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

[Gary Guo]

On Wed Apr 1, 2026 at 12:45 PM BST, 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)
>        |
> 
>     warning: operator precedence can trip the unwary
>        --> drivers/gpu/nova-core/vbios.rs:511:17
>         |
>     511 | /                 u32::from(data[29]) << 24
>     512 | |                     | u32::from(data[28]) << 16
>     513 | |                     | u32::from(data[27]) << 8
>         | |______________________________________________^
>         |
>         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
>     help: consider parenthesizing your expression
>         |
>     511 ~                 u32::from(data[29]) << 24
>     512 +                     | u32::from(data[28]) << 16 | (u32::from(data[27]) << 8)
>         |
> 
>     warning: operator precedence can trip the unwary
>        --> drivers/gpu/nova-core/vbios.rs:511:17
>         |
>     511 | /                 u32::from(data[29]) << 24
>     512 | |                     | u32::from(data[28]) << 16
>         | |_______________________________________________^ help: consider parenthesizing your expression: `(u32::from(data[29]) << 24) | (u32::from(data[28]) << 16)`
>         |
>         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
> 
> 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 "false positives"
> 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]
> Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>

Link: https://lore.kernel.org/rust-for-linux/DFVDKMMA7KPC.2DN0951H3H55Y@xxxxxxxxxx/
Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>

> ---
>  Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)