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

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On Wed, Mar 12, 2025 at 5:04 PM Tamir Duberstein <tamird@xxxxxxxxx> wrote:
>
> On Wed, Mar 12, 2025 at 5:01 PM Benno Lossin <benno.lossin@xxxxxxxxx> wrote:
> >
> > On Wed Mar 12, 2025 at 9:41 PM CET, Tamir Duberstein wrote:
> > > On Wed, Mar 12, 2025 at 4:07 PM Tamir Duberstein <tamird@xxxxxxxxx> wrote:
> > >>
> > >> On Wed, Mar 12, 2025 at 3:43 PM Benno Lossin <benno.lossin@xxxxxxxxx> 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?
> >
> > Always enable the features, we have `allow(stable_features)` for this
> > reason (then you don't have to do this dance with checking if it's
> > already stable or not :)
>
> It's not so simple. In rustc < 1.84.0 the lints *and* the strict
> provenance APIs are behind `feature(strict_provenance)`. In rustc >=
> 1.84.0 the lints are behind `feature(strict_provenance_lints)`. So you
> need to read the config to learn that you need to enable
> `feature(strict_provenance_lints)`.

Actually this isn't even the only problem. It seems that
`-Astable_features` doesn't affect features enabled on the command
line at all:

error[E0725]: the feature `strict_provenance` is not in the list of
allowed features
 --> <crate attribute>:1:9
  |
1 | feature(strict_provenance)
  |         ^^^^^^^^^^^^^^^^^





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