[PATCH v2 04/13] rust: relax most deny-level lints to warnings

[Miguel Ojeda <ojeda@kernel.org>]

Since we are starting to support several Rust toolchains, lints (including
Clippy ones) now may behave differently and lint groups may include
new lints.

Therefore, to maximize the chances a given version works, relax some
deny-level lints to warnings. It may also make our lives a bit easier
while developing new code or refactoring.

To be clear, the requirements for in-tree code are still the same, since
Rust code still needs to be warning-free (patches should be clean under
`WERROR=y`) and the set of lints is not changed.

`unsafe_op_in_unsafe_fn` is left unmodified, i.e. as an error, since it is
becoming the default in the language (warn-by-default in Rust 2024 [1] and
ideally an error later on) and thus it should also be very well tested. In
addition, it is simple enough that it should not have false positives
(unlike e.g. `rust_2018_idioms`'s `explicit_outlives_requirements`).

`non_ascii_idents` is left unmodified as well, i.e. as an error, since
it is unlikely one gains any productivity during development if it
were a warning (in fact, it may be worse, since it is likely one made
a typo). In addition, it should not have false positives.

Finally, put the two `-D` ones at the top and take the chance to do one
per line.

Link: https://github.com/rust-lang/rust/pull/112038 [1]
Reviewed-by: Finn Behrens <me@kloenk.dev>
Tested-by: Benno Lossin <benno.lossin@proton.me>
Tested-by: Andreas Hindborg <a.hindborg@samsung.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
v2:
  - Kept `non_ascii_idents` as an error. (Björn, Finn)

 Makefile      | 24 +++++++++++++-----------
 rust/Makefile |  4 ++--
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/Makefile b/Makefile
index fea263aaa492..7ea526814fdb 100644
--- a/Makefile
+++ b/Makefile
@@ -461,17 +461,19 @@ KBUILD_USERLDFLAGS := $(USERLDFLAGS)
 # host programs.
 export rust_common_flags := --edition=2021 \
 			    -Zbinary_dep_depinfo=y \
-			    -Dunsafe_op_in_unsafe_fn -Drust_2018_idioms \
-			    -Dunreachable_pub -Dnon_ascii_idents \
+			    -Dunsafe_op_in_unsafe_fn \
+			    -Dnon_ascii_idents \
+			    -Wrust_2018_idioms \
+			    -Wunreachable_pub \
 			    -Wmissing_docs \
-			    -Drustdoc::missing_crate_level_docs \
-			    -Dclippy::correctness -Dclippy::style \
-			    -Dclippy::suspicious -Dclippy::complexity \
-			    -Dclippy::perf \
-			    -Dclippy::let_unit_value -Dclippy::mut_mut \
-			    -Dclippy::needless_bitwise_bool \
-			    -Dclippy::needless_continue \
-			    -Dclippy::no_mangle_with_rust_abi \
+			    -Wrustdoc::missing_crate_level_docs \
+			    -Wclippy::correctness -Wclippy::style \
+			    -Wclippy::suspicious -Wclippy::complexity \
+			    -Wclippy::perf \
+			    -Wclippy::let_unit_value -Wclippy::mut_mut \
+			    -Wclippy::needless_bitwise_bool \
+			    -Wclippy::needless_continue \
+			    -Wclippy::no_mangle_with_rust_abi \
 			    -Wclippy::dbg_macro

 KBUILD_HOSTCFLAGS   := $(KBUILD_USERHOSTCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS)
@@ -572,7 +574,7 @@ KBUILD_RUSTFLAGS := $(rust_common_flags) \
 		    -Csymbol-mangling-version=v0 \
 		    -Crelocation-model=static \
 		    -Zfunction-sections=n \
-		    -Dclippy::float_arithmetic
+		    -Wclippy::float_arithmetic

 KBUILD_AFLAGS_KERNEL :=
 KBUILD_CFLAGS_KERNEL :=
diff --git a/rust/Makefile b/rust/Makefile
index 385378311322..bf05e65365da 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -367,7 +367,7 @@ ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
 endif

 $(obj)/core.o: private skip_clippy = 1
-$(obj)/core.o: private skip_flags = -Dunreachable_pub
+$(obj)/core.o: private skip_flags = -Wunreachable_pub
 $(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 FORCE
@@ -381,7 +381,7 @@ $(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
 	+$(call if_changed_dep,rustc_library)

 $(obj)/alloc.o: private skip_clippy = 1
-$(obj)/alloc.o: private skip_flags = -Dunreachable_pub
+$(obj)/alloc.o: private skip_flags = -Wunreachable_pub
 $(obj)/alloc.o: private rustc_target_flags = $(alloc-cfgs)
 $(obj)/alloc.o: $(RUST_LIB_SRC)/alloc/src/lib.rs $(obj)/compiler_builtins.o FORCE
 	+$(call if_changed_dep,rustc_library)
--
2.45.2