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

On Fri Jul 24, 2026 at 5:08 AM BST, FUJITA Tomonori wrote:
> 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.

Given that this is closely related to $flags I'd do it in a single patch.

Best,
Gary