Re: [PATCH 02/13] rust: init: simplify from `map_err` to `inspect_err`

Björn Roy Baron
2024-07-01T20:05:41Z

On Monday, July 1st, 2024 at 20:36, Miguel Ojeda <ojeda@kernel.org> wrote:

> A new complexity lint, `manual_inspect` [1], has been introduced in
> the upcoming Rust 1.81 (currently in nightly), which checks for uses of
> `map*` which return the original item:
>
> error:
> --> rust/kernel/init.rs:846:23
> |
> 846 | (self.1)(val).map_err(|e| {
> | ^^^^^^^
> |
> = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_inspect
> = note: `-D clippy::manual-inspect` implied by `-D warnings`
> = help: to override `-D warnings` add `#[allow(clippy::manual_inspect)]`
> help: try
> |
> 846 ~ (self.1)(val).inspect_err(|e| {
> 847 | // SAFETY: `slot` was initialized above.
> 848 ~ unsafe { core::ptr::drop_in_place(slot) };
> |
>
> Thus clean them up.
>
> Link: https://rust-lang.github.io/rust-clippy/master/index.html#/manual_inspect [1]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
> rust/kernel/init.rs | 12 ++++--------
> 1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
> index 68605b633e73..07bacf134c19 100644
> --- a/rust/kernel/init.rs
> +++ b/rust/kernel/init.rs
> @@ -843,11 +843,9 @@ unsafe fn __pinned_init(self, slot: *mut T) -> Result<(), E> {
> let val = unsafe { &mut *slot };
> // SAFETY: `slot` is considered pinned.
> let val = unsafe { Pin::new_unchecked(val) };
> - (self.1)(val).map_err(|e| {
> + (self.1)(val).inspect_err(|_|
> // SAFETY: `slot` was initialized above.
> - unsafe { core::ptr::drop_in_place(slot) };
> - e
> - })
> + unsafe { core::ptr::drop_in_place(slot) })

The formatting here is a bit weird. I would have expected the ) ending the inspect_err call to be placed on a new line given that the unsafe block isn't placed on the same line as the start of the inspect_err call either. This seems to be a case where rustfmt mostly gives up on formatting. If I deindent the comment and unsafe block rustfmt will keep it that way and if I add a trailing space to the inspect_err line it will keep it and emit an error that it left behind trailing whitespace. Maybe add a block around the comment and unsafe block to make rustfmt work again?

> }
> }
>
> @@ -941,11 +939,9 @@ unsafe fn __init(self, slot: *mut T) -> Result<(), E> {
> // SAFETY: All requirements fulfilled since this function is `__init`.
> unsafe { self.0.__pinned_init(slot)? };
> // SAFETY: The above call initialized `slot` and we still have unique access.
> - (self.1)(unsafe { &mut *slot }).map_err(|e| {
> + (self.1)(unsafe { &mut *slot }).inspect_err(|_|
> // SAFETY: `slot` was initialized above.
> - unsafe { core::ptr::drop_in_place(slot) };
> - e
> - })
> + unsafe { core::ptr::drop_in_place(slot) })
> }
> }
>
> --
> 2.45.2