Re: [PATCH v3] rust: bug: prevent dead_code warning from warn_on!'s flags constant

On Sat, Aug 1, 2026 at 6:04 AM FUJITA Tomonori <[email protected]> wrote:
>
> From: FUJITA Tomonori <[email protected]>
>
> Fix the following dead_code warning on some configurations in an
> atomic development branch:
>
> warning: constant `WARN_ON_FLAGS` is never used
>    --> linux/rust/kernel/bug.rs:126:19
>     |
> 126 |               const WARN_ON_FLAGS: u32 = $crate::bug::bugflag_taint($crate::bindings::TAINT_WARN);
>     |                     ^^^^^^^^^^^^^
>     |
>    ::: linux/rust/kernel/sync/srcu.rs:106:12
>     |
> 106 |           if crate::warn_on!(
>     |  ____________-
> 107 | |             // SAFETY: By the type invariants, `self` contains a valid and pinned `struct srcu_struct`
> 108 | |             // and `srcu_readers_active()` only checks the active reader count.
> 109 | |             unsafe { bindings::srcu_readers_active(ptr) }
> 110 | |         ) {
>     | |_________- in this macro invocation
>     |
>     = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default
>     = note: this warning originates in the macro `crate::warn_on` (in Nightly builds, run with -Z macro-backtrace for more info)
>
> The warn_on! macro always defines a WARN_ON_FLAGS constant and hands it
> to warn_flags!. On configurations where warn_flags! does not reference
> its flags argument (the LOONGARCH/ARM variant, which only calls
> WARN_ON(), and the !CONFIG_BUG no-op variant), the constant is left
> unused and triggers a dead_code warning.
>
> warn_flags! is the macro that accepts (and here discards) the flags
> argument, so make it responsible for the argument it drops.
>
> Also rename `_COND_STR` to `COND_STR` and consume `$file` for consistency.
>
> Fixes: dff64b072708 ("rust: Add warn_on macro")
> Signed-off-by: FUJITA Tomonori <[email protected]>

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

    Cc: [email protected]

    [ Added newlines. - Miguel ]

Cheers,
Miguel