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
>  ///   pointer must result in a valid `U`.
> -#[expect(clippy::let_and_return)]
>  pub const unsafe fn cast_init<T, U, E>(init: impl Init<T, E>) -> impl Init<U, E> {
>      // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
>      // requirements.
>      let res = unsafe { init_from_closure(|ptr: *mut U| init.__init(ptr.cast::<T>())) };
>      // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
>      // cycle when computing the type returned by this function)
> +    #[allow(clippy::let_and_return)]
>      res
>  }
>  
> 
> base-commit: ca4ee40bf13dbd3a4be3b40a00c33a1153d487e5

Re: [PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Benno Lossin 1 month, 2 weeks ago

On Mon Feb 16, 2026 at 2:36 AM CET, Gary Guo wrote:
> On 2026-02-15 13:22, Benno Lossin wrote:
>> `clippy` has changed behavior in [1] (Rust 1.95) where it no longer
>> warns about the `let_and_return` lint when a comment is placed between
>> the let binding and the return expression. Nightly thus fails to build,
>> because the expectation is no longer fulfilled.
>> 
>> Thus replace the expectation with an `allow`.
>> 
>> Link: https://github.com/rust-lang/rust-clippy/pull/16461 [1]
>> Signed-off-by: Benno Lossin <lossin@kernel.org>
>
> I think it's worth adding a comment (or reason) that this is no longer needed after 1.95.

We'll remove the let binding when we raise the MSRV above 1.78 and then
the `allow` should also be gone. Do you still want me to add it?

Cheers,
Benno

Re: [PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Gary Guo 1 month, 1 week ago

On 2026-02-16 11:17, Benno Lossin wrote:
> On Mon Feb 16, 2026 at 2:36 AM CET, Gary Guo wrote:
>> On 2026-02-15 13:22, Benno Lossin wrote:
>>> `clippy` has changed behavior in [1] (Rust 1.95) where it no longer
>>> warns about the `let_and_return` lint when a comment is placed 
>>> between
>>> the let binding and the return expression. Nightly thus fails to 
>>> build,
>>> because the expectation is no longer fulfilled.
>>> 
>>> Thus replace the expectation with an `allow`.
>>> 
>>> Link: https://github.com/rust-lang/rust-clippy/pull/16461 [1]
>>> Signed-off-by: Benno Lossin <lossin@kernel.org>
>> 
>> I think it's worth adding a comment (or reason) that this is no longer 
>> needed after 1.95.
> 
> We'll remove the let binding when we raise the MSRV above 1.78 and then
> the `allow` should also be gone. Do you still want me to add it?
> 
> Cheers,
> Benno

The existing comment just says that the bug exists in 1.78. So is it 
fixed in 1.79+? If so,
please update the comment to say the MSRV that this is no longer needed, 
then I'm fine
without reason for clippy allow.

Best,
Gary

Re: [PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Benno Lossin 1 month, 1 week ago

On Wed Feb 18, 2026 at 4:08 PM CET, Gary Guo wrote:
> On 2026-02-16 11:17, Benno Lossin wrote:
>> On Mon Feb 16, 2026 at 2:36 AM CET, Gary Guo wrote:
>>> On 2026-02-15 13:22, Benno Lossin wrote:
>>>> `clippy` has changed behavior in [1] (Rust 1.95) where it no longer
>>>> warns about the `let_and_return` lint when a comment is placed 
>>>> between
>>>> the let binding and the return expression. Nightly thus fails to 
>>>> build,
>>>> because the expectation is no longer fulfilled.
>>>> 
>>>> Thus replace the expectation with an `allow`.
>>>> 
>>>> Link: https://github.com/rust-lang/rust-clippy/pull/16461 [1]
>>>> Signed-off-by: Benno Lossin <lossin@kernel.org>
>>> 
>>> I think it's worth adding a comment (or reason) that this is no longer 
>>> needed after 1.95.
>> 
>> We'll remove the let binding when we raise the MSRV above 1.78 and then
>> the `allow` should also be gone. Do you still want me to add it?
>> 
>> Cheers,
>> Benno
>
> The existing comment just says that the bug exists in 1.78. So is it 
> fixed in 1.79+? If so,
> please update the comment to say the MSRV that this is no longer needed, 
> then I'm fine
> without reason for clippy allow.

We discussed this in the meeting, Miguel will pick this patch as-is and
I'll send a follow up to change the comment.

Cheers,
Benno

Re: [PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Tamir Duberstein 1 month, 2 weeks ago

On Sun, Feb 15, 2026 at 8:22 AM Benno Lossin <lossin@kernel.org> wrote:
>
> `clippy` has changed behavior in [1] (Rust 1.95) where it no longer
> warns about the `let_and_return` lint when a comment is placed between
> the let binding and the return expression. Nightly thus fails to build,
> because the expectation is no longer fulfilled.
>
> Thus replace the expectation with an `allow`.
>
> Link: https://github.com/rust-lang/rust-clippy/pull/16461 [1]
> Signed-off-by: Benno Lossin <lossin@kernel.org>
> ---
>  rust/pin-init/src/lib.rs | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/rust/pin-init/src/lib.rs b/rust/pin-init/src/lib.rs
> index 49945fc07f25..fe4c85ae3f02 100644
> --- a/rust/pin-init/src/lib.rs
> +++ b/rust/pin-init/src/lib.rs
> @@ -1143,13 +1143,13 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
>  ///
>  /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
>  ///   pointer must result in a valid `U`.
> -#[expect(clippy::let_and_return)]
>  pub const unsafe fn cast_pin_init<T, U, E>(init: impl PinInit<T, E>) -> impl PinInit<U, E> {
>      // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
>      // requirements.
>      let res = unsafe { pin_init_from_closure(|ptr: *mut U| init.__pinned_init(ptr.cast::<T>())) };
>      // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
>      // cycle when computing the type returned by this function)
> +    #[allow(clippy::let_and_return)]

Consider adding `reason = "..."`.

>      res
>  }
>
> @@ -1159,13 +1159,13 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
>  ///
>  /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
>  ///   pointer must result in a valid `U`.
> -#[expect(clippy::let_and_return)]
>  pub const unsafe fn cast_init<T, U, E>(init: impl Init<T, E>) -> impl Init<U, E> {
>      // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
>      // requirements.
>      let res = unsafe { init_from_closure(|ptr: *mut U| init.__init(ptr.cast::<T>())) };
>      // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
>      // cycle when computing the type returned by this function)
> +    #[allow(clippy::let_and_return)]

Consider adding `reason = "..."`.

>      res
>  }
>
>
> base-commit: ca4ee40bf13dbd3a4be3b40a00c33a1153d487e5
> --
> 2.52.0
>
>

Re: [PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Benno Lossin 1 month, 2 weeks ago

On Sun Feb 15, 2026 at 3:24 PM CET, Tamir Duberstein wrote:
> On Sun, Feb 15, 2026 at 8:22 AM Benno Lossin <lossin@kernel.org> wrote:
>>
>> `clippy` has changed behavior in [1] (Rust 1.95) where it no longer
>> warns about the `let_and_return` lint when a comment is placed between
>> the let binding and the return expression. Nightly thus fails to build,
>> because the expectation is no longer fulfilled.
>>
>> Thus replace the expectation with an `allow`.
>>
>> Link: https://github.com/rust-lang/rust-clippy/pull/16461 [1]
>> Signed-off-by: Benno Lossin <lossin@kernel.org>
>> ---
>>  rust/pin-init/src/lib.rs | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/rust/pin-init/src/lib.rs b/rust/pin-init/src/lib.rs
>> index 49945fc07f25..fe4c85ae3f02 100644
>> --- a/rust/pin-init/src/lib.rs
>> +++ b/rust/pin-init/src/lib.rs
>> @@ -1143,13 +1143,13 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
>>  ///
>>  /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
>>  ///   pointer must result in a valid `U`.
>> -#[expect(clippy::let_and_return)]
>>  pub const unsafe fn cast_pin_init<T, U, E>(init: impl PinInit<T, E>) -> impl PinInit<U, E> {
>>      // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
>>      // requirements.
>>      let res = unsafe { pin_init_from_closure(|ptr: *mut U| init.__pinned_init(ptr.cast::<T>())) };
>>      // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
>>      // cycle when computing the type returned by this function)
>> +    #[allow(clippy::let_and_return)]
>
> Consider adding `reason = "..."`.

Isn't the FIXME comment directly above enough? I don't want to duplicate
the information and the string constant explaining the reason looks
ugly.

Cheers,
Benno

Re: [PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Tamir Duberstein 1 month, 2 weeks ago

On Sun, Feb 15, 2026 at 9:57 AM Benno Lossin <lossin@kernel.org> wrote:
>
> On Sun Feb 15, 2026 at 3:24 PM CET, Tamir Duberstein wrote:
> > On Sun, Feb 15, 2026 at 8:22 AM Benno Lossin <lossin@kernel.org> wrote:
> >>
> >> `clippy` has changed behavior in [1] (Rust 1.95) where it no longer
> >> warns about the `let_and_return` lint when a comment is placed between
> >> the let binding and the return expression. Nightly thus fails to build,
> >> because the expectation is no longer fulfilled.
> >>
> >> Thus replace the expectation with an `allow`.
> >>
> >> Link: https://github.com/rust-lang/rust-clippy/pull/16461 [1]
> >> Signed-off-by: Benno Lossin <lossin@kernel.org>
> >> ---
> >>  rust/pin-init/src/lib.rs | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/rust/pin-init/src/lib.rs b/rust/pin-init/src/lib.rs
> >> index 49945fc07f25..fe4c85ae3f02 100644
> >> --- a/rust/pin-init/src/lib.rs
> >> +++ b/rust/pin-init/src/lib.rs
> >> @@ -1143,13 +1143,13 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
> >>  ///
> >>  /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
> >>  ///   pointer must result in a valid `U`.
> >> -#[expect(clippy::let_and_return)]
> >>  pub const unsafe fn cast_pin_init<T, U, E>(init: impl PinInit<T, E>) -> impl PinInit<U, E> {
> >>      // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
> >>      // requirements.
> >>      let res = unsafe { pin_init_from_closure(|ptr: *mut U| init.__pinned_init(ptr.cast::<T>())) };
> >>      // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
> >>      // cycle when computing the type returned by this function)
> >> +    #[allow(clippy::let_and_return)]
> >
> > Consider adding `reason = "..."`.
>
> Isn't the FIXME comment directly above enough? I don't want to duplicate
> the information and the string constant explaining the reason looks
> ugly.

The FIXME explains why the allowance is needed, but it doesn't explain
why it is an allow rather than an expect.

Re: [PATCH] rust: pin-init: replace clippy `expect` with `allow`

Posted by Benno Lossin 1 month, 2 weeks ago

On Sun Feb 15, 2026 at 4:19 PM CET, Tamir Duberstein wrote:
> On Sun, Feb 15, 2026 at 9:57 AM Benno Lossin <lossin@kernel.org> wrote:
>> On Sun Feb 15, 2026 at 3:24 PM CET, Tamir Duberstein wrote:
>> > On Sun, Feb 15, 2026 at 8:22 AM Benno Lossin <lossin@kernel.org> wrote:
>> >> @@ -1143,13 +1143,13 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
>> >>  ///
>> >>  /// - `*mut U` must be castable to `*mut T` and any value of type `T` written through such a
>> >>  ///   pointer must result in a valid `U`.
>> >> -#[expect(clippy::let_and_return)]
>> >>  pub const unsafe fn cast_pin_init<T, U, E>(init: impl PinInit<T, E>) -> impl PinInit<U, E> {
>> >>      // SAFETY: initialization delegated to a valid initializer. Cast is valid by function safety
>> >>      // requirements.
>> >>      let res = unsafe { pin_init_from_closure(|ptr: *mut U| init.__pinned_init(ptr.cast::<T>())) };
>> >>      // FIXME: remove the let statement once the nightly-MSRV allows it (1.78 otherwise encounters a
>> >>      // cycle when computing the type returned by this function)
>> >> +    #[allow(clippy::let_and_return)]
>> >
>> > Consider adding `reason = "..."`.
>>
>> Isn't the FIXME comment directly above enough? I don't want to duplicate
>> the information and the string constant explaining the reason looks
>> ugly.
>
> The FIXME explains why the allowance is needed, but it doesn't explain
> why it is an allow rather than an expect.

I don't see much value in documenting that in the code. This'll be
removed once we raise the MSRV, which should happen later this year. If
one really wants to know why it's there, there is the git log.

Cheers,
Benno