Re: [PATCH v2 5/5] rust: enable `clippy::as_underscore` lint

Tamir Duberstein
2025-03-12T20:42:18Z

On Wed, Mar 12, 2025 at 4:07 PM Tamir Duberstein <tamird@gmail.com> wrote:
>
> On Wed, Mar 12, 2025 at 3:43 PM Benno Lossin <benno.lossin@proton.me> wrote:
> >
> > On Wed Mar 12, 2025 at 8:19 PM CET, Tamir Duberstein wrote:
> > > I tried using the strict provenance lints locally and I think we can't
> > > until we properly bump MSRV due to `clippy::incompatible_msrv`:
> > >
> > > warning: current MSRV (Minimum Supported Rust Version) is `1.78.0` but
> > > this item is stable since `1.84.0`
> > > --> ../rust/kernel/str.rs:696:22
> > > |
> > > 696 | pos: pos.expose_provenance(),
> > > | ^^^^^^^^^^^^^^^^^^^
> > > |
> > > = help: for further information visit
> > > https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv
> >
> > Oh this is annoying...
> >
> > > This is with `#![feature(strict_provenance)]`. I can file the issue
> > > but I think it's blocked on MSRV >= 1.84.0. But maybe you know of a
> > > path forward :)
> >
> > I think we should be able to just `allow(clippy::incompatible_msrv)`,
> > since Miguel & other maintainers will test with 1.78 (or at least are
> > supposed to :).
>
> Alright, you've sniped me. This is coming in v3.

I just realized I only covered the kernel crate. In order to cover all
Rust code, I need to move the lints and the features out to the root
Makefile. I tried something like this:

> diff --git a/Makefile b/Makefile
> index 2af40bfed9ce..10af1e44370b 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -466,13 +466,21 @@ KBUILD_USERHOSTCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \
> KBUILD_USERCFLAGS := $(KBUILD_USERHOSTCFLAGS) $(USERCFLAGS)
> KBUILD_USERLDFLAGS := $(USERLDFLAGS)
>
> +# Lints were moved to `strict_provenance_lints` when `strict_provenance` was stabilized.
> +#
> +# See https://github.com/rust-lang/rust/commit/56ee492a6e7a917b2b3f888e33dd52a13d3ecb64.
> +KBUILD_RUST_STRICT_PROVENANCE_FEATURE = $(if $(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE),strict_provenance_lints,strict_provenance)
> +
> # These flags apply to all Rust code in the tree, including the kernel and
> # host programs.
> export rust_common_flags := --edition=2021 \
> -Zbinary_dep_depinfo=y \
> + -Zcrate-attr="feature($(KBUILD_RUST_STRICT_PROVENANCE_FEATURE))" \
> -Astable_features \
> -Dnon_ascii_idents \
> -Dunsafe_op_in_unsafe_fn \
> + -Wfuzzy_provenance_casts \
> + -Wlossy_provenance_casts \
> -Wmissing_docs \
> -Wrust_2018_idioms \
> -Wunreachable_pub \
> diff --git a/rust/Makefile b/rust/Makefile
> index ea3849eb78f6..d7d5be741245 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -435,8 +435,10 @@ $(obj)/helpers/helpers.o: $(src)/helpers/helpers.c $(recordmcount_source) FORCE
> # symbol versions generated from Rust objects.
> $(obj)/exports.o: private skip_gendwarfksyms = 1
>
> +KBUILD_RUST_STRICT_PROVENANCE_FEATURE := $(if $(CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE),strict_provenance_lints,strict_provenance)
> +
> $(obj)/core.o: private skip_clippy = 1
> -$(obj)/core.o: private skip_flags = -Wunreachable_pub
> +$(obj)/core.o: private skip_flags = -Zcrate-attr="feature($(KBUILD_RUST_STRICT_PROVENANCE_FEATURE))" -Wunreachable_pub -Wfuzzy_provenance_casts -Wlossy_provenance_casts
> $(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
> $(obj)/core.o: private rustc_target_flags = $(core-cfgs)
> $(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs \

but this doesn't work because
`CONFIG_RUSTC_HAS_STABLE_STRICT_PROVENANCE` is not yet defined when I
read it in the root Makefile. I can read it lower down and then append
the feature flag to `KBUILD_RUSTFLAGS` but by then the rustdoc flags
have been copied from `rust_common_flags` and so rustdoc doesn't get
the feature flag, resulting in unknown lint warnings in rustdoc and
kunit tests.

Any ideas?