Re: [PATCH v2] rust: kunit: fix warning when !CONFIG_PRINTK

[David Gow]

Le 24/02/2026 à 9:07 PM, 'Alexandre Courbot' via KUnit Development a écrit :
> On Tue Feb 24, 2026 at 8:51 PM JST, Andreas Hindborg wrote:
> > "Alexandre Courbot" <acourbot@xxxxxxxxxx> writes:
> >
> > > If `CONFIG_PRINTK` is not set, then the following warnings are issued
> > > during build:
> > >
> > >    warning: unused variable: `args`
> > >      --> ../rust/kernel/kunit.rs:16:12
> > >      |
> > >    16 | pub fn err(args: fmt::Arguments<'_>) {
> > >      |            ^^^^ help: if this is intentional, prefix it with an underscore: `_args`
> > >      |
> > >      = note: `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default
> > >
> > >    warning: unused variable: `args`
> > >      --> ../rust/kernel/kunit.rs:32:13
> > >      |
> > >    32 | pub fn info(args: fmt::Arguments<'_>) {
> > >      |             ^^^^ help: if this is intentional, prefix it with an underscore: `_args`
> > >
> > > Fix this by adding a no-op assignment using `args` when `CONFIG_PRINTK`
> > > is not set.
> > >
> > > Fixes: a66d733da801 ("rust: support running Rust documentation tests as KUnit ones")
> > > Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
> > > ---
> > > Changes in v2:
> > > - Use a no-op assignment instead of the wider `#[allow(unused_variables)]`.
> > > - Link to v1: https://patch.msgid.link/20260224-unused_var_err-v1-1-c51d805eceb5@xxxxxxxxxx
> > > ---
> > >   rust/kernel/kunit.rs | 8 ++++++++
> > >   1 file changed, 8 insertions(+)
> > >
> > > diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
> > > index f93f24a60bdd..a1edf7491579 100644
> > > --- a/rust/kernel/kunit.rs
> > > +++ b/rust/kernel/kunit.rs
> > > @@ -14,6 +14,10 @@
> > >   /// Public but hidden since it should only be used from KUnit generated code.
> > >   #[doc(hidden)]
> > >   pub fn err(args: fmt::Arguments<'_>) {
> > > +    // `args` is unused if `CONFIG_PRINTK` is not set - this avoids a build-time warning.
> > > +    #[cfg(not(CONFIG_PRINTK))]
> > > +    let _ = args;
> >
> > I think (didn't test) that you can use a conditional attribute [1] instead:
> >
> >   pub fn err(
> >       #[cfg_attr(not(CONFIG_PRINTK), expect(unused))]
> >       args: fmt::Arguments<'_>
> >   ) {
>
> Yup, that works as well, and I think I like it better as it is more
> localized. Alice, WDYT?

Personally, I have a slight preference for the current `let _ = args` 
option -- we'll still want to be able to format (at least some of) these 
messages to the KUnit test log, even if printk is disabled. So in the 
interest of avoiding churn in the function prototype, this version seems 
more future-proof.

But I'm not enormously worried either way.

Cheers,
-- David