linux-kernel - Re: [PATCH v2 5/5] rust: enable `clippy::as

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Message-ID: <CAJ-ks9=TRDg3g=NG7k97P_5jXpZ4K4v0DxrmJFR+uF0-3zJkXw@mail.gmail.com>
Date: Wed, 12 Mar 2025 17:04:12 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Brendan Higgins <brendan.higgins@...ux.dev>, David Gow <davidgow@...gle.com>, 
	Rae Moar <rmoar@...gle.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Luis Chamberlain <mcgrof@...nel.org>, Russ Weight <russ.weight@...ux.dev>, Rob Herring <robh@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com, 
	linux-pci@...r.kernel.org, linux-block@...r.kernel.org, 
	devicetree@...r.kernel.org
Subject: Re: [PATCH v2 5/5] rust: enable `clippy::as_underscore` lint

On Wed, Mar 12, 2025 at 5:01 PM Benno Lossin <benno.lossin@...ton.me> 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@...il.com> wrote:
> >>
> >> On Wed, Mar 12, 2025 at 3:43 PM Benno Lossin <benno.lossin@...ton.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?
>
> 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)`.