[PATCH 11/19] rust: introduce `.clippy.toml`

[Miguel Ojeda <ojeda@kernel.org>]

Some Clippy lints can be configured/tweaked. We will use these knobs to
our advantage in later commits.

This is done via a configuration file, `.clippy.toml` [1]. The file is
currently unstable. This may be a problem in the future, but we can adapt
as needed. In addition, we proposed adding Clippy to the Rust CI's RFL
job [2], so we should be able to catch issues pre-merge.

Thus introduce the file.

Link: https://doc.rust-lang.org/clippy/configuration.html [1]
Link: https://github.com/rust-lang/rust/pull/128928 [2]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 .clippy.toml | 1 +
 .gitignore   | 1 +
 MAINTAINERS  | 1 +
 Makefile     | 3 +++
 4 files changed, 6 insertions(+)
 create mode 100644 .clippy.toml

diff --git a/.clippy.toml b/.clippy.toml
new file mode 100644
index 000000000000..f66554cd5c45
--- /dev/null
+++ b/.clippy.toml
@@ -0,0 +1 @@
+# SPDX-License-Identifier: GPL-2.0
diff --git a/.gitignore b/.gitignore
index 7902adf4f7f1..907c782962d2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -102,6 +102,7 @@ modules.order
 # We don't want to ignore the following even if they are dot-files
 #
 !.clang-format
+!.clippy.toml
 !.cocciconfig
 !.editorconfig
 !.get_maintainer.ignore
diff --git a/MAINTAINERS b/MAINTAINERS
index 77b395476a80..cb63f1f97556 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -19922,6 +19922,7 @@ B:	https://github.com/Rust-for-Linux/linux/issues
 C:	zulip://rust-for-linux.zulipchat.com
 P:	https://rust-for-linux.com/contributing
 T:	git https://github.com/Rust-for-Linux/linux.git rust-next
+F:	.clippy.toml
 F:	Documentation/rust/
 F:	rust/
 F:	samples/rust/
diff --git a/Makefile b/Makefile
index fc66bac4b4f1..234ab97de796 100644
--- a/Makefile
+++ b/Makefile
@@ -590,6 +590,9 @@ endif
 # Allows the usage of unstable features in stable compilers.
 export RUSTC_BOOTSTRAP := 1
 
+# Allows finding `.clippy.toml` in out-of-srctree builds.
+export CLIPPY_CONF_DIR := $(srctree)
+
 export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC HOSTPKG_CONFIG
 export RUSTC RUSTDOC RUSTFMT RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN
 export HOSTRUSTC KBUILD_HOSTRUSTFLAGS
-- 
2.46.0