Hi Andreas,
> On 11 Jul 2025, at 08:43, Andreas Hindborg <a.hindborg@xxxxxxxxxx> wrote:
>
> Improve `Formatter` so that it can write to an array or slice buffer.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
> ---
> rust/kernel/str.rs | 19 ++++++++++++++-----
> 1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index 488b0e97004e..41af456a46c8 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -6,6 +6,7 @@
> use crate::prelude::*;
> use core::{
> fmt::{self, Write},
> + marker::PhantomData,
> ops::{self, Deref, DerefMut, Index},
> };
>
> @@ -794,9 +795,9 @@ fn write_str(&mut self, s: &str) -> fmt::Result {
> /// Allows formatting of [`fmt::Arguments`] into a raw buffer.
> ///
> /// Fails if callers attempt to write more than will fit in the buffer.
> -pub(crate) struct Formatter(RawFormatter);
> +pub(crate) struct Formatter<'a>(RawFormatter, PhantomData<&'a mut ()>);
>
> -impl Formatter {
> +impl Formatter<'_> {
> /// Creates a new instance of [`Formatter`] with the given buffer.
> ///
> /// # Safety
> @@ -805,11 +806,19 @@ impl Formatter {
> /// for the lifetime of the returned [`Formatter`].
> pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
> // SAFETY: The safety requirements of this function satisfy those of the callee.
> - Self(unsafe { RawFormatter::from_buffer(buf, len) })
> + Self(unsafe { RawFormatter::from_buffer(buf, len) }, PhantomData)
> + }
> +
> + /// Create a new [`Self`] instance.
> + #[expect(dead_code)]
> + pub(crate) fn new<'a>(buffer: &'a mut [u8]) -> Formatter<'a> {
nit: the function above this one returns Self, and this one returns Formatter.
Perhaps this one should also return Self for consistency?
> + // SAFETY: `buffer` is valid for writes for the entire length for
> + // the lifetime of `Self`.
> + unsafe { Formatter::from_buffer(buffer.as_mut_ptr(), buffer.len()) }
> }
> }
>
> -impl Deref for Formatter {
> +impl Deref for Formatter<'_> {
> type Target = RawFormatter;
>
> fn deref(&self) -> &Self::Target {
> @@ -817,7 +826,7 @@ fn deref(&self) -> &Self::Target {
> }
> }
>
> -impl fmt::Write for Formatter {
> +impl fmt::Write for Formatter<'_> {
> fn write_str(&mut self, s: &str) -> fmt::Result {
> self.0.write_str(s)?;
>
>
> --
> 2.47.2
>
>
>
Reviewed-by: Daniel Almeida <daniel.almeida@xxxxxxxxxxxxx>
