[PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[Alexandre Courbot]

The `clippy::unwrap_or_default` warning triggers on
`rust/kernel/soc.rs` since rustc 1.88:

    warning: use of `unwrap_or` to construct default value
      --> ../rust/kernel/soc.rs:66:10
      |
   66 |         .unwrap_or(core::ptr::null())
      |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unwrap_or_default()`
      |
      = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.96.0/index.html#unwrap_or_default
      = note: `-W clippy::unwrap-or-default` implied by `-W clippy::all`
      = help: to override `-W clippy::all` add `#[allow(clippy::unwrap_or_default)]`

Since our current MSRV is 1.85, we cannot fix the warning as
recommended, so allow the lint on the `cstring_to_c` function instead.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
 rust/kernel/soc.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/rust/kernel/soc.rs b/rust/kernel/soc.rs
index 0d6a36c83cb6..7998962560f8 100644
--- a/rust/kernel/soc.rs
+++ b/rust/kernel/soc.rs
@@ -60,6 +60,9 @@ struct BuiltAttributes {
     inner: Opaque<bindings::soc_device_attribute>,
 }
 
+// `unwrap_or_default()` on a raw pointer requires `Default for *const T`, which is stable since
+// Rust 1.88. Remove when the MSRV allows it.
+#[allow(clippy::unwrap_or_default)]
 fn cstring_to_c(mcs: &Option<CString>) -> *const kernel::ffi::c_char {
     mcs.as_ref()
         .map(|cs| cs.as_char_ptr())

---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260707-soc_unwrap_or-ed37e674a759

Best regards,
--  
Alexandre Courbot <acourbot@nvidia.com>

Re: [PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[Onur Özkan]

On Tue, 07 Jul 2026 19:12:21 +0900
Alexandre Courbot <acourbot@nvidia.com> wrote:

> The `clippy::unwrap_or_default` warning triggers on
> `rust/kernel/soc.rs` since rustc 1.88:
> 
>     warning: use of `unwrap_or` to construct default value
>       --> ../rust/kernel/soc.rs:66:10
>       |
>    66 |         .unwrap_or(core::ptr::null())
>       |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unwrap_or_default()`
>       |
>       = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.96.0/index.html#unwrap_or_default
>       = note: `-W clippy::unwrap-or-default` implied by `-W clippy::all`
>       = help: to override `-W clippy::all` add `#[allow(clippy::unwrap_or_default)]`
> 
> Since our current MSRV is 1.85, we cannot fix the warning as
> recommended, so allow the lint on the `cstring_to_c` function instead.
> 
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
>  rust/kernel/soc.rs | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/rust/kernel/soc.rs b/rust/kernel/soc.rs
> index 0d6a36c83cb6..7998962560f8 100644
> --- a/rust/kernel/soc.rs
> +++ b/rust/kernel/soc.rs
> @@ -60,6 +60,9 @@ struct BuiltAttributes {
>      inner: Opaque<bindings::soc_device_attribute>,
>  }
>  
> +// `unwrap_or_default()` on a raw pointer requires `Default for *const T`, which is stable since
> +// Rust 1.88. Remove when the MSRV allows it.

I would move "Remove when the MSRV allows it." to the next line as TODO.

Regards,
Onur

> +#[allow(clippy::unwrap_or_default)]
>  fn cstring_to_c(mcs: &Option<CString>) -> *const kernel::ffi::c_char {
>      mcs.as_ref()
>          .map(|cs| cs.as_char_ptr())
> 
> ---
> base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
> change-id: 20260707-soc_unwrap_or-ed37e674a759
> 
> Best regards,
> --  
> Alexandre Courbot <acourbot@nvidia.com>
> 

Re: [PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[Gary Guo]

On Tue Jul 7, 2026 at 11:12 AM BST, Alexandre Courbot wrote:
> The `clippy::unwrap_or_default` warning triggers on
> `rust/kernel/soc.rs` since rustc 1.88:
>
>     warning: use of `unwrap_or` to construct default value
>       --> ../rust/kernel/soc.rs:66:10
>       |
>    66 |         .unwrap_or(core::ptr::null())
>       |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unwrap_or_default()`
>       |
>       = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.96.0/index.html#unwrap_or_default
>       = note: `-W clippy::unwrap-or-default` implied by `-W clippy::all`
>       = help: to override `-W clippy::all` add `#[allow(clippy::unwrap_or_default)]`
>
> Since our current MSRV is 1.85, we cannot fix the warning as
> recommended, so allow the lint on the `cstring_to_c` function instead.

We set `msrv = "1.85"` in our .clippy.toml, and my local testing with 1.88 and
1.96.1 doesn't produce this warning.

Best,
Gary

>
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
>  rust/kernel/soc.rs | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/rust/kernel/soc.rs b/rust/kernel/soc.rs
> index 0d6a36c83cb6..7998962560f8 100644
> --- a/rust/kernel/soc.rs
> +++ b/rust/kernel/soc.rs
> @@ -60,6 +60,9 @@ struct BuiltAttributes {
>      inner: Opaque<bindings::soc_device_attribute>,
>  }
>  
> +// `unwrap_or_default()` on a raw pointer requires `Default for *const T`, which is stable since
> +// Rust 1.88. Remove when the MSRV allows it.
> +#[allow(clippy::unwrap_or_default)]
>  fn cstring_to_c(mcs: &Option<CString>) -> *const kernel::ffi::c_char {
>      mcs.as_ref()
>          .map(|cs| cs.as_char_ptr())
>
> ---
> base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
> change-id: 20260707-soc_unwrap_or-ed37e674a759
>
> Best regards,
> --  
> Alexandre Courbot <acourbot@nvidia.com>

Re: [PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[Alexandre Courbot]

On Tue Jul 7, 2026 at 8:43 PM JST, Gary Guo wrote:
> On Tue Jul 7, 2026 at 11:12 AM BST, Alexandre Courbot wrote:
>> The `clippy::unwrap_or_default` warning triggers on
>> `rust/kernel/soc.rs` since rustc 1.88:
>>
>>     warning: use of `unwrap_or` to construct default value
>>       --> ../rust/kernel/soc.rs:66:10
>>       |
>>    66 |         .unwrap_or(core::ptr::null())
>>       |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unwrap_or_default()`
>>       |
>>       = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.96.0/index.html#unwrap_or_default
>>       = note: `-W clippy::unwrap-or-default` implied by `-W clippy::all`
>>       = help: to override `-W clippy::all` add `#[allow(clippy::unwrap_or_default)]`
>>
>> Since our current MSRV is 1.85, we cannot fix the warning as
>> recommended, so allow the lint on the `cstring_to_c` function instead.
>
> We set `msrv = "1.85"` in our .clippy.toml, and my local testing with 1.88 and
> 1.96.1 doesn't produce this warning.

Then I guess we will want to understand why I am getting this warning
locally. I'd also expect the `msrv = "1.85"` to prevent this from
happening.

Re: [PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[Miguel Ojeda]

On Tue, Jul 7, 2026 at 1:43 PM Gary Guo <gary@garyguo.net> wrote:
>
> We set `msrv = "1.85"` in our .clippy.toml, and my local testing with 1.88 and
> 1.96.1 doesn't produce this warning.

Yeah, I was trying to reproduce it locally too and didn't succeed yet.

If it does reproduce somehow (e.g. a particular toolchain), then we
probably want:

  Cc: stable@vger.kernel.org
  Fixes: 057d44b05775 ("rust: Add soc_device support")

Cheers,
Miguel

Re: [PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[Alexandre Courbot]

On Tue Jul 7, 2026 at 9:12 PM JST, Miguel Ojeda wrote:
> On Tue, Jul 7, 2026 at 1:43 PM Gary Guo <gary@garyguo.net> wrote:
>>
>> We set `msrv = "1.85"` in our .clippy.toml, and my local testing with 1.88 and
>> 1.96.1 doesn't produce this warning.
>
> Yeah, I was trying to reproduce it locally too and didn't succeed yet.

Ok so this is nuts but it appears to only reproduce when
`CONFIG_CC_OPTIMIZE_FOR_SIZE=y` (and `CONFIG_SAMPLE_RUST_SOC=m` to build
`soc.rs`)

Re: [PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[Gary Guo]

On Tue Jul 7, 2026 at 3:19 PM BST, Alexandre Courbot wrote:
> On Tue Jul 7, 2026 at 9:12 PM JST, Miguel Ojeda wrote:
>> On Tue, Jul 7, 2026 at 1:43 PM Gary Guo <gary@garyguo.net> wrote:
>>>
>>> We set `msrv = "1.85"` in our .clippy.toml, and my local testing with 1.88 and
>>> 1.96.1 doesn't produce this warning.
>>
>> Yeah, I was trying to reproduce it locally too and didn't succeed yet.
>
> Ok so this is nuts but it appears to only reproduce when
> `CONFIG_CC_OPTIMIZE_FOR_SIZE=y` (and `CONFIG_SAMPLE_RUST_SOC=m` to build
> `soc.rs`)

That's crazy. Turns out that clippy's default equivalent check relies on MIR:
https://github.com/rust-lang/rust-clippy/blob/60f8c3a019cfda37e07de60e9cfd7ee77b290fb5/clippy_utils/src/lib.rs#L570
and somehow this check misses `null()` when opt level is high enough. There
isn't a check for MSRV in the trait impl.

Please report a clippy bug.

Best,
Gary

Re: [PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[Alexandre Courbot]

On Tue Jul 7, 2026 at 11:30 PM JST, Gary Guo wrote:
> On Tue Jul 7, 2026 at 3:19 PM BST, Alexandre Courbot wrote:
>> On Tue Jul 7, 2026 at 9:12 PM JST, Miguel Ojeda wrote:
>>> On Tue, Jul 7, 2026 at 1:43 PM Gary Guo <gary@garyguo.net> wrote:
>>>>
>>>> We set `msrv = "1.85"` in our .clippy.toml, and my local testing with 1.88 and
>>>> 1.96.1 doesn't produce this warning.
>>>
>>> Yeah, I was trying to reproduce it locally too and didn't succeed yet.
>>
>> Ok so this is nuts but it appears to only reproduce when
>> `CONFIG_CC_OPTIMIZE_FOR_SIZE=y` (and `CONFIG_SAMPLE_RUST_SOC=m` to build
>> `soc.rs`)
>
> That's crazy. Turns out that clippy's default equivalent check relies on MIR:
> https://github.com/rust-lang/rust-clippy/blob/60f8c3a019cfda37e07de60e9cfd7ee77b290fb5/clippy_utils/src/lib.rs#L570
> and somehow this check misses `null()` when opt level is high enough. There
> isn't a check for MSRV in the trait impl.
>
> Please report a clippy bug.

Done: https://github.com/rust-lang/rust-clippy/issues/17379

As for this patch, I guess we don't need it then?

Re: [PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[Miguel Ojeda]

On Wed, Jul 8, 2026 at 10:25 AM Alexandre Courbot <acourbot@nvidia.com> wrote:
>
> Done: https://github.com/rust-lang/rust-clippy/issues/17379
>
> As for this patch, I guess we don't need it then?

Thanks a lot for taking the time to fill the issue! Linked to our usual list:

  https://github.com/Rust-for-Linux/linux/issues/349

But why do you mean we don't need it? It is still reproducible within
our possible toolchains, right? Or did I misunderstand something? Or
do you mean it is fairly rare and thus maybe not needed?

We can also always just disable that particular lint, and perhaps
later on re-enable it conditionally when fixed -- we have support for
that now.

Cheers,
Miguel

Re: [PATCH] rust: soc: silence clippy warning with rustc >= 1.88

[Alexandre Courbot]

On Wed Jul 8, 2026 at 6:04 PM JST, Miguel Ojeda wrote:
> On Wed, Jul 8, 2026 at 10:25 AM Alexandre Courbot <acourbot@nvidia.com> wrote:
>>
>> Done: https://github.com/rust-lang/rust-clippy/issues/17379
>>
>> As for this patch, I guess we don't need it then?
>
> Thanks a lot for taking the time to fill the issue! Linked to our usual list:
>
>   https://github.com/Rust-for-Linux/linux/issues/349
>
> But why do you mean we don't need it? It is still reproducible within
> our possible toolchains, right? Or did I misunderstand something? Or
> do you mean it is fairly rare and thus maybe not needed?

I mean that both the code and clippy setting are properly set, so
using a workaround for this particular occurrence seems like a
half-measure, as the problem can very well arise somewhere else.

>
> We can also always just disable that particular lint, and perhaps
> later on re-enable it conditionally when fixed -- we have support for
> that now.

That sounds like a better way to address this, yes.