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In Rust, it is possible to `allow` particular warnings (diagnostics,
lints) locally, making the compiler ignore instances of a given warning
within a given function, module, block, etc.
It is similar to `#pragma GCC diagnostic push` + `ignored` + `pop` in C:
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-function"
static void f(void) {}
#pragma GCC diagnostic pop
But way less verbose:
#[allow(dead_code)]
fn f() {}
By that virtue, it makes it possible to comfortably enable more
diagnostics by default (i.e. outside `W=` levels) that may have some
false positives but that are otherwise quite useful to keep enabled to
catch potential mistakes.
The `#[expect(...)]` attribute [1] takes this further, and makes the
compiler warn if the diagnostic was _not_ produced. For instance, the
following will ensure that, when `f()` is called somewhere, we will have
to remove the attribute:
#[expect(dead_code)]
fn f() {}
If we do not, we get a warning from the compiler:
warning: this lint expectation is unfulfilled
--> x.rs:3:10
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3 | #[expect(dead_code)]
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= note: `#[warn(unfulfilled_lint_expectations)]` on by default
This means that `expect`s do not get forgotten when they are not needed.
See the next commit for more details, nuances on its usage and
documentation on the feature.
The attribute requires the `lint_reasons` [2] unstable feature, but it
is becoming stable in 1.81.0 (to be released on 2024-09-05) and it has
already been useful to clean things up in this patch series, finding
cases where the `allow`s should not have been there.
Thus, enable `lint_reasons` and convert some of our `allow`s to `expect`s
where possible.
This feature was also an example of the ongoing collaboration between
Rust and the kernel -- we tested it in the kernel early on and found an
issue that was quickly resolved [3].
Cc: Fridtjof Stoldt <xfrednet@gmail.com>
Cc: Urgau <urgau@numericable.fr>
Link: https://rust-lang.github.io/rfcs/2383-lint-reasons.html#expect-lint-attribute [1]
Link: https://github.com/rust-lang/rust/issues/54503 [2]
Link: https://github.com/rust-lang/rust/issues/114557 [3]
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Trevor Gross <tmgross@umich.edu>
Tested-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/r/20240904204347.168520-18-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
82 lines
2.3 KiB
Rust
82 lines
2.3 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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//! Rust printing macros sample.
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use kernel::pr_cont;
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use kernel::prelude::*;
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module! {
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type: RustPrint,
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name: "rust_print",
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author: "Rust for Linux Contributors",
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description: "Rust printing macros sample",
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license: "GPL",
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}
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struct RustPrint;
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#[expect(clippy::disallowed_macros)]
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fn arc_print() -> Result {
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use kernel::sync::*;
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let a = Arc::new(1, GFP_KERNEL)?;
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let b = UniqueArc::new("hello, world", GFP_KERNEL)?;
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// Prints the value of data in `a`.
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pr_info!("{}", a);
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// Uses ":?" to print debug fmt of `b`.
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pr_info!("{:?}", b);
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let a: Arc<&str> = b.into();
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let c = a.clone();
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// Uses `dbg` to print, will move `c` (for temporary debugging purposes).
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dbg!(c);
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// Pretty-prints the debug formatting with lower-case hexadecimal integers.
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pr_info!("{:#x?}", a);
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Ok(())
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}
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impl kernel::Module for RustPrint {
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fn init(_module: &'static ThisModule) -> Result<Self> {
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pr_info!("Rust printing macros sample (init)\n");
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pr_emerg!("Emergency message (level 0) without args\n");
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pr_alert!("Alert message (level 1) without args\n");
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pr_crit!("Critical message (level 2) without args\n");
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pr_err!("Error message (level 3) without args\n");
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pr_warn!("Warning message (level 4) without args\n");
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pr_notice!("Notice message (level 5) without args\n");
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pr_info!("Info message (level 6) without args\n");
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pr_info!("A line that");
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pr_cont!(" is continued");
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pr_cont!(" without args\n");
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pr_emerg!("{} message (level {}) with args\n", "Emergency", 0);
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pr_alert!("{} message (level {}) with args\n", "Alert", 1);
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pr_crit!("{} message (level {}) with args\n", "Critical", 2);
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pr_err!("{} message (level {}) with args\n", "Error", 3);
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pr_warn!("{} message (level {}) with args\n", "Warning", 4);
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pr_notice!("{} message (level {}) with args\n", "Notice", 5);
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pr_info!("{} message (level {}) with args\n", "Info", 6);
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pr_info!("A {} that", "line");
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pr_cont!(" is {}", "continued");
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pr_cont!(" with {}\n", "args");
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arc_print()?;
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Ok(RustPrint)
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}
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}
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impl Drop for RustPrint {
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fn drop(&mut self) {
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pr_info!("Rust printing macros sample (exit)\n");
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}
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}
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