Re: [PATCH v2 1/5] rust: add warn_on_err macro

["Alexandre Courbot" <acourbot@nvidia.com>]

On Thu Apr 23, 2026 at 8:34 PM JST, Gary Guo wrote:
> On Tue Apr 21, 2026 at 7:16 AM BST, Alexandre Courbot wrote:
>> While we already have the `warn_on` macro, a common usage pattern in
>> Rust is to check whether a `Result` is an error. Add a helper macro that
>> allows this.
>>
>> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
>> ---
>>  rust/kernel/bug.rs | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/rust/kernel/bug.rs b/rust/kernel/bug.rs
>> index ed943960f851..2fefc0aeef81 100644
>> --- a/rust/kernel/bug.rs
>> +++ b/rust/kernel/bug.rs
>> @@ -130,3 +130,13 @@ macro_rules! warn_on {
>>          cond
>>      }};
>>  }
>> +
>> +/// Report a warning if `res` is an error and return it unmodified.
>> +#[macro_export]
>> +macro_rules! warn_on_err {
>> +    ($res:expr) => {{
>> +        let res = $res;
>> +        let _ = $crate::warn_on!(res.is_err());
>> +        res
>> +    }};
>> +}
>
>
> I think `warn_on_err` could just be expressed as
>
>     res.inspect_err(|_| warn_on!(true))

This would turn the verbose error message into something like

  [true] module.rs

I.e. the expression passed as argument won't be printed.

That being said, my version has the exact same problem and I don't see
how we can fix this without splitting `warn_on` and making it more
complex.

Since this was done as a small convenience, I think I will just remove
this from this patchset and revisit later as a separate series.