Re: [PATCH v2 33/33] rust: kbuild: allow `clippy::precedence` for Rust < 1.86.0

Nicolas Schier
2026-04-07T19:39:59Z

On Mon, Apr 06, 2026 at 01:53:09AM +0200, Miguel Ojeda wrote:
> The Clippy `precedence` lint was extended in Rust 1.85.0 to include
> bitmasking and shift operations [1]. However, because it generated
> many hits, in Rust 1.86.0 it was split into a new `precedence_bits`
> lint which is not enabled by default [2].
>
> In other words, only Rust 1.85 has a different behavior. For instance,
> it reports:
>
> warning: operator precedence can trip the unwary
> --> drivers/gpu/nova-core/fb/hal/ga100.rs:16:5
> |
> 16 | / u64::from(regs::NV_PFB_NISO_FLUSH_SYSMEM_ADDR::read(bar).adr_39_08()) << FLUSH_SYSMEM_ADDR_SHIFT
> 17 | | | u64::from(regs::NV_PFB_NISO_FLUSH_SYSMEM_ADDR_HI::read(bar).adr_63_40())
> 18 | | << FLUSH_SYSMEM_ADDR_SHIFT_HI
> | |_________________________________________^
> |
> = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
> = note: `-W clippy::precedence` implied by `-W clippy::all`
> = help: to override `-W clippy::all` add `#[allow(clippy::precedence)]`
> help: consider parenthesizing your expression
> |
> 16 ~ (u64::from(regs::NV_PFB_NISO_FLUSH_SYSMEM_ADDR::read(bar).adr_39_08()) << FLUSH_SYSMEM_ADDR_SHIFT) | (u64::from(regs::NV_PFB_NISO_FLUSH_SYSMEM_ADDR_HI::read(bar).adr_63_40())
> 17 + << FLUSH_SYSMEM_ADDR_SHIFT_HI)
> |
>
> While so far we try our best to keep all versions Clippy-clean, the
> minimum (which is now Rust 1.85.0 after the bump) and the latest stable
> are the most important ones; and this may be considered a "false positive"
> with respect to the behavior in other versions.
>
> Thus allow this lint for this version using the per-version flags
> mechanism introduced in the previous commit.
>
> Link: https://github.com/rust-lang/rust-clippy/issues/14097 [1]
> Link: https://github.com/rust-lang/rust-clippy/pull/14115 [2]
> Link: https://lore.kernel.org/rust-for-linux/DFVDKMMA7KPC.2DN0951H3H55Y@kernel.org/
> Reviewed-by: Tamir Duberstein <tamird@kernel.org>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
> Makefile | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>

Acked-by: Nicolas Schier <nsc@kernel.org>

--
Nicolas