Re: [PATCH v1] rust: bug: prevent dead_code warning from warn_on!'s flags constant

On Fri, 24 Jul 2026 00:40:04 +0100
"Gary Guo" <[email protected]> wrote:

>> diff --git a/rust/kernel/bug.rs b/rust/kernel/bug.rs
>> index ed943960f851..2fd7ee25abcb 100644
>> --- a/rust/kernel/bug.rs
>> +++ b/rust/kernel/bug.rs
>> @@ -123,9 +123,9 @@ macro_rules! warn_on {
>>          const _COND_STR: &str = file!();
>>  
>>          if cond {
>> -            const WARN_ON_FLAGS: u32 = $crate::bug::bugflag_taint($crate::bindings::TAINT_WARN);
>> +            const _WARN_ON_FLAGS: u32 = $crate::bug::bugflag_taint($crate::bindings::TAINT_WARN);
>>  
>> -            $crate::warn_flags!(_COND_STR, WARN_ON_FLAGS);
>> +            $crate::warn_flags!(_COND_STR, _WARN_ON_FLAGS);
> 
> Hmm, why bother adding a const for this rather than just invoke
> 
>     $crate::warn_flags!(
>         _COND_STR,
>         const { ... }
>     )
> 
> ?

Ah, `(const { ... })` works.


> Also, the proper fix would be to mark it as used in the `warn_flags` macro
> that discard the expression.
> 
>     if false {
>         _ = $flags;
>     }


Yeah, having the callee that discards the argument consume it is more
logical than working around it at the caller. I'll send v2 shortly.

The same reasoning applies to `$file`. Since there is no warning right
now, I'll rename `_COND_STR` to `COND_STR` and consume `$file` in a
separate patch for consistency.